WO2014182332A1 - Aerospace fuel cell power control system - Google Patents
Aerospace fuel cell power control system Download PDFInfo
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- WO2014182332A1 WO2014182332A1 PCT/US2013/066750 US2013066750W WO2014182332A1 WO 2014182332 A1 WO2014182332 A1 WO 2014182332A1 US 2013066750 W US2013066750 W US 2013066750W WO 2014182332 A1 WO2014182332 A1 WO 2014182332A1
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- Prior art keywords
- fuel cell
- cell stack
- power
- storage device
- energy storage
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04537—Electric variables
- H01M8/04544—Voltage
- H01M8/04552—Voltage of the individual fuel cell
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M16/00—Structural combinations of different types of electrochemical generators
- H01M16/003—Structural combinations of different types of electrochemical generators of fuel cells with other electrochemical devices, e.g. capacitors, electrolysers
- H01M16/006—Structural combinations of different types of electrochemical generators of fuel cells with other electrochemical devices, e.g. capacitors, electrolysers of fuel cells with rechargeable batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04223—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
- H01M8/04268—Heating of fuel cells during the start-up of the fuel cells
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/0438—Pressure; Ambient pressure; Flow
- H01M8/04395—Pressure; Ambient pressure; Flow of cathode reactants at the inlet or inside the fuel cell
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
- H01M8/04537—Electric variables
- H01M8/04604—Power, energy, capacity or load
- H01M8/04619—Power, energy, capacity or load of fuel cell stacks
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
- H01M8/04858—Electric variables
- H01M8/04895—Current
- H01M8/0491—Current of fuel cell stacks
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
- H01M8/04858—Electric variables
- H01M8/04925—Power, energy, capacity or load
- H01M8/0494—Power, energy, capacity or load of fuel cell stacks
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
- H01M8/04955—Shut-off or shut-down of fuel cells
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04298—Processes for controlling fuel cells or fuel cell systems
- H01M8/04992—Processes for controlling fuel cells or fuel cell systems characterised by the implementation of mathematical or computational algorithms, e.g. feedback control loops, fuzzy logic, neural networks or artificial intelligence
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2250/00—Fuel cells for particular applications; Specific features of fuel cell system
- H01M2250/20—Fuel cells in motive systems, e.g. vehicle, ship, plane
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02T90/40—Application of hydrogen technology to transportation, e.g. using fuel cells
Definitions
- the present invention relates to an aerospace fuel cell power control system and, in particular, to a system and method for controlling operation of one or more fuel cells and/or fuel cell stacks using battery fill-in power in an aerospace vehicle.
- Fuel cell systems typically contain fuel cell stacks that comprise a number of individual fuel cells.
- the individual fuel cells and the stacks are usually supplied with reactant streams in parallel, with a hydrogen-containing fuel stream being supplied to the anode, and an oxidant stream, such as air or oxygen, being supplied to the cathode to produce an output power
- a problem with conventional fuel cell control systems is they fail to prevent a fuel cell from delivering more power than the fuel cell's current capability, which may result in breakdown and failure of the fuel cell or the reduced power fuel cell is used to only partially power the load coupled to the fuel cell. This is especially problematic in an aerospace environment where safety is paramount. Summary
- One aspect of the invention relates to a system including: an aerospace power control system including: a fuel cell stack formed from a plurality of fuel cells, wherein the fuel cell stack has a maximum power and/or current output based on power and/or current aggregated amongst the plurality of fuel cells; an energy storage device; and a controller coupled to the fuel cell and the energy storage device, wherein the controller is configured to calculate the maximum power and/or current the fuel cell stack is capable of supplying to an associated load; and the controller is configured to
- Another aspect of the invention relates to the controller selecting the maximum power and/or current of the fuel cell stack is selected to prevent a cathode stoichiometry ratio associated with the fuel cell stack from falling below a prescribed value.
- Another aspect of the invention relates to the fuel cell stack and the energy storage device is coupled in parallel to a direct current to direct current (DC-DC) converter that is coupled to the associated load.
- DC-DC direct current to direct current
- Another aspect of the invention relates to the controller being configured to provide power to one or more aircraft systems.
- Another aspect of the invention relates to the controller preventing an aggregate current output from the fuel cell stack exceeding a prescribed amount.
- One aspect of the invention relates to a method for managing power output between a fuel cell stack and an energy storage device in an aerospace power control system, the method including: calculating a maximum power the fuel cell stack is capable of supplying to an associated load of the aerospace vehicle; monitoring output power of the fuel stack to the associated load; and selectively outputting additional power from the energy storage device when the associated load seeks an amount of power greater than the maximum power the fuel cell stack is capable of supplying to the associated load.
