U.S. patent application number 14/492062 was filed with the patent office on 2016-12-01 for passive power management and battery charging for hybrid fuel cell/battery system.
The applicant listed for this patent is ENERGYOR TECHNOLOGIES INC. Invention is credited to Thomas David Jones, Seyoung Kim.
Application Number | 20160351983 14/492062 |
Document ID | / |
Family ID | 45493072 |
Filed Date | 2016-12-01 |
United States Patent
Application |
20160351983 |
Kind Code |
A1 |
Jones; Thomas David ; et
al. |
December 1, 2016 |
PASSIVE POWER MANAGEMENT AND BATTERY CHARGING FOR HYBRID FUEL
CELL/BATTERY SYSTEM
Abstract
Disclosed herein is a circuit for passively managing power
between a fuel cell stack and a battery in a hybrid system. The
circuit includes a buck-boost converter circuit, a direct charge
circuit; and a network which interconnects them. The network is
configured so that in response to a voltage level in the network
being lower than or equal to a maximum battery charge voltage, the
battery is charged via the direct charge circuit; and in response
to another voltage level in the network which is higher than the
maximum battery charge voltage, the battery is charged via the
buck-boost converter circuit. Also disclosed is a device
incorporating the circuit and a method of passively managing
power.
Inventors: |
Jones; Thomas David;
(Montreal, CA) ; Kim; Seyoung; (Brossard,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ENERGYOR TECHNOLOGIES INC |
Saint-Laurent |
|
CA |
|
|
Family ID: |
45493072 |
Appl. No.: |
14/492062 |
Filed: |
September 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13185859 |
Jul 19, 2011 |
9054385 |
|
|
14492062 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 8/24 20130101; H02J 2300/30 20200101; H01M 12/08 20130101;
H01M 8/04567 20130101; H02J 7/34 20130101; H02J 7/007 20130101;
H02J 2310/40 20200101; H02J 1/06 20130101; H01M 10/44 20130101;
Y02E 60/50 20130101; H01M 16/00 20130101; H01M 10/46 20130101; H02J
7/342 20200101; H01M 10/48 20130101; H01M 16/003 20130101; H01M
10/446 20130101 |
International
Class: |
H01M 12/08 20060101
H01M012/08; H01M 10/46 20060101 H01M010/46; H02J 7/00 20060101
H02J007/00; H01M 8/04537 20060101 H01M008/04537; H01M 8/24 20060101
H01M008/24; H01M 10/44 20060101 H01M010/44; H01M 10/48 20060101
H01M010/48 |
Claims
1. A device for passively managing the power between a fuel cell
stack and a battery in a hybrid system, the device comprising: a) a
fuel cell stack having a first voltage and current characteristic;
b) a battery having a second voltage and current characteristic; c)
a network having a bus, the network electrically interconnecting
the fuel cell stack, the battery and the bus, the fuel cell stack
and the battery being matched to permit passive power sharing
between the fuel cell stack and the battery depending on the amount
of current being drawn from the hybrid system, so as to share power
based on the resulting voltage in the bus.
2. The device, according to claim 1, in which the network
electrically interconnects the fuel cell stack, the battery, and
the bus in parallel configuration.
3. The device, according to claim 1, in which the network includes
a buck-boost converter circuit.
4. The device, according to claim 3, in which the network includes
a direct charge circuit.
5. The device, according to claim 4, in which the network includes
a mode selector, a current limit circuit, which network
interconnects the buck-boost converter, the direct charge circuit,
the mode selector, the current limit circuit and the network is
configured such that: i) in response to the first voltage level in
the network being lower than or equal to the maximum battery charge
voltage, the mode selector connects the direct charge circuit to
the battery so that the battery is charged; and ii) in response to
the second voltage level in the network being higher than the
maximum battery charge voltage, the mode selector connects the
buck-boost converter circuit to the battery so that the battery is
charged.
6. The device, according to claim 5, in which the network is
configured such that when the first voltage level is higher than or
equal to the maximum voltage charge of the battery, the mode
selector passively connects the fuel cell stack and a buck-boost
converter circuit to the battery so as to charge the battery.
