U.S. patent application number 09/741988 was filed with the patent office on 2001-06-21 for dc-dc converter and energy management system.
This patent application is currently assigned to MOTOROLA, INC.. Invention is credited to Miller, Peter.
Application Number | 20010004205 09/741988 |
Document ID | / |
Family ID | 10866543 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004205 |
Kind Code |
A1 |
Miller, Peter |
June 21, 2001 |
DC-DC converter and energy management system
Abstract
An energy management system for a motor vehicle has a first
voltage supply terminal having a first nominal voltage and a second
voltage supply terminal having a second nominal voltage. At least
one of the first and second voltage supply terminals has a battery.
A universal bi-directional DC-DC converter is coupled to exchange
energy between the first and second voltage supply terminals. A
third voltage supply terminal is provided for exchanging energy
between the DC-DC converter and an external vehicle electrical
system or battery charger. The energy exchanged between the first
or second voltage supply terminals and the third voltage supply
terminal is independent of the voltage and polarity of the external
vehicle electrical system or battery charger.
Inventors: |
Miller, Peter; (Shefford,
GB) |
Correspondence
Address: |
MOTOROLA, INC.
1303 EAST ALGONQUIN ROAD
IL01/3RD
SCHAUMBURG
IL
60196
|
Assignee: |
MOTOROLA, INC.
|
Family ID: |
10866543 |
Appl. No.: |
09/741988 |
Filed: |
December 20, 2000 |
Current U.S.
Class: |
323/224 ;
323/282 |
Current CPC
Class: |
H02J 7/1423 20130101;
H02M 3/1582 20130101; Y02T 90/12 20130101; H02J 1/122 20200101;
Y02T 10/70 20130101 |
Class at
Publication: |
323/224 ;
323/282 |
International
Class: |
G05F 001/44 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 1999 |
GB |
992985.2 |
Claims
What is claimed is:
1. A DC-DC converter for use with an energy management system of a
motor vehicle, comprising: first and second voltage supply
terminals having first and second nominal voltages respectively, at
least one of the first and second voltage supply terminals being
arranged for coupling to a battery; and a third voltage supply
terminal for exchanging energy with an external energy means;
wherein the DC-DC converter is arranged to exchange energy between
the first or second voltage supply terminals and the third voltage
supply terminal independent of the voltage and polarity of the
external energy means.
2. The DC-DC converter of claim 1 wherein the universal
bi-directional DC-DC converter comprises five switches, an inductor
and control logic arranged such that energy is exchanged via
step-up and step-down conversion from the first to the second
voltage supply terminal and from the second to the first voltage
supply terminal.
3. The DC-DC converter of claim 1 wherein the switches of the
universal bi-directional DC-DC converter are implemented using
Metal Oxide Semiconductor Field Effect Transistors.
4. The DC-DC converter of claim 3 wherein at least two of the Metal
Oxide Semiconductor Field Effect Transistors are implemented as a
pair of inverse series transistors.
5. The DC-DC converter of claim 1 wherein the external energy means
is an electrical system of another vehicle, such that the energy
management system is coupled to exchange energy with the electrical
system of the other vehicle.
6. The DC-DC converter of claim 5 wherein the exchange of energy is
the charging of a battery of the electrical system of the other
vehicle by the energy management system.
7. The DC-DC converter of claim 5 wherein the exchange of energy is
the charging of the at least one battery by the electrical system
of the other vehicle.
8. The DC-DC converter of claim 1 wherein the external energy means
is a battery charger coupled to charge the energy management
system.
9. The DC-DC converter of claim 1 wherein the external energy means
is an accessory coupled to the third voltage terminal via a
cigarette lighter socket of the vehicle.
10. The DC-DC converter or system of claim 1 wherein the nominal
voltages of the first and second voltage supply terminals are 36
volts and 12 volts respectively.
11. An energy management system for a motor vehicle, comprising:
first and second voltage supply terminals having first and second
nominal voltages respectively; at least one battery coupled to at
least one of the first and second voltage supply terminals; a
universal bi-directional DC-DC converter coupled between the first
and second voltage supply terminals for exchanging energy
therebetween; and a third voltage supply terminal for exchanging
energy between the DC-DC converter and an external energy means;
wherein the energy exchanged between the first or second voltage
supply terminals and the third voltage supply terminal is
independent of the voltage and polarity of the external energy
means.
