U.S. patent application number 15/608890 was filed with the patent office on 2017-09-21 for system and method for connecting a first battery in parallel with a second battery by charging for equalization.
The applicant listed for this patent is DAVIDE ANDREA. Invention is credited to DAVIDE ANDREA.
Application Number | 20170271863 15/608890 |
Document ID | / |
Family ID | 49878009 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170271863 |
Kind Code |
A1 |
ANDREA; DAVIDE |
September 21, 2017 |
SYSTEM AND METHOD FOR CONNECTING A FIRST BATTERY IN PARALLEL WITH A
SECOND BATTERY BY CHARGING FOR EQUALIZATION
Abstract
Disclosed is a battery and load equalization circuit that
prevents the in-rush of current when batteries and/or loads are
initially connected in parallel. Various techniques are used
including charging, discharging and use of DC to DC converters to
equalize charges between batteries and between batteries and
capacitive loads.
Inventors: |
ANDREA; DAVIDE; (BOULDER,
CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ANDREA; DAVIDE |
BOULDER |
CO |
US |
|
|
Family ID: |
49878009 |
Appl. No.: |
15/608890 |
Filed: |
May 30, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13544100 |
Jul 9, 2012 |
9711962 |
|
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15608890 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02H 9/002 20130101;
H02J 7/0018 20130101; Y02T 10/7055 20130101; Y02T 10/70
20130101 |
International
Class: |
H02H 9/00 20060101
H02H009/00; H02J 7/00 20060101 H02J007/00 |
Claims
1. A charging system for safely connecting a first battery in
parallel with a second battery comprising: a controller in
communication with a first battery to detect a first terminal
voltage, the controller in communication with a second battery to
detect a second terminal voltage; a first charger connected to the
first battery, the first charger activated by the controller; a
second charger connected to the second battery, the second charger
activated by the controller; a switch operable to connect the first
battery and the second battery in parallel, the switch activated by
the controller; wherein in a first instance the controller
activating the first charger to charge the first battery to a first
voltage when the first terminal voltage is less than the second
terminal voltage, and in a second instance the controller
activating the second charger to charge the second battery to a
second voltage when the second terminal voltage is less than the
first terminal voltage, the controller activating the switch when
the first voltage and the second voltage are sufficiently close to
permit parallel connection of the first battery to the second
battery without a damaging current flowing there between.
2. The charging system of claim 1, wherein the controller activates
the switch when the first voltage and the second voltage are
equal.
3. The charging system of claim 1, wherein an initial current
between the parallel connected first battery and the second battery
is essentially zero.
4. The charging system of claim 1, wherein the first charger and
the second charger are both activated by the controller to charge
the first battery and the second battery to about an equal third
voltage.
5. The charging system of claim 1, wherein the controller generates
a first control signal to activate the first charger, generates a
second control signal to activate the second charger, and a third
control signal to activate the switch to connect the first battery
and the second battery in parallel.
6. The charging system of claim 1, wherein the controller
indirectly directs the activation of at least one of, the first
charger, the second charger, and/or the switch.
7. The charging system of claim 1, wherein the second charger is
the first charger.
8. The charging system of claim 1, wherein the first charger and
second charger are disconnected upon equalization.
9. A charging system for safely connecting a first battery in
parallel with a second battery comprising: a controller that
detects a first terminal voltage of terminals of a first battery,
and a second terminal voltage of terminals of a second battery; a
first charge adjuster activated by the controller to either charge
or discharge the first battery to a first voltage when the first
terminal voltage is different from the second terminal voltage, the
charging or discharging equalizing the voltage; a second charge
adjuster activated by the controller to either charge or discharge
the second battery to a second voltage when the second terminal
voltage is different from the first terminal voltage, the charging
or discharging equalizing the voltage; a switch activated by the
controller when the first voltage and the second voltage are
sufficiently close to permit parallel connection of the first
battery to the second battery without a damaging current flowing
there between.
10. The charging system of claim 9, wherein the first charge
adjuster is selected from the group consisting of: a first charger,
a first load, a first discharging resistor.
11. The charging system of claim 9, wherein the second charge
adjuster is selected from the group consisting of: a second
charger, a second load, a second discharging resistor.
12. The charging system of claim 9, wherein the controller
activates the switch when the first voltage and the second voltage
are essentially equal.
13. The charging system of claim 9, wherein the controller
indirectly directs the activation of at least one of, the first
charge adjuster, the second charge adjuster, and/or the switch.
14. The charging system of claim 9, wherein an initial current
between the parallel connected first battery and the second battery
is essentially zero.
15. The charging system of claim 9, wherein the first charge
adjuster and the second charge adjuster are both activated by the
controller to change the first battery and the second battery to
about an equal third voltage.
16. The charging system of claim 9, wherein the controller
generates a first control signal to activate the first charger,
generates a second control signal to activate the second charger,
and a third control signal to activate the switch to connect the
first battery and the second battery in parallel.
17. The charging system of claim 9, wherein the second charger is
the first charger.
18. The charging system of claim 9, wherein the first adjuster and
second adjuster are disconnected upon equalization.
19. A method of charging for safely connecting a first battery in
parallel with a second battery comprising: providing a controller
in communication with a first battery to detect a first terminal
voltage, the controller in communication with a second battery to
detect a second terminal voltage; providing a first charger
connected to the first battery, the first charger activated by the
controller: providing a second charger connected to the second
battery, the second charger activated by the controller; providing
a switch operable to connect the first battery and the second
battery in parallel, the switch activated by the controller;
detecting the first terminal voltage and the second terminal
voltage, wherein in a first instance the controller activating the
first charger to charge the first battery to a first voltage when
the first terminal voltage is less than the second terminal
voltage, and in a second instance the controller activating the
second charger to charge the second battery to a second voltage
when the second terminal voltage is less than the first terminal
voltage, the controller activating the switch when the first
voltage and the second voltage are sufficiently close to permit
parallel connection of the first battery to the second battery
without a damaging current flowing there between.
20. The method of claim 19, wherein the controller activates the
switch when the first voltage and the second voltage are
essentially equal.
21. The method of claim 19, wherein an initial current between the
parallel connected first battery and the second battery is
essentially zero.
22. The method of claim 19, wherein the first charger and the
second charger are both activated by the controller to charge the
first battery and the second battery to about an equal third
voltage.
23. The method of claim 19, wherein the controller generates a
first control signal to activate the first charger, generates a
second control signal to activate the second charger, and a third
control signal to activate the switch to connect the first battery
and the second battery in parallel.
24. The method of claim 19, wherein the second charger is the first
charger.
25. The method of claim 19, wherein the controller indirectly
directs the activation of at least one of, the first charger, the
second charger, and/or the switch.
26. The method of claim 19, wherein the first charger and second
charger are disconnected upon equalization.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Divisional of U.S. patent
application Ser. No. 13/544,100, filed Jul. 9, 2012, now U.S. Pat.
No. ______. This Divisional application claims the benefit of U.S.
patent application Ser. No. 13/544,100, filed Jul. 9, 2012,
incorporated herein by reference.
BACKGROUND
[0002] Batteries are used as an important source of electrical
energy in portable applications and can also function as important
stationary electrical energy storage devices. Batteries can provide
a source of electrical energy for many purposes. For example,
batteries provide electrical energy for handheld devices, electric
cars, various types of electronic vehicles, alternative energy
storage, etc. Batteries can also be used for storage of electrical
energy when sources of electronic energy are not otherwise
available.
[0003] In order to provide a sufficient supply of electrical
energy, cells, as well as batteries, may be connected in parallel
and/or in series. Various series/parallel connections can provide a
desired current and voltage, for a wide number of applications.
SUMMARY OF THE INVENTION
[0004] An embodiment of the present invention may therefore
comprise a method of safely connecting a first battery in parallel
with a second battery using chargers comprising: detecting a first
terminal voltage of terminals of the first battery; detecting a
second terminal voltage of terminals of the second battery;
charging the first battery to a first voltage if the first terminal
voltage of the first battery is less than the second terminal
voltage of the second battery; charging the second battery to a
second voltage if the second terminal voltage of the second battery
is less than the first terminal voltage of the first battery;
connecting the terminals of the first battery and the terminals of
the second battery in parallel if the first voltage is sufficiently
close to the second terminal voltage, or if the second voltage is
sufficiently close to the first terminal voltage, so that currents
flowing between the first battery and the second battery upon
initially connecting the terminals of the first battery to the
terminals of the second battery are less than a first maximum
current
[0005] An embodiment of the present invention may further comprise
a method of safely connecting a first battery in parallel with a
second battery using discharging techniques comprising: detecting a
first terminal voltage of terminals of the first battery; detecting
a second terminal voltage of terminals of the second battery;
actively discharging the second battery to a second voltage if the
terminal voltage of the second battery is greater than the terminal
voltage of the first battery; actively discharging the first
battery to a first voltage if the terminal voltage of the first
battery is greater than the terminal voltage of the second battery;
connecting terminals of the first battery and the terminals of the
second battery in parallel if the second voltage is sufficiently
close to the first terminal voltage, or the first voltage is
sufficiently close to the second terminal voltage, so that currents
created upon initially connecting the first battery and the second
battery are less than a first desired maximum current.
[0006] An embodiment of the present invention may further comprise
a method of safely connecting a first battery in parallel with a
second battery using DC to DC converters comprising: detecting a
first terminal voltage of terminals at the first battery; detecting
a second terminal voltage of terminals of the second battery;
connecting an input of a step-down DC to DC converter to terminals
of the first battery and an output of the step-down DC to DC
converter to terminals of the second battery if the first terminal
voltage is greater than the second terminal voltage; connecting the
input of the step-down DC to DC converter to the terminals of the
second battery and an output of the step-down DC to DC converter to
terminals of the first battery if the second terminal voltage is
greater than the first terminal voltage.
[0007] An embodiment of the present invention may further comprise
a method of safely connecting a first battery in parallel with a
second battery using DC to DC converters comprising: detecting a
first terminal voltage of terminals at the first battery; detecting
a second terminal voltage of terminals of the second battery;
detecting a first state of charge of the first battery; detecting a
second state of charge of the second battery; connecting an input
of a step-up DC to DC converter to the first battery and an output
of the step-up DC to DC converter to the second battery if the
state of charge of the first battery is greater than the state of
charge of the second battery and if the first terminal voltage is
less than the second terminal voltage; connecting an input of the
step-up DC to DC converter to the second battery and an output of
the step-up DC to DC converter to the first battery if the state of
charge of the second battery is greater than the state of charge of
the first battery and if the first terminal voltage is greater than
the second terminal voltage.
[0008] An embodiment of the present invention may further comprise
a method of safely connecting a first battery in parallel with a
second battery using a bi-directional DC to DC converter
comprising: connecting terminals of the first battery to a first
input of the bi-directional DC to DC converter; connecting
terminals of a second battery to a second input of the
bi-directional DC to DC converter; using the bi-directional DC to
DC converter to transfer charge between the first battery and the
second battery in the direction that reduces the resulting current
at the moment of initial connection of the first terminals to the
second terminals; connecting the terminals of the first battery to
the terminals of the second battery when the first battery has a
first terminal voltage and open circuit voltage that is
sufficiently close to a second terminal voltage and open circuit
voltage on the second battery so that currents flowing between the
first battery and the second battery, when the first battery is
initially connected in parallel to the second battery, are less
than a maximum current.
[0009] An embodiment of the present invention may further comprise
a method of safely connecting a battery in parallel with a
capacitive load using a DC to DC converter comprising: connecting
terminals of the battery to a first input of the DC to DC
converter; connecting terminals of the capacitive load to a second
input of the DC to DC converter; using the DC to DC converter to
transfer charges between the battery and the capacitive load;
connecting the terminals of the battery to the terminals of the
load when the battery has a first charge that is sufficiently close
to a second charge on the capacitive load so that currents flowing
between the battery and the capacitive load when the battery is
initially connected to the capacitive load are less than a maximum
current.
[0010] An embodiment of the present invention may further comprise
a system for safely connecting a first battery in parallel with a
second battery using charging techniques comprising: a controller
that detects a first terminal voltage of terminals of the first
battery, and a second terminal voltage of terminals of the second
battery; a first charger connected to the first battery, which
charges the first battery to a first voltage, the first charger
activated by the controller if the first terminal voltage is less
than the second terminal voltage; a second charger connected to the
second battery, which charges the second battery to a second
voltage, the second charger activated by the controller if the
second terminal voltage is less than the first terminal voltage; a
switch that connects the first battery in parallel with the second
battery that is activated by the controller if the first voltage is
sufficiently close to the second terminal voltage, or if the second
voltage is sufficiently close to the first terminal voltage, so
that currents flowing between the first battery and the second
battery when the switch is initially activated by the controller
are less than a first maximum current.
[0011] An embodiment of the present invention may further comprise
a system for safely connecting a first battery in parallel with a
second battery using automated discharging techniques comprising: a
controller that detects a first terminal voltage of terminals of
the first battery and a second terminal voltage of terminals of a
second battery; a first switch that is activated by the controller
that connects a first resistive element in parallel with the first
battery to actively discharge the first battery to a first voltage
if the first terminal voltage is greater than the second terminal
voltage; a second switch that is activated by the controller that
connects a second resistive element in parallel with the second
battery to actively discharge the second battery to a second
voltage if the second terminal voltage is greater than the first
terminal voltage; a third switch activated by the controller, that
connects the first battery in parallel with the second battery if
the first voltage, if present, is sufficiently close to the second
terminal voltage, or the second voltage, if present, is
sufficiently close to the first terminal voltage, so that currents
flowing between the first battery and the second battery, when the
third switch is initially activated by the controller, are less
than a first maximum current.
[0012] An embodiment of the present invention may further comprise
a system for safely connecting a first battery in parallel with a
second battery using DC to DC converters comprising: a controller
that detects a first terminal voltage of terminals of a first
battery, and a second terminal voltage of terminals of a second
battery; a step-down DC to DC converter having an input and an
output; at least one switch that connects the input to the
terminals of the first battery, and the output to the terminals of
the second battery when the first terminal voltage is greater than
the second terminal voltage, and the input to the terminals of the
second battery and the output to the terminals of the first battery
when the second terminal voltage is greater than the first terminal
voltage.
[0013] An embodiment of the present invention may further comprise
a system for safely connecting a first battery in parallel with a
second battery comprising: a bi-directional DC to DC converter
having a first input and a second input; a controller that
generates control signals; a plurality of first electronic
switches, responsive to the control signals, that connect terminals
of the first battery to a first input of the bi-directional DC to
DC converter, and terminals of the second battery to a second input
of the bi-directional DC to DC converter, to transfer charge
between the first battery and the second battery; at least one
second electronic switch that connects the terminals of the first
battery in parallel to the terminals of the second battery when the
first battery has a first charge that is sufficiently close to a
second charge on the second battery so that current flowing between
the first battery and the second battery, when the second
electronic switch is activated, is less than a maximum current.