- Another aspect of the invention relates to limiting power and/or current output from the fuel cell stack to a prescribed value, wherein the prescribed value is selected to prevent a cathode stoichiometry ratio associated with the fuel stack from falling below a prescribed value.
- Another aspect of the invention relates to the additional power is provided to one or more aircraft systems.
- One aspect of the invention relates to a method for managing power output between a fuel cell stack and an energy storage device in an aerospace power control system, the method including: monitoring voltage of each of a plurality of fuel cells that form a fuel cell stack, wherein the fuel cell stack is providing power and/or current to an associated load of the aircraft system; determining if one or more of the fuel cells have an output voltage less than or greater a prescribed threshold of voltage output from one or more other fuel cells in the fuel cell stack; receiving power from and/or current from the energy storage device if the output voltage is greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack; and decreasing power and/or current from the fuel cell stack.
- Another aspect of the invention relates to performing a remedial action on the one or more fuel cells having an output voltage greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack.
- Another aspect of the invention relates to the energy storage device is provided to power one or more aircraft systems.
- One aspect of the invention relates to a method for managing power output between a fuel cell stack and an energy storage device in an aerospace power control system, the method including: preventing a fuel cell stack from outputting power and/or current prior to the fuel cell stack reaching steady-state; output power and/or current from the energy storage device to an associated load of the aircraft system prior to the fuel cell stack reaching steady-state; wherein, when the fuel cell stack reaches steady state, output power from the fuel cell stack is provided to the associated load and power and/or current provided from the energy storage device is terminated.
- Another aspect of the invention relates to the energy is provided from an energy storage device to the associated load of the aircraft system prior to the fuel cell reaching steady state.
- One aspect of the invention relates to a method for operating a fuel cell stack in an aircraft system, the method including: monitoring electrical characteristics associated with the fuel cell stack over time, wherein the fuel cell stack is a component of the aerospace power control system; calculating a maximum power the fuel cell stack is capable of supplying to an associated load of the aerospace power control system, wherein the maximum power varies as a function of variation of electrical characteristics monitored over time; controlling the maximum power and/or current the fuel cell stack is capable of supplying to an associated load based on the variation of electrical characteristics monitored over time.
- Another aspect of the invention relates to including storing the electrical characteristics associated with the fuel cell stack in a memory. Another aspect of the invention relates to the memory further including reference data suitable for comparing with the stored electrical characteristics to determine health of the fuel cell stack.
- the memory further includes reference data suitable for comparing with the stored electrical characteristics to determine anomalous behavior associated with the fuel cell stack.
- Another aspect of the invention relates to further including supplying power from an energy storage device when the health of the fuel stack is outside a prescribed performance range.
- Another aspect of the invention relates to the energy storage device being a battery, a flywheel, a capacitor and/or any other suitable device for storing energy.
- One aspect of the invention relates to a method for starting a fuel cell stack in cold temperatures with an energy storage device, the method including: preventing a fuel cell stack from outputting power and/or current to an associated load prior to the fuel cell stack reaching steady-state; initiating the fuel stack, wherein the energy storage device warms the fuel cell stack by progressive electrical loading of the fuel cell stack by actively managing the fuel cell stack using a plurality of cell voltage monitors, wherein one of the cell voltage monitors is at a level below other cell voltage monitors, the fuel cell stack is unloaded and the energy storage device is used to power the associated load; and outputing power and/or current from the energy storage device to an associated load prior to the fuel cell stack reaching steady-state; wherein, when the fuel cell stack reaches steady state, output power from the fuel cell stack is provided to the associated load and power and/or current provided from the energy storage device is terminated.
- One aspect of the invention relates to a method for starting a fuel cell stack in cold temperatures with an energy storage device, the method including: preventing a fuel cell stack from outputting power and/or current to an associated load prior to the fuel cell stack reaching a desired operating temperature; wherein the energy storage device power provides power to a balance of plant and passively warms the fuel stack to a first operating temperature; and power provided from the balance of plant is proportionately switched away from the energy storage device and loaded onto the fuel cell stack based upon distribution of voltage measurements from a plurality of cell voltage monitors until the energy storage device is reliably offloaded; and powering the balance of plant with fuel cell stack while recharging the energy storage device until the desired operating temperature of the fuel cell stack is reached, wherein upon reaching the desired operating temperature, power and/or current is output from the fuel cell stack to power the associated load.
- Figure 1 is a block schematic drawing of an exemplary system in accordance with aspects of the present invention.
- Figure 2 is a block schematic diagram illustrating a current limitation process based on chemistry of the Proton Exchange Member and abundance of hb and O 2 reactancts.