7. The device, according to claim 5, in which a voltage comparator
controls a switch located in the mode selector to passively switch
charging of the battery between the buck-boost converter circuit
and the direct charge circuit.
8. The device, according to claim 5, in which the current limit
circuit is connected to the buck-boost converter circuit and the
direct charge circuit to limit current delivered to the
battery.
9. The device, according to claim 1, in which the network includes
a first diode and a second diode, the first diode being connected
to the fuel cell stack, the second diode being connected between
the battery and the bus.
10. The device, according to claim 1, further includes an onboard
balancing circuit to monitor individual battery voltages.
11. A method for passively managing the power between a fuel cell
stack and a battery in a hybrid system, the method comprising: in a
network having a bus, matching a fuel cell stack, having a first
voltage and current characteristic, with a battery, having a second
voltage and current characteristic, so as to permit passive power
sharing between the fuel cell stack and the battery depending on
the amount of current being drawn from the hybrid system, so as to
share power based on the resulting voltage in the bus.
12. The method, according to claim 11, comprising: charging the
battery charged via the direct charge circuit when the bus voltage
level is lower than the maximum recommended battery charge voltage
thereby coupling the bus directly to the battery.
13. The method, according to claim 11, comprising: charging the
battery via the buck-boost converter charging circuit when the bus
voltage level is higher than the maximum recommended battery charge
voltage.
14. The method, according to claim 11, in which the fuel cell stack
has plurality of unit cells each being sized so as to provide a
desired current and voltage characteristic of the cell.
15. The method, according to claim 14, comprises selecting the
number of fuel cells to provide the overall voltage characteristic
of the fuel stack.
16. The method, according to claim 16, further comprises matching
the number of fuel cells with the voltage and current
characteristic of the battery so that as long as the fuel cell
stack voltage is higher than that of the battery, power will be
supplied from the fuel cell stack.
17. The method, according to claim 11, further includes: i) in
response to the first voltage level in the network being lower than
or equal to the maximum battery charge voltage, selectively
connecting the battery to a direct charge circuit so that the
battery is charged; and ii) in response to the second voltage level
in the network being higher than the maximum battery charge
voltage, selectively connecting the battery to a buck-boost
converter circuit so that the battery is charged.
18. The method, according to claim 17, further includes limiting
current delivered to the battery by connecting either the
buck-boost converter circuit or the direct charge circuit to the
battery.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present is a continuation application of pending U.S.
patent application Ser. No. US 13/185,859 filed on Jul. 19, 2011
and claims priority therefrom.
FIELD OF THE INVENTION
[0002] The present generally concerns electrochemical fuel cells
and more particularly to passive power management and battery
charging for a hybrid fuel cell/battery system.
BACKGROUND OF THE INVENTION
[0003] Polymer electrolyte membrane or proton exchange membrane
(PEM) fuel cells have intrinsic benefits and a wide range of
applications due to their relatively low operating temperatures
(room temperature to approximately 80.degree. C.). The active
portion of a PEM is a membrane sandwiched between an anode and a
cathode layer. Fuel containing hydrogen is passed over the anode
and oxygen (air) is passed over the cathode. The reactants, through
the electrolyte (membrane), react indirectly with each other
generating an electrical voltage between the cathode and anode.
Typical electrical potentials of PEM cells can range from 0.5 to
0.9 volts; the higher the voltage the greater the electrochemical
efficiency. However, at higher current densities, the cell voltage
is lower and there is eventually a peak value in power density for
a given set of operating conditions.
[0004] Multiple cells are combined by stacking, interconnecting
individual cells in electrical series. The voltage generated by the
cell stack is effectively the sum of the individual cell voltages.
There are designs that use multiple cells in parallel or in a
combination series, parallel configuration. Separator plates
(bipolar plates) are inserted between the cells to separate the
anode reactant of one cell from the cathode reactant of the next
cell. To provide hydrogen to the anode and oxygen to the cathode
without mixing, a system of fluid distribution and seals is
required.
[0005] A number of applications require a wide range of power; for
example, the Unmanned Aerial Vehicle (UAV). High powers are
required during take-off and climb, with lower average powers for
cruise. A typical hybrid fuel cell and battery system would require
a DC/DC converter to manage the different voltages from the battery
and fuel cell. This is a disadvantage for system weight, volume and
efficiency.
