U.S. patent application number 15/624321 was filed with the patent office on 2017-10-05 for redundant residential power sources.
The applicant listed for this patent is Google Inc.. Invention is credited to Sangsun Kim, Anand Ramesh.
Application Number | 20170288454 15/624321 |
Document ID | / |
Family ID | 56611572 |
Filed Date | 2017-10-05 |
United States Patent
Application |
20170288454 |
Kind Code |
A1 |
Kim; Sangsun ; et
al. |
October 5, 2017 |
REDUNDANT RESIDENTIAL POWER SOURCES
Abstract
Methods, systems, and apparatus, including computer programs
encoded on a computer storage medium, for controlling a battery
power source. In one aspect, a system includes a first MOSFET
having a first gate, a first source, and a first drain. A second
MOSFET having a second gate, a second source, and a second drain.
The first source is connected to the second source, and the second
drain is coupled to a ground. A control circuit connected to the
first gate and the second gate and that provides control signals to
the first gate and the second gate that cause the first and second
MOSFETS to operate in saturation regions during a first operational
state to cause the first power source to discharge and the first
MOSFET operates in a linear region during a second operational
state to limit a charging current that charges the first power
source.
Inventors: |
Kim; Sangsun; (San Jose,
CA) ; Ramesh; Anand; (Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Google Inc. |
Mountain View |
CA |
US |
|
|
Family ID: |
56611572 |
Appl. No.: |
15/624321 |
Filed: |
June 15, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14808917 |
Jul 24, 2015 |
9716408 |
|
|
15624321 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 7/0068 20130101;
H02J 7/0077 20130101; H02J 7/0031 20130101; H02J 1/10 20130101;
H02J 9/061 20130101 |
International
Class: |
H02J 9/06 20060101
H02J009/06; H02J 1/10 20060101 H02J001/10; H02J 7/00 20060101
H02J007/00 |
Claims
1. A system, comprising: a bidirectional switching circuit having a
first switch terminal and a second switch terminal, wherein the
second switch terminal is coupled to a ground; a first power source
having a first power terminal and a second power terminal, wherein
the first power terminal is connected to the first switch terminal
and second power terminal is connected to a DC bus; a second power
source having a third power terminal and a fourth power terminal,
wherein the third power terminal is connected to the ground and the
fourth power terminal is connected to the DC bus; and a control
circuit connected bidirectional switching circuit and that provides
control signals to the bidirectional switching circuit that cause:
the bidirectional switching circuit to operate in a closed state
during a first operational state to cause the first power source to
discharge; and the bidirectional switching circuit operates in a
current controlling state during a second operational state to
limit a charging current that charges the first power source.
2. The system of claim 1, wherein: the first operational state
occurs when a reference voltage is higher than a voltage of the
first power source as measured between the first power terminal and
the second power terminal; and the second operational state occurs
when: the voltage of the DC bus is greater than the voltage of the
first power source as measured between the first power terminal and
the second power terminal; and the voltage of the first power
source is less than a reference voltage.
3. The system of claim 1, wherein the control circuit provides
further control signals to the bidirectional switching circuit that
causes the bidirectional switching circuit to regulate a voltage of
the first power source.
4. The system of claim 3, wherein the third operational state
occurs when: the voltage of the DC bus is greater than the voltage
of the first power source as measured between the first power
terminal and the second power terminal; and the voltage of the
first power source is less than the reference voltage.
5. The system of claim 3, wherein the control circuit comprises: a
charging voltage control circuit that generates signals to regulate
voltage; and a charging current control circuit that generates
signals to regulate current.
6. The system of claim 1, wherein the bidirectional switching
circuit comprises a first transistor and a second transistor, and
the first and second transistors operate in saturation regions
during the first operational state to cause the first power source
to discharge, and operate in linear regions during the second
operational state to limit the charging current.
7. A method, comprising: monitoring a voltage of a DC bus, the
voltage for the DC bus being provided by a primary power source;
determining that the voltage of the DC bus is below a battery
voltage and in response operating a bidirectional switching circuit
in a first state to cause the battery to discharge onto the DC bus;
determining that the voltage of the DC bus is above the battery
voltage and the battery voltage is below a reference voltage and in
response operating the bidirectional switching circuit to causes
the battery to charge from the DC bus by a controlled current that
is independent of control of the battery voltage; and determining
that the voltage of the DC bus is above the battery voltage and
that the voltage of the battery meets the reference voltage and in
response operating the bidirectional switching circuit to cause the
battery to charge from the DC bus by a controlled voltage that is
independent of control of the current.