[0014] An embodiment of the present invention may further comprise
a system for safely connecting a battery in parallel with a
capacitive load comprising: a DC to DC converter having a first
input and a second input; a controller that generates control
signals; a plurality of first electronic switches, responsive to
the control signals, that connect terminals of the battery to a
first input of the DC to DC converter, and terminals of the
capacitive load to a second input of the bi-directional DC to DC
converter, to transfer charge between the battery and the
capacitive load; at least one second electronic switch that
connects the terminals of the battery in parallel to the terminals
of the capacitive load when the battery has a first charge that is
sufficiently close to a second charge on the capacitive load so
that current flowing between the battery and the capacitive load,
when the second electronic switch is activate, is less than a
maximum current.
[0015] An embodiment of the present invention may further comprise
an isolated, bi-directional DC to DC converter comprising: a first
DC voltage source; an inductor; a first pair of switches that
connected the inductor to the first DC voltage source in a first
polarity direction during a first phase of operation; a second DC
voltage source; a second pair of switches that connect the inductor
to a second DC voltage source in a second polarity direction, that
is opposite to the first polarity direction, during a second phase
of operation, so that current flows in the inductor in the first
polarity direction while the inductor is connected to the first
voltage source, during the first phase of operation, and the
current through the inductor is reduced during the second phase of
operation.
[0016] An embodiment of the present invention may further comprise
an isolated, uni-directional DC to DC converter comprising: a DC
voltage source; an inductor; a pair of switches that connect the
inductor to the DC voltage source during a first phase of operation
so that current flows through the inductor in a first direction; a
load; a pair of diodes that allow the current to continue to flow
through the inductor during a second phase of operation when the
first pair of switches are opened and the DC voltage source is
isolated from the inductor.
[0017] An embodiment of the present invention may further comprise
an isolated, uni-directional DC to DC converter comprising: a DC
voltage source; an inductor; a first pair of switches that connect
the inductor to the DC voltage source during a first phase of
operation so that current flows through the inductor in a first
direction; a load; a second pair of switches that connect the
inductor to the load that allows the current to continue to flow
through the inductor in the first direction during a second phase
of operation when the first pair of switches are opened and the
second pair of switches are substantially simultaneously closed and
the DC voltage source is isolated from the inductor.
[0018] An embodiment of the present invention may further comprise
a method of converting a first DC voltage to a second DC voltage
using an isolated, bi-directional DC to DC converter comprising:
generating the first DC voltage using a first DC voltage source;
applying the first DC voltage to an inductor using a first pair of
switches that connect the first DC voltage source to the inductor
in a first polarity direction; generating the second DC voltage
using a second DC voltage source; applying the second DC voltage to
the inductor using a second pair of switches that connect the
second DC voltage source to the inductor in a second polarity
direction that is opposite to the first polarity direction.
[0019] An embodiment of the present invention may further comprise
a method of converting a first DC voltage to a second DC voltage
using an isolated, uni-directional DC to DC converter comprising:
generating the first DC voltage using a DC voltage source; applying
the DC voltage source to an inductor using at least a first pair of
switches that connect the DC voltage source to the inductor that
generates a current in the conductor; opening the at least first
pair of switches and substantially simultaneously closing the at
least second pair of switches so that the current continues to flow
through the inductor into a load.
[0020] An embodiment of the present invention may further comprise
a method of converting a first DC voltage to a second DC voltage
using an isolated, uni-directional DC to DC converter comprising:
generating the first DC voltage using a DC voltage source; applying
the DC voltage source to an inductor using at least a first pair of
switches that connect the DC voltage source to the inductor that
generates a current in the inductor; opening the at least first
pair of switches so that current flows through the inductor and
through a pair of diodes and a load connected to the diodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic view of an embodiment of two batteries
that are wired for parallel connection through a switch.
[0022] FIG. 2 is a schematic illustration of an embodiment of two
batteries that are connected in parallel with a switch.
[0023] FIG. 3 is a schematic illustration of an embodiment of two
ideal voltage sources that are wired in parallel for connection
with a switch.
[0024] FIG. 4 is a schematic illustration of an embodiment of the
two ideal voltage sources of FIG. 3 that are connected in parallel
with a switch.
[0025] FIG. 5 is a graph of an embodiment of a current pulse
produced when connecting two ideal batteries.
[0026] FIG. 6 is a graph of the voltages that are produced when
connecting two ideal batteries in parallel.
[0027] FIG. 7 is a schematic illustration of an embodiment of two
real world batteries wired for connection parallel.
[0028] FIG. 8 is a schematic block diagram of an embodiment of the
two real world batteries of FIG. 7 that are connected in parallel
with a switch.
[0029] FIG. 9 is a plot of the current flowing between two real
world batteries versus time.
[0030] FIG. 10 is a plot of the internal, open circuit voltages of
each battery.
[0031] FIG. 11 is a schematic illustration of an embodiment of two
batteries connected in parallel with highly differing voltages
[0032] FIG. 12 is an equation illustrating the amount of current
that initially flows between the two batteries with highly
differing voltages are initially connected in parallel.
[0033] FIG. 13 is a schematic illustration of an embodiment of two
batteries connected in parallel with medium differing voltages.
[0034] FIG. 14 is an equation illustrating the amount of current
that initially flows between the two batteries with medium
differing voltages are initially connected in parallel.
[0035] FIG. 15 is a schematic block diagram of an embodiment of two
batteries connected in parallel with low differing voltages.
[0036] FIG. 16 is an equation illustrating the amount of current
flowing when the two batteries with low differing voltages are
initially connected in parallel.
[0037] FIG. 17 is a schematic illustration of an embodiment of a
pre-charge circuit in a first state.
[0038] FIG. 18 is a schematic illustration of an embodiment of the
pre-charge circuit of FIG. 17 in a second state.
[0039] FIG. 19 is a schematic diagram of an embodiment of the
circuit of FIG. 17 in a third state.
[0040] FIG. 20 is a plot of the current versus time of current
flowing in the circuit illustrated in FIG. 18.
[0041] FIG. 21 is a plot of the voltage of the capacitive load
versus time in the circuit of FIG. 18.
[0042] FIG. 22 is a schematic illustration of an embodiment of a
post-discharge circuit in a first state.
[0043] FIG. 23 is a schematic illustration of an embodiment of the
discharge circuit illustrated in FIG. 22 in a second state.
[0044] FIG. 24 is a plot of current flowing versus time in the
discharge circuit illustrated in FIG. 23.
[0045] FIG. 25 is a plot of voltage of the capacitive load versus
time in the circuit illustrated in FIG. 23.
[0046] FIG. 26 is a schematic illustration of an embodiment of a
battery equalization circuit in a first state.
[0047] FIG. 27 is an illustration of current flowing in the
embodiment of FIG. 26 versus time.
[0048] FIG. 28 is a schematic illustration of an embodiment of the
battery equalization circuit of FIG. 26 in a second state.
[0049] FIG. 29 is a graph of the current flowing in the circuit of
FIG. 28 versus time.
[0050] FIGS. 30-33 are schematic illustrations of an embodiment of
a battery equalization circuit in various states, wherein FIG. 30
illustrates a first battery at a lower voltage than a second
battery, FIG. 31 illustrates a charger charging first battery, FIG.
32 illustrates a first battery charged to same voltage as a second
battery, charger goes off, and FIG. 33 illustrates a first battery
connected to a second battery.
[0051] FIGS. 34-37 are schematic illustrations of an embodiment of
a battery equalization circuit in various states, wherein FIG. 34
illustrates a first battery at a higher voltage than a second
battery, FIG. 35 illustrates a charger charging a second battery,
FIG. 36 illustrates a second battery charged to the same voltage as
a first battery, charger goes off, and FIG. 37 illustrates a first
battery connected to second battery.
[0052] FIGS. 38-41 are schematic illustrations of an embodiment of
a discharging equalization circuit in various states where FIG. 38
illustrates a voltage of first battery that is higher than a
voltage of a second battery, FIG. 39 illustrates a discharge load
connected across first battery, to remove charge from the battery,
FIG. 40 illustrates a first battery discharged to the same voltage
as a second battery, load disconnected, and FIG. 41 illustrates a
first battery connected to a second battery.
[0053] FIGS. 42-45 are schematic illustrations of an embodiment of
a discharging equalization circuit in various states.
[0054] FIG. 46A is a schematic block diagram of an embodiment of an
energy exchange equalization circuit between two batteries.
[0055] FIG. 46B is a schematic block diagram of another embodiment
of an energy exchange equalization circuit between a battery and a
capacitive load.
[0056] FIG. 47 is a schematic illustration of an embodiment of an
energy exchange equalization circuit in the case that the state of
charge of a first battery is greater that the second battery, using
a step-down DC-DC converter.
[0057] FIG. 48 is a schematic illustration of an embodiment of an
energy exchange equalization circuit in the case that the state of
charge of a first battery is greater that the second battery, using
a step-up DC-DC converter.
[0058] FIG. 49 is a schematic illustration of an embodiment an
energy exchange equalization circuit in the case that the state of
charge of a first battery is lower that the second battery, using
of a step-up DC-DC converter.
[0059] FIG. 50 is a schematic illustration of an embodiment of an
energy exchange equalization circuit in the case that the state of
charge of a first battery is lower that the second battery, using a
step-down DC-DC converter.
[0060] FIG. 51 is a schematic illustration of an embodiment of an
energy exchange battery equalization circuit using a step-up DC-DC
converter, a step-down DC-DC converter, and a multitude of
switches.
[0061] FIG. 52 is a schematic diagram of an embodiment of a
bi-directional, same polarity DC to DC converter.
[0062] FIG. 53 is a schematic diagram of an embodiment of an
inverting DC to DC converter in a first state.
[0063] FIG. 54 is a schematic diagram of an embodiment with the
inverting DC to DC converter of FIG. 53 disabled, and the batteries
connected directly in parallel.
[0064] FIG. 55 is a schematic diagram of an embodiment of a
three-terminal, non-isolated, step-up DC to DC converter
system.
[0065] FIG. 56 is a schematic diagram of a three-terminal,
non-isolated step-down DC to DC converter system.
[0066] FIG. 57 is a schematic diagram of a three-terminal,
non-isolated, inverting DC to DC converter system.
[0067] FIG. 58 is a schematic diagram of an isolated, four-terminal
DC to DC converter system.
[0068] FIG. 59 is a schematic diagram of an embodiment of a four
terminal, flying inductor, DC to DC converter system that is a
transformer-less, DC-DC converter with limited isolation.
[0069] FIG. 60 is a schematic illustration of a flying inductor DC
to DC converter system that has the negative input terminals
connected together.
[0070] FIG. 61 is a schematic illustration of a flying inductor DC
to DC converter system that has the positive input terminals
connected together.
[0071] FIG. 62 is a schematic illustration of a flying inductor DC
to DC converter system that has the negative input terminal
connected to the positive output terminal
[0072] FIG. 63 is a schematic illustration of a flying inductor DC
to DC converter system that has the positive input terminal
connected to the negative output terminal
[0073] FIG. 64 illustrates a unidirectional DC to DC converter.
[0074] FIG. 65 is a schematic illustration of a bi-directional DC
to DC converter system.
[0075] FIG. 66 illustrates the differential voltages in a
bi-directional flying inductor DC to DC converter system.
[0076] FIG. 67A is a schematic diagram of an embodiment of a flying
inductor DC to DC converter system.
[0077] FIG. 67B is a schematic diagram of another embodiment of a
flying inductor DC to DC converter system.
[0078] FIG. 68 is a schematic diagram of the flying inductor DC to
DC converter in phase-A.
[0079] FIG. 69 is a schematic diagram of the flying inductor DC to
DC converter in phase-B.
[0080] FIG. 70 is a schematic diagram of the flying inductor DC to
DC converter in a dead time phase.
[0081] FIG. 71 is a schematic diagram of a uni-directional flying
inductor DC to DC converter.
[0082] FIG. 72 is a plot of inductor current versus time of the
uni-directional flying inductor DC to DC converter illustrated in
FIG. 71 that is operating in a discontinuous mode.
[0083] FIG. 73 is a plot of inductor voltage versus time for the
uni-directional DC to DC converter of FIG. 71.
[0084] FIG. 74 is a schematic illustration of the phase-A operation
of a uni-directional flying inductor DC to DC converter.
[0085] FIG. 75A is a schematic illustration of the phase-B
operation of a uni-directional flying inductor DC to DC
converter.
[0086] FIGS. 75B, 75C illustrate the current flow into an external
circuit that results from the loss of isolation due to mismatch in
the opening and closing times of switches 7404, 7410.
[0087] FIG. 76 is a schematic illustration of the dead time
operation of a uni-directional flying inductor DC to DC
converter.
[0088] FIG. 77 is a plot of inductor current versus time of a
uni-directional flying inductor DC to DC converter that is
operating in critical mode.
[0089] FIG. 78 is a plot of inductor voltage versus time of a
uni-directional flying inductor DC to DC converter operating in
critical mode.
[0090] FIG. 79 is a plot of inductor current versus time of a
uni-directional flying inductor DC to DC converter in continuous
mode.
[0091] FIG. 80 is a plot of inductor voltage of a uni-directional
flying inductor DC to DC converter versus time that is operating in
a continuous mode.
[0092] FIG. 81A is a schematic diagram of a uni-directional, flying
inductor, DC to DC converter employing a biased inductor.
[0093] FIG. 81B is a schematic illustration of a uni-directional
flying inductor DC to DC converter indicating the path of current
that limits the input-output isolation when the voltage of the load
is more negative than the voltage of the power source.
[0094] FIG. 82 is a schematic illustration of a uni-directional
flying inductor DC to DC converter indicating the path of current
that limits the input-output isolation when the voltage of the load
is more positive than the voltage of the power source.
[0095] FIG. 83 is a schematic illustration of a uni-directional
flying inductor DC to DC converter using bi-directional active
switches, indicating the path of current that limits the
input-output isolation when the voltage of the load is more
negative than the voltage of the power source.
[0096] FIG. 84A is a schematic illustration of a uni-directional
flying inductor DC to DC converter using bi-directional active
switches, indicating the path of current that limits the
input-output isolation when the voltage of the load is more
positive than the voltage of the power source.
[0097] FIG. 84B is a schematic illustration of a uni-directional
flying inductor DC to DC converter using bi-directional active
switches, indicating the path of current that limits the
input-output isolation when the voltage of the load is more
negative than the voltage of the power source.
[0098] FIG. 85 is a schematic illustration of a bi-directional DC
to DC converter for transferring charges between voltage
sources.
[0099] FIG. 86 is a schematic illustration of a bi-directional DC
to DC converter for transferring a charge from a voltage source to
a load.
[0100] FIG. 87 is a schematic illustration of a bi-directional
flying inductor DC-DC converter transferring power from V1 to V2,
in phase-A.
[0101] FIG. 88 is a schematic illustration of a bi-directional
flying inductor DC-DC converter transferring power from V1 to V2,
in phase-B.
[0102] FIG. 89 is a plot of current through the inductor versus
time for critical mode operation of the bi-directional DC to DC
converter of FIGS. 87 and 88 as the power transfer direction is
from V1 to V2.
[0103] FIG. 90 is a plot of the voltage across the inductor versus
time for critical mode operation of the bi-directional DC to DC
converter, regardless of the direction of power transfer.
[0104] FIG. 91 is an illustration of a bi-directional flying
inductor DC to DC converter illustrating the power transfer
direction from V2 to V1 that is initiated, in a phase-B
operation.
[0105] FIG. 92 illustrates the phase-A operation of the flying
inductor DC to DC converter of FIG. 91 showing the power transfer
direction from V2 to V1, in a phase-A.
