U.S. patent application number 10/426942 was filed with the patent office on 2004-11-04 for power converter architecture and method for integrated fuel cell based power supplies.
This patent application is currently assigned to Ballard Power Systems Inc.. Invention is credited to Davis, Roy I., Hampo, Richard J., Van Dyke, John M., Wells, Brian W., Zhu, Lizhi.
Application Number | 20040217732 10/426942 |
Document ID | / |
Family ID | 33309997 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040217732 |
Kind Code |
A1 |
Zhu, Lizhi ; et al. |
November 4, 2004 |
Power converter architecture and method for integrated fuel cell
based power supplies
Abstract
A fuel cell based power supply comprises a main power converter
architecture that allows the fuel cell stack to operate
independently of a desired output voltage. The fuel cell stack may
be directly connected to the main power converter eliminating high
current switches and diodes. Switches are operable to selectively
power an auxiliary component such as a cooling fan to the fuel cell
stack or to a storage device via an auxiliary power converter. A
single auxiliary power converter can replace a dedicated cooling
fan power supply. The power supply operates in a variety of
states.
Inventors: |
Zhu, Lizhi; (Canton, MI)
; Hampo, Richard J.; (Plymouth, MI) ; Davis, Roy
I.; (Saline, MI) ; Van Dyke, John M.;
(Plymouth, MI) ; Wells, Brian W.; (Vancouver,
CA) |
Correspondence
Address: |
SEED INTELLECTUAL PROPERTY LAW GROUP PLLC
701 FIFTH AVE
SUITE 6300
SEATTLE
WA
98104-7092
US
|
Assignee: |
Ballard Power Systems Inc.
Burnaby
CA
|
Family ID: |
33309997 |
Appl. No.: |
10/426942 |
Filed: |
April 29, 2003 |
Current U.S.
Class: |
320/101 |
Current CPC
Class: |
B60L 58/40 20190201;
H02J 2300/30 20200101; Y02T 90/40 20130101; H01M 8/04753 20130101;
Y02T 10/70 20130101; Y02E 60/10 20130101; H01M 8/04395 20130101;
H02M 3/28 20130101; H01M 8/04604 20130101; H01M 16/006 20130101;
H01M 8/04388 20130101; H01M 8/04768 20130101; H01M 8/0494 20130101;
H01M 8/04947 20130101; H01M 2250/20 20130101; H01M 8/0432 20130101;
H02J 7/34 20130101; H01M 8/04955 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
320/101 |
International
Class: |
H02J 007/00 |
Claims
We/I claim:
1. A circuit to selectively provide power between a power source
and a load, the circuit comprising: a main power converter
comprising a primary side and a secondary side, the primary side of
the main power converter electrically coupled directly to the power
source Without at least one of a switch and a diode therebetween,
and the secondary side of the main power converter electrically
couplable to the load; and at least one controller coupled to
control the main power converter.
2. The circuit of claim 1, further comprising: a power storage
device electrically coupled in parallel across the secondary side
of the main power converter.
3. The circuit of claim 1, further comprising: a power storage
device electrically coupled in parallel across the secondary side
of the main power converter; and an auxiliary power converter
electrically coupled between the power storage device and the at
least one controller to provide power to the at least one
controller from the power storage device.
4. The circuit of claim 1, further comprising: a power storage
device electrically coupled in parallel across the secondary side
of the main power converter; an auxiliary power converter
electrically coupled between the power storage device and the at
least one controller to provide power to the at least one
controller; and at least a first switch selectively operable to
electrically couple the auxiliary power converter to a first
auxiliary load to provide power to the first auxiliary load from
the power storage device.
5. The circuit of claim 1, further comprising: a power storage
device electrically coupled in parallel across the secondary side
of the main power converter; an auxiliary power converter
electrically coupled between the power storage device and the at
least one controller to provide power to the at least one
controller; and at least a first switch selectively operable to
electrically couple the auxiliary power converter to a first
auxiliary load to provide power to the first auxiliary load from
the power storage device in at least a first state, and
alternatively, to electrically couple the power source to the first
auxiliary load to provide power to the first auxiliary load from
the power source in at least a second state.
6. The circuit of claim 1, further comprising: a super capacitor
electrically coupled in parallel across the secondary side of the
main power converter; an auxiliary power converter electrically
coupled between the super capacitor and the at least one controller
to provide power to the at least one controller; at least a first
switch selectively operable to electrically couple the auxiliary
power converter to a first auxiliary load to provide power to the
first auxiliary load from the super capacitor during at least a
first time; and at least a second switch selectively operable to
electrically couple the power source to the first auxiliary load to
provide power to the first auxiliary load from the power source,
during at least a second time different from the first time.
7. The circuit of claim 1 wherein the at least one controller is a
main power converter controller, and the circuit further comprises:
a fuel cell controller coupled to receive user input and to control
the power source and the main power converter controller.
8. The circuit of claim 1 wherein the main power converter is an
isolated DC/DC converter comprising a transformer and a plurality
of semiconductor power transistor switches configured as at least a
portion of a bridge.
9. The circuit of claim 8 wherein the main power converter
comprises a high frequency transformer, and the auxiliary power
converter is a second isolated DC/DC converter.
10. A power supply that selectively provides power to a load, the
power supply comprising: a fuel cell stack; a main isolated DC/DC
converter comprising a transformer, a primary side, and a secondary
side, the primary side of the main isolated DC/DC converter
electrically connected directly to the fuel cell stack; a power
storage device electrically coupled to the secondary side of the
main isolated DC/DC converter to receive power therefrom; and at
least a first auxiliary fuel cell system component load
alternatively electrically couplable to: the fuel cell stack to
receive power therefrom, and the power storage device to receive
power therefrom.