8. The method of claim 7, further comprising: detecting a fault
condition on the DC bus; and in response to detecting the fault
condition, operating the bidirectional switching circuit in an open
state to open a portion of a circuit that is connected to the
battery disabling the flow of current within the portion of the
circuit.
9. The method of claim 7, wherein the bidirectional switching
circuit comprises first and second transistors, and operating the
bidirectional switching circuit to causes the battery to charge
from the DC bus comprises: operating the first and second
transistors in a linear region to limit the amount of current
provided to the battery.
10. The method of claim 9, further comprising: determining that the
voltage for the DC bus meets a reference voltage; and regulating
the battery voltage using a charging voltage control circuit,
wherein regulating the battery voltage comprises modulating a
voltage between an input terminal and an output terminal on the
first transistor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of, and
claims priority to, U.S. patent application Ser. No. 14/808,917,
titled "REDUNDANT RESIDENTIAL POWER SOURCES," filed on Jul. 24,
2015. The disclosure of the foregoing application is incorporated
herein by reference in its entirety for all purposes.
BACKGROUND
[0002] This specification relates to bi-directional switches and
disconnects for redundant power systems.
[0003] Many redundant commercial and residential power systems
include a power source (e.g., AC grid, solar power, wind power,
etc.) and a back-up power source (e.g., battery, battery bank,
generator, etc.). The power source can be an AC or DC power source
that provides power to a load. The back-up power source can include
an inverter to convert DC power to AC power to provide AC power to
the load. The power systems supply power to critical and
non-critical loads and the system ensures that in the event the
power source loses functionality, the back-up power source provides
power to continue the load's operation and functionality.
SUMMARY
[0004] In general, one innovative aspect of the subject matter
described in this specification can be embodied in systems and
methods that include a first MOSFET having a first gate, a first
source, and a first drain. A second MOSFET having a second gate, a
second source, and a second drain. The first source is connected to
the second source, and the second drain is coupled to a ground. A
first power source having a first power terminal and a second power
terminal, where the first power terminal is connected to the first
drain and second power terminal is connected to a DC bus. A second
power source having a third power terminal and a fourth power
terminal, where the third power terminal is connected to the ground
and the fourth power terminal is connected to the DC bus. A control
circuit connected to the first gate and the second gate and that
provides control signals to the first gate and the second gate that
cause the first and second MOSFETS to operate in saturation regions
during a first operational state to cause the first power source to
discharge and the first MOSFET operates in a linear region during a
second operational state to limit a charging current that charges
the first power source. Other embodiments of this aspect include
corresponding systems, apparatus, and computer programs, configured
to perform the actions of the methods.
[0005] Particular embodiments of the subject matter described in
this specification can be implemented so as to realize one or more
of the following advantages. The systems and methods disclosed
herein facilitate a transition of providing power from a primary
power source to a secondary power source using inexpensive MOSFET
switches instead of an active battery converter. By utilizing a
bi-directional switch, the systems and methods can discharge (e.g.,
provide power) a secondary power source and can charge the
secondary power source. In doing so, charging to discharging and
discharging to charging transitions are automatically achieved by
voltage and current controllers. In addition, the bi-directional
switch can disconnect the secondary load from a power bus in the
event of a fault on the power bus. The transition from charging to
discharging to disconnecting is achieved with voltage and current
controllers each independently regulating current and voltage
during charging.
[0006] The details of one or more embodiments of the subject matter
described in this specification are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages of the subject matter will become apparent from the
description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a block diagram of an example redundant power
system.
[0008] FIG. 2 is a block diagram of the example redundant power
system that includes a switch and a controller.
[0009] FIG. 3 is a circuit diagram of an example controller.
[0010] FIG. 4 is a diagram illustrating example current and voltage
waveforms representative of various operations of the redundant
power system.
[0011] FIG. 5 is flow diagram of a redundant power system
operation.