[0106] FIG. 93 is a plot of the current through the inductor versus
time for critical mode operation of the bi-directional DC to DC
converter, showing the direction of power transfer is from V2 to
V1, as illustrated in FIGS. 91 and 92.
[0107] FIG. 94 is a plot of inductor current versus time for
critical mode operation of the bi-directional DC to DC converter,
showing the direction of power transfer from V2 to V1.
[0108] FIG. 95 is a plot of inductor current versus time for
discontinuous mode of operation of the bi-directional DC to DC
converter, as the direction of power transfer is from V1 to V2.
[0109] FIG. 96 is a plot of the inductor voltage versus time for a
discontinuous mode of operation of the bi-directional DC to DC
converter, as the direction of power transfer is from V1 to V2.
[0110] FIG. 97 is a plot of the inductor current versus time for a
discontinuous mode of operation of the bi-directional DC to DC
converter, as the direction of power transfer is from V2 to V1.
[0111] FIG. 98 is a plot of inductor voltage versus time for a
discontinuous mode of operation of the bi-directional DC to DC
converter, as the direction of power transfer is from V2 to V1.
[0112] FIG. 99 is a plot of inductor current versus time for a
continuous mode of operation as the direction of power transfer is
from V1 to V2.
[0113] FIG. 100 is a plot of inductor voltage versus time for a
continuous mode of operation as the direction of power transfer is
from V1 to V2.
[0114] FIG. 101 is a plot of inductor current versus time for a
continuous mode of operation as the direction of power transfer is
from V2 to V1.
[0115] FIG. 102 is a plot of inductor voltage versus time for a
continuous mode of operation was the direction of power transfer is
from V2 to V1.
[0116] FIG. 103 is a schematic diagram of a bi-directional, flying
bridge DC to DC converter using bi-directional switches.
[0117] FIG. 104 is a schematic diagram of a flying inductor DC to
DC converter system converted to a three terminal device by
connecting the positive terminals together.
[0118] FIG. 105 is a schematic diagram of a flying inductor DC to
DC converter converted to a three terminal device by connecting the
negative terminals together.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0119] FIG. 1 is a schematic view of an embodiment of two batteries
that are wired for connection in parallel through a switch 108. As
shown in FIG. 1, battery 100 can be schematically illustrated as a
voltage source 104 having a voltage V.sub.1 and a series resistance
110. Similarly, battery 102 is schematically illustrated as a
voltage source 106 having a voltage V.sub.2 and a series resistance
112. The two batteries 100, 102 can be connected in parallel using
switch 108.
[0120] FIG. 2 is a schematic illustration of the batteries
illustrated in FIG. 1, which are connected in parallel. As
illustrated in FIG. 2, battery 100 includes a voltage source 104
and an internal series resistance 110. Battery 102 includes a
voltage source 106 and an internal series resistance 112. When the
switch 108 is connected, current 110 flows between the two
batteries if the terminal voltages of the batteries are different.
As illustrated in FIG. 2, the terminal voltage of battery 100 is
greater than the terminal voltage of battery 102 so the current 110
flows in the direction of the arrow from battery 100 to battery
102. The difference in the terminal voltages as well as the
magnitude of the internal resistances of the batteries control the
magnitude of the current 110 that flows between the parallel
connected batteries 100, 102.
[0121] FIG. 3 is a schematic illustration of an embodiment of two
ideal voltage sources 300, 302 that are wired in parallel for
connection with a switch 304. As illustrated in FIG. 3, the ideal
voltage source 300 includes a voltage source 306 that produces a
voltage V.sub.1 without any series resistance. Ideal voltage source
302 includes a voltage source 308 that produces a voltage V.sub.2
without any series resistance. Switch 304 is used to connect the
ideal voltage source 300 in parallel with the ideal voltage source
302.
[0122] FIG. 4 is a schematic block diagram of the embodiment of
FIG. 3 with the switch 304 closed. As shown in FIG. 4, the ideal
voltage source 300 is connected in parallel through switch 304 to
the ideal voltage source 302. Current 310 flows in the direction of
the arrow when V.sub.1 is greater than V.sub.2. Since voltage
source 300 is an ideal voltage source and voltage source 302 is an
ideal voltage source, instantaneous current 310, upon closing
switch 304, is infinite.
[0123] FIG. 5 is a graph of the current 310 versus time. The plot
500 shows an infinite pulse 502 of current 310 that occurs at t=0
when the switch 304 is closed.
[0124] FIG. 6 is a plot of voltage versus time. As shown in FIG. 6,
the plot 606 shows the individual voltages 606, 608 of the ideal
voltage sources 300 (V.sub.1) and 302 (V.sub.2), which combine at
t=0 to create the average of V.sub.1 and V.sub.2, which is shown as
voltage 604 (V.sub.3). It is physically impossible for the voltages
606 and 608 of ideal voltage sources 306 and 308 to change
instantaneously, and hence the intensity of current pulse 502 is
infinite
[0125] FIG. 7 is a schematic illustration of an embodiment of two
batteries that are wired for connection in parallel by switch 704.
As illustrated in FIG. 7, voltage source 710 having a voltage
V.sub.1 is connected in series with series resistance 706 in
battery 700. Battery 702 includes a voltage source 712 having a
voltage V.sub.2 that is connected in series with series resistance
708. Switch 704 is in an open position until time t=0.
[0126] FIG. 8 is a schematic illustration of the embodiment of FIG.
7 with switch 704 closed. As illustrated in FIG. 8, battery 700,
which includes the voltage source 710 having voltage V.sub.1 and
series resistance 706, is connected in parallel using switch 704
with battery 702, which has a voltage source 712, having a voltage
V.sub.2, that is connected to series resistance 706. When switch
704 is closed, current 714 flows from battery 700 to battery 702
assuming V.sub.1 is greater than V.sub.2.
[0127] FIG. 9 is a graph of current versus time for the current 714
flowing between battery 700 and battery 702 in FIG. 8. As shown in
FIG. 9, the current 714 increases instantaneously at time t=0, when
switch 704 is closed, and gradually decays to 0 current as
batteries 700, 702 equalize charges. The peak value of the current
in the plot illustrated in FIG. 9 is proportional to the difference
in the terminal voltages of batteries 700 and 708, and inversely
proportional to the magnitude of the series resistance 706, 708,
which limit the current flowing between batteries 700, 702. The
decay time constant of the current 714 illustrated in FIG. 9 is
proportional to the sum of the capacities of batteries 700 and 702,
assuming they are the same, and inversely proportional to the sum
of the series resistances 706, 708.
[0128] FIG. 10 is a plot of the open circuit voltages of battery
710 and battery 712 versus time. Prior to the switch 704 being
closed at t=0, the voltages V.sub.1 and V.sub.2 of batteries 710,
712, respectively, are illustrated in the graph of FIG. 10. At t=0,
the voltages gradually equalize to create a third voltage (V.sub.3)
716, which is the average of V.sub.1 and V.sub.2, assuming that
battery 700 and 708 have the same capacity. The gradual averaging
of the voltages occurs over time that is proportional to the sum of
the capacities of batteries 700 and 702, assuming they are the
same, and inversely proportional to the sum of the series
resistances 706, 708. Since batteries have a non-zero series
resistance, which limits the current to a finite value when two
devices are first connected, the current decays asymptotically
towards 0, as illustrated in FIG. 9, until enough charge has been
transferred between the batteries to equalize the voltage, as
illustrated in FIG. 10 The level of the current resulting from the
initial interconnection of two batteries in parallel may be on the
order of 0.1 C to 100 C (where C is the value of the capacitance of
the battery), depending on the chemistry and the state of charge
levels of the two batteries. A current of 1 C means that such
current, if sustained, would discharge a full battery in 1 hour.
Similarly, a current of 0.1 C means that such current, if
sustained, would discharge a full battery in 10 hours. Similarly, a
current of 100 C means that such current, if sustained, would
discharge a full battery in 36 seconds, which is 1/100.sup.th of an
hour. Batteries can typically handle currents of up to 1 C,
although a charging current of 1 C may be a problem for some cells.
Charging currents of greater than 1 C are often too much current
for charging a battery. Batteries that have a steep slope in their
voltage versus state of charge curve, and a very low internal
resistance and are close to being full, present an extreme case for
charging currents, since when a cell is completely full, the
internal charging resistance of the cell increases, thereby
reducing the resulting current.
[0129] This extreme case exists for lithium ion batteries using
"high power" cells. High power cells have a resistance that is
particularly low (on the order of 25 mOhm*Ah) and the slope of the
voltage versus state of charge curve for these cells is somewhat
steep, especially when the cells are nearly full (on the order of
250 mV/1% SOC). As a consequence, when two such batteries, one at
100 percent SOC and the other at 90 percent SOC, are connected
together in parallel, the initial current will be on the order of
100 C. The initial current of 100 C quickly drops to a lower value,
but the initial current can be damaging, especially to the battery
being charged. Lithium ion cells are normally rated to handle as
much as 30 C of discharging current and therefore a mostly charged
cell may be able to handle being connected in parallel with a
lesser charged cell. However, lithium ion cells should only be
charged at 0.5 C, or at most, 4 C. Therefore, cells will be damaged
if charged at 100 C.
[0130] Lithium ion cells may be particularly sensitive to abuse,
and they react by exploding and bursting in flames. Accordingly,
the most care must be exercised when connecting such batteries in
parallel. Lithium ion batteries should be connected directly in
parallel only when the voltages on these batteries are equal or
nearly equal so that the resulting current is minimized and damage
does not occur to the batteries or cells.
[0131] In fact, applications that use any batteries with low series
resistance require methods of safely connecting these batteries in
parallel to avoid damage that may occur from excessive currents on
initial connection. The peak surge current when two batteries are
connected in parallel is equal to the difference in voltage divided
by the total series resistance in the circuit, which is mostly the
internal resistance of the batteries. To reduce that peak, either
the numerator, which is the difference in the voltages of the
batteries, should be minimized, or the denominator, which is the
total series resistance, should be maximized. Newer battery
technologies are characterized by low internal series resistance
which is a desirable feature. Hence, attempting to reduce the peak
current by increasing the series resistance is not a viable
solution since increasing the series resistance will result in a
significant amount of energy being dissipated as heat during normal
operation. As such, minimizing the difference in battery voltages
presents the best technique for minimizing initial peak currents
when batteries are initially connected in parallel.
[0132] FIG. 11 is a schematic illustration of an embodiment of two
parallel connected batteries 1100. As illustrated in FIG. 11,
battery 1102 includes a voltage source 1114 having a voltage
(V.sub.1) that is equal to 12 volts. The series resistance 1110 of
battery 1102 is 0.5 mOhm. Battery 1104 has a voltage source 1116
having a voltage V.sub.2 that is equal to 10 volts. The series
resistance 1112 is the same as series resistance 1110 of battery
1102, which is 0.5 mOhm.
[0133] FIG. 12 is a calculation 1200 of the initial current 1106
created when batteries 1102, 1104 are connected in parallel, as
illustrated in FIG. 11. As shown in FIG. 12, the initial current is
the difference in the voltages, i.e., 12 volts minus 10 volts (2.0
volts), which is divided by the total of the series resistances,
which is 1 mOhm. This results in an initial current of 2,000
amps.
[0134] FIG. 13 is a schematic illustration of an embodiment of two
parallel connected batteries 1300. Battery 1302 is connected in
parallel with battery 1304 by switch 1308. Voltage source 1314 of
battery 1302 provides a voltage of 10.2 volts. The series
resistance 1310 of battery 1302 is 0.5 mOhm. Battery 1304 includes
a voltage source 1316, which provides a voltage V.sub.2 equal to 10
volts. Series resistance 1312 of battery 1304 is 0.5 mOhm. When
switch 1308 is closed, current 1306 flows between batteries 1302,
1304.
[0135] FIG. 14 is an equation illustrating a calculation 1400 of
the initial current 1306 that flows between the two batteries 1302,
1304 when switch 1308 is initially closed. As illustrated in FIG.
14, the current (i) 1306 is equal to the difference in voltages,
which is 10.2 volts minus 10 volts (0.2 volts) divided by the total
resistance of the two batteries, which is 1 mOhm. The initial
current is calculated as 200 amps. Hence, the change of voltage
from a difference of 2 volts to a difference of 0.2 volts reduces
the initial current by an order of magnitude from 2000 amps to 200
amps.
[0136] FIG. 15 is a schematic illustration of an embodiment of two
parallel connected batteries 1500. As illustrated in FIG. 15,
battery 1502 includes a voltage source that has a voltage V.sub.1
equal to 10.02 volts. The series resistance 1510 of the battery
1502 is 0.5 mOhm. Battery 1504 has a voltage source 1516 that has a
voltage V.sub.2 equal to 10 volts. The series resistance 1512 of
battery 1504 is 0.5 mOhm. Switch 1508 connects battery 1502 in
parallel with battery 1504 so that a current 1506 flows between the
batteries.
[0137] FIG. 16 is a calculation 1600 of the initial current 1506
that flows between battery 1502 and battery 1504 when initially
connected. The current (i) 1506 is equal to the difference in
voltages 10.02 minus 10 volts, which is 0.02 volts, divided by the
total series resistance of batteries 1502 and 1504, which is 1
mOhm. This produces an initial current of 20 amps. The difference
in voltages is reduced by an order of magnitude, which reduces the
initial current by an order of magnitude to 20 amps from 200 amps,
as illustrated in FIG. 14.
[0138] Accordingly, FIGS. 11-16 illustrate the manner in which the
initial current can be greatly reduced by connecting batteries that
have output voltages that are very close. FIGS. 11-16 also provide
a perspective that a difference between the batteries of only 0.02
volts can still result in an initial current of 20 amps.
[0139] These same problems are also encountered when a battery is
connected to a load that has a large capacitance. The initial
in-rush of current to charge up the capacitor of the load to the
battery voltage can result in damage to the battery, the load,
and/or interconnections between the battery and the load.
[0140] As illustrated in FIG. 17-21, precharging of a load can be
used to equalize the charge on the load and the battery, which can
limit the initial in-rush of current when the capacitive load and
the battery are initially connected. As illustrated in FIG. 17,
battery 1702 has a voltage V.sub.1. A precharge resistor 1710 is
used, which may have a resistance of 100 ohms. Precharge switch
1708 is used to connect the battery 1702 to a capacitive load 1704
to charge the load 1704 to a charge level that is substantially
equal to the charge level V.sub.1 of battery 1702.
[0141] As shown in FIG. 18, pre-charge switch 1708 is closed, and
current flows from the battery 1702 to charge the load 1704. The
precharge switch remains closed until the battery 1702 and load
1704 are equalized.
[0142] As illustrated in FIG. 19, once the capacitive load 1704 is
charged to the voltage V.sub.1, the main switch 1706 is closed and
the pre-charge switch 1708 is opened. Current can then flow from
the battery 1702 directly to the load 1704, such as during
operation of the load 1704. The precharge resistor 1710 is
eliminated from the circuit since the pre-charge switch 1708 is
open.
[0143] FIG. 20 illustrates a graph 1900 that illustrates the
current by flowing from the battery 1702 through the load 1704 when
the pre-charge switch 1708 is initially connected. As illustrated
in FIG. 20, the initial current has a spike, which gradually
decays. The initial current is equal to V.sub.1 over R, which may
range from approximately 10 amps to 100 amps.