12. The system of claim 11 wherein the universal bidirectional
DC-DC converter comprises five switches, an inductor and control
logic arranged such that energy is exchanged via step-up and
step-down conversion from the first to the second voltage supply
terminal and from the second to the first voltage supply
terminal.
13. The system of claim 11 wherein the switches of the universal
bi-directional DC-DC converter 200 are implemented using Metal
Oxide Semiconductor Field Effect Transistors.
14. The system of claim 13 wherein at least two of the Metal Oxide
Semiconductor Field Effect Transistors are implemented as a pair of
inverse series transistors.
15. The system of claim 11 wherein the external energy means is an
electrical system of another vehicle, such that the energy
management system is coupled to exchange energy with the electrical
system of the other vehicle.
16. The system of claim 15 wherein the exchange of energy is the
charging of a battery of the electrical system of the other vehicle
by the energy management system.
17. The system of claim 15 wherein the exchange of energy is the
charging of the at least one battery by the electrical system of
the other vehicle.
18. The system of claim 11 wherein the external energy means is a
battery charger coupled to charge the energy management system.
19. The system of claim 11 wherein the external energy means is an
accessory coupled to the third voltage terminal via a cigarette
lighter socket of the vehicle.
20. The system of claim 11 wherein the nominal voltages of the
first and second voltage supply terminals are 36 volts and 12 volts
respectively.
Description
FIELD OF THE INVENTION
[0001] This invention relates to energy management systems and
particularly but not exclusively to such systems for motor vehicles
employing dual voltage electrical schemes.
BACKGROUND OF THE INVENTION
[0002] Many motor vehicle electrical systems are now being designed
with a dual voltage schemes requiring two batteries having nominal
voltages of 14 V and 42 V (12 V and 36 V rated batteries
respectively) as shown in FIG. 1. The 12 V battery 40 typically has
a high amp-hour rating and is used to provide energy to 14 V loads
50 such as lighting circuits and other circuits which are difficult
to implement at higher voltages. The 36 V battery 80 typically has
a high cranking current capability and is coupled to a 42 V
generator and higher voltage loads 70, which may include the engine
starter motor.
[0003] In the event that one or other of these batteries becomes
depleted of charge, there is a need to transfer power between them
in a bi-directional manner. In order to do this, it is known to
provide a conventional bi-directional DC-DC converter 60, coupled
between the 12 V battery 50 and the 36 V battery 80. The
bi-directional DC-DC converter 60 acts as a step-down converter
(right to left in FIG. 1) or a step-up converter (left to right in
FIG. 1) through switching charge through an inductor in a well
known manner.
[0004] An external `start aid` post 10 is also provided, to enable
an external means of charging the batteries. A switch 30 switches
between the start aid post 10 and the 12 V battery 40, and a fuse
and diode arrangement 20 is coupled between the switch 30 and the
start aid post 10. When a positive DC voltage is applied to the
start aid post 10, the switch 30 isolates the 12 V battery 40 and
the DC voltage is coupled through the fuse and diode arrangement 20
to charge the 36 V battery 80 via the bi-directional DC-DC
converter 60. When the DC voltage is removed from the start aid
post 10, the switch 30 isolates the start aid post 10 and
re-couples the 12 V battery 40 to the bidirectional DC-DC converter
60, whereupon (if necessary) the 12 V battery 40 is charged by the
36 V battery 80 via the bidirectional DC-DC converter 60.
[0005] FIG. 2 shows the internal architecture of the bi-directional
DC-DC converter 60, which has a first path 100 coupled to the 36 V
battery 80 (not shown), a second path 170 coupled to the 12 V
battery 40 (not shown), first and second switches 130 and 150
respectively and an inductor 140. The first and second switches 130
and 150 respectively are coupled in series between the first path
100 and earth. The inductor 140 is coupled between the second path
170 and a node between the first and second switches 130 and 150
respectively. The switches are switched by control logic in one of
two ways: to transfer energy from the first path 100 to the second
path 170 (step-down); and to transfer energy from the second path
170 to the first path 100 (step-up). Both of these are achieved by
switching charge through the inductor 140.