[0006] With a hybrid fuel cell/battery system, it is also a
significant advantage to charge the batteries while in operation
when there is available energy from the fuel cell. For this to
occur in a safe and reliable manner, the maximum battery charging
voltage and current must be carefully controlled.
[0007] There are several methods to achieve this, but each has its
own disadvantages.
[0008] For battery charging, one method is to use a buck DC/DC
converter which will reduce the stack voltage down to the maximum
allowable battery charge voltage. The issue with this approach is
that there are losses associated (.about 0.90% efficiency), and
therefore the stack voltage must be significantly higher than the
battery charge voltage to enable battery charging. This means that
the battery will be charged only when the stack voltage is very
high.
[0009] Another method is to use a buck-boost DC/DC converter which
will supply the charge voltage at any stack input voltage. The
issue with this approach is that when the electrical load requires
high power levels, energy from the stack will be supplied directly
to the bus through the battery charger, thereby imposing an
unnecessary efficiency loss.
[0010] Thus, there is a need for improved power management and
battery charging for a fuel cell/battery system.
SUMMARY OF THE INVENTION
[0011] We have discovered that by eliminating a DC/DC converter, a
fuel cell stack can be sized to match the voltage/current
relationship to that of the battery pack, thereby allowing power to
be drawn from the fuel cell up to its rated power, and additional
power from the battery over and above this value.
[0012] Accordingly, there is provided a circuit for passively
managing power between a fuel cell stack and a battery in a hybrid
system, the circuit comprising: [0013] a) a buck-boost converter
circuit; [0014] b) a direct charge circuit; and [0015] c) a network
interconnecting the buck-boost converter, the direct charge, the
network being configured such that: [0016] i) in response to a
first voltage level in the network being lower than or equal to a
maximum battery charge voltage, the battery is charged via the
direct charge circuit; and [0017] ii) in response to a second
voltage level in the network being higher than the maximum battery
charge voltage, the battery is charged via the buck-boost converter
circuit.
[0018] In one example, the circuit further includes: [0019] a) a
mode selector; and [0020] b) a current limit circuit; and wherein
the network interconnects the buck-boost converter, the direct
charge, the mode selector, the current limit circuit and the
network is configured such that: [0021] i) in response to the first
voltage level in the network being lower than or equal to the
maximum battery charge voltage, the mode selector connects the
direct charge circuit to the battery so that the battery is
charged; and [0022] ii) in response to the second voltage level in
the network being higher than the maximum battery charge voltage,
the mode selector connects the buck-boost converter circuit to the
battery so that the battery is charged.
[0023] In one example, a voltage comparator controls a switch
located in the mode selector to passively switch charging of the
battery between the buck-boost converter circuit and the direct
charge circuit.
[0024] In another example, the current limit circuit is connected
to the buck-boost converter circuit and the direct charge circuit
to limit current delivered to the battery.
[0025] In another example, the network includes a bus which
interconnects the fuel cell stack with the battery. The network
includes a first diode and a second diode, the first diode being
connected to the fuel cell stack, the second diode being connected
between the battery and the bus. First and second voltage levels
are measured in the bus.
[0026] In one example, the battery has low internal resistance.
[0027] In another example, the bus has a low voltage limit.
[0028] In another example, the circuit further includes an onboard
balancing circuit to monitor individual battery voltages.
[0029] In another example, the number of fuel cell stack unit cell
active area and fuel cell number are characterized by a specific
overall voltage and current characteristic which matches the
battery's overall voltage and current characteristic and cell
number, thereby permitting passive power management between the
battery and fuel cell stack depending on the resulting combined
voltage and current characteristic of the fuel cell stack and
battery.
[0030] According to another aspect, there is provided a device for
passively managing power, the device comprising: [0031] a) a fuel
cell stack; [0032] b) a battery; and [0033] c) the circuit, as
described above.
[0034] According to another aspect, there is provided a method of
passively managing power between a fuel cell stack and a battery in
a hybrid system, the method comprising: [0035] i) in response to a
first voltage level in a network being lower than or equal to a
maximum battery charge voltage, charging a battery via a direct
charge circuit; and [0036] ii) in response to a second voltage
level in the network being higher than the maximum battery charge
voltage, charging the battery via a buck-boost converter
circuit.