[0144] FIG. 21 is a graph of the voltage across the load 1704
versus time. As shown in FIG. 21, the voltage plot 1704 of the
voltage across the load 1704 increases rapidly until it reaches the
battery voltage V.sub.1 at approximately t=1.
[0145] The use of a resistor, such as precharge resistor 1710, as
illustrated in FIGS. 17-21, for precharging has the disadvantage of
dissipating energy, which is undesirable in situations in which
battery charge is a valuable commodity. An additional surge may
occur when the main switch is connected to the load if the voltages
are not sufficiently equalized.
[0146] Post discharging of loads may also be necessary for safety
reasons and other reasons. Post discharging resistors can be used
for this process, such as illustrated in FIGS. 22-25. FIG. 22
illustrates a post discharge circuit 2200. As illustrated in FIG.
22, battery 2202 has a voltage V.sub.1. Battery 2202 is connected
to switch 2208 so that current 2302 is supplied to load 2204.
Switch 2210 is open, which isolates the discharge resistor
2206.
[0147] FIG. 23 is an illustration of the discharge circuit 2200
during the post discharge mode. As illustrated in FIG. 23, switch
2208 is open and switch 2210 is closed. Discharge resistor 2206
discharges the current 2400 on the load 2204 through dissipation in
discharge resistor 2206 while switch 2210 is closed. Battery 2202
is disconnected from the circuit by switch 2208.
[0148] FIG. 24 is a graph 2400 of the current flowing through the
discharge resistor 2206. As shown in FIG. 24, at t=0 the current
has an initial spike when switch 2210 is closed and decays to 0
over time proportional to the size of the discharge resistor 2206
and to the capacity of load 2204.
[0149] FIG. 25 is a graph of the voltage across the load 2400
versus time. At time t=0, the voltage is equal to V.sub.1. The
voltage across the load 2204 slowly decays as the current 2400
flows through the discharge resistor 2206. Again, the charge on the
capacitive load is wasted as dissipated heat.
[0150] FIG. 26 is a schematic illustration of an embodiment a
battery connection circuit 2600. Battery module 2602 includes a
battery 2208 and a controller 2612. Controller 2612 controls the
operation of switch 2610 and detects the terminal voltage of
battery 2608 on nodes 2630, 2628 and a second battery 2604 on nodes
2620, 2628. Battery 2604 is connected to battery module 2602 by
terminals 2620, 2622. Controller 2612 may also be connected to the
battery 2604 to detect any current flowing from the battery 2604 to
load 2626. Detection of current may occur over a communication link
from a module mounted on the battery 2604 or from a separate
circuit (not shown) connected to the battery 2604.
[0151] As shown in FIG. 26, switch 2610 is open. Hence, current
2606 does not flow between battery 2608 and battery 2604.
Controller 2612 generates a control signal 2614, which activates
the switch 2610. Controller 2612 activates the switch 2610 when it
is determined that the terminal voltages of battery 2608 and
battery 2604 are sufficiently close that an initial rush of current
between battery 2608 and battery 2604 will not damage either of the
batteries, terminals 2620, 2622 or switch 2610. Controller 2612 may
also detect current flowing from battery 2604 to a load 2626, as
indicated above. If current is flowing from the battery 2604, the
open circuit voltage may be different from the terminal voltage of
the battery 2604 since the load 2626 may draw down the terminal
voltage of battery 2604, due to the internal series resistance of
battery 2604. If the switch 2610 is closed when the battery 2604 is
connected to a load 2626 and a substantial amount of current is
flowing between the battery 2604 and the load 2626, a surge in
current may occur between battery 2604 and battery 2608 if the load
2626 is disconnected or the current between battery 2604 and the
load 2626 changes. As such, controller 2612 includes logic that may
prevent the generation of control signal 2614 to close the switch
2610 if the current from the battery 2604 to a load 2626 is
high.
[0152] FIG. 27 is a graph of the current 2606 versus time. Since
the switch 2610 is in an open condition, the current 2606 is zero
until t=0. When t>0, there is no current since battery 2608 has
the same exact terminal voltage as the terminal voltage of battery
2604.
[0153] FIG. 28 is an illustration of the battery connection circuit
2600 of FIG. 26 with the switch 2610 in a closed position. As shown
in FIG. 28, at time t=0 switch 2610 closes. Controller 2612 detects
the terminal voltage of battery 2604 and battery 2608 to determine
if the switch 2610 can be safely closed without causing a large
in-rush of current that may damage the batteries. Having done so,
even after switch 2610 closes at time t=0, there is no significant
current, as shown in FIG. 28.
[0154] FIG. 29 is a graph showing the voltage at terminals 2620,
2622. At time t=0, switch 2610 is closed, which applies the voltage
(V.sub.1) of battery 2608 to the terminals 2620, 2622, which is the
same as the terminal voltage of battery 2604. As controller 2612
ensured that the voltage of battery module 2602 was close to the
voltage of battery 2604 before closing switch 2610, the voltage
across terminals 2620 and 2622 remains the same after switch 2610
is closed.
[0155] FIGS. 30-33 disclose a charging battery equalization circuit
3000 in different states of operation. As illustrated in FIG. 30, a
battery module 3002 is wired for connection to battery 3012 having
a voltage (V.sub.2). Battery module 3002 includes a battery 3006
having a voltage (V.sub.1). A charger 3004 is connected to battery
3006 and is controlled by a controller 3010. Controller 3010 is
connected to the terminals of battery 3012 to detect the terminal
voltage of battery 3012. In addition, controller 3010 is connected
to the terminals of battery 3006 to detect the terminal voltage of
battery 3006. Controller 3010 also controls the operation of switch
3008.
[0156] In FIG. 31, the battery module 3002 is connected to battery
3012. Controller 3010 detects that the terminal voltage (V.sub.2)
is greater than the battery voltage (V.sub.1) of battery 3006.
Controller 3010 generates a control signal 3014 to activate charger
3004 to charge battery 3006. Switch 3008 remains in the open
position while battery 3006 is being charged.
[0157] In FIG. 32, controller 3010 detects that the terminal
voltage of battery 3006 is charged to same voltage level as the
terminal voltage of battery 3012. In other words, battery 3006 is
charged until V.sub.1 equals V.sub.2. Controller 3010 then turns
off the charger 3004. Switch 3008 remains in the open position.
[0158] In FIG. 33, controller 3010 closes the switch 3008 after
detecting that the voltage (V.sub.1) in battery 3006 is
substantially equal to the voltage (V.sub.2) in battery 3012.
Charger 3004 remains in the off position. Current 3016 that flows
initially between the battery module 3002 and battery 3012 is
essentially zero.
[0159] FIGS. 34-37 illustrate a battery equalization circuit 3400
in different states of operation. As illustrated in FIGS. 34-37, a
charger 3414 is used to charge battery 3412, which has a voltage
(V.sub.2) that is less than the voltage (V.sub.1) on battery
3404.
[0160] As illustrated in FIG. 34, battery module 3402 is wired for
connection with battery module 3410. Battery module 3402 includes a
battery 3404 that has a terminal voltage (V.sub.1). Controller 3408
generates a control signal 3416 to control switch 3406. Controller
3408 also generates a control signal 3418 that controls the
operation of charger 3414 to charge battery 3412 in battery module
3410.
[0161] As illustrated in FIG. 35, battery module 3410 is connected
to battery module 3402, but no current is flowing between battery
3404 and battery 3412 since switch 3406 is in the open position.
Controller 3408 detects the terminal voltage of battery 3412 at
nodes 3420, 3422. Similarly, controller 3408 detects the terminal
voltage of battery 3404 at nodes 3424, 3422. The value of the
measurement of the voltage of battery 3412 can also be provided to
controller 3408 over a communication link from a controller in
battery module 3410 (not shown). Controller 3408 detects that the
battery 3412 has a terminal voltage (V.sub.2) that is less than the
terminal voltage (V.sub.1) of battery 3404. Controller 3408 then
generates control signal 3418 to turn on charger 3414 to charge
battery 3412.
[0162] As illustrated in FIG. 36, controller 3408 detects that
battery 3412 has been charged to a voltage which is substantially
equal to the voltage of battery 3404, and generates a control
signal 3418 to turn off the charger 3414. In other words,
controller 3408 detects that V.sub.1 is substantially equal to
V.sub.2. Switch 3406 of battery module 3402 remains in an open
position so that no current is flowing between battery module 3402
and battery module 3410.
[0163] As illustrated in FIG. 37, the controller generates the
control signal 3416 to close switch 3406, once the controller 3408
has detected that the voltage (V.sub.1) of battery 3404 is
substantially equal to the voltage (V.sub.2) of battery 3412.
Control signal 3418 causes the charger 3414 to remain in an off
condition. A low level current (i) 3420 then may flow between the
battery module 3402 and battery module 3410 to further equalize the
charges between batteries 3404, 3412. Current 3420 should remain at
a sufficiently low level so the damage is not caused to batteries
3404, 3412 since battery 3412 has been charged so that V.sub.2 is
substantially equal to V.sub.1.
[0164] Of course, chargers can be placed in both battery modules,
which would constitute a combination of the circuits illustrated in
FIGS. 30-33 and FIGS. 34-37.
[0165] FIGS. 38-41 illustrate a discharging equalizer circuit 3800.
If there is no external source of power to charge the batteries,
the battery modules may include a load resistor to dissipate energy
and lower the voltage of the battery that is at a higher voltage in
order to equalize the voltages between the batteries prior to
connection.
[0166] As illustrated in FIG. 38, the discharging equalizer circuit
3800 includes a battery module 3802 that is wired for connection
with a battery 3804. Battery module 3802 includes a battery 3806
that has a terminal voltage (V.sub.1). Discharging resistor 3842 is
wired to be connected in parallel with battery 3806 upon activation
of switch 3848. Controller 3808 generates a control signal 3844
that activates switch 3848 to connect the discharging resistor 3842
in parallel with battery 3806. Controller 3808 also generates a
control signal 3840 to activate switch 3846. Battery 3804 has a
voltage (V.sub.2) that is greater than V.sub.1 in the example
illustrated in FIGS. 38-39.
[0167] As shown in FIG. 39, controller 3808 has determined that the
battery 3806 has a voltage that is greater than the voltage of
battery 3804 by detecting the terminal voltage of battery 3804 on
nodes 3850, 3852 and battery 3806 on nodes 3854, 3852. Battery
voltages can also be reported through a communication link from a
controller on battery 3804 (not shown). Switch 3848 is activated by
a control signal 3844 from controller 3808, which connects the
discharging resistor 3842 in parallel with the battery 3806. The
discharge resistor causes the battery 3806 to discharge by
dissipating energy in the discharging resistor 3842.
[0168] In FIG. 40, the controller 3808 detects the voltage on the
battery 3806 on nodes 3854, 3852 and voltage on battery 3804 on
nodes 3850, 3852, or through a communications link. Once the
voltage on battery 3806 is substantially equal to the charge of
battery 3804, the controller 3808 deactivates control signal 3844
to open switch 3848, as illustrated in FIG. 40.
[0169] As illustrated in FIG. 41, controller closes the switch 3846
to connect battery 3806 in parallel with battery 3804 after switch
3848 has been opened, and the voltages on batteries 3806, 3804 are
substantially equal so that an initial in-rush of current does not
occur.
[0170] FIGS. 42-45 illustrate a discharging circuit 4200, which
discharges battery module 4204. As illustrated in FIG. 42, battery
4206 has a voltage that is lower than battery 4216 of battery
module 4204. Battery module 4202 is wired for connection in
parallel with the battery module 4204. Controller 4208 generates a
control signal 4214 that operates switch 4220. Switch 4220 connects
discharge resistor 4218 in parallel with battery 4216 to discharge
battery 4216. Controller 4208 also generates a control signal 4212
to activate switch 4210, which connects battery module 4202 in
parallel with battery module 4204 when the voltages on batteries
4206, 4216 are substantially equal so that a large in-rush of
current does not occur.
[0171] FIG. 43 is another illustration of the discharging
equalization circuit 4200. As shown in FIG. 43, battery module 4202
is connected to battery module 4204. However, current does not flow
between battery module 4202 and battery module 4204 since switch
4210 is in the open position. Controller 4208 detects the terminal
voltages of battery 4216 on nodes 4224, 4226. Similarly, controller
4208 detects the terminal voltages of battery 4206 on nodes 4228,
4226. Since the controller 4208 detects that the voltage on battery
4216 is greater than the voltage of battery 4206, controller 4208
activates control line 4214 to close switch 4220. Switch 4220
connects discharging resistor 4218 in parallel with battery 4216 to
discharge battery 4216.
[0172] FIG. 44 is a schematic illustration of the discharging
equalization circuit 4200 with switch 4220 in an open position.
Controller 4208 generates a control signal 4214 that opens switch
4220 once the terminal voltage of battery 4216 is substantially
equal to the terminal voltage of battery 4206.
[0173] As illustrated in FIG. 45, controller 4208 then activates
switch 4210 to connect battery module 4202 in parallel with battery
module 4204. Current 4222 is sufficiently low that damage is not
caused to batteries 4206, 4216.
[0174] Although FIGS. 38-41 illustrate the discharging of one of
the batteries, and FIGS. 42-45 illustrate the discharging of the
other battery, these circuits can be combined to allow discharge of
either set of batteries by a controller.
[0175] FIG. 46A is a schematic block diagram of an energy exchange
battery equalization circuit 4600. The circuits illustrated in
FIGS. 38-45 disclose energy dissipation circuits, which dissipate
energy from one of the batteries to equalize the charge on the
batteries so that the initial in-rush of current does not damage
the batteries. However, dissipation of energy from the batteries is
inefficient. The energy exchange battery equalization circuit 4600
does not require charging, which requires an external energy
source, or dissipation of charge, which results in wasted energy.
The energy exchange battery equalization circuit 4600 operates by
exchanging charge between the batteries prior to connection of the
batteries in parallel so that the terminal voltages of the
batteries, when connected in parallel, are substantially equal so
that a large amount of current is not created, which may cause
damage to the batteries. As illustrated in FIG. 46A, controller
4608 detects the terminal voltage of battery 4606 at nodes 4220,
4222. Similarly, controller 4608 detects the terminal voltage of
battery 4604 at nodes 4624, 4622. All of this is performed while
the main switch 4616 is open. The DC to DC converter 4610 is
disposed in the battery module 4602. The DC to DC converter 4610 is
connected between battery 4606, 4604 upon closing of the DC to DC
switch 4612 in response to a control signal 4618. When the
controller 4608 detects a difference in the terminal voltages of
batteries 4606, 4604, controller 4608 generates a control signal
4618 that connects the DC to DC converter 4610 to batteries 4606,
4604. The DC to DC converter 4610 may comprise a bi-directional DC
to DC converter that is capable of transferring charge in either
direction between batteries 4606, 4604. In addition, the DC to DC
converter 4610 may comprise a pair of DC to DC converters including
a step-up converter and a step-down converter that can be connected
in the proper orientation in response to the detected voltages and
states of charge of the batteries 4606, 4604 by controller 4608.