[0006] A problem with this arrangement is that for it to function
correctly as a step-up converter, the first path 100 (and hence the
36 battery 80) must be at a higher potential than the second path
170, otherwise the intrinsic body diode 135 of the first switch 130
will conduct. Therefore if the 36 V battery 80 is faulty, greatly
discharged or replaced by a new battery, and therefore has a
voltage less than that of the 12 V battery 40 (or the start aid
post 10, if appropriate), then the current flow will be
uncontrolled, with potentially catastrophic results. It is possible
to prevent this current flow by adding another switch in inverse
series with the first switch 130, but this would still not enable
charging in this state. This problem is compounded by the emergence
of vehicles with an exclusively 42 V electrical system, because
such vehicles cannot be used to provide a jump-start via the start
aid post 10.
[0007] A further problem is that by adding an additional switch the
DC-DC converter 60, the circuit of FIG. 1 would require 7 MOSFETs
(metal-oxide semiconductor field-effect transistors), as the
change-over switch in the start aid post 10 requires 2 sets of
inverse series MOSFETs, in addition to the three required in the
DC-DC converter 60.
[0008] There is therefore a need for a more flexible arrangement
which enables a two-battery vehicle to re-charge either battery
from the other, and which also provides improved flexibility for to
charge and be charged via a start aid post.
[0009] This invention seeks to provide a DC-DC converter and energy
management system which mitigate the above mentioned
disadvantages.
SUMMARY OF THE INVENTION
[0010] According to a first aspect of the present invention there
is provided a DC-DC converter for use with an energy management
system of a motor vehicle, comprising: first and second voltage
supply terminals having first and second nominal voltages
respectively, at least one of the first and second voltage supply
terminals being arranged for coupling to a battery; and a third
voltage supply terminal for exchanging energy with an external
energy means; wherein the DC-DC converter is arranged to exchange
energy between the first or second voltage supply terminals and the
third voltage supply terminal independent of the voltage and
polarity of the external energy means.
[0011] According to a second aspect of the present invention there
is provided an energy management system for a motor vehicle,
comprising: first and second voltage supply terminals having first
and second nominal voltages respectively; at least one battery
coupled to at least one of the first and second voltage supply
terminals; a universal bi-directional DC-DC converter coupled
between the first and second voltage supply terminals for
exchanging energy therebetween; and a third voltage supply terminal
for exchanging energy between the DC-DC converter and an external
energy means; wherein the energy exchanged between the first or
second voltage supply terminals and the third voltage supply
terminal is independent of the voltage and polarity of the external
energy means.
[0012] Preferably the universal bi-directional DC-DC converter
comprises five switches, an inductor and control logic arranged
such that energy is exchanged via step-up and step-down conversion
from the first to the second voltage supply terminal and from the
second to the first voltage supply terminal. The switches of the
universal bi-directional DC-DC converter are preferably implemented
using Metal Oxide Semiconductor Field Effect Transistors, and
preferably at least two of the Metal Oxide Semiconductor Field
Effect Transistors are implemented as a pair of inverse series
transistors.
[0013] Preferably the external energy means is an electrical system
of another vehicle, such that the energy management system is
coupled to exchange energy with the electrical system of the other
vehicle. The exchange of energy is preferably the charging of a
battery of the electrical system of the other vehicle by the energy
management system. Alternatively the exchange of energy is the
charging of the at least one battery by the electrical system of
the other vehicle.
[0014] Alternatively the external energy means is preferably a
battery charger coupled to charge the energy management system.
Preferably the nominal voltages of the first and second voltage
supply terminals are 12 volts and 36 volts respectively.