11. The power supply of claim 10 wherein the main isolated DC/DC
converter is electrically connected directly to the fuel cell stack
without at least one of a switch and a diode.
12. The power supply of claim 10 wherein the first auxiliary fuel
cell system component load is a fan and driver electronics.
13. The power supply of claim 10 wherein the power storage device
is at least one of a battery and a super capacitor electrically
coupled in parallel across the secondary side of the main isolated
DC/DC converter.
14. The power supply of claim 10, further comprising: an auxiliary
isolated DC/DC converter comprising a primary side and a secondary
side, the primary side electrically coupled to at least one of the
power storage device and the secondary side of the main isolated
DC/DC converter; and a first controller electrically coupled to the
secondary side of the auxiliary isolated DC/DC converter to receive
power from the power storage device via the auxiliary isolated
DC/DC converter, the first controller controllingly coupled to
control the main isolated DC/DC converter.
15. The power supply of claim 10, further comprising: at least one
switch selectively operable to electrically couple the first
auxiliary fuel cell system component load, alternatively, to the
fuel cell stack to receive power therefrom, and to the power
storage device to receive power therefrom.
16. The power supply of claim 10, further comprising: an auxiliary
isolated DC/DC converter comprising a primary side and a secondary
side, the primary side electrically coupled to at least one of the
power storage device and the secondary side of the main isolated
DC/DC converter; and at least one switch selectively operable to
electrically couple the first auxiliary fuel cell system component
load to the auxiliary isolated DC/DC converter to receive power
from the power storage device at a first time, to electrically
couple the first auxiliary fuel cell system component load to the
fuel cell stack to receive power therefrom at a second time, and to
electrically uncouple the first auxiliary fuel cell system
component load from both the fuel cell stack and the auxiliary
isolated DC/DC converter at a third time.
17. The power supply of claim 10 wherein the auxiliary fuel cell
system component load is a fuel cell stack cooling fan and driver
electronics, further comprising: an auxiliary isolated DC/DC
converter comprising a primary side and a secondary side, the
primary side electrically coupled to at least one of the power
storage device and the secondary side of the main isolated DC/DC
converter; and a first controller electrically coupled to the
secondary side of the auxiliary isolated DC/DC converter to receive
power via the auxiliary isolated DC/DC converter, the first
controller controllingly coupled to control the main isolated DC/DC
converter and at least one switch, the first controller configured
to: electrically couple the cooling fan to the power storage device
via the auxiliary isolated DC/DC converter and electrically
uncouple the cooling fan from the fuel cell stack in a startup
state; and electrically uncouple the cooling fan from the power
storage device and electrically couple the cooling fan to the fuel
cell stack in a boost state.
18. The power supply of claim 10 wherein the auxiliary fuel cell
system component load is a fuel cell stack cooling fan, further
comprising: an auxiliary isolated DC/DC converter comprising a
primary side and a secondary side, the primary side electrically
coupled to at least one of the power storage device and the
secondary side of the main isolated DC/DC converter; and a first
controller electrically coupled to the secondary side of the
auxiliary isolated DC/DC converter to receive power via the
auxiliary isolated DC/DC converter, the first controller
controllingly coupled to control the main isolated DC/DC converter
and at least one switch, the first controller configured to:
electrically couple the cooling fan to the power storage device via
the auxiliary isolated DC/DC converter and electrically uncouple
the cooling fan from the fuel cell stack in a startup state;
electrically uncouple the cooling fan from the power storage device
and electrically couple the cooling fan to the fuel cell stack in a
boost state; electrically couple the cooling fan to the fuel cell
stack and disable the main isolated DC/DC converter in an idle
state; electrically uncouple the cooling fan from the fuel cell
stack, electrically couple the cooling fan to the power storage
device and disable the main isolated DC/DC converter in a failure
state; and electrically uncouple the cooling fan from both the
power storage device and the fuel cell stack and maintain the
auxiliary isolated DC/DC converter active in a standby state.
19. The power supply of claim 10 wherein the main isolated DC/DC
converter comprises a high frequency transformer.
20. A power supply that selectively provides power to a load via a
voltage bus, the power supply comprising: a fuel cell stack; a
power bus to electrically couple at least one external load to the
fuel cell stack, the power bus comprising a main isolated DC/DC
converter wherein the main isolated DC/DC converter is the only
ON/OFF switching device between the fuel cell stack and the load;
and at least one controller coupled to control the main isolated
DC/DC converter.
21. The power supply of claim 20, further comprising: a power
storage device electrically coupled to the main isolated DC/DC
converter to receive power from the fuel cell stack via the main
isolated DC/DC converter.
22. The power supply of claim 20, further comprising: a power
storage device electrically coupled to the main isolated DC/DC
converter to receive power from the fuel cell stack via the main
isolated DC/DC converter; and at least a first auxiliary fuel cell
system component load electrically couplable alternatively to: the
fuel cell stack to receive power therefrom, and the power storage
device to receive power therefrom.
23. A method of selectively providing power to a load from a fuel
cell stack, comprising: electrically directly connecting a fuel
cell stack to a main isolated DC/DC converter; selectively
operating the main isolated DC/DC converter to supply power to the
load at a first time, and selectively stopping operation of the
main isolated DC/DC converter to stop supplying power to the load
at a second time.
24. The method of claim 23 wherein electrically directly connecting
a fuel cell stack to a main isolated DC/DC converter comprises
electrically connecting the fuel cell stack to the main isolated
DC/DC converter without either a switch or a diode electrically
coupled therebetween.
25. The method of claim 23 wherein selectively operating the main
isolated DC/DC converter to supply power to the load at a first
time comprises adjusting an ON state pulse-width at an operating
frequency of the main isolated DC/DC converter to regulate a
voltage of the power supplied to the load, while maintaining a
reactant flow to the fuel cell stack approximately constant.