[0012] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0013] Overview
[0014] A redundant power system enables a load to receive
uninterrupted power if a primary power source is unable to
independently provide power to the load. Typically, the redundant
power system includes a power source and/or a back-up power source
to power the load by transitioning the supply of power from the
primary power source to the power source and/or back-up power
source. A bi-directional switch that is activated by a controller
can effectuate the back-up power source during a loss of
functionality by the primary power source and/or the power source.
In addition, the bi-directional switch also enables a reverse flow
of current to charge or re-charge the back-up power source.
[0015] The bi-directional switch also operates as a disconnect
switch that can isolate the back-up power source from the load. For
example, in the event of a fault within the system the controller
operates the bi-directional switch to disconnect the back-up power
supply from the load mitigating an over-current situation that may
damage the back-up power source.
[0016] The redundant power system can include a power conversion
architecture for a residential home that is based on one or more
energy sources coupled together with a battery system. For example,
the load may be an AC load or a DC load, the primary power source
can be the AC grid, and the power source can be a photovoltaic
system, a wind turbine, a generator, etc. The power source includes
an AC power source coupled with a converter or a DC power source
that includes an energy conversion mechanism (e.g., buck-boost
transformer). The back-up power source can include a battery or
some other direct current supplying energy source (e.g.,
photovoltaic system, wind turbine, etc.) that supplements power to
the redundant power system.
[0017] These features and other features will be described in more
detail below.
[0018] FIG. 1 is a block diagram of an example redundant power
system 100. The power system 100 provides uninterruptable power to
a load 114. In the example that follows, the system 100 will be
described in the application of a residential power system.
However, the system can be applied in other settings, such as in
commercial applications and industrial applications.
[0019] The power conversion architecture for a residential home is
based on at least one energy source couple with a battery system.
For example, the redundant power system 100 can include a
controller 102, a switch 104, a battery 106, a DC bus 108, a
secondary power source 110, an inverter/rectifier 112, and a
primary power source 116. Typically, the primary power source 116
is the main source of power (e.g., AC grid).
[0020] The secondary power source 110 can include an energy
converter that can convert AC power to DC power or can transform a
DC voltage to a different DC voltage. The secondary power source
can be a solar power system, a wind turbine system, a generator, or
any other power delivery system of the like. The secondary power
source 110 provides DC power to the DC bus 108.
[0021] The inverter/rectifier 112 receives power from the DC bus
108, converts the DC power to AC power to supply to a load 114.
Here the load 114 represents common household electronic devices
that are used within a home, commercial buildings, or utility
infastructure. The inverter/rectifier 112 can be a rectifier, a
solar inverter/rectifier, or any other mechanism that converts AC
power to DC power.
[0022] In some implementations, the inverter/rectifier 112 can be a
rectifier that converts AC power received from the grid to DC
power. For example, the inverter/rectifier 112 may receive power
from the AC grid, convert the power to DC to supply DC power to the
DC bus 118. Often a power system may have a second harmonic (e.g.,
120 Hz) ripple voltage that can exist on the DC bus that is
proportional to the current of the inverter/rectifier output power.
The second harmonic ripple voltage is also inversely proportional
to the DC bus capacitance. The ripple voltage can be minimized by
increasing the DC bus capacitance or lowering the
inverter/rectifier output current.
[0023] The battery 106 is a back-up power source that provides
direct current to the DC bus 108 in the event the primary and
secondary power source 110 fail to independently provide power to
the load 114. The battery 106 can be a single battery or a group of
batteries coupled together, which ever configuration is sufficient
to provide enough current to power the load 114. Typically, the
battery 106 is a rechargeable battery that can discharge stored
energy when it is providing DC power and can charge by accepting a
direct current to replenish stored energy within the battery. For
example, the battery 106 may receive DC power that is supplied by
the AC grid and rectified by the inverter/rectifier 112.
[0024] The battery 106 can also operate in response to an
additional power demand. In some instances, the load may require
more power than can be supplied by the primary and/or secondary
power source. In such an event, the battery 106 may supply
supplemental power to the load 114. In addition, the battery 106
can be operational for charging and discharging for efficient
energy flow that maintains a constant voltage and/or current
supplied to the load 114.
[0025] The battery 106 works in conjunction with a switch 104
during charging and discharging of the battery 106. The switch 104
enables a bi-directional flow of current to and from the DC bus
108. For example, when the battery is discharging, current is
flowing out of the battery. Conversely, when the battery is
charging, current is flowing into the battery. In addition, the
switch can also disconnect the battery 106 from the bus if an event
occurs that may adversely affect the battery, such as a fault being
detected on the bus.