[0037] In one example, the method further includes: [0038] i) in
response to the first voltage level in the network being lower than
or equal to the maximum battery charge voltage, selectively
connecting the battery to the direct charge circuit so that the
battery is charged; and [0039] ii) in response to the second
voltage level in the network being higher than the maximum battery
charge voltage, selectively connecting the battery to the
buck-boost converter circuit so that the battery is charged.
[0040] In another example, the method further includes limiting
current delivered to the battery by connecting either the
buck-boost converter circuit or the direct charge circuit to the
battery.
[0041] In another example, the battery is passively selectively
charged.
BRIEF DESCRIPTION OF THE FIGURES
[0042] These and other features of that described herein will
become more apparent from the following description in which
reference is made to the appended drawing wherein:
[0043] FIG. 1 is a schematic block diagram of a device
incorporating a circuit for passively managing a fuel cell/battery
hybrid power system.
DETAILED DESCRIPTION OF THE INVENTION
[0044] Referring now to FIG. 1, a device for passively managing a
fuel cell/hybrid power system is shown generally at 10. The device
10 comprises a fuel cell stack 12 that is electrically connected in
a parallel configuration to a battery 26. The battery 26 has low
internal resistance.
[0045] Still referring to FIG. 1, the device 10 includes a passive
control circuit 30 which is connected between the fuel cell stack
12 and the battery 26. The circuit 30 comprises a mode selector 16,
a buck-boost DC/DC converter circuit 18, a direct charge circuit
20, and a current limit circuit 22. The mode selector 16 passively
selectively electrically connects either the buck-boost converter
circuit 18 or the direct charge circuit 20 to the battery 26.
[0046] A current limit circuit 22 electrically connects the
buck-boost converter 18 or the direct charger 20 to the battery 26.
The mode selector 16, the buck-boost converter circuit 18, the
direct charge circuit 20, and the current limit circuit 22 are
electrically interconnected via a network 32. Internal to the mode
selector 16, a comparator circuit compares the input voltage to a
predetermined set voltage level. The buck-boost converter 18 is a
switching power supply which is capable of converting its output
voltage to either lower or higher that of the input voltage. It is
comprised of switching transistor, inductor, capacitor, diode and a
control circuit. The direct charging circuit 20 is comprised of a
switching transistor and some other passive components. The mode
selector 16 activates the internal switching transistor of the
direct charging circuit 20 to allow current flow through this
circuit. The current limit circuit 22 is necessary so that the
battery is not overcharged. The current limit circuit is comprised
of a current shunt resistor, switching transistor and a sense
circuit. This circuit senses charge current and when the charge
current is higher than predetermined set current, it throttles
current path. The network 32 includes a bus 34 which interconnects
the fuel cell stack 12 to the circuit 30 and the battery 26. Two
diodes 14 and 24 are connected respectively to the fuel cell stack
12 and the battery 26 to protect them from reverse (back-feed)
current and uncontrolled battery charging. The circuit 30 may also
include an onboard balancing circuit (not shown) to monitor
individual battery voltages.
[0047] Load 28 is connected to the fuel cell stack 12 and the
battery 26, via the bus 34 with electrical management to the load
28 being determined passively as will be described below.