26. The method of claim 23, further comprising: from time-to-time,
generating a current pulse to decontaminate the fuel cell
stack.
27. The method of claim 23, further comprising: electrically
coupling a power storage device in parallel across an output side
of the main isolated DC/DC converter.
28. A method of operating a fuel cell system comprising a fuel cell
stack, a fan, a main isolated power converter, an auxiliary power
converter, and a power converter controller, the method comprising:
electrically coupling a power storage device in parallel across an
output side of the main isolated power converter; supplying power
to the power converter controller via the auxiliary power
converter; supplying power to the fan via the auxiliary power
converter at a first time; and supplying power to the fan directly
from the fuel cell stack without the use of the auxiliary power
converter at a second time.
29. The method of claim 28, further comprising: storing power from
the fuel cell stack in a power storage device via the main isolated
power converter, wherein supplying power to the fan via the
auxiliary power converter at a first time comprises supplying power
to the fan from the power storage device via the auxiliary power
converter.
30. A method of operating a fuel cell system comprising a fuel cell
stack, a fan, a main isolated power converter, an auxiliary power
converter, and a power converter controller, the method comprising:
electrically coupling a power storage device in parallel across an
output side of the main isolated power converter; supplying power
to the power converter controller via the auxiliary power
converter; supplying power to the fan via the auxiliary power
converter at a first time; supplying power to the fan directly from
the fuel cell stack without the use of the auxiliary power
converter at a second time; and operating the fuel cell stack at an
approximately maximum efficiency polarization curve without regard
to a desired output voltage.
31. A method of operating a power supply comprising a fuel cell
stack, a fan and at least one power storage device, the method
comprising: in a startup state, supplying power to the fan from the
power storage device via an auxiliary power converter; and in a
boost state, supplying power to the fan from the fuel cell stack,
and enabling a main power converter to supply power to a load from
the fuel cell stack via the main power converter.
32. The method of claim 31 wherein the main power converter is
directly connected to the fuel cell stack without any intervening
switches and diodes therebetween.
33. The method of claim 31, further comprising: in an idle state,
supplying power to the fan from the fuel cell stack, and disabling
the main power converter to prevent the supplying of power to the
load from the fuel cell stack.
34. The method of claim 31, further comprising: in a failure state,
disabling the main power converter to prevent the supplying of
power to the load from the fuel cell stack, and supplying power to
the fan from the power storage device via the auxiliary power
converter.
35. The method of claim 31, further comprising: in a standby state,
operating the auxiliary power converter, stopping a reactant flow
to the fuel cell stack to stop the fuel cell stack from operating,
and disabling the main power converter to prevent the supplying of
power to the load from the fuel cell stack.
36. A power supply system, comprising: a power bus; a first power
supply comprising a first fuel cell stack, a first fan, a first
main power converter selectively operable to supply power to the
power bus, a first power converter controller coupled to control
the first main power converter, a first auxiliary power converter
coupled to supply power to the first power converter controller and
to selectively supply power to the first fan wherein the first fuel
cell stack is selectively couplable to directly supply power to the
first fan; and at least a second power supply comprising a second
fuel cell stack, a second fan, a second main power converter
selectively operable to supply power to the power bus, a second
power converter controller coupled to control the second main power
converter, a second auxiliary power supply coupled to supply power
to the second power converter controller and to selectively supply
power to the second fan wherein the second fuel cell stack is
selectively couplable to directly supply power to the second fan,
wherein the first and the second power supplies are electrically
coupled to the power bus.
37. The power supply system of claim 36 wherein the first and the
second power supplies are electrically coupled to the power bus in
parallel, each of the main power converters comprising a first
desired output voltage.
38. The power supply system of claim 36 wherein the first and the
second power supplies are electrically coupled to the power bus in
series.
39. The power supply system of claim 36 wherein the first and the
second main power converters are each a respective DC/DC converter
comprising a bridge circuit and a transformer comprising a turns
ratio selected according to a desired output voltage range.
40. A method of forming a power supply system, the method
comprising: determining a desired voltage output of the power
supply system; selecting a DC/DC converter based on the determined
desired voltage output; determining a desired power output of the
power supply system; determining a number of power supply modules
required based on the desired power output of the power supply
system, each of the power supply modules comprising a respective
fuel cell stack and a respective DC/DC converter; for each of the
determined number of power supply modules, electrically coupling an
input of a respective one of the DC/DC converters to an output of
the respective fuel cell stack; and electrically coupling an output
of each of the DC/DC converters to a power bus.
41. The method of claim 40 wherein each of the power supply modules
further comprises a fan and a power storage device electrically
coupled in parallel with the output of the respective fuel cell
stack.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present power converter architectures and methods
generally relate to fuel cell systems, and more particularly to
controlling an output power, voltage and/or current of a power
supply including one or more fuel cell systems.
[0003] 2. Description of the Related Art
[0004] Electrochemical fuel cells convert fuel and oxygen to
electricity. Solid polymer electrochemical fuel cells generally
employ a membrane electrode assembly ("MEA") which includes an ion
exchange membrane or solid polymer electrolyte disposed between two
electrodes typically comprising a layer of porous, electrically
conductive sheet material, such as carbon fiber paper or carbon
cloth. The MEA contains a layer of catalyst, typically in the form
of finely comminuted platinum, at each membrane electrode interface
to induce the desired electrochemical reaction. In operation, the
electrodes are electrically coupled to conduct electrons between
the electrodes through an external circuit. Typically, a number of
MEAs are electrically coupled in series to form a fuel cell stack
having a desired power output.