[0026] To manipulate the various functions of the switch 104, the
switch 104 is controlled by the controller 102. The controller 102
operates the switch to enable current to flow in the direction
determined by the redundant power system 100. For example, the
controller 102 can provide a control signal to the switch that
dictates an operational state of the switch (e.g., forward current
flow, reverse current flow, no current flow, etc.) In some
implementations, the controller 102 can be an analog controller or
a digital (e.g., processor, electronic control system, etc.).
Further details regarding the switch 104, the controller 102, and
different implementations of the switch 106 and the controller 102
are described in connection with FIGS. 2, 3, and 4 below.
[0027] FIG. 2 is a block diagram of the example redundant power
system 100 that includes a switch 104 and a controller 102. In one
implementation, the switch 104 is a bi-directional switching
circuit 104 that includes two transistors connected in series. For
example, the two transistors can be MOSFETs 202, 204. By operating
the MOSFETs 202, 204 in their various operational states (e.g.,
linear region, saturation region, cut-off region, etc.), the
MOSFETs function to direct the flow of current as determined by the
redundant power system controller 102.
[0028] As shown in FIG. 2, the bi-directional switching circuit 104
includes a first MOSFET 202 that has a first gate 206, a first
drain 208, and a first source 210. The bi-directional switching
circuit 104 also includes a second MOSFET 204 having a second gate
212, a second source 214, and a second drain 216. In one
implementation, the first source 210 of the first MOSFET 202 is
connected to the second source 214 of the second MOSFET 204, and
the second drain 216 of the second MOSFET 204 is coupled to a
ground 218. In other implementations, the first drain 208 of the
first MOSFET 202 can be connected to the second drain 216 of the
second MOSFET 206.
[0029] The redundant power system 100 includes a first power source
(e.g., the battery 106) having a first power terminal 220 and a
second power terminal 222. In one example, the first power terminal
220 is connected to the first drain 208 and the second power
terminal 222 is connected to a DC bus 108. As previously described,
the first power source provides power to the DC bus 106 when the
first power source is discharging. Generally, the battery 106
discharges when the second power source (e.g., the primary power
source and/or the secondary power source) 110 is unable to
independently power the load 114.
[0030] The redundant power system also includes a second power
source (e.g., the secondary power source) 110 having a third power
terminal 224 and a fourth power terminal 226. In one
implementation, the third power terminal 224 is connected to the
ground 218 and the fourth power terminal 226 is connected to the DC
bus 108. Generally, the second power source 110 is the secondary
power source that can provide power to the load 114 for the
redundant power system 100.
[0031] The operational state of the MOSFETS 202, 204 is typically
controlled by a control circuit (e.g., the controller 102) that is
connected to the first gate 206 and the second gate 212. The
controller 102 provides control signals to the first gate 206 and
the second gate 212. In the example shown, the gates 206 and 212
are coupled to the same control signal; however, depending on the
controller design, the gates can be operated separately and the
MOSFETs 202 and 204 can be operated in different states so long as
the charging and discharging characteristic described below are
realized.
[0032] In some implementations, the control signal causes the first
and second MOSFETs 202, 204 to operate in saturation regions during
a first operational state to cause current to flow (e.g.,
0.about.100 A) from the first power source (e.g., the battery 106).
The controller can also provide control signals to the first and
second MOSFETs 202, 204 to cause the first MOSFET 202 to operate in
a linear region during a second operational state (i.e., the linear
region). Operating in the linear region limits the amount of
charging current that is provided to the first power source during
the charging process. Limiting the charging current that is
received by the first power source enables a controlled charging of
the first power source and ensures that the current draw does not
exceed the current capability of the primary source.
[0033] Operational states of the switching circuit 104 is
dependent, in part, on the DC Bus voltage. Upon failure of the
second power source 110 to independently provide power to the load,
the voltage on the DC bus 108 diminishes. The control circuit
(e.g., the controller 102) determines that the first operational
state occurs when the voltage of the DC bus 108 is less than a
voltage of the first power source (e.g., the battery 106) as
measured between the first power terminal 220 and the second power
terminal 222. The control circuit sends a control signal to the
MOSFETs that cause the MOSFETs to operate in the first operational
state (e.g., saturation region). Operating in the saturation region
enables the first power source to begin powering the load and
deplete the energy stored within the first power source.