[0015] In this way an energy management system is provided for a
two-battery vehicle in which either battery may be re-charged from
the other, and in which a start aid post may also be used to charge
one or other battery and be charged by one or other battery,
irrespective of voltage or polarity. The system is also simply
implemented with a minimum number of switches.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] An exemplary embodiment of the invention will now be
described with reference to the drawings in which:
[0017] FIG. 1 shows a prior art energy management system;
[0018] FIG. 2 shows a circuit diagram of the prior art energy
management system of FIG. 1; and,
[0019] FIG. 3 shows a preferred embodiment of an energy management
system in accordance with the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0020] Referring to FIG. 3, there is shown a universal
bi-directional DC-DC converter 200 forming part of an energy
management system of a motor vehicle electrical system having 36 V
and 12 V circuits. The system 200 comprises an inductor 230 and
five switches implemented using MOSFETs: 210 (first), 220 (second),
240 (third) and 250 (fourth) switches use single MOSFETs, and the
fifth switch 260 uses an inverse series pair formed by MOSFETs 262
and 270. Each of the MOSFETs have an inherent body diode 215, 225,
245, 255, 265 and 275 respectively.
[0021] The first switch 210 has a first conducting electrode
coupled to a 36 V terminal 205 (which in turn is coupled to a 36 V
battery (not shown)) and a second conducting electrode coupled to a
first terminal of the inductor 230. The second switch 220 has a
first conducting electrode coupled to the first terminal of the
inductor 230, and a second conducting electrode coupled to a ground
terminal 300.
[0022] The third switch 240 has a first conducting electrode
coupled to a second terminal of the inductor 230, and a second
conducting electrode coupled to a ground terminal 300. The fourth
switch 250 has a first conducting electrode coupled to a 12 V
terminal 290 (which in turn is coupled to a 12 V battery (not
shown)) and a second conducting electrode coupled to the second
terminal of the inductor 230.
[0023] The fifth switch is formed by first and second MOSFETs 262
and 270. The first MOSFET 262 has a first conducting electrode
coupled to the second terminal of the inductor 230 and a second
conducting electrode. The second MOSFET 270 has a first conducting
electrode coupled to the second conducting electrode of the first
MOSFET 262 and a second conducting electrode coupled to a start aid
terminal 280, to which the battery of another vehicle or a battery
charger (not shown) can be connected for the purpose of
jump-starting. In this way the fifth MOSFET 260 and the sixth
MOSFET 270 form the switch 260 for the purpose of switching the
start aid terminal 280.
[0024] In this way the first, second, third and fourth switches
210, 220, 240 and 250 respectively, form a universal bidirectional
step-up/step-down converter between the 36 V battery and the 12 V
battery (not shown), and the fifth switch 260 provides a path to a
start aid post, the path being integrated with the DC-DC
converter.
[0025] Each of the switches 210, 220, 240, 250 and the two MOSFETs
262 and 270 have a control electrode coupled to control logic (not
shown). The control logic manages the switching of the switches
210, 220, 240, 250 and 260 in a manner to be further described
below.
[0026] In operation, the DC-DC converter 200 is arranged to
function in a number of modes, in dependence upon the voltages at
the 36 V terminal 205, the start aid terminal 280 and the 12 V
terminal 290. The control logic uses these voltages to choose a
configuration which satisfies the required transfer of charge, and
to select this configuration by setting the switches 210, 220, 240,
250 and 260 accordingly. The configurations and their respective
switch settings are as follows:
[0027] a) Step-down from 36 V battery terminal 205 to 12 V battery
terminal 290: The first and second switches 210 and 220
respectively are switched in antiphase, the third and fifth
switches 240 and 260 respectively are held in a non-conductive
state and the fourth switch 250 is held in a conductive state. It
should be noted that only the first switch 210 need be switched,
because of the body diodes. However switching the second switch 220
increases the efficiency using a well known technique of active
rectification. This basic approach is true for all the states
below, the following configurations will assume that active
rectification is always used.
[0028] b) Step-down from 12 V battery terminal 290 to 36 V battery
terminal 205 (when the 36 V battery is depleted to a terminal
voltage of less than 12 V): The third and fourth switches 240 and
250 respectively are switched in antiphase, the first switch 210 is
held in a conductive state and the remaining switches are held in a
non-conductive state.
[0029] c) Step-up from 12 V battery terminal 290 to 36 V battery
terminal 205: The first and second switches 210 and 220
respectively are switched in antiphase, the fourth switch 250 is
held in a conductive state and the remaining switches are held in a
non-conductive state.