[0005] In typical fuel cells, the MEA is disposed between two
electrically conductive fluid flow field plates or separator
plates. Fluid flow field plates have flow passages to direct fuel
and oxygen to the electrodes, namely the anode and the cathode,
respectively. The fluid flow field plates act as current
collectors, provide support for the electrodes, provide access
channels for the fuel and oxygen, and provide channels for the
removal of reaction products, such as water formed during the fuel
cell operation. The fuel cell system may use the reaction products
in maintaining the reaction. For example, reaction water may be
used for hydrating the ion exchange membrane and/or maintaining the
temperature of the fuel cell stack.
[0006] The stack's capability to produce current flow is a direct
function of the amount of available reactant. Increased reactant
flow increases reactant availability. Stack voltage varies
inversely with respect to the stack current in a non-linear
mathematical relationship. The relationship between stack voltage
and stack current at a given flow of reactant is typically
represented as a polarization curve for the fuel cell stack. A set
or family of polarization curves can represent the stack
voltage-current relationship at a variety of reactant flow rates.
Fuel cell stacks are generally more efficient under high loads. In
typical applications, the desired output voltage is the controlling
parameter, and the reactant flow is adjusted accordingly. This
results in the fuel cell stack operating less efficiently (i.e.,
along a less than optimal polarization curve) than desired.
[0007] In most practical applications, it is desirable to maintain
an approximately constant voltage output from the fuel cell stack.
One approach is to employ a battery electrically coupled in
parallel with the fuel cell system to provide additional current
when the demand of the load exceeds the output of the fuel cell
stack and to store current when the output of the fuel cell stack
exceeds the demand of the load.
[0008] The many different practical applications for fuel cell
based power supplies require a large variety of different
power/voltage delivery capabilities. Typically this requires using
a fuel cell stack with a higher rating than actually required, or
alternatively, specially designing the fuel cell stack for the
particular application. In most instances, it is prohibitively
costly and operationally inefficient to employ a power supply
capable of providing more power than required by the application.
It is also costly and inefficient to design, manufacture, validate,
and maintain inventories of different power supplies capable of
meeting the demand of each potential application (e.g., 1 kW, 2 kW,
5 kW, 10 kW, etc. in power, 24V, 48V, etc. in voltage). Further, it
is desirable to increase the reliability of the power supply
without significantly increasing the cost. Thus, a less costly,
less complex, more flexible, and/or more efficient approach to fuel
cell based power supplies is desirable.
BRIEF SUMMARY OF THE INVENTION
[0009] In one aspect, a circuit to selectively provide power
between a power source and a load comprises a main power converter
having a primary side and a secondary side, the primary side of the
main power converter electrically coupled directly to the power
source without at least one of a switch and a diode therebetween,
and the secondary side of the main power converter electrically
couplable to the load; and at least one controller coupled to
control the main power converter. A power storage device may be
electrically coupled in parallel across the secondary side of the
main power converter to buffer power. Further, an auxiliary
isolated power supply may be electrically coupled between the power
storage device and at least one controller to provide power to the
main converter controller and at least one controller to provide
power to the main converter power stage and driver and to at least
one first auxiliary load of the power supply, for example a fan
such as such as a cooling fan of a fuel cell system. One or more
switches may be selectively operable to electrically couple the
auxiliary isolated power supply to the first auxiliary load in a
first state and to alternatively electrically couple the power
source to the first auxiliary load in a second state.
[0010] In another aspect a power supply that selectively provides
power to a load comprises a fuel cell stack; a main isolated DC/DC
converter comprising a transformer, a primary side and a secondary
side, the primary side of the main isolated DC/DC converter
electrically connected directly to the fuel cell stack; a power
storage device electrically coupled to the secondary side of the
main isolated DC/DC converter to receive power therefrom; and at
least a first auxiliary fuel cell system component load
alternatively electrically couplable to the fuel cell stack to
receive power therefrom and the power storage device to receive
power therefrom.
[0011] In yet another aspect, a power supply that selectively
provides power to a load Via voltage bus, comprises a fuel cell
stack; a power bus to electrically couple at least one external
load to the fuel cell stack, the power bus comprising a main
isolated DC/DC converter wherein the main isolated DC/DC converter
is the only on/off switching device between the fuel cell stack and
the load; and at least one controller coupled to control the main
isolated DC/DC converter.
[0012] In a further aspect a method of selectively providing power
to a load from a fuel cell stack comprises: electrically directly
connecting a fuel cell stack to a main isolated DC/DC converter;
selectively operating the main isolated DC/DC converter to supply
power to the load a first time; and selectively stopping operation
of the main isolated DC/DC converter to stop supplying power to the
load at a second time.
[0013] In an even further aspect, a method of operating a fuel cell
system comprising a fuel cell stack, a fan, a main isolated power
converter, and a power converter controller comprises electrically
coupling a power storage device in parallel across a secondary or
output side of the main isolated DC/DC converter; supplying power
to the power converter controller via the auxiliary power supply;
supplying power to the fan via the auxiliary power supply at a
first time; and supplying power to the fan directly from a fuel
cell stack without the use of the auxiliary power supply at a
second time.
[0014] In even a further aspect a method of operating a power
supply comprising a fuel stack, a fan and at least one power
storage device comprises: in a startup state, supplying power to
the fan from the power storage device via an auxiliary power
supply; and in a boost state, supplying power to the fan from a
fuel cell stack, and enabling a main power converter to supply
power to a load from the fuel cell stack via the main power
converter. The method may further comprise in an idle state,
supplying power to the fan from a fuel cell stack, and disabling
the main power converter to prevent the supplying of power to the
load from a fuel cell stack. The method may further include: in a
failure state, disabling the main power converter to prevent the
supplying of power to the load from a fuel cell stack, and
supplying power to the fan from the power storage device via the
auxiliary power supply. The method may even further include in a
standby state, operating the auxiliary power supply, stopping a
reactant flow to the fuel stack to stop the fuel cell stack
operation, and disabling the main power converter to prevent the
supplying of power to the load from a fuel cell stack.