[0034] The control circuit (e.g., the controller 102) also
determines the second operational state occurs when the voltage of
the DC bus 108 is greater than the voltage of the first power
source as measured between the first power terminal 220 and the
second power terminal 222. The voltage of the DC bus 108 being
higher than the voltage of the first power source is usually
indicative of the second power source (e.g., the secondary power
source 110) and/or the primary power source 116 returning to
operation. After the battery discharges and the second power source
110 returns to operation, the second operational state (e.g.,
linear mode) enables current to be delivered to the first power
source to charge the first power source. Operating the MOSFETs in
linear mode provides a current controlling mechanism that limits
the amount of current delivered to the first power source.
[0035] The control circuit (e.g., the controller 102) can also
detect a fault condition on the DC bus 108. To protect the first
power source from damage caused by a potential over current
situation, the control circuit sends a control signal to operate
the first MOSFET and the second MOSFET in a cut-off mode. The
cut-off mode opens the portion of the circuit that is connected to
the first power source which disables the flow of current to the
first power source.
[0036] In some implementations (not shown), the redundant power
system can be scaled to include multiple sets of MOSFETs. For
example, the redundant power system 100 can include two or more
sets of MOSFETs connected in parallel between the battery 106 and
ground 218. In some implementations, each pair of MOSFETs can have
a dedicated controller to dictate the operational states for each
pair of MOSFETs. In other implementations, each individual MOSFET
can have its own dedicated controller to dictate the operational
state for an individual MOSFET. The controllers can be
communicatively linked and determine collectively the operational
state for each of the MOSFETs or each controller can independently
determine the operational state for its MOSFET.
[0037] In some implementations, the controller 102 can include an
analog circuit or a digital circuit. For example, the control
circuit (e.g., the controller 102) can include a processing device
that is coupled to the first and the second gate 206, 212 and
provides control signals to the first and second MOSFETs 202, 204
to operate the MOSFETs in the different operational states.
[0038] One example implementation using analog components is shown
in FIG. 3, which is a circuit diagram of an example controller 102.
The control circuit of the controller 102 includes a charging
voltage control circuit 302 and a charging current control circuit
306. The charging voltage control circuit 302 includes a first
amplifier 304 and an output of the first amplifier is coupled to
the first gate 206 and the second gate 212 through a diode D1. The
charging voltage control circuit 302 can sense the voltage of the
battery 106 and compares it to a reference voltage, e.g., a voltage
that is less than the voltage of the DC bus. When the battery
voltage is much less than the reference voltage, the output Vu2
will be high. When the battery voltage is much higher than the
reference voltage, the output Vu2 will be low; otherwise Vu2 will
be adjusted to regulate the battery voltage. Further details about
the reference voltage will be described in connection with FIG.
4.
[0039] The charging current control circuit 306 includes a second
amplifier 308 that has an output that is coupled to the first gate
206 and the second gate 212. The charging current control circuit
306 senses the battery current by means of the current sense
resistor R1. Similar to the battery voltage, when the battery
current is much less than the reference current, the output of the
Vu1 will be high. When the battery current is much higher than the
reference current, the output of the VU1 will be low; otherwise VU1
will be adjusted to limit or regulate the battery current.
[0040] Together the outputs Vu1 and Vu2 cooperative control
charging and discharging of the battery. More specifically, the
output of u1 regulates or limits the charging current by adjusting
the gate-to-source voltage of the MOSFETs 206 and 212 to operate in
the linear operational region during charging. The output of u2 is
coupled by a diode (D1) so that the battery voltage is regulated at
a certain level.
[0041] In some implementations, the operations of the controller
102 may be further subject to a battery management system 310 that
would govern, according to one or more optimization constraints,
when the battery can discharge or charge. The battery management
system 310 can override the controller 102 to either enable or
disable charging and discharging of the battery dependent upon the
optimization constraints. For example, during peak power times,
when it may be more expensive to consume power, the battery
management system 310 may suspend or limit the battery charging
operation.
[0042] The battery management system 310 can govern other aspects
of the redundant power system 100. In some implementations, the
battery management system 310 can override operations of the system
to dictate voltage levels, current draw, operational state of the
switch (e.g., MOSFETS 202, 204), and other operations of the like.