The DC to DC converter 4610 transfers charge between the batteries
4606, 4604 until the voltages or states of charge are substantially
equal. At that point, controller 4608 generates a control signal
4616 that closes the main switch 4614 to connect battery 4606 in
parallel with battery 4604. A substantial in-rush of current does
not occur as long as the voltages of batteries 4606, 4604 are
substantially equalized by the DC to DC converter 4610.
[0176] FIG. 46B discloses an energy exchange battery/load
equalization circuit 4650. The energy exchange battery/load
equalization circuit 4650 is similar to the energy exchange battery
equalization circuit 4600, illustrated in FIG. 46A. The difference
between the circuits is that the charge on a capacitive load 4652
is equalized with the charge on battery 4654 prior to connecting
the circuits to prevent damage to battery 4654 and/or load 4652.
Load 4652 may include a large capacitive load such as may be
present at the input of a motor controller circuit. For example,
motor controller circuits are used in electric cars and other
electric vehicles to control the application of current to the
motors of the vehicles. Controller 4662 can detect the terminal
voltages of the load 4652 and the battery 4654 to determine when
the terminal voltages become substantially equal. Controller 4662
activates switch 4658 to allow the DC to DC converter 4656 to
charge the load 4652 to the voltage of the battery 4654. Once the
load 4652 has a voltage that is substantially the same as the
voltage of the battery 4654, the switch 4658 is opened by
controller 4662, and the main switch 4660 is closed. After switch
4660 is opened, the DC to DC converter 4656 can also be used to
discharge the charge on load 4652 and apply that charge to the
battery 4654 to further conserve energy. Discharging the load 4652
is also done to remove voltage from load 4652, for safety
purposes.
[0177] FIG. 47 illustrates the manner in which a step-down
converter system 4700 can be used to transfer charge between a
first battery 4706 and a second battery 4708. As illustrated at
block 4702, the voltage Vb.sub.1 of battery 4706 is greater than
the voltage Vb.sub.2 of battery 4708. A step-down DC to DC
converter 4716 has an input 4712 that is connected to battery 4706.
The output of the step-down DC to DC converter 4716 is connected to
battery 4708. As indicated at block 4704, the state of charge SOC1
of battery 4706 is greater than the state of charge SOC2 of battery
4708. In this manner, energy can be transferred from battery 4706
to battery 4708 in the direction of the arrow 4710.
[0178] As illustrated in FIG. 48, a step-up converter 4716 is
connected between battery 4806 and battery 4808. As shown in FIG.
48, battery 4806 is connected to the input 4812 of the step-up DC
to DC converter, while the output 4814 of the step-up DC to DC
converter is connected to battery 4808. As indicated by block 4802,
battery 4806 has a terminal voltage Vb.sub.1 that is less than the
terminal voltage Vb.sub.2 of battery 4808. However, the state of
charge of battery 4806 is greater than the state of charge of
battery 4808 as indicated by block 4804. Battery 4806 is connected
to a load 4818 that causes the terminal voltage of battery 4806 to
be lower than the terminal voltage (Vb.sub.2) of battery 4808. In
that regard, if load 4818 were disconnected from the battery 4806,
battery 4806 would have a higher terminal voltage than battery
4808. However, since the battery 4806 is connected to the load 4818
and has a lower terminal voltage (Vb.sub.1) than the terminal
voltage (Vb.sub.2) of battery 4808, a step-up DC to DC converter
4816 must be utilized so that energy can be transferred from
battery 4806 (with a higher state of charge, SOC1) to battery 4808
(with a lower state of charge, SOC2), in the direction shown by the
arrow 4810.
[0179] FIG. 49 is a schematic illustration of a step-up converter
system 4900. As illustrated in FIG. 49, the input 4912 of the
step-up DC to DC converter 4916 is connected to battery 4906.
Battery 4906 is also connected to load 4918. The output 4914 of the
step-up DC to DC converter 4916 is connected to battery 4906 having
a terminal voltage (Vb.sub.1) that is greater than the terminal
voltage (Vb.sub.2) of battery 4908. The state of charge of the
battery 4806 is greater than the state of charge of battery 4906,
as indicated at block 4904, even though the terminal voltage of the
battery 4806 (Vb.sub.2) is less than the terminal voltage
(Vb.sub.1) of battery 4906. This is a result of the fact that
battery 4806 is connected to load 4918, which reduces the terminal
voltage Vb.sub.2 of battery 4908. Accordingly, step-up DC to DC
converter 4916 is used to transfer energy from the battery 4806,
that has a higher state of charge, to battery 4906, which has a
lower state of charge, which causes energy to flow in the direction
of the arrow 4910.
[0180] FIG. 50 is a schematic illustration of a step-down converter
system 5000. As illustrated in FIG. 50, battery 5008, having a
terminal voltage Vb.sub.2, is connected to the input 5014 of a
step-down DC to DC converter 5016. Battery 5006, having a terminal
voltage Vb.sub.1, is connected to the output 5012 of the step-down
DC to DC converter 5016. As illustrated in block 5002, battery 5008
has a terminal voltage (Vb.sub.2) that is greater than the terminal
voltage (Vb.sub.1) of battery 5006. In addition, the state of
charge of battery 5008 is greater than the state of charge of
battery 5006. Accordingly, energy flows in the direction of the
arrow 5010.
[0181] FIG. 51 is a schematic illustration of an energy exchange
battery equalization circuit 5100. As illustrated in FIG. 51,
battery 5106 has a voltage (V.sub.1) and is disposed in the battery
module 5102. Battery 5104 has a terminal voltage (V.sub.2) and is
connected to the battery module 5102. Until the main switch 5110 is
closed in response to a control signal 5108 from controller 5104,
no current flows between batteries 5106, 5104. Controller 5104
detects the terminal voltage of battery 5106 at nodes 5132, 5134.
Similarly, controller 5104 detects the terminal voltage of battery
5104 at nodes 5136, 5134. A communication link from modules mounted
on the batteries 5104, 5106 can also supply this information.
Controller 5104 may also receive signals indicating the amount of
current flowing from batteries 5106, 5104 and can calculate the
state of charge of the batteries 5106, 5104. In response to these
signals, controller 5104 can generate control signals to operate
switches 5116, 5118, 5120, 5122 to connect the input and the output
of the step-up DC to DC converter 5112, or activate switches 5124,
5126, 5128, 5130 to connect the input and the output of step-down
DC to DC converter 5114. In this manner, energy can be transferred
between the batteries 5106, 5104 in accordance with the detected
voltages, and states of charge of batteries 5106, 5104, in response
to control signals from controller 5104. Once the voltages or
states of charge are equalized, the controller 5104 can activate
the main switch 5110 to connect the batteries 5106, 5104 in
parallel. If the battery voltage versus the state of charge is not
monotonic, or if the battery resistance is undetermined, the
controller 5104 can use the state of charge information instead of
a calculated open circuit voltage to determine the direction in
which the DC to DC converter should transfer energy. The open
circuit voltage of a loaded battery can be estimated by the
voltage, resistance and current of the battery. As indicated above,
after a sufficient amount of energy is transferred by the selected
DC to DC converter, the main switch 5110 is closed and the DC to DC
converts 5112, 5114 are isolated from the circuit. The controller
5104 monitors a communication link between the battery module 5102
and the battery 5104. If the battery module 5102 becomes
disconnected from battery 5104, controller 5104 opens the main
switch 5110 and the system returns to the initial condition for
safety reasons.
[0182] FIG. 52 illustrates a bi-directional, non-isolated, uk DC to
DC converter 5220 that is capable of transferring charge between
batteries 5222, 5224. Switches 5230, 5232 are alternately closed
which alternately connects the capacitor 5238 in parallel across
the batteries 5222, 5224. In this manner, voltages are temporarily
stored by capacitor 5238. Conductors 5226, 5228 limit the amount of
current that flows through the capacitor 5238 when the switches
5230, 5232 are alternatively closed. The charges stored on the
capacitor 5238 are transferred between the batteries 5222, 5224 to
equalize the charges on batteries 5222, 5224. Switches 5230, 5232
are constructed from MOS technology and include diodes 5234, 5236,
respectively, that temporarily allow current to flow through the
switches 5230, 5232 if the opening and closing of switches 5230,
5232 are not accurately synchronized. The pulse width of the pulses
that operate the switches 5230, 5232 determines the flow of energy
between batteries 5222, 5224. The bi-directional DC to DC converter
5220 is a variation of a uk converter, which uses two active
switches rather a single active switch.
[0183] FIGS. 53 and 54 illustrate an inverting DC to DC converter
5300. Initially, switches 5314, 5316 are closed, which connects the
inverting DC to DC converter in a reverse polarity direction so
that the batteries 5302, 5304 are connected with the proper
polarity. Switch 5318 opens and closes at a high frequency, so that
energy is stored from battery 5303 in inductor 5306, and then
transferred through diode 5308 to battery 5304. Once the batteries
5302, 5304 are equalized, switches 5314, 5316 are opened and then
switches 5310, 5312 are closed as illustrated in FIG. 54.
[0184] Non-isolated DC to DC converters, such as disclosed above,
typically use an inductor, which provides a simpler circuit that is
less expensive and allows essentially all of the input current to
flow to the output. However, non-isolated DC to DC converters do
not isolate the input from the output, which results in noise and
other interference, that may be present on the input, to be
transmitted to the output. Additionally, in simpler topology
non-isolated DC to DC converters, the output voltage is constrained
by the input voltage as explained in more detail below.
[0185] On the other hand, isolated DC to DC converters isolate
noise between the input and output or a first port and a second
port, and the output voltage is not constrained by the polarity or
level of the input voltage. However, isolated DC to DC converters
employ a transformer, which is expensive and less efficient than
simply using an inductor, such as employed in a non-isolated DC to
DC converter.
[0186] Classic, non-isolated DC to DC converters are three-terminal
devices. The output voltage of a non-isolated DC to DC converter
can be either higher than the input voltage, in which case a
step-up converter is used, or lower than the input voltage, in
which case a step-down converter may be used, or may be the
opposite polarity of the input voltage, in which case an inverting
non-isolated DC to DC converter would be used.
[0187] FIGS. 55-66 disclose various implementations of non-isolated
DC to DC converters. For example, FIG. 55 discloses a
three-terminal, non-isolated step-up DC to DC converter system
5500. As illustrated in FIG. 55, battery 5502 has a voltage (Vb)
and is connected to input 5506 of the step-up DC to DC converter
5510. Load 5504 has a voltage (V.sub.1) and is connected to the
output 5508 of the step-up DC to DC converter 5510. The voltage
(Vb) of battery 5502 is less than the voltage (V.sub.1) across the
load 5504. As such, a step-up DC to DC converter 5510 is used to
transfer energy from the battery 5502 to the load 5504.
[0188] FIG. 56 discloses a three-terminal non-isolated step-down DC
to DC converter system 5600. As illustrated in FIG. 56, battery
5602 has a voltage (V.sub.2) and is connected to the input 5606 of
the step-down DC to DC converter 5610. Load 5604 is connected to
the output 5608 of the step-down DC to DC converter 5610. The
voltage (V.sub.1) across load 5604 is less than the voltage (Vb)
across battery 5602. Accordingly, a step-down converter 5610 is
used to transfer energy from the battery 5602 to the load 5604.
[0189] FIG. 57 discloses an inverting DC to DC converter system
5700. As illustrated in FIG. 57, battery 5702 is connected to the
input 5706 of the inverting DC to DC converter 5710. Load 5704 is
connected to the output 5708 of the inverting DC to DC converter
5710. Since the inverting DC to DC converter 5710 inverts the
voltage, the load 5704 is connected in opposite polarity to the
battery 5702.
[0190] FIG. 58 illustrates an isolated four-terminal DC to DC
converter system 5800. As illustrated in FIG. 58, battery 5802 has
a voltage (Vb.sub.1) and is connected to the input 5806 of the
isolated DC to DC converter 5810. Load 5804 has a voltage (V.sub.1)
across its terminals and is connected to an output 5808 of the
isolated DC to DC converter 5810. The isolated DC to DC converter
5810 can be operated such that Vb can be less than V.sub.1, Vb can
be equal to V.sub.1 and Vb can be greater than V.sub.1. In
addition, the polarities of the input and output voltages can be
inverted.
[0191] FIG. 59 is a schematic illustration of a flying inductor DC
to DC converter system 5900. As shown in FIG. 59, battery 5902 has
a voltage (Vb) and is connected to the input 5908 of the flying
inductor DC to DC converter 5912. Load 5904 has a voltage V.sub.1
across its terminals and is connected to the output 5910 of the
flying inductor DC to DC converter 5912. In a manner similar to the
isolated DC to DC converter, Vb can be greater than V.sub.1, Vb can
be less than V.sub.1, Vb can be equal to V.sub.1 and the polarity
of V.sub.1 can be inverted with respect to Vb.
[0192] The flying inductor DC to DC converters share many of the
advantages of the isolated DC to DC converters as well as many of
the advantages of the non-isolated DC to DC converters. Just like
the isolated DC to DC converters, the flying inductor DC to DC
converter essentially isolates noise from being transmitted between
the input and the output of the flying inductor DC to DC converter.
Additionally, the flying inductor DC to DC converter provides a
degree of electrical isolation between its input and output.
Finally, the output voltage level and polarity of the flying
inductor DC to DC converter is not constrained by the input voltage
level and polarity of the input voltage.
[0193] In a manner similar to the non-isolated DC to DC converters,
the flying inductor topology does not require the use of an
expensive and bulky transformer and has the ability to transfer
essentially all of the input current to the output. Accordingly,
the flying inductor DC to DC converter has advantages of both the
isolated and non-isolated converters and can be effectively used as
a DC to DC converter and in systems for equalizing charges on
batteries or between batteries and capacitive loads.
[0194] Further, the flying inductor DC to DC converter system can
be reduced to a three-terminal system from a four-terminal system
by connecting one of the input terminals to one of the output
terminals. In that regard, the negative input terminals can be
connected together, the positive terminals can be connected
together, a negative input terminal can be connected to a positive
output terminal, or a positive input terminal can be connected to a
negative output terminal. FIGS. 60-63 illustrate these various
typologies.
[0195] FIG. 60 is a schematic illustration of the flying inductor
DC to DC converter system 6000 that has the negative input
terminals connected together. As illustrated in FIG. 60, battery
6002 has a voltage Vb. Battery 6002 is connected through the input
6006 that includes a positive terminal and negative terminal 6010.
Battery 6002 supplies a voltage Vb to the flying inductor DC to DC
converter 6000. Load 6004 is connected to output 6008, which has a
positive terminal and a negative terminal 6012. Conductor 6014
connects the negative terminals 6010, 6012 of the flying inductor
together. The negative terminal of the battery 6002 and the
negative terminal of the load 6004 are also connected to the
negative terminals of the flying inductor. The voltage across load
6004 is equal to V.sub.1. The topology illustrated in FIG. 60
allows the voltage Vb to be less than, greater than, or equal to
the voltage V.sub.1. In other words, the flying inductor DC to DC
converter 6016 can operate as a step-up or step-down converter. In
that regard, it is similar to a non-isolated uk converter, but
simpler in operation.