[0015] In an even further aspect, multiple power supplies may be
electrically coupled in series and/or parallel, preferably in
parallel, in a modular fashion to provide power at a different
power rating and at a desired voltage.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0016] In the drawings, identical reference numbers identify
similar elements or acts. The sizes and relative positions of
elements in the drawings are not necessarily drawn to scale. For
example, the shapes of various elements and angles are not drawn to
scale, and some of these elements and angles are arbitrarily
enlarged and positioned to improve drawing legibility. Further, the
particular shapes of the elements as drawn, are not intended to
convey any information regarding the actual shape of the particular
elements, and have been solely selected for ease of recognition in
the drawings.
[0017] FIG. 1 is a schematic diagram of a fuel cell system powering
an external load, the fuel cell system comprising a fuel cell
stack, fan, main isolated power converter, isolated auxiliary power
converter, power storage device, fuel cell controller, DC/DC
controller and a pair of switches, according to one illustrated
embodiment.
[0018] FIG. 2 is a schematic diagram of the fuel cell system
including a single throw, double pole switch, according to one
alternative embodiment.
[0019] FIG. 3A is a state transition diagram for operating the fuel
cell system according to one illustrated embodiment.
[0020] FIGS. 3B and 3C are a state transition table for operating
the fuel cell system according to the state transition diagram of
FIG. 3A.
[0021] FIG. 4 is a schematic diagram of a number of fuel cell
systems electrically coupled in series to supply a desired power a
load at a desired voltage.
[0022] FIG. 5 is a schematic diagram of a number of fuel cell
systems electrically coupled in parallel to supply power a load at
a desired voltage.
DETAILED DESCRIPTION OF THE INVENTION
[0023] In the following description, certain specific details are
set forth in order to provide a thorough understanding of the
various embodiments of the present power converter architectures
and methods. However, one skilled in the art will understand that
the present power converter architectures and methods may be
practiced without these details. In other instances, well-known
structures associated with fuel cells, fuel cell stacks, fuel cell
systems, reactant delivery systems, power storage devices such as
batteries and "super" or "ultra" capacitors, temperature control
systems, controllers, and power converters such as DC/DC
converters, have not been shown or described in detail to avoid
unnecessarily obscuring descriptions of the embodiments of the
present power converter architectures and methods.
[0024] Unless the context requires otherwise, throughout the
specification and claims which follow, the word "comprises" and
variations thereof, such as "comprises" and "comprising" are to be
construed in an open, inclusive sense, that is as "including, but
not limited to."
[0025] FIG. 1 shows a power supply 6 providing power to an external
load 8 according to one illustrated embodiment of the present power
converter architectures and methods. The external load 8 typically
constitutes the device to be powered by the power supply 6, such as
a vehicle, appliance, computer and/or associated peripherals,
lighting, and/or communications equipment. The power supply 6 may
also provide power to one or more internal loads, for example
control electronics, as discussed below.
[0026] The power supply 6 comprises a fuel cell system 10, a main
power converter 12, and a voltage bus 14.
[0027] Fuel cell system 10 comprises a fuel cell stack 16 composed
of a number of individual fuel cells electrically coupled in
series. The fuel cell stack 16 receives reactants, such as hydrogen
and air via reactant supply systems (not shown) which may include
one or more reactant supply reservoirs or sources, a reformer,
and/or one or more control elements such as compressors, pumps
and/or valves. Operation of the fuel cell stack 16 produces
reactant product, typically including water. The fuel cell system
10 may reuse some or all of the reactant products. For example
returning some of the water to the fuel cell stack 16 to humidify
the hydrogen and air at the correct temperature, to hydrate the ion
exchange membranes, and/or to control the temperature of the fuel
cell stack 16. Operation of the fuel cell stack 16 produces a
voltage V.sub.FC across rails 14a, 14b of the voltage bus 14. In
some embodiments, the voltage bus 14 electrically couples the fuel
cell stack directly to a primary side of the main power converter
12 without the use of any intervening switches or diodes. This
takes advantage of galvanic isolation between the fuel cell stack
16 and load 8, discussed in detail below. Eliminating unnecessary
switches and diodes provides a number of benefits such as reducing
the parts counts, reducing costs associated with high current rated
devices such as high current rated power relays and high current
rated diodes, and reducing the significant losses associated with
such devices.
[0028] The fuel cell system 10 may include one or more controllers,
such as fuel cell controller 18. The fuel cell controller 18 can
take a variety of forms, for example, a microprocessor, application
specific integrated circuit (ASIC), or other programmed or
programmable integrated circuit and the like. The fuel cell
controller 18 receives input from one or more customer interfaces
20 such as an ON/OFF switch, voltage adjusting switch, etc. The
fuel cell controller 18 also receives operational data 22 for the
fuel cell stack 16, for example, readings or measurements of
temperature, reactant flows, and valve and/or switch conditions.
The fuel cell controller 18 provides commands or stack control
signals 24 to various actuators for controlling the operation of
the fuel cell stack 16. For example, stack control signals 24 may
actuate actuators such as solenoids for opening and closing valves
to start, stop or adjust reactant flows.
[0029] The fuel cell system 10 includes one or more fans, such as a
cooling fan 26 that is selectively operable to provide an air flow
28 for maintaining the temperature of the fuel cell stack 16 within
acceptable bounds or reactant supply fan for supplying fuel or
oxidant (e.g., air or oxygen) to the fuel cell stack 16. The fuel
cell controller 18 may control the cooling fan 26 via fan speed
commands 30.