For example, the battery management system 310 may determine, due
to load constraints or some other system attribute, to adjust
(e.g., lower or raise) the voltage the of the DC bus 108 by sending
operational instructions to the inverter 112.
[0043] Operation of the circuit of FIG. 3 is described with
reference to FIG. 4, which is a diagram illustrating example
current and voltage waveforms representative of one example of the
redundant power system's various operations. The current and
voltage waveforms detail one example of the redundant power system
operations for providing uninterruptable power to a load 114.
[0044] Referring to FIG. 4, at time t0, the redundant power system
is operating with the secondary power source 110 independently
providing power to the inverter/rectifier 112. The DC bus voltage
is maintained at a higher voltage than the battery voltage, Vbat,
during the charging mode or when the secondary power source 110 is
independently provding power to the inverter/rectifier 112. The
battery is fully charged and thus the current, Ibat, is almost zero
(or some nominal leakage or inactive value) since the battery is
not providing power to the inverter/rectifier 112. The output
voltage of the charging current controller 306, VU1, is high (e.g.,
significantly greater than a "zero" output, such as at or near the
positive rail).
[0045] The output of the charging voltage controller 302, Vu2, is
low. Because the battery voltage is at or above the reference
voltage value, the charging voltage controller is regulating the
battery voltage. In some implementations, the reference voltage
value is a reference value that is less than the specified DC bus
voltage since the DC bus has the 120 Hz (2.sup.nd harmonic) ripple
voltage 418. As will be explained below, the reference value being
less than the specified DC bus values enables regulation of the
battery voltage during the last portion of the battery recharging
phase, which is referred to as a third operational state.
[0046] Time t1 illustrates the secondary power source 110 failing
to independently supply power to the inverter/rectifier 112. During
this time, the battery is discharging. In some implementations, the
battery can deliver power to the inverter/rectifier 112 without an
failure of the primary and/or secondary power sources. The
controller 102 monitors a voltage of the DC bus 108 indirectly by
means of monitoring the battery 106 voltage. The battery voltage
falling below a reference voltage is indicative of the DC bus being
at or below the battery voltage. The voltage for the DC bus is
typically provided by the secondary power source 110, but as shown
at t1 the DC bus voltage has reached the battery voltage.
Thereafter, the controller determines that the voltage of the DC
bus 108 is below a battery voltage (402) due to the battery voltage
falling below the reference voltage. In response to determining
that the battery voltage is below the reference voltage and the
battery charging current is less than a reference current, the
controller 102 provides a control signal to operate the first and
second MOSFETS 202, 204 in saturation regions to cause the battery
to discharge onto the DC bus 108.
[0047] As shown at time t1 in the circuit of FIG. 3, the output of
the charging current controller, Vu1, remains high and the charging
voltage controller, Vu2, switches its output to high. This results
is a high gate voltage at Vgate (404). The high Vgate voltage
drives the MOSFETs 202, 204 to a saturation region allowing current
to flow from the battery 106 to the DC bus 108. Between the times
t1 and t2, the battery 106 is discharging as indicated by the
decreasing battery voltage Vbat (406). Accordingly, the battery
current, Ibat, is negative (408), indicating power being supplied
by the battery 106 to the inverter/rectifier 112. The negative
value of Ibat also maintains the output VU1 high, as the negative
results in a current sense signal that is less than the reference
current voltage signal. Thus, the time from t1 to t2 is a first
operational state in which the first and second MOSFETS to operate
in saturation regions and the first operational state occurs when
the voltage of the DC bus is less than a voltage of the battery as
measured between the first power terminal and the second power
terminal of the battery.