[0030] d) Step-up from start aid terminal 280 to 36 V battery
terminal 205: The first and second switches 210 and 220
respectively are switched in antiphase, the fifth switch 260 is
held in a conductive state, and the remaining switches are held in
a non-conductive state.
[0031] e) Step-down from start aid terminal 280 to 36 V battery
terminal 205 (when the 36 V battery has a terminal voltage of less
than that of the start aid terminal 280): The third and fifth
switches 240 and 260 respectively are switched in antiphase, the
first switch 210 is held in a conductive state, and the remaining
switches are held in a non-conductive state.
[0032] f) Invert (step up or down) from start aid terminal 280 to
12 V battery terminal 290: The fourth and fifth switches 250 and
260 respectively are switched in antiphase, the second switch 220
is held in a conductive state and the remaining switches are held
in a non-conductive state.
[0033] g) Step down from 36 V battery terminal 205 to start aid
terminal 280: The first and second switches 210 and 220
respectively are switched in antiphase, the fifth switch 260 is
held in a conductive state and the remaining switches are held in a
non-conductive state.
[0034] h) Step up from 36 V battery terminal 205 to start aid
terminal 280: The third and fifth switches 240 and 260 respectively
are switched in antiphase, the first switch 210 is held in a
conductive state and the remaining switches are held in a
non-conductive state.
[0035] i) Invert from 12 V battery terminal 290 to start aid
terminal 280: The fourth and fifth switches 250 and 260
respectively are switched in antiphase, the second switch 220 is
held in a conductive state and the remaining switches are held in a
non-conductive state. It will be evident that this is the same
configuration as f) above but with the energy flow in the other
direction.
[0036] In this way the start aid terminal 280 can accept any
positive voltage and provide energy to the 36 V terminal 205, and
can accept a negative voltage and use an inverting configuration to
provide energy to the 12 V terminal 290. Once either the 12 V or 36
V battery is charged this can be used to charge the other battery
without use of the start aid terminal 280. It will also be seen
that the start aid terminal 280 can be used as a source of power of
any (reasonable) voltage and polarity (for example to jump start
another vehicle or to provide power to an electrical accessory). It
is possible that the start aid terminal 280 could be coupled to an
internal electrical socket such as a conventional cigarette lighter
socket, and could thus be used to provide DC voltage to accessories
plugged into the socket. As all of the switches are present active
rectification is possible in all configurations, providing high
efficiency.
[0037] It will be appreciated that that some configurations may be
used simultaneously. For example operations a) and g) can occur
simultaneously by also switching the fourth and sixth switches 250
and 260 respectfully (thus giving energy to both the 12 V battery
terminal 290 and to the start aid terminal 280 simultaneously,
which is not possible in the prior art arrangement of FIG. 1).
[0038] As can be seen from FIG. 3, six MOSFETs (or equivalent
switches) are used to implement both the universal DC-DC converter
and the start aid terminal 280 switching. This implementation
provides for operation in any battery state and for jump starting
from any reasonable voltage, with one less switch (seven switches
are required in the prior art arrangement of FIGS. 1 and 2).
Furthermore by providing further MOSFETs in inverse series with the
MOSFETs forming the third and fourth switches 240 and 250
respectively (thus making the switch arrangement of the 12 V
terminal 290 similar to that of the start aid terminal 280),
reverse 12 V battery protection is also achieved.
[0039] Therefore vehicles having electrical systems employing
widely differing voltages, such as motorcycles (6 V), conventional
vehicles (12 V), trucks (24 V) and new vehicles (42 V), are able to
provide a jump-start to the motor vehicle, and are able to receive
a jump-start from the motor vehicle, via the start aid terminal
280.
[0040] It will be appreciated that alternative embodiments to the
one described above are possible. For example, the voltages of the
motor vehicle electrical system may differ from those described
above in terms of nominal voltage values and number of batteries.
For example, rather than the two batteries described above, it is
possible to use a single battery (for example a 36 V battery) for
one voltage terminal and a capacitor bank or similar charge storage
arrangement for the other voltage terminal.
[0041] Furthermore the implementation may differ from that
described above. An alternative to the MOSFET technology described
above, such as Insulation Gate Bipolar Transistors (IGBTs) could be
utilised.
* * * * *