[0030] The main power converter 12 may take a variety of forms such
as a full-bridge DC/DC converter, a half-bridge DC/DC converter, a
forward DC/DC converter, or their derivatives. For example, the
main power converter 12 may take the form of an isolated,
full-bridge DC/DC converter power stage and driver electrically
coupled on the voltage bus 14 between the fuel cell stack 16 and
the load 8, as illustrated in FIGS. 1 and 2. In the illustrated
embodiment, the main power converter 12 is operable to convert the
DC voltage V.sub.FC produced by the fuel cell stack 16 to a desired
DC output voltage V.sub.OUT suitable for the load 8.
[0031] A variety of DC/DC converter topologies may be suitable,
which typically employ semiconductor switching devices in a circuit
that uses an inductor, a transformer or a capacitor as an energy
storage and filter element to transfer energy from the input to the
output in discrete packets or pulses. For example, the DC/DC
converter may employ a full-bridge DC/DC converter topology, a
push-pull DC/DC converter topology, a half-bridge DC/DC converter
topology, or a forward DC/DC converter topology. In particular, the
main power converter 12 may employ a high switching frequency
(e.g., 100 kHz) approach, in order to reduce size, cost and weight.
The details of these and other suitable converter topologies will
be apparent to those of skill in the art. The main power converter
12 may rely on the galvanic isolation inherent in the transformer
in the main power converter 12 to provide isolation between a
primary side and a secondary side of the main power converter
12.
[0032] The main power converter 12 is operable under a variety of
control techniques, such as frequency modulation, pulse-width
modulation (i.e., PWM), average-current control, and peak-current
control, as will be apparent to those of skill in the art.
[0033] The power supply 6 may include one or more power converter
controllers to control the main power converter 12 via appropriate
drivers, for example, a DC/DC controller 32. The DC/DC controller
32 may operate in conjunction with the fuel cell controller 18,
communicating data and/or commands therebetween. For example, the
fuel cell controller 18 may provide to the DC/DC controller 32: a
voltage reference signal 34 representing the value of a desired
output voltage V.sub.OUT, a fan enable signal 36 identifying a
state (e.g., ON/OFF; High, Medium, Low) of the cooling fan 26, a
DC/DC enable signal 38 identifying a desired state (e.g., ON/OFF)
of the main power converter 12, and/or a wakeup signal 40
identifying a state (e.g., ON/OFF) of main power converter 12. The
DC/DC controller 32 may provide a status signal 42 to the fuel cell
controller 18 identifying an operational status of the DC/DC
controller 32 and/or main power converter 12. The DC/DC controller
32 may also receive feedback signals 44 from the main power
converter 12. The DC/DC controller 32 produces control signals,
such as pulse width modulated signals 46, to control the operation
of the main power converter 12 via appropriate drivers. Since some
embodiments directly couple the fuel cell stack 16 to the main
power converter 12 without any intervening switches and/or diodes,
the operation of the main power converter 12 serves as the ON/OFF
control between the fuel cell stack 16 and main power converter 12
and/or load 8. Thus, power from the fuel cell stack 16 can be
turned ON and OFF by enabling and disabling the main power
converter 12.
[0034] The power supply 6 may also include an power storage device
48, such as a "super" or "ultra" capacitor and/or a battery,
electrically coupled in parallel across the load 8, at the output
side of the main power converter 12. The open circuit voltage of
the power storage device 48 is selected to be similar to the
desired maximum output voltage of the power supply 6. An internal
resistance of the power storage device 48 is selected to be much
lower than an internal resistance of the main power converter 12,
thus the power storage device 48 acts as a buffer, absorbing excess
current when the fuel cell stack 16 produces more current than the
load 8 requires, and providing current to the load 8 when the fuel
cell stack 16 produces less current than the load 8 requires. The
coupling of the power storage device 48 across the load 8 reduces
the maximum power rating requirement of the fuel cell stack 16. The
power storage device 48 also supplies energy to the internal loads
of the power supply 6 when the fuel cell stack 16 is, for example,
in a startup state, failure state and/or standby state, as more
fully discussed below.
[0035] The power supply 6 includes an auxiliary power converter 50
to provide power to the various internal loads of the fuel cell
system 10. For example, the auxiliary power converter 50 may
provide power to the main power converter 12, the DC/DC controller
32 and/or the fuel cell controller 18. A single auxiliary power
converter 50 may also supply power to other internal loads of the
fuel cell system for example the cooling fan 26. Thus, the
architecture of the power supply 6 takes advantage of the existing
auxiliary power converter used to power the control circuitry
(e.g., DC/DC controller 32, fuel cell controller 18) to eliminate a
dedicated cooling fan power supply typically found in fuel cell
systems. The auxiliary power converter 50 may take the form of a
widely-used flyback converter. The auxiliary power converter 50 may
be isolated, for example, relying on the galvanic isolation
associated with the flyback transformer in the auxiliary power
converter 50, to provide protection between the remainder of the
power supply 6 and/or the load 8.
[0036] The power supply 6 may employ one or more switches
selectively operable to supply power to the cooling fan 26 directly
from the fuel cell stack 16, or alternatively, supply power to the
cooling fan 26 via the auxiliary power converter 50. For example, a
first switch SW.sub.1 may electrically couple the cooling fan 26 to
the voltage bus 14 in a closed state, and electrically uncouple the
cooling fan 26 from the voltage bus 14 in an open state. A second
switch SW.sub.2 may electrically couple the cooling fan 26 to the
auxiliary power converter 50 in a closed state, and electrically
uncouple the cooling fan 26 from the auxiliary power converter 50
in an open state. The DC/DC controller 32 may control the state
(e.g., ON/OFF) of the switches SW.sub.1, SW.sub.2 in response to
the fuel cell controller 18. The power supply 6 may further include
a pair of diodes D.sub.1, D.sub.2 to protect against reverse
current flow.