[0196] FIG. 61 is a schematic illustration of the flying inductor
DC to DC converter system 6100 that has the positive terminals
connected together. As illustrated in FIG. 61, battery 6102 is
connected to the input 6106 of the flying inductor DC to DC
converter 6100. Battery 6102 supplies a voltage Vb to the flying
inductor DC to DC converter 6100. Load 6104 is connected to the
output 6108 of the flying inductor DC to DC converter 6100. Load
6104 has a voltage V.sub.1 across its terminals. Conductor 6110
connects the positive terminals of the input to the positive
terminal of the output of the flying inductor DC to DC converter
6100. Accordingly, the flying inductor DC to DC converter 6100 is a
three-terminal device similar to the three-terminal device
illustrated in FIG. 60, but with input and out voltages that are
negative with respect to common conductor 6110. Accordingly, the
flying inductor DC to DC converter 6112 can operate as a step-up
converter or a step-down converter and is also similar to the
non-isolated uk converter.
[0197] FIG. 62 is a schematic illustration of a flying inductor DC
to DC converter system 6200 that has the negative input terminals
connected to the positive output terminal. As illustrated in FIG.
62, battery Vb is connected to the input 6206 of the flying
inductor DC to DC converter 6200. Battery 6202 supplies a voltage
Vb to the flying inductor DC to DC converter 6200. Load 6204 is
connected to the output 6208 of the flying inductor DC to DC
converter 6210. The negative terminal of the input 6206 is
connected to the positive terminal of the output 6208 by conductor
6203, to render this as a three-terminal device. By connecting
these terminals together, the system 6200 becomes an inverting
converter, such as disclosed herein.
[0198] FIG. 63 is a schematic illustration of a flying inductor DC
to DC converter 6300 that has the positive input terminals
connected to the negative output terminal. As illustrated in FIG.
63, battery 6302 is connected to the input 6310 of the flying
inductor DC to DC converter 6314. Battery 6302 supplies a voltage
Vb to the flying inductor DC to DC converter 6300. Load 6304 is
connected to the output 6312 of the flying inductor DC to DC
converter 6300. Load 6304 has a voltage Vb plus V.sub.1 across its
terminals since conductor 6308 connects the positive terminal of
the battery 6302 to the negative terminal of the load 6304. By
connecting the positive terminal of the input to the negative
terminal of the output causes the system illustrated in FIG. 63 to
simply be an inverting converter, as is the one in FIG. 62, though
the polarity is opposite.
[0199] FIG. 64 illustrates a unidirectional DC to DC converter
6400. As illustrated in FIG. 64, energy flows in the direction from
the input to the output as illustrated by arrow 6412. Battery 6402
applies a voltage to the input of the unidirectional DC to DC
converter 6400 that is equal to Vb. The load 6404 is connected to
the output 6408 of the unidirectional DC to DC converter 6410. The
negative terminals of the battery 6402, the load 6404 and the
unidirectional DC to DC converter 6410 are connected together. The
unidirectional DC to DC converter 6410 can only transfer energy
from the input 6406 to the output 6408 in the direction of the
arrow 6412.
[0200] FIG. 65 is a schematic illustration of a bi-directional DC
to DC converter system 6500. As illustrated in FIG. 65, battery
6502 is connected to the first port of the bi-directional DC to DC
converter 6510 and applies a voltage (Vb) to the first port 6506.
Battery 6504 is connected to a second port 6508 of the
bi-directional DC to DC converter 6510 and applies a voltage
Vb.sub.2 to the second port 6508. The bi-directional DC to DC
converter 6510 is capable of transferring energy in either
direction between battery 6502 and battery 6504 as illustrated by
arrow 6512. Bi-directional DC to DC converters may operate to
transfer energy in either direction. Bi-directional DC to DC
converters use active switches in place of rectifier diodes.
[0201] The flying inductor DC to DC converter may also be designed
to operate bi-directionally. However, the flying inductor topology
suffers from several limitations. First, the flying inductor
topology is inherently less efficient than a simple, non-isolated
DC to DC converter because the current path includes two switches
rather than one switch in the non-isolated DC to DC converter.
Further, the flying inductor DC to DC converter does not offer true
galvanic isolation. For example, the maximum voltage difference
between any input terminal and any output terminal is determined by
the relative value of the input and output voltages, as long as the
breakdown voltages of the components used in the flying inductor DC
to DC converter are sufficiently high.
[0202] FIG. 66 illustrates a bi-directional flying inductor DC to
DC converter system 6600. As illustrated in FIG. 66, a first
voltage source 6606 has a voltage V.sub.1 that is connected to the
input 6602 of the bi-directional flying inductor DC to DC converter
6610. Voltage source 6608 has a voltage (V.sub.2) and is connected
to the output 6604 of the bi-directional flying inductor DC to DC
converter 6610. The voltage constraints of the bi-directional
flying inductor DC to DC converter 6610 are that the output voltage
V.sub.2 minus input voltage V.sub.1 can only range between minus
V.sub.2 and plus V.sub.1.
[0203] FIG. 67A is a schematic diagram of an embodiment of a
bi-directional flying inductor DC to DC converter system 6700,
which is unable to include a dead time. As illustrated in FIG. 67,
the flying inductor DC to DC converter 6700 transfers charge in
either direction between battery 6702 and battery 6704. Switches
6716, 6718 are driven by inverting buffers 6708, 6710,
respectively. Switches 6720, 6722 are driven by non-inverting
buffers 6712, 6714, respectively. When the waveform from pulse
waveform generator 6706 is low, switches 6716, 6718 are closed and
switches 6720, 6722 are open. This is defined as Phase A. When the
waveform from pulse waveform generator 6706 goes low, switches
6716, 6718 are open and switches 6720, 6722 are closed. This is
defined as Phase B. As such, when switches 6716, 6718 are open,
switches 6720, 6722 are closed, and vice versa. The opening and
closing of the switches is substantially simultaneous, as a result
of the topology of the circuit of the flying inductor DC to DC
converter 6700. Inductor 6724 is therefore alternately connected
between battery 6702, and battery 6704. Current in the inductor
6724 increases, decreases, and changes direction, depending upon
the pulse width of the pulse waveform generator 6706. In this
fashion, the direction and amount of energy transferred between
batteries 6702, 6704 can be controlled by controlling the timing of
the pulse of waveform generator 6706. Each of the switches 6720,
6722, 6516, 6518 may be implemented with a MOSFET (Metal Oxide
Semiconductor Field Effect Transistor) that includes a reverse
rectifier diode. The reverse rectifier diodes allow for slight
variations in the simultaneity of the opening and closing of the
switches. MOSFETs and IBGTs include intrinsic reverse rectifier
diodes as part of their structure. Discrete rectifier diodes may be
added in parallel with each switch to improve performance of the
intrinsic rectifier diodes, or for switches that do not include an
intrinsic rectifier diode.
[0204] FIG. 67B is a schematic diagram of another embodiment of a
bi-directional flying inductor DC to DC converter system 6720,
which is able to include a dead time. As illustrated in FIG. 67B,
the flying inductor DC to DC converter 6720 transfers charge in
either direction between battery 6702 and battery 6704. Switches
6716, 6718 are driven by buffers 6728, 6730, respectively. When the
waveform 6740 from pulse waveform generator 6736 is high, switches
6716, 6718 are closed. When the waveform 6740 from pulse waveform
generator 6736 is low, switches 6716, 6718 are open. Switches 6720,
6722 are driven by buffers 6712, 6714 respectively. When the
waveform 6741 from pulse waveform generator 6736 is high, switches
6720, 6722 are closed. When the waveform 6741 is low, switches
6720, 6722 are open. As such, switches 6716, 67518 close and open
together. Similarly, switches 6720, 6722 alternately close and open
together. When waveforms 6740 and 6741 are both low, switches 6712,
6722, 6728 and 6730 are all open. This is the Dead Time. Waveforms
6740 and 6741 are never both high. In other words, at no time are
switches 6712, 6722, 6728 and 6730 all closed. Inductor 6724 is
therefore alternately connected between battery 6702, and battery
6704 or not connected to either battery 6702 or battery 6704.
Current in the inductor 6724 increases, decreases, and changes
direction, depending upon the timing of the pulse waveforms 6740,
6741 from generator 6736. In this fashion, waveform generator 6736
can control the direction and amount of energy transferred between
batteries 6702, 6704.
[0205] FIGS. 68-70 illustrate the three operating phases of the
bi-directional flying inductor DC to DC converter of FIG. 67B. FIG.
68 illustrates the phase-A 6800 operating mode of the flying
inductor DC to DC converter. In phase-A, switches 6806, 6808 are in
a closed position and switches 6810, 6812 are in an open position.
During phase-A, the voltage source V.sub.1 is applied across
inductor 6814, with the polarity illustrated in FIG. 68. Voltage
source V.sub.2 6804 is isolated from the inductor.
[0206] FIG. 69 illustrates the operation of the flying inductor DC
to DC converter in phase-B 6900. As illustrated in FIG. 69,
switches 6810, 6812 are in a closed position, while switches 6806,
6808 are in an open position. Voltage source V.sub.2 is applied to
inductor 6814 with the polarity illustrated in FIG. 69. Voltage
source V.sub.1 6802 is isolated from inductor 6814.
[0207] FIG. 70 is a schematic illustration of the flying inductor
DC to DC converter in a dead time phase 7000. As illustrated in
FIG. 70, switches 6806, 6808, 6810, 6812 are all in an open
position. Inductor 6814 is isolated from both voltage sources 6082,
6804.
[0208] The switches illustrated in FIGS. 68-70 may be implemented
as active switches, such as transistors, such as MOSFETs, IGBTs,
BJTs, or thyristors, such as SCRs, GTOs, TRIACs. In some cases,
isolation of the voltage sources is not complete because of the
structure of these switches, such as MOSFETs and IBGTs, as
explained in more detail below.
[0209] FIG. 71 is a schematic diagram of a uni-directional flying
inductor DC to DC converter system 7100. As illustrated in FIG. 71,
a voltage source 7102 supplies a voltage (V.sub.1) to the
uni-directional flying inductor DC to DC converter 7100. The
uni-directional flying inductor DC to DC converter 7100 has two
active switches 7106, 7108, and two rectifier diodes 7114, 7116.
Switch 7106 is operated by non-inverting buffer 7110. Switch 7108
is operated by inverting buffer 7112. Waveform generator 7118
generates a variable duty cycle square wave waveform that operates
buffers 7110, 7112. Accordingly, when the waveform from waveform
generator 7118 goes low, during phase A, switches 7106, 7108 are
closed. When waveform generator 7118 goes high, during phase B,
switches 7106, 7108 are open. Switches 7106, 7108, when closed,
allow current to flow from the voltage source 7102 through the
inductor 7120 in a direction from left to right, as illustrated in
FIG. 71. When switches 7106, 7108 are open, diodes 7114, 7116 allow
current to flow through the inductor 7120 from left to right
through load 7104. The current decays linearly over time when the
current is applied to the resistive load 7104. If the energy in
inductor 7120 is depleted, current ceases to flow, during the dead
time. In this manner, energy is transferred from the voltage source
7102 to the load 7104 in the uni-directional flying inductor DC to
DC converter 7100, illustrated in FIG. 71.
[0210] FIG. 72 is a graph of inductor current versus time of the
uni-directional flying inductor DC to DC converter illustrated in
FIG. 71 that is operating in a discontinuous mode. As illustrated
in FIG. 72, in the first time period, designated as phase-A 7202,
the inductor current increases in a direction from left to right
(positive direction), as illustrated in FIG. 71, because the
voltage V.sub.1 is supplied across inductor 7120. When switches
7106, 7108 are opened at the end of the time period phase-A 7202,
diodes 7114, 7116 conduct the current through the inductor 7120
through the load 7104. The inductor current decays to zero through
the time period phase-B 7104, until the current reaches zero.
During dead time 7206, the output of waveform generator 7118
remains low, so switches 7106, 7108 remain open. At the end of the
period of dead time 7106, waveform generator 7118 generates a pulse
so that switches 7106, 7108 are closed, which begins phase-A
again.
[0211] FIG. 73 is a graph of inductor voltage versus time for the
uni-directional DC to DC converter, which is operating in the
discontinuous mode, such as illustrated in FIG. 72. As illustrated
in FIG. 73, during phase-A 7302, the voltage across inductor 7120
is equal to V.sub.1. The voltage (V.sub.1) of voltage source 7102
is applied across the inductor 7120, as a result of switches 7110,
7112 being closed. During phase-B 7304, the voltage across inductor
7120 is equal to the negative of voltage of load 7104, -V.sub.L,
since switches 7106, 7108 are open and the voltage across load 7104
is applied across the inductor 7120 in a direction opposite
(negative polarity) to the voltage applied by the voltage source
7102. During the period of the dead time 7306, zero voltage is
applied across the inductor 7120. The process then begins again
with phase-A 7308.
[0212] FIG. 74 is a schematic illustration of the phase-A operation
7400 of the uni-directional flying inductor DC to DC converter. As
illustrated in FIG. 74, switches 7404, 7406 are on and diodes 7414,
7416 are off. Waveform generator 7422 is high, which causes buffers
7406, 7412 to generate an output to close switches 7404, 7410, so
that current 7420 flows through switch 7404, inductor 7408 and
switch 7410. As diodes 7414 and 7416 are not conducting, load 7418
is substantially isolated from the voltage source 7402.
[0213] FIG. 75A is a schematic illustration of the phase-B
operation 7500 of the uni-directional flying inductor DC to DC
converter. The output 7422 of waveform generator 7422 is low,
which, through buffers 7406 and 7410, drives switches 7404 and 7410
respectively in an open condition. As such, the voltage 7402 of
voltage source is isolated from inductor 7408. Simultaneously, the
current 7520 in inductor 7408, which was generated during phase-A
operation and which cannot be interrupted, creates a voltage across
inductor 7408 of the opposite polarity from phase A of FIG. 74,
until its amplitude is sufficiently high to forward-bias rectifier
diodes 7414 and 7416. As such, inductor 7408 is connected to load
7418, and current 7520 flows into load 7418. The current flowing
through load 7418, in the manner illustrated in FIG. 75, decays due
to dissipation from the resistive load 7418. Phase B ends when the
current 7520 in inductor 7408 has decreased to 0, at which point
the entire energy in the inductor 7408 has been transferred to load
7418.
[0214] The switches 7404, 7410 of FIG. 75 are assumed to open
essentially simultaneously at the transition between phase-A and
phase-B. However, there can be a short period between the end of
phase-A and the beginning of phase-B during which only one of
switches 7404, 7410 remains closed.
[0215] FIGS. 75B, 75C illustrate the current flow into an external
circuit that results from the loss of isolation due to mismatch in
the opening and closing times of switches 7404, 7410. Specifically,
if switch 7404 were to open first, the current 7420 of FIG. 74
would be interrupted, but the current 7520 would start immediately,
because the current through inductor 7408 cannot be interrupted.
This would connect the inductor 7408 to load 7418 through forward
biased diode rectifiers 7414, 7416, as illustrated in FIG. 75A.
However, switch 7410 would is still closed, connecting the negative
terminal of voltage source 7402 to the positive terminal of load
7418. Similarly, if switch 7410 were to open first, the current
7420 of FIG. 74 would be interrupted, but the current 7520 would
start immediately, because the current through inductor 7408 cannot
be interrupted. This would connect the inductor 7408 to load 7418
through forward biased diode rectifiers 7414, 7416, as illustrated
in FIG. 75A. However, switch 7404 would is still closed, connecting
the positive terminal of voltage source 7402 to the negative
terminal of load 7418. Either one of these conditions result in a
temporary loss of isolation between voltage source 7402 and load
7418.