[0048] Referring still to FIG. 1, electrical power management to
load 28 from the fuel cell stack 12 and the battery 26 is
determined passively by matching the fuel cell stack's 12 voltage
and current relationship to that of the battery 26, thereby
allowing power to be drawn from the fuel cell stack 12 up to its
rated power, with additional power being supplied from the battery
26 at power levels above this value. This power management strategy
also depends on the battery 26 state-of-charge (SOC), which
determines the battery's 26 resulting voltage for a given
electrical current. The battery 26 is charged by two methods,
passive selection of which depends on the voltage of the fuel cell
stack 12, which directly determines the electrical bus 34 voltage
when the fuel stack's 12 voltage is higher than the battery 26
voltage. When the bus 34 voltage level is lower than the maximum
recommended battery charge voltage, the battery 26 is charged via
the direct charge circuit 20, thereby coupling the electrical bus
34 directly to the battery 26. The battery 26 charge current is
determined by the difference between the electrical bus 34 voltage
and the battery 26 voltage, the battery's 26 internal resistance,
where the maximum charge current is limited by the current limit
circuit 22. If the bus 34 voltage level equals the battery 26
voltage, no charging will occur. Conversely, when the bus 34
voltage level is higher than the maximum recommended battery 26
charge voltage, the battery 26 is charged via the buck-boost
converter charging circuit 18, whose output voltage is set to the
maximum recommended battery charge voltage. The maximum charge
current is limited via current limit circuit 22. As previously
described, a switch inside the mode selector circuit 16 is
controlled via a voltage comparator, which passively switches
between the direct charge circuit 20 and the buck-boost charge
circuit 18 depending on the bus 34 voltage level. The bus 34 has a
low voltage limit on the electrical bus load output, thereby
reducing output power levels when this low voltage limit is reached
in order to protect the stack from overload when the battery
state-of-charge (SOC) is low.
[0049] By omitting the conventionally used DC/DC converter for
power management to the electrical load 28, we have reduced the
overall system mass and correspondingly improved system efficiency.
Furthermore, we have increased the efficiency and safety of battery
charging over the full stack voltage range and have reduced system
complexity as a result of the passive power management and battery
charging circuit. Due to its decreased weight, volume and
complexity, the device 10 can be used in fuel cell/battery hybrid
power generation applications, such as for example, in Unmanned
Aerial Vehicle (UAV) applications.
[0050] When the fuel cell stack 12 provides a voltage at or below
the required battery charging voltage, it is effectively connected
directly to the battery 26. The current limit circuit 22 is
integrated into the circuit 34 to regulate the maximum current.
This allows the fuel cell stack 12 to charge the battery 26 at any
time when the battery 26 voltage is lower than the fuel cell stack
12 voltage, until it reaches the maximum recommend charging
voltage. When the fuel cell stack 12 provides the bus 34 with
voltage that is higher than the maximum recommended charging
voltage, the buck-boost DC/DC converter 18 is used to provide the
recommended charging voltage. The buck-boost converter 18
eliminates the "dead zone" associated with the buck only charging
method. The voltage comparator is used to switch between the direct
and buck-boost charging methods. Thus, the direct-buck-boost
charging strategy therefore allows the battery 26 to be charged
over the full stack voltage range when the battery 26 voltage is
below its maximum recommended charging voltage, and when there is
available energy from the fuel cell stack 12.
[0051] Moreover, the fuel cell stack unit cell is sized in a way
(i.e. active area) to provide the desired current and voltage
characteristic of the cell. The number of fuel cells is then chosen
to provide the overall voltage characteristic of the stack. This is
then matched with the voltage and current characteristic, as well
as the number of cells, of the battery. Therefore, as long as the
stack voltage is higher than that of the battery, power will be
supplied from the stack. As increasing power is drawn, the voltage
of the stack drops down to meet the battery voltage, and then the
power sharing between the stack and battery depends on the
corresponding voltage/current characteristics in that region of
their operation. Thus, the battery tends to have a "stiffer"
voltage which acts as a safety net for the stack, so the stack is
not overloaded.
Operation
[0052] Still referring to FIG. 1, the network 32 is configured so
that in response to a first voltage level in the network 32 which
is lower than a maximum battery charge voltage, the battery 26 is
charged via the direct charge circuit 20. Similarly, in response to
a second voltage level in the network 32 being higher than the
maximum battery charge voltage, the battery 26 is charged via the
buck-boost converter circuit 18. Also, in response to the first
voltage level in the network 32 being lower than or equal to the
maximum battery charge voltage, the mode selector 16 passively
connects the battery 26 to the direct charge circuit 18 so that the
battery 26 is charged; and in response to the second voltage level
in the network 32 being higher than the maximum battery charge
voltage, the mode selector 16 passively connects the battery 26 to
the buck-boost converter circuit 18 so that the battery 26 is
charged.
Other Embodiments
[0053] From the foregoing description, it will be apparent to one
of ordinary skill in the art that variations and modifications may
be made to the embodiments described herein to adapt it to various
usages and conditions.
* * * * *