[0037] FIG. 2 shows an alternative embodiment of the power supply
6. This alternative embodiment, and those alternative embodiments
and other alternatives described herein, are substantially similar
to previously described embodiments, and common acts and structures
are identified by the same reference numbers. Only significant
differences in the operation and structure are described below.
[0038] In particular, the power supply 6 of FIG. 2 employs a single
switch SW.sub.3 in place of the first and second switches SW.sub.1,
SW.sub.2, and a single diode D.sub.3. The switch SW.sub.3 is
selectively operable to alternatively electrically couple the
cooling fan 26 directly to the fuel cell stack 16 or to the power
storage device 48 via the auxiliary power converter 50. This
alternative embodiment may be simpler to operate and less costly
than the embodiment of FIG. 1, but may not be capable of
functioning under several of the operating states discussed
below.
[0039] FIG. 3A is a state transition diagram and FIGS. 3B and 3C
are a state transition table illustrating a state machine 100 for
operating the power supply 6.
[0040] The state machine 100 involves a variety of states or
operating modes, some of Which are activated by a user selecting an
appropriate control on the customer interface 20, and others which
are automatically entered via the fuel cell controller 18 and/or
DC/DC controller 32 in response to certain operating
conditions.
[0041] FIG. 3A shows the valid transitions for the state machine
100. For example, the power supply 6 may transition from an off
state 102 to a standby state 104. The power supply 6 may transition
from the standby state 104 to the off state 102 or to a startup
state 106. The power supply 6 may transition from the startup state
106 to the standby state 104, to a fault state 108, or to an idle
state 110. The power supply 6 may transition from the fault state
108 to the standby state 104. The power supply 6 may transition
from the idle state 110 to the fault state 108 or to a boost state
112. The power supply 6 may transition from the boost state 112 to
the fault state 108 or the idle state 110.
[0042] The above transitions are represented by arrows on the state
transition diagram (FIG. 3A), each of the arrows having a reference
number that identifies the transitions in the state transition
table (FIGS. 3B and 3C).
[0043] The off state 102 is the beginning state for the power
supply 6. In the off state 102 the various subsystems such as the
fuel cell stack 16, main power converter 12, fuel cell controller
18, cooling fan 26, DC/DC controller 32 and/or auxiliary power
converter 50 are not operating.
[0044] The standby state 104 maintains the controllers in an
operational state after receiving the wake-up command, while the
housekeeping power supply for controllers is activated, and
controllers in power supply 6 are awake and ready to communicate
with customer interface 20. The standby state 104 may be activated
by an appropriate user input via the customer interface 20. To
enter the standby state 104, the fuel cell controller 18 causes the
DC/DC controller 32 to open the first switch SW.sub.1, if not
already open, to electrically uncouple the cooling fan 26 from the
fuel cell stack 16. The fuel cell controller 18 also causes the
DC/DC controller 32 to open the second switch SW.sub.2, if not
already open, to electrically uncouple the cooling fan 26 from the
auxiliary power converter 50. The fuel cell controller 18 further
disables the fuel cell stack 16, for example, by stopping reactant
flow to the fuel cell stack 16. The fuel cell controller 18 further
causes the DC/DC controller 32 to disable the main power converter
12.
[0045] The startup state 106 may be entered in response to the user
selecting an appropriate ON/OFF switch, or the automatic sensing of
a loss of power from an independent power source such as a public
or private electrical grid. The startup state 106 may allow the
various subsystems of the power supply 6 to come up to operational
levels, for example, allowing the fuel cell stack 16 to come up to
its open circuit voltage V.sub.FC. To enter the startup state 106,
the fuel cell controller 18 causes the DC/DC controller 32 to open
the first switch SW.sub.1, if not already open, in step 106 to
electrically uncouple the cooling fan 26 from the voltage bus 14.
The fuel cell controller 18 also causes the DC/DC controller 32 to
close the second switch SW.sub.2, if not already closed, to
electrically couple the cooling fan 26 to the power storage device
48 to receive power via the auxiliary power converter 50.
[0046] The fault state 108 may be entered when one or more
operating values goes out of bounds or some other erroneous
condition occurs, the failure state protecting the various
subsystems of the power supply 6, as well as the load 8. To enter
the fault state 108, the fuel cell controller 18 causes the DC/DC
controller 32 to open the first switch SW.sub.1, if not already
open, to electrically uncouple the cooling fan 26 from the voltage
bus 14. The fuel cell controller 18 also causes the DC/DC
controller 32 to disable the main power converter 12. The fuel cell
controller 18 further causes the DC/DC controller 32 to close the
second switch SW.sub.2, if not already closed, to electrically
couple the cooling fan 26 to the power storage device 48 via the
auxiliary power converter 50.
[0047] The idle state 110 may be entered to maintain the power
supply 6 in an operational state, while the load 8 does not require
power. The idle state 110 may be activated by an appropriate user
input via the customer interface 20, or by automatically sensing of
the loss of load 8. To enter the idle state 110, the fuel cell
controller 18 causes the DC/DC controller 32 to open the second
switch SW.sub.2, if not already open, to electrically uncouple the
cooling fan 26 from the auxiliary power converter 50. The fuel cell
controller 18 also causes the DC/DC controller 32 to close the
first switch SW.sub.1, if not already closed, to electrically
couple the cooling fan 26 directly to the fuel cell stack 16 via
the voltage bus 14. The fuel cell controller 18 further causes the
DC/DC controller 32 to disable the main power converter 12.