[0048] During this time, the power loss of MOSFET 204 determined by
the on-resistance R.sub.M2 of the MOSFET 204 during
discharging:
P.sub.Loss=I.sub.Bat,dischgR.sub.M2
[0049] The time t2 represents a second operational state during
which the first MOSFET operates in a linear region to limit a
charging current that charges the battery. This state is caused by
the combination of the voltage of the DC bus being greater than the
voltage of the battery and the voltage of the battery being less
than the reference voltage input amplifier 304, which results in a
battery current regulated at a reference current. In particular, in
the example circuit of FIG. 3, this condition of the DC bus voltage
being higher than the battery voltage causes the battery to
charge
[0050] Referring to FIG. 4, the time t2 illustrates the secondary
power source 110 returning to operation as the DC bus voltage,
Vbus, is higher than the battery voltage, Vbat (410). In response
to the DC bus voltage being higher than the battery voltage but
lower than the reference voltage, the controller 102 cooperatively
operates the first and second MOSFETs 202, 204 to cause the battery
to charge from the DC bus by a controlled current and independent
of control of the battery voltage. For example, the controller 102
provides a control signal to the MOSFETs 202, 204 by changing the
output voltage of the charging current controller 306, VU1. The
voltage Vgate is determined by a voltage drop across resistor R1
that places the first and second MOSFETs 202, 204 in a linear mode,
limiting the amount of current provided to the battery.
[0051] Operating at least the first MOSFET 202 in linear mode
effectuates charging the battery 106 with limited current. As shown
in FIG. 4, Ibat is positive (412), indicating that the battery 106
is receiving current during the charging process.
[0052] Time t3 illustrates a time when the battery voltage has
reached a reference voltage and the battery 106 begins to be
charged with a controlled voltage. This is referred to as a third
operational state. In this state, the nominal voltage of the DC bus
(414) is higher than the battery voltage (416), and the battery
voltage is at least equal or close to the reference voltage.
Because the reference voltage is less than the specified DC bus
voltage, the battery voltage is thus controlled to maintain the
battery voltage below the DC bus voltage to prevent damage and
cycling effects of the battery due to the second harmonic (e.g.,
120 Hz) ripple voltage 418 that is on the DC bus 108.
[0053] In operation, the controller 102 senses that the voltage of
the DC bus 108 meets a reference voltage. In response, the
controller 102 cooperatively operates the first and second MOSFETs
202, 204 to cause the battery to charge from the DC bus 108 by a
controlled voltage and independent of control of the current. For
example, the charging voltage controller 302 changes its output
voltage, VU2. The resulting decreases in Ibat causes the output VU1
to go high. The resulting gate voltage Vgate, determined by the
blocking diode D1 operates the MOSFET 202 in the linear region, but
the battery voltage is regulated by the positive difference between
the battery voltage and the reference voltage.
[0054] During the second and third operational state (during
charging), MOSFET 202 operates in the linear operational region.
Power loss of the MOSFET during charging is mainly determined by
Vbus as,
P.sub.Loss=(V.sub.bus-V.sub.bat).times.I.sub.bat,chg
[0055] In some implementations, to lower Ploss during charging, the
DC bus voltage Vbus remains close to the battery voltage Vbat. Thus
Vbus is adjusted/regulated at slightly higher voltage than the
battery voltage Vbat by an energy converter and/or an
inverter/rectifier.
[0056] FIG. 5 is flow diagram of a redundant power system
operation. The flow diagram describes one implementation of
providing back-up power to a load 114 by a primary and/or secondary
power source 110, a battery 106, a controller 102, and a
bi-directional switching converter 104. In some implementations,
the redundant power system 100 can be used as an uninterruptable
power supply. In other implementations, the redundant power system
100 can be used as a back-up power supply to supply supplemental
power, additional power, etc. to the inverter/rectifier 112. The
process includes a processing device (e.g., analog controller,
digital controller, etc.) that is configured to monitor a voltage
of a DC bus 108 (502). As previously described, when the primary
and/or secondary power source 110 is independently powering the
load 113, the voltage for the DC bus 108 is being provided by a
primary and/or secondary power source.
[0057] The process determines that the battery voltage and current
are below a reference voltage and a reference current and in
response operating the first and second MOSFETs 202, 204 in
saturation regions (504). Operating the first and second MOSFETs
202, 204 in saturation regions closes the portion of the circuit
that is connected to the battery 106 enabling the battery to
discharge current onto the DC bus providing back-up power to the
load 114.
[0058] Upon the primary and/or secondary power source 110 returning
to operation, the process determines that the voltage of the DC bus
108 is above the battery voltage and the battery voltage is below a
reference voltage, and in response cooperatively operates the first
and second MOSFETs 202, 204 to cause the battery to charge by a
limited charging current (506). The battery receives current from
the DC bus 108 by a controlled current and independent of control
of the battery voltage. The first and second MOSFETs 202, 204
operate in a linear mode to provide a current limiting mechanism
that controls the amount of current received by the battery. In
some implementations, during this portion of the charging process,
the charging voltage controller does not control the voltage of the
battery (e.g., Vbat). For example, the voltage of the battery 106
is enabled to recover at an uncontrolled rate according to the
amount of current that is delivered to the battery, and is only
limited by the charging current.