- Figure 3 is a block schematic drawing of an exemplary system in accordance with aspects of the present invention pertaining to calculated current limitations.
- Figure 4 is a block schematic drawing of an exemplary system in accordance with aspects of the present invention illustrating battery augmentation at the point of current regulation.
- Figure 5 is a graphical representation of the polarization curve illustrating the relationship between fuel cell voltage and current density.
- Figure 6 is another exemplary polarization curve illustrating various flow rates.
- Figures 7A-7D are exemplary graphical representations that illustrate poor voltage triggering voltage-based fill-in.
- Figure 8 is a block schematic drawing illustrating an exemplary system in accordance with aspects of the present invention.
- FIGS. 9-11 are exemplary methods in accordance with aspects of the present invention. Description of the Preferred Embodiments
- Battery “fill-in” control for a fuel cell stack is triggered and metered by a family of computations. These computations predict the fuel cell stack's instantaneous capability to deliver power, current and voltage to prevent the fuel cell from exceeding this limit.
- the present invention takes an observational-based understanding (e.g., when a step load (dl/dt), battery fill-in is needed) to a model-based understanding (e.g., battery fill-in is necessary when the fuel cell computations indicate that the fuel cell and/or fuel cell stack cannot provide more than a certain power (e.g., X kilowatts (kW) that is required by the load).
- a certain power e.g., X kilowatts (kW) that is required by the load.
- an exemplary aerospace power control system 10 is illustrated.
- two fuel cell stacks (FC1 and FC2) are illustrated.
- the optimal fuel cell stack voltage is approximately: 150 Volts at maximum load and 240 Volts at minimum load.
- a fuel cell stack operating at partial load is susceptible to voltage drops when a large electrical load instantaneously appears.
- the relatively slow changing air stream will cause the fuel cell stack (FC1 , FC2) to be dragged away from its "Ohmic" region and crash. This results in fuel cell damage and shutdown may occur.
- the DC/DC converter is designed to produce +/-270 voltage until the fuel cell stack has been dragged down to 130 Volts, after which it will cease to convert.
- the present invention seeks to design robustness against fuel cell voltage drop (potentially resulting in fuel cell stack driven into shutdown) during large power transients.
- a load 12 can be added to the fuel cell without warning, and produce shutdowns from voltage dips.
- the load 12 may be any type of electrical load from one or more aircraft systems.
- Exemplary aircraft systems include cockpit controls, communication systems, air systems, connecting linkages, engine controls, and operating mechanisms to control an aircraft's speed, direction and altitude in flight, etc.
- HVDC01 DC/DC converter
- the controller 14 computes the capability in kW (or current limit) of the stack based on airflow, fuel, humidity, pressure, temperature etc.
- HVDC01 will only convert at the fuel cell stack's full capacity (kW) when the compressor and injectors are ready to handle the load, and not before.
- HVDC01 will limit its
- HVDC01 will be commanded to convert only what the stack is capable of delivering at a given point in time. If an aircraft or a component of an aircraft instantaneously draws a larger load than the fuel cell stack can accommodate, the result will be that the electrical bus 16 will start to go low. This "lower voltage" is the trigger for the other DC/DC converter to start drawing power from the energy storage device 18.
- the energy storage device 18 may be a battery, a flywheel, a capacitor and/or any other suitable device for storing energy.
- the energy storage device 18 is a 144 V lead acid battery, which is used to augment the HVDC01.
- the energy storage device 18 generally needs to step-in before the fuel cell stack output voltage drops below a prescribed voltage.
- the energy storage device 18 steps in preemptively at the moment (or with a nominal latency delay) that the system controller 14 calculates that the air and fuel cannot satisfy the electrical demand. This allows for the fuel cell controller to catch up to the electrical loads giving time for compressor to spool, fuel to be delivered, etc.
- Triggers There are two general types of triggers to initiate battery fill-in: 1) Fuel Cell Capability based Triggers; and 2) Voltage based Triggers.
- FUEL CELL CAPABILITY BASED TRIGGERS A fuel cell stack's ability to produce power and current is calculated based upon fuel cell operating conditions, primarily airflow and hydrogen (H 2 ) supply.
- dl/dt instantaneous current draw against the fuel cell
- This "limit” controls the fuel cells cathode stoichiometry ratio from falling below a predetermined floor. Active prevention may occur by commanding current limits to the multiple DC/DC converters that draw power from the fuel cell. In general, a power budget is determined, and allocated to each of the DC/DC converters in a manner not to overtax the fuel cell.
- each fuel cell (FC1 , FC2) includes an anode 20 and a cathode 22 separated by an electrolyte 24.