[0216] As illustrated in FIG. 75B, an impulse of current 7532 flows
in the clockwise direction through an external circuit 7536 during
the time that switch 7404, is closed and switch 7410 is open.
[0217] Conversely, as illustrated in FIG. 75C, an impulse 7534 of
current flows in the counter-clockwise direction through the
external circuit 7536 during the time that switch 7410, is closed
and switch 7404 is open. The current of these pulses can be limited
through the use of low pass filter 7530. If these current impulses
are symmetrical, there is no net DC flow in the external circuit.
However, an asymmetrical mismatch between the opening and closing
times of switches 7404 and 7410 results in a net flow of DC current
through the external circuit. To minimize this loss of isolation,
the opening and closing moments of switches 7404 and 7410 must be
synchronized to a great extent. At the minimum, the asymmetry in
the times must be minimized, so that only AC flows in the external
circuit which can be minimized through the use of filter 7530.
[0218] FIG. 76 is a schematic illustration of the dead time
operation 7600 of a uni-directional flying inductor DC to DC
converter. As illustrated in FIG. 76, switches 7404, 7410 are open,
since buffers 7406, 7412 are off, as a result of the waveform
generator 7422 being in a low condition. After the current in
inductor 7408 decays to zero, no current is flowing through
inductor 7408. The voltage source 7402 is therefore substantially
isolated from the load 7418 during the dead time.
[0219] FIG. 77 is a graph 7700 of inductor current of the
uni-directional flying inductor DC to DC converter 7100 that is
operating in critical mode. As illustrated in FIG. 77, during
phase-A 7702, inductor current gradually builds, since the voltage
V.sub.1 is applied across the inductor 7408. During phase-B 7704,
the switches 7404, 7410 are opened and the current 7424 (FIG. 75),
through the inductor 7408, decays as a result of dissipation and
the resistive load 7418. As soon as the current 7424 decays to
zero, switches 7404, 7410 are closed, as a result of the waveform
generator 7422 going high, and another phase-A 7706 is initiated
and the current again starts to build in the inductor 7408.
[0220] FIG. 78 is a graph 7800 of inductor voltage of a
uni-directional flying inductor DC to DC converter 7100 operating
in critical mode. As illustrated in FIG. 78, the voltage waveform
7808 has a voltage equal to V.sub.1 during phase-A 7802. During
phase-B 7804, the voltage waveform 7808 has a voltage equal to the
negative of the load voltage, -VL. The voltage waveform then
returns to the voltage V.sub.1 during phase C 7806. Phase-B is
timed so that the inductor current decreases to 0 when the next
phase is initiated.
[0221] FIG. 79 is a graph 7900 of inductor current of a
uni-directional flying inductor DC to DC converter 7100 in
continuous mode. The continuous mode of operation is similar to the
critical mode, except that the next phase is initiated before the
current 7424 decays to zero so that there is still current in the
inductor 7408. The new phase is started and more current is added
to the inductor 7408, which is an addition to the current that is
already flowing in the inductor. The continuous mode of operation
is considered continuous because there is always current flowing in
the inductor 7408. The amount of energy transferred is regulated by
adjusting the pulse width modulation of the control signal, which
is the ratio of the duty cycle of phase-A versus the sum of phase-A
plus phase-B. The higher the average inductor current , the higher
the amount of energy transferred. Referring again to FIG. 79,
during phase-A 7902 inductor current increases to I.sub.2, as
illustrated by plot 7908. Phase-B 7904 is such that the current
decreases to I.sub.1 as shown by current plot 7908. Although
Phase-B is shown as shorter, Phase-B could be longer, depending
upon the ratio of the input and output voltage. Phase-A 7906 then
begins again before the inductor current 7908 decreases to
zero.
[0222] FIG. 80 is a plot 8000 of conductor voltage of a
uni-directional flying inductor DC to DC converter 7100 versus time
that is operating in a continuous mode. As illustrated in FIG. 80,
during phase-A 8002, the inductor voltage is at voltage level
V.sub.1. During phase-B 8004 the inductor voltage is the negative
of the load voltage, V.
[0223] FIG. 81A is an illustration of another embodiment 8100 of a
uni-directional flying inductor DC-DC converter, using a biased
inductor. The current in inductor 7408 in FIG. 74 flows in only one
direction, therefore using only one half of the available
magnetization of inductor 7408. Use of a magnetically biased
inductor 8102 allows use of the full range of the available
magnetization of inductor 8102, and therefore allows the use of a
physically smaller inductor for a given amount of power
transferred.
[0224] FIG. 81B is an illustration of the uni-directional flying
inductor DC to DC converter 8100 illustrating an analysis of the
isolation limits of the uni-directional flying inductor DC to DC
converter 8100 with the load pulled as far negative as possible.
Node 8114, on the negative terminal of voltage source 8102, is the
reference, by definition at 0 Volt. Node 8116, on the positive
terminal of load 8104, can be pulled in the negative direction
until rectifier diode 8108 and the intrinsic diode in switch 8112
are forward biased. At that point, the voltage drop across
rectifier diode 8108 is approximately 1 V, as is the voltage drop
across the intrinsic diode in switch 8112. Therefore, the voltage
of terminal 8116 is unable to go any more negative than 2 V below
the reference node 8114. The voltage on node 8118, on the negative
terminal of load 8104, is lower than the voltage on node 8116, on
the positive terminal of load 8104, by an amount equal to the
voltage across the load 8104. Therefore, the voltage on node 8118
is unable to go any more negative than the load voltage, VL, plus 2
V. In other words, the negative end of load 8104 is clamped to
-VL-2 V. The voltage on node 8118 will not be clamped if the
components 8108, 8112 are not allowed to be forward biased, that is
if the voltage on node 8118 is not allowed to go below -VL, the
negative of the voltage of the load 8104.
[0225] FIG. 82 is the illustration of the uni-directional, flying
inductor DC to DC converter 8100 illustrating an analysis of the
isolation limits of a uni-directional flying inductor DC to DC
converter 8100 with the load pulled as far positive as possible.
Node 8116, on the negative terminal of voltage source 8102, is the
reference, by definition at 0 Volt. Node 8118, on the negative
terminal of load 8104, can be pulled in the positive direction
until rectifier diode 8106 and the intrinsic diode in switch 8110
are forward biased. At that point, the voltage drop across
rectifier diode 8106 is approximately 1 V, as is the voltage drop
across the intrinsic diode in switch 8110. Therefore, the voltage
of terminal 8118 is unable to go any more positive than 2 V above
the voltage of node 8122 on the positive terminal of voltage source
8102. The voltage on node 8122 is higher than the voltage on
reference node 8114, on the negative terminal of voltage source
8102, by V1. Therefore, the voltage on node 8118 is unable to go
any more positive than the voltage source voltage, V1, plus 2 V. In
other words, the negative end of load 8104 is clamped to V1-2 V.
The voltage on node 8118 will not be clamped if the components
8106, 8110 are not allowed to be forward biased, that is if the
voltage on node 8118 is not allowed to go above V1, the voltage of
the voltage source 8102.
[0226] The analysis of FIGS. 81A, 81B and 82 show that the voltage
source 8102, and the load 8104, are essentially isolated from each
other as long as the voltage on node 8118 remains within the range
-VL and V1, where VL is the voltage of the load 8104, and V1 is the
voltage of the voltage source 8012. Outside of that range, the
uni-directional, flying inductor DC-DC converter is not
isolated.
[0227] FIG. 83 is a schematic illustration of another embodiment
8300 of the uni-directional DC-DC converter that has a higher
isolation voltage range than the circuit of FIGS. 81A, 81B and 82.
The active switches 8110 and 8112 of FIG. 81A, 81B and 82 are
replaced by bidirectional active switches 8302 and 8304,
respectively. When closed, bidirectional switches 8302 and 8304 are
able to conduct current in either direction. When open,
bidirectional switches 8302 and 8304 do not conduct current in any
direction. A bidirectional switch may consist of two transistors in
series though in the opposite direction, such as two MOSFETs, two
IGBTs, two BJTs. A bidirectional switch may also consist of a
transistor and a rectifier diode in series, with the transistor in
the normal orientation, such as switches 8110 and 8112 in FIG. 82,
and the rectifier diode in the direction that is the opposite of
the intrinsic diode across the transistor. The use of bidirectional
switches removes the limitation of the circuit in FIG. 82, because
there is no longer a series of diodes that can be forward biased
when the load is pulled negatively or positively.
[0228] FIG. 84A is the illustration of a uni-directional, flying
inductor, DC to DC converter 8400 that provides an analysis of the
isolation limits of the uni-directional flying inductor DC to DC
converter 8400, as the load is pulled in the positive direction.
Rectifier diodes 8312, 8314 may have a reverse breakdown voltage of
1.2 kV, that is, they are able to withstand a voltage across them
of 1200 V without conducting or damage. Bidirectional switches
8302, 8304 may have a breakdown voltage of 1.2 kV, that is, they
are able to withstand a voltage across them in either direction of
1200 V without conducting or damage. Node 8306, on the negative
terminal of the voltage source 8308 is defined as a reference. The
voltage on node 8306 is, by definition, 0 V. The voltage on node
8316, on the negative terminal of the load 8316, is pulled up to
positive 1 kV above the reference node 8306. Rectifier diode 8312
is forward biased, allowing the positive 1 KV voltage to be applied
to inductor 8318. The intrinsic diode in the bottom component in
bidirectional switch 8302 is also forward biased, allowing the
positive 1 KV voltage to be applied to the mid-point voltage inside
switch 8302. However, the top component in bidirectional switch
8302 is oriented in the opposite direction, and is therefore
reverse biased. As the breakdown voltage of bidirectional switch
8302 is 1.2 kV, it can withstand that reverse voltage, preventing
the positive 1 KV voltage to be applied to node 8307, on the
positive terminal of voltage source 8308. Therefore, in the
unidirectional, flying inductor DC-DC converter, the voltage source
8308 is isolated from the load 8310 as long as the voltage on the
load 8310 is no more positive than 1 kV.
[0229] FIG. 84B is an illustration of the uni-directional, flying
inductor, DC to DC converter 8400 that provides an analysis of the
isolation limits of a uni-directional flying inductor DC to DC
converter 8400, as the load is pulled in the negative direction.
Node 8306, on the negative terminal of the voltage source 8308 is
defined as a reference, at 0 V by definition. The voltage on node
8316, on the negative terminal of the load 8316, is pulled down to
negative 1 kV below the reference node 8306. Rectifier diode 8314
is forward biased, allowing the negative 1 kV voltage to be applied
to inductor 8318. The intrinsic diode in the top component in
bidirectional switch 8304 is also forward biased, allowing the
negative 1 kV voltage to be applied to the mid-point voltage inside
switch 8304. However, the bottom component in bidirectional switch
8304 is oriented in the opposite direction, and is therefore
reverse biased. As the breakdown voltage of bidirectional switch
8304 is 1.2 kV, it can withstand that reverse voltage, preventing
the negative 1 kV voltage to be applied to node 8306. Therefore, in
the unidirectional, flying inductor DC-DC converter, the voltage
source 8308 is isolated from the load 8310 as long as the voltage
on the load 8310 is no more negative than 1 kV.
[0230] The analysis of FIGS. 84A and 84B shows that the voltage
source 8102, and the load 8104, are essentially isolated from each
other as long as the voltage on node 8316 remains within the range
-Vbreakdown and +Vbreakdown, where Vbreakdown is the breakdown
voltage of the components 8312, 8314, 8302, 8304. Outside of that
range, the uni-directional, flying inductor DC-DC converter with
bidirectional switches is not isolated.
[0231] FIG. 85 is a schematic illustration of a bi-directional DC
to DC converter 8500 for transferring charges between voltage
sources. As illustrated in FIG. 85, two voltage sources 8502, 8504
are connected to the bi-directional DC to DC converter 8500.
Waveform generator 8506 generates a waveform on output 8508 and
waveform on output 8510. At any given time, waveform 8508 can be
low, or waveform 8510 can be low, of both can be low. At no time
can waveform 8508 and 0810 be both high. These waveforms are
typically variable duty cycle, square wave waveforms. Buffers 8512,
8514 are driven by output 8508 and close switches 8520, 8526 on the
high portion of the waveform at output 8508 of waveform generator
8506. Buffers 8516, 8518 are driven by output 8510 and close
switches 8520, 8526 on the high portion of the waveform at output
8510. As such, switches 8520, 8526 are closed only during a first
phase, phase-A and are opened otherwise. Switches 8522, 8524 are
closed only during a second phase, phase-B and are opened
otherwise. All switches 8520, 8524, 8522, 8526 are opened during a
dead time phase. Hence, current flows through inductor 8528 in
accordance with the timing of the voltage that is alternatively
applied to inductor 8528, resulting in flow of power from either
voltage source 8502 to voltage source 8504, or in the reverse
direction.
[0232] FIG. 86 is a schematic illustration of a bi-directional
flying inductor DC to DC converter 8600 for transferring a charge
from a voltage source 8602 to a load 8604. As illustrated in FIG.
86, the bi-directional DC to DC converter 8600 operates in the same
manner as the bi-directional DC to DC converter 8500, illustrated
in FIG. 85, with the exception that the pulse width of the waveform
that is applied by the waveform generator 8606 controls the amount
of energy that is transferred from the voltage source 8602 to the
load 8604.
[0233] The topology of the circuits illustrated in FIGS. 85 and 86
differs from the uni-directional topology 7100 that is disclosed in
FIG. 71, in that the two rectifier diodes are replaced by active
switches, making the topology of the bi-directional DC to DC
converter 8600 fully symmetrical. The bi-directional DC to DC
converter 8600, illustrated in FIG. 86, has better efficiency than
the uni-directional DC to DC converter 7600, illustrated in FIG.
76, since the active switches in the bi-directional DC to DC
converter 8600 can be designed to have a lower voltage drop than
the forward voltage drop of rectifier diodes 7414, 7416. Therefore,
the bidirectional converter is preferable to the unidirectional
converter even in unidirectional applications, due to its higher
efficiency, though at a slightly higher parts cost.
[0234] The bi-directional DC to DC converter, such as illustrated
in FIGS. 85 and 86, can operate in the discontinuous mode, critical
mode and continuous mode, and in either two or three phases, such
as phase-A, phase-B or an optional dead time phase. In the
bi-directional DC to DC converter, either phase-A or phase-B can
occur first depending upon the direction in which power is to be
transferred. For example, if phase-A occurs first, energy is
transferred from a first power source to a second power source, or
if phase-B occurs first, energy is transferred from a second power
source to a first power source, as disclosed in more detail
below.
[0235] With respect to FIGS. 87-102, current flowing through an
inductor, such as inductor 8726 or 9106, from left to right is
considered to be in a positive direction and current flowing
through inductor 8726 or 9106 from right to left is considered to
be in a negative direction. Similarly, voltage with a voltage more
positive on the right end of the inductor, such as inductor 8726 or
9106, is considered to be a positive voltage, while a voltage more
negative on the right end of the inductor, such as inductor 8726 or
9106, is considered to be a negative voltage.