[0048] The boost state 112 may be entered once the power supply 6
is fully operational, to supply power to the load 8. The boost
state 112 may be activated by an appropriate user input via the
customer interface 20, or by automatically sensing of the load 8.
To enter the boost state 112, the fuel cell controller 18 causes
the DC/DC controller 32 to open the second switch SW.sub.2, if not
already open, to electrically uncouple the cooling fan 26 from the
auxiliary power converter 50. The fuel cell controller 18 also
causes the DC/DC controller 32 to close the first switch SW.sub.1,
if not already closed, to electrically couple the cooling fan 26
directly to the fuel cell stack 16 via the voltage bus 14. The fuel
cell controller 18 further causes the DC/DC controller 32 to
provide PWM signals 46 to the main power converter 12, enabling the
main power converter 12 in order to supply power to the load 8 from
the fuel stack 16.
[0049] The above teachings may be implemented in a modular approach
to providing power supply systems of a large variety of output
powers and voltages, as illustrated in FIGS. 4 and 5.
[0050] FIG. 4 shows a number of power supplies 6.sub.1-6.sub.n
electrically coupled in series on a voltage bus 14 to power a load
8. The ellipses indicate that any number of additional power
supplies may be electrically coupled between the first power supply
6.sub.1 and the n.sup.th power supply 6.sub.n. This modular
approach allows customers to reconfigure a power supply system of a
n times output power at n times output voltage while utilizing the
same fuel cell stack design and the same power supply 6 module.
[0051] FIG. 5 shows a number of power supplies 6.sub.1-6.sub.n
electrically coupled in parallel on a voltage bus 14 formed by
voltage rails 14a, 14b to power a load 8. This modular approach
allows a customer to reconfigure a power supply system of a n times
output power at the same voltage, while utilizing the same fuel
cell stack design and the same power supply 6 module. The
embodiments of FIGS. 4 and 5 can be combined in various
arrangements of series and parallel coupled to provide a modular
approach to the manufacture, validation, and distribution of power
supply systems.
[0052] The disclosed embodiments may provide a number of advantages
over existing systems. For example, the above described approaches
may reduce the time required to produce a suitable power supply
system that meets a customer's specific desired power and voltage
requirements. Having a power supply system more closely tailored to
the actual load requirements and/or capable of adjusting the output
voltage via a power converter saves costs since fewer cells are
required in the fuel cell stack 16, and since only a relatively
few, or even only one, standard fuel cell stack 16 must be
designed, validated, manufactured, inventoried and distributed.
Further, having a power supply system more closely tailored to the
actual load requirements allows the fuel cell stack 16 to operate
more efficiently. Use of the power converter to adjust the voltage,
allows the fuel cell stack 16 to operate at maximum load,
independent of the desired load voltage, also allowing the fuel
cell stack to operate more efficiently along the optimum
polarization curve. As noted above, the elimination of costly and
lossy high voltage switches and/or diodes also adds to the savings
in cost and efficiency. As further discussed above, the elimination
of a dedicated power supply for the fan provides significant cost
and efficiency savings. The coupling of the power storage device 48
across the load 8 provides significant saving by reducing the
maximum power rating of the fuel cell stack 16. Even further, the
main power converter 12 may from time-to-time, or as required,
generate a current pulse to decontaminate the fuel cell stack 16,
thereby improving fuel cell stack performance.
[0053] Although specific embodiments of, and examples for, the
power supply are described herein for illustrative purposes,
various equivalent modifications can be made without departing from
the spirit and scope of the present power converter architectures
and methods, as will be recognized by those skilled in the relevant
art. The teachings provided herein can be applied to other fuel
cell systems, not necessarily the exemplary fuel cell systems
generally described above.
[0054] The various embodiments described above can be combined to
provide further embodiments. All of the above U.S. patents, patent
applications and publications referred to in this specification,
including but not limited to, commonly assigned pending U.S. patent
applications Ser. No. 10/017,480, entitled "Method and Apparatus
for Controlling Voltage From a Fuel Cell System" (Attorney Docket
No. 130109.436); Ser. No. 10/017,462, entitled "Method and
Apparatus for Multiple Mode Control of Voltage From a Fuel Cell
System" (Attorney Docket No. 130109.442); and Serial No.
10/017,461, entitled "Fuel Cell System Multiple Stage Voltage
Control Method and Apparatus" (Attorney Docket No. 130109.446), all
filed Dec. 14, 2001; Serial No. 60/421,126, entitled "Adjustable
Array Of Fuel Cell Systems In Power Supply" filed May 16, 2002
(Atty. Docket No. 130109.449P1); and serial No. 60/436,759,
entitled "Electric Power Plan With Adjustable Array Of Fuel Cell
Systems" filed Dec. 17, 2002 (Atty. Docket No. 130109.449P2), are
all incorporated herein by reference, in their entirety. Aspects of
the present power converter architectures and methods can be
modified, if necessary, to employ systems, circuits and concepts of
the various patents, applications and publications to provide yet
further embodiments of the present power converter architectures
and methods. Suitable methods of operation may include additional
steps, eliminate some steps, and/or perform some steps in a
different order. For example, the fuel cell controller 18 may
employ a different order for determining the operating state,
and/or for opening and closing the switches SW.sub.1, SW.sub.2.
[0055] These and other changes can be made to the present power
converter architectures and methods in light of the above-detailed
description. In general, in the following claims, the terms used
should not be construed to limit the invention to the specific
embodiments disclosed in the specification and the claims, but
should be construed to include all fuel cell systems that operate
in accordance with the claims. Accordingly, the invention is not
limited by the disclosure, but instead its scope is to be
determined entirely by the following claims.
* * * * *