[0059] The battery voltage recovers until it is determined that the
voltage of the battery meets the reference voltage, the battery
current is below a reference current, and in response the process
500 cooperatively operating the first and second MOSFETs 202, 204
to cause the battery to charge from the DC bus 108 by a controlled
voltage and independent of control of the current (508). As
previously described, the charging voltage controller 302 adjusts
the voltage of the battery 106 by adjusting the gate voltage of the
first MOSFET 202. Vbat is maintained at a voltage lower than Vbus
to ensure the second harmonic ripple voltage that is present on the
DC bus does not have an adverse effect on the battery 106.
[0060] The example implementations above are described in the
context of an analog circuit that cooperative controls gate
voltages of the MOSFETS based on a battery voltage and charger
current. Other appropriate analog or digital control circuits can
be used to realize the functional operational states described
above. For example, in other implementations, the control circuit
can drive the MOSFETS 202 and 204 separately. Additionally, the
controller 102 can be implemented as a processing device (not
shown) to control the instructions provided to the bi-directional
switching circuit 104.
[0061] Embodiments of the subject matter and the operations
described in this specification can be implemented in digital
electronic circuitry, or in computer software, firmware, or
hardware, including the structures disclosed in this specification
and their structural equivalents, or in combinations of one or more
of them.
[0062] The operations described in this specification can also be
implemented as operations performed by a data processing apparatus
on data stored on one or more computer-readable storage devices or
received from other sources.
[0063] The term "data processing apparatus" encompasses all kinds
of apparatus, devices, and machines for processing data, including
by way of example a programmable processor, a computer, a system on
a chip, or multiple ones, or combinations, of the foregoing. The
apparatus can include special purpose logic circuitry, e.g., an
FPGA (field programmable gate array) or an ASIC
(application-specific integrated circuit). The apparatus can also
include, in addition to hardware, code that creates an execution
environment for the computer program in question, e.g., code that
constitutes processor firmware, a protocol stack, a database
management system, an operating system, a cross-platform runtime
environment, a virtual machine, or a combination of one or more of
them. The apparatus and execution environment can realize various
different computing model infrastructures, such as web services,
distributed computing and grid computing infrastructures.
[0064] The processes and logic flows described in this
specification can be performed by one or more programmable
processors executing one or more computer programs to perform
actions by operating on input data and generating output. The
processes and logic flows can also be performed by, and apparatus
can also be implemented as, special purpose logic circuitry, e.g.,
a FPGA (field programmable gate array) or an ASIC
(application-specific integrated circuit).
[0065] While this specification contains many specific
implementation details, these should not be construed as
limitations on the scope of any features or of what may be claimed,
but rather as descriptions of features specific to particular
embodiments. Certain features that are described in this
specification in the context of separate embodiments can also be
implemented in combination in a single embodiment. Conversely,
various features that are described in the context of a single
embodiment can also be implemented in multiple embodiments
separately or in any suitable subcombination. Moreover, although
features may be described above as acting in certain combinations
and even initially claimed as such, one or more features from a
claimed combination can in some cases be excised from the
combination, and the claimed combination may be directed to a
subcombination or variation of a subcombination.
[0066] Similarly, while operations are depicted in the drawings in
a particular order, this should not be understood as requiring that
such operations be performed in the particular order shown or in
sequential order, or that all illustrated operations be performed,
to achieve desirable results. In certain circumstances,
multitasking and parallel processing may be advantageous. Moreover,
the separation of various system components in the embodiments
described above should not be understood as requiring such
separation in all embodiments, and it should be understood that the
described program components and systems can generally be
integrated together in a single software product or packaged into
multiple software products.
[0067] Thus, particular embodiments of the subject matter have been
described. Other embodiments are within the scope of the following
claims. In some cases, the actions recited in the claims can be
performed in a different order and still achieve desirable results.
In addition, the processes depicted in the accompanying figures do
not necessarily require the particular order shown, or sequential
order, to achieve desirable results. In certain implementations,
multitasking and parallel processing may be advantageous.
* * * * *