[0236] FIGS. 87-90 disclose the manner in which energy is
transferred from a first voltage source 8702 to a second voltage
source 8728 by first initiating the operation of the bi-directional
inductor DC to DC converter in phase-A.
[0237] FIG. 87 illustrates phase-A operation 8700 of the
bidirectional floating inductor DC-DC converter transferring energy
in the forward direction. The waveform generator 8704 generates the
first output 8706 in a high condition. As such, buffer 8710 closes
switch 8718 and buffer 8716 closes switch 8720. In this manner, the
current 8730 flows from voltage source 8702 through switch 8718,
through inductor 8726 through switch 8720 and returns to the
voltage generator 8702, transferring energy from voltage source
8702 to inductor 8726. The waveform generator 8704 generates signal
8708 in a low condition. As such, buffers 8712, 8714 open switches
8722, 8724, respectively, isolating inductor 8726 from the second
voltage source 8728.
[0238] FIG. 88 illustrates the phase-B operation 8800 of the
bi-directional flying inductor DC to DC converter, that is
illustrated in FIG. 87, transferring energy in the forward
direction. As shown in FIG. 88, the waveform generator 8704
generates a low signal on output 8706. As such, buffers 8710, 8716
open switches 8718, 8720, respectively, isolating inductor 8726
from the first voltage source 8702. The waveform generator 8704
generates a high signal on output 8708. As such, buffer 8712 closes
switch 8722 and buffer 8714 closes switch 8724. The voltage V.sub.2
from voltage source 8728 is asserted across inductor 8726 in the
manner illustrated in FIG. 88. In other words, the voltage
(V.sub.1) that is asserted across the inductor 8726 in phase-A (in
a positive direction), as illustrated in FIG. 87, is the opposite
of the voltage (V.sub.2) that is asserted across the inductor 8726
during phase-B (in a negative direction), as illustrated in FIG.
88. In this manner, the current in inductor 8726 is discharged onto
second voltage source 8728, transferring the energy stored in
inductor 8726 onto second voltage source 8728. As such, the flying
inductor DC-DC converter succeeded in transferring energy in the
forward directions, from the first voltage source 8702 to the
second voltage source 8728.
[0239] FIG. 89 illustrates a plot 8900 of current through the
inductor for critical mode operation of the bi-directional DC to DC
converter transferring energy in the forward direction illustrated
in FIGS. 87-88. As illustrated in FIG. 89, the inductor current
increases linearly from 0 during phase-A 8902, as illustrated by
the highlighted path 8730 of FIG. 87, as a result of the voltage
V.sub.1 applied across the inductor 8726 in a positive direction.
During phase-B 8904, the current decreases linearly to zero because
of the voltage V.sub.2 that is asserted across the inductor 8726 in
an opposite direction from V.sub.1, as illustrated in FIG. 87,
which decreases the flow of current from left to right in inductor
8726. FIG. 89 shows the inductor current in plot 8908, which is
reduced to zero at the end of phase-B 8904. At the end of phase-B
8904, the voltage of the waveform 8910 (FIG. 90) transitions to a
positive voltage, which causes the inductor current 8908 to
increase again during phase-A 8906.
[0240] FIG. 90 is a plot 9000 of the voltage across the inductor
8726 for critical mode operation of the bi-directional DC to DC
converter 8700 transferring energy in the forward direction. As
illustrated in FIG. 90, the voltage 8910 is initiated at a level V1
during phase-A 8902. During phase-B 8904, the voltage waveform 8910
transitions to a minus V2. Phase-A 8906 is then initiated again, so
that the voltage waveform 8910 transitions to a voltage of V1. The
voltage waveform 8910 is timed so that the inductor current 8908
reaches a maximum during phase-A. During phase-B 8904, the voltage
waveform 8910 has a pulse width so that the current 8908 decays to
zero volts, so that critical mode operation is established.
[0241] FIGS. 91 and 92 are illustrations of a bi-directional flying
inductor DC to DC converter 9100 that transfers energy in the
reverse direction.
[0242] As illustrated in FIG. 91, the processes initiated in
phase-B by the waveform generator 9116, which initially generates a
low condition on control line 9112, and a high condition on control
line 9114. The high condition in control line 9114 causes buffers
9107, 9103 to close switches 9108, 9104, respectively. The voltage
(V.sub.2) is applied to across inductor 9106 with a negative
polarity. Buffers 9120, 9122 are off, which causes switches 9124,
9126 to be open. Consequently, current flows from second voltage
source 910 to inductor 9106, transferring energy from second
voltage source 910 to inductor 9106. Current 9102 flows in inductor
9106 from right to left, in the opposite direction from the
direction illustrated in FIG. 87. The low condition in control line
9112 causes buffers 9121, 9123 to open switches 9122, 9123,
respectively, isolating inductor 9106 from first voltage source
9120.
[0243] FIG. 92 illustrates phase-A operation 9200 of the flying
inductor DC to DC converter that transfers energy in the reverse
direction. As shown in FIG. 92, the waveform generator 9116
generates a low condition on control line 9114. As such, buffers
9103, 9107 open switches 9104, 9108 respectively, isolating the
inductor 9106 from second voltage source 9110. The waveform
generator 9116 generates a high condition on control line 9112. As
such, buffers 9121, 9123 close switches 9122, 9124 respectively.
This causes voltage V.sub.1 to be applied across the inductor 9106
in a positive direction, which is the opposite of the direction in
which V.sub.2 was applied to inductor 9106 during phase B of FIG.
91. Consequently, current 9118 flows from the inductor 9106 to
first voltage source 9120, transferring the energy stored in the
inductor 9106 to first voltage source 9120. As such, the flying
inductor DC-DC converter succeeded in transferring energy in the
reverse directions, from the second voltage source 9110 to first
voltage source 9120.
[0244] FIGS. 93 is a plot 9300 of the current through the inductor
9106 for critical mode operation of the bi-directional DC to DC
converter transferring power in the reverse direction, illustrated
in FIGS. 91-92. As illustrated in FIG. 93, during phase-B 9302 the
inductor current, as shown by plot 9308, starts from 0, then
linearly increases in the negative direction since the current is
flowing from right to left through the inductor 9106, as
illustrated in FIG. 91. At the end of phase-B 9302, as illustrated
in FIG. 94, the voltage V.sub.1 from voltage generator 9120 is
applied across the inductor 9106 in a positive direction during
phase-A 9404 that is opposite to the voltage V.sub.2 that is
applied to inductor 9106 during phase-B 9402. This causes the
current to decrease linearly during phase-A to zero current. As
shown in FIG. 94, at the end of phase-A 9404, the voltage waveform
9308 transitions to a negative pulse, which initiates phase-B 9406.
Since the initiation of phase-B 9406 is at the same time that the
current 9308 reaches zero, this is considered to be the critical
mode of operation of the bi-directional DC to DC converter.
[0245] FIG. 95 is a plot 9500 of inductor current versus time for
discontinuous mode of operation transferring power in the forward
direction. Compared to critical mode, discontinuous mode adds a
dead time, which allows fixing the period of a complete cycle, and
therefore to set the overall switching frequency. As illustrated in
FIG. 95, during phase-A 9502, the current builds from zero to h.
Phase-B 9504 has a period that depends on the ratio of V1 over V2.
The inductor current 9510 decreases to zero during phase-B. During
dead time 9506, the current 9510 is not flowing through the
inductor 9106. Phase-A 9508 then starts and the current 9510 starts
increasing for the period of phase-A 9508.
[0246] FIG. 96 is a plot 9600 of the voltage across the inductor
9106 versus time for a discontinuous mode of operation transferring
energy in the forward direction. As illustrated in FIG. 96, the
voltage waveform 9512 is at a voltage level equal to V.sub.1 during
phase-A 9502. During phase-B 9504, the voltage 9512 transitions to
minus V.sub.2. At the end of phase-B 9504, the voltage transitions
to zero during dead time 9506. Phase-A then begins again at 9508
where the voltage transitions to voltage V.sub.1.
[0247] FIG. 97 is a graph 9700 of the inductor current versus time
for a discontinuous mode of operation while transferring energy in
the reverse direction. As illustrated in FIG. 97, the current 9710
starts at 0 and increases in the negative direction during phase-B
9702, which occurs first. Phase-A 9704 is then initiated and the
voltage V.sub.1 is applied across the inductor, which causes the
magnitude of the current 9710 to decrease until the current reaches
zero. During dead time 9706, no current is flowing in the inductor
since all the switches are off. Phase-B 9708 is then initiated and
the current 9710 begins to increase negatively.
[0248] FIG. 98 is a plot 9800 of inductor voltage 9710 versus time
for a discontinuous mode of operation while transferring energy in
the reverse direction. As illustrated in FIG. 98, the voltage
waveform 9712 across the inductor 9106 is initiated at phase-B 9702
with a voltage of minus V.sub.2 since the voltage source of V.sub.2
is applied across the inductor, such as inductor 9106 in FIG. 91,
as a negative voltage. Phase-A 9704 is then initiated and the
voltage 9712 transitions to a positive voltage V.sub.1 since the
voltage across the inductor 9106, as illustrated in FIG. 92, is
applied in a positive direction. At the end of phase-A 9704, there
is a dead time 9706 in which no voltage is applied across the
inductor 9106. At the end of the dead time 9706, phase-B 9708 is
initiated as a negative pulse.
[0249] FIG. 99 is a plot 9900 of inductor current 9808 versus time
for a continuous mode of operation while transferring energy in the
forward direction. Compared to critical mode, in continuous mode
the inductor current never decays to 0. This allows the total
period of a cycle to be constant, and therefore the switching
frequency to be fixed. As illustrated in FIG. 99, the inductor
current 9908 starts at zero and increases during phase-A 9902.
During phase-B 9904, a voltage equal to minus V.sub.2 is applied
across the inductor in a negative direction, which causes the
current 9908 to linearly decrease to a level i.sub.1. Phase-A 9906
is initiated prior to the time that the current 9908 reaches zero,
which causes the DC to DC converter 8500 to operate in a continuous
mode.
[0250] FIG. 100 is a plot of the voltage of the inductor for a
continuous mode of operation while transferring energy in the
forward direction. During phase-A 10002, a positive voltage V.sub.1
is applied across the inductor. During phase-B 10004, a negative
voltage minus V.sub.2 is applied across the inductor as illustrated
by voltage waveform 10008. Phase-B 1004 is a period that is less
than it would be for critical mode of FIG. 90 so that the current
9908 does not reach zero at the end of phase-B 10004. Phase-A 10006
is initiated prior to the current 9908 reaching zero so that the
flying inductor DC to DC converter is operating in a continuous
mode.
[0251] FIG. 101 is a plot 10100 of inductor current 10108 versus
time for a continuous mode of operation while transferring energy
in the reverse direction. As illustrated in FIG. 101, during
phase-B 10102 the current 10108 starts at 0 and increases linearly
in the negative direction. At the end of phase-B, phase-A 10104 is
initiated, which causes the negative current to steadily decrease.
Prior to the time that the current 10108 reaches zero, phase-B
10106 is initiated so that the flying bridge DC to DC converter
8500 is operating in a continuous mode.
[0252] FIG. 102 is a plot 10200 of inductor voltage 10208 versus
time for a continuous mode of operation while transferring energy
in the reverse direction. As illustrated in FIG. 102, the process
initiated in phase-B 10202 with a negative voltage minus V.sub.2
that is applied to the inductor. Phase-A 10204 is then initiated,
which causes the voltage waveform 10208 to transition to a voltage
of positive V.sub.1. Phase-B 10206 is then initiated at the end of
phase-A 10204. As illustrated in FIG. 102, the pulse width of
phase-A 10204 is less than the pulse width of phase-B 9406 of FIG.
94 for critical mode so that the current 10108 does not reach zero
prior to the time that phase-B 10106 is initiated.
[0253] FIG. 103 is an analysis of the schematic diagram of a
bi-directional, flying inductor DC to DC converter 10300 using
bi-directional switches. As shown in FIG. 103, voltage source 10302
has a voltage V.sub.1. Voltage source 10304 has a voltage V.sub.2.
The circuit illustrated in FIG. 103 operates in the same manner as
described above with regard to the flying inductor converter 8500.
However, each switch is replaced with a bi-directional switch such
as bi-directional switches 10306, 10308, 10310, 10312. The
bi-directional switches 10306-10312 can comprise TRIACs or
transistors/thyristors in series. In bi-directional flying inductor
DC to DC converter circuits, such as illustrated in FIGS. 85-86,
the circuit is limited to a certain differential voltage. For
example, the differential voltage between negative terminal of the
first power source, such as power source 8502 illustrated in FIG.
85, and the negative terminal of the second power source 8504, may
only vary between minus V.sub.1 and plus V.sub.2, where V.sub.1 is
the voltage of the first power source 8502 and V.sub.2 is the
voltage of the second power source 8504. However, the
bi-directional switches 10306-10312 eliminate these restrictions as
there is no intrinsic diode across the active switch that can be
forward biased. However, the input/output voltage differential is
limited by the breakdown voltage of the component used. For
example, as illustrated in FIG. 103, switches 10306-10312 have a
breakdown voltage of 1.2 kilovolts. As such, the circuit
illustrated in FIG. 103 would be able to operate within input to
output differential voltage of plus or minus 1 kilovolt
[0254] FIGS. 104, 105, illustrate other embodiments of the
bi-directional, flying inductor DC-DC converter, reduced from a 4
terminal device to three terminal devices, by connecting one an
input terminal to an output terminal. Such embodiments no longer
provide isolation between the input and the output. Since in the
4-terminal embodiment of the lying inductor DC-DC converter the
input and output are isolated, connecting one an input terminal to
an output terminal is possible without affecting the operation of
the flying inductor DC-DC converter.
[0255] FIG. 104 illustrates another embodiment of the
four-terminal, bi-directional flying inductor DC to DC converter
system 10400, reduced to a three-terminal device with negative
input and output. As shown in FIG. 104, the positive terminal of
batteries 10402, 10404 are connected together by conductor 10410.
Similarly, the positive terminal of battery 10404 is connected to
conductor 10408. Since the switches are alternately opened and
closed, conductors 10406, 10408 can be connected at node 10410
without changing the operation of the circuit.
[0256] FIG. 105 is another embodiment of the four-terminal,
bi-directional flying inductor DC to DC converter 10500, reduced to
a three-terminal device with positive input and output. As shown in
FIG. 105, the flying inductor DC to DC converter 10500 includes
batteries 10502, 10504 that have their negative terminals that are
connected to each other through conductor 10510. Since the switches
10512, 10514, 10516, 10518 are alternately opened and closed,
conductor 10506, 10508 can be connected at node 10510 without
changing the operation of the flying inductor DC to DC converter
10500.
[0257] The foregoing description of the invention has been
presented for purposes of illustration and description. It is not
intended to be exhaustive or to limit the invention to the precise
form disclosed, and other modifications and variations may be
possible in light of the above teachings. The embodiment was chosen
and described in order to best explain the principles of the
invention and its practical application to thereby enable others
skilled in the art to best utilize the invention in various
embodiments and various modifications as are suited to the
particular use contemplated. It is intended that the appended
claims be construed to include other alternative embodiments of the
invention except insofar as limited by the prior art.
* * * * *