- Airflow sensors in FC1 and FC2 determine how much oxygen is available. The governing control law provides that the total current leaving the fuel cell is limited by the multiple DC/DC converters (sum total orchestrated by master controller). Software control prevents the
- stoichiometry ratio from going below a minimum floor. For example a fuel cell stack crash may occurs at a stoichiometry ratio ⁇ 1.4.
- availability of hydrogen for Proton Exchange is calculated in software by pressure and flow abundance. Electrical limiting within the plurality of DC/DC converters occurs when insufficient hydrogen is present to supply the electrical load.
- both fuel cell stacks (FC1 and FC2) are coupled to a communication channel, which is configured to provide current limit signals to the DC/DC converters 32 associated with each fuel cell stack. The remaining energy is stored in the balance of plant (BOP) 33 ( Figure 4).
- the energy storage device 18 is operatively coupled to the fuel cell stacks (FC1 , FC2) to provide fill-in power. That is, when the load coupled to the fuel cell stack (FC1 , FC2) attempts to use more energy than available by the fuel cell stack; the energy storage device 18 is configured to provide the needed power.
- the fill- in power combines with the fuel cell power to fulfill all electrical loads. Accordingly, this invention prevents the fuel cell stack (FC1 , FC2) from being driven beyond its "Ohmic region” and into the undesirable "transport loss region” of the polarization curve, illustrated in Figure 5.
- the multiple facets of the control scheme prevent the fuel cell stack from crashing resulting in fuel cell system reset.
- polarization curve is illustrated for each different reactive air system (e.g., a compressor pushing air through the fuel cell) over various flow rates.
- the airflow is controlled such that the device is operating in the middle portion of the graph (e.g., not in the "concentration over-potential" or "transport loss” regions of the graph).
- the polarization curves illustrated in Figure 6 are exemplary in nature and not intended to limit the scope of the present invention.
- Fuel cell stack undervoltage determined by the existing load also triggers power fill-in. These voltage triggered fill-ins not only protect the stack from crashing, but allow the MFFCS system to continue operating under adverse conditions with occasional fixed short bursts of battery fill-in.
- Adverse conditions include:
- Figures 7A-7D illustrate various examples of anomalous fuel cell behavior, which voltage triggering and "voltage based" power fill-in is designed to abate.
- Figure 7A illustrates the effect of Cathode pressure loss on the voltage- current graph of a typical fuel cell.
- the upper graph illustrates higher pressure (P2) than the lower graph (low pressure (P1).
- P2 higher pressure
- P1 low pressure
- a step loss in pressure resulting in a downward step voltage will trigger battery fill-in.
- Figure 7B illustrates voltage (V) and power (W) plotted over current density for the balance of load, age of 2000 hours and age of 5000 hours. As can be seen from the graphs, with increased time, there is a downward translation (e.g., decreased voltage output) associated with the operational time of the fuel cell.
- Figure 7C illustrates voltage (V) and power (W) plotted over current density age at 2000 hours and age at 5000 hours. Degradation is observed where the Ohmic losses have increased over time.
- Figure 7D illustrates voltage (V) and power (W) plotted over current density age at 2000 hours and age at 5000 hours. Observed is anomalous behavior or malfunction causing a limit to gas diffusion layer capability, or potentially a limited availability of fuel cell reactancts.
- FIG 8. An exemplary method 30 for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device 18 in an aerospace power control system 10 is illustrated in Figure 8.
- the method 30 includes a controller 14 (or other device) calculating a maximum power the fuel cell stack (FC1 , FC2) is capable of supplying to an associated load 12 to one or more aircraft systems of an aerospace vehicle.
- the output power of the fuel stack to the associated load is monitored. Monitoring may be performed in any desired manner using conventional current monitoring and/or voltage monitoring devices.
- additional power is selectively output from the energy storage device to the associated load 12 when the associated load 12 seeks an amount of power greater than the maximum power the fuel cell stack (FC1 , FC2) is capable of supplying to the associated load 12.
- the method 30 may optionally include limiting power and/or current output from the fuel cell stack (FC1 , FC2) to a prescribed value, wherein the prescribed value is selected to prevent a cathode stoichiometry ratio associated with the fuel stack from falling below a prescribed value.
- the solution for a cold starting fuel cell may involve a current limit from the master controller 14 being set to 0 A, which triggers power fill-in from the energy storage device.
- the BOP's current limits are set to zero, forcing battery operation.
- the fuel cell stack is progressively un-throttled as temperature permit, minimizing the total battery draw for the warm-up process.
- the energy storage device is used to externally and passively warm the system before a fuel cell start-up routine is attempted.
- a progressive gentle electrical loading of the fuel cell is done by actively managing that the voltage of the multiple cell voltage monitors (CVM) to stay tight within a nominal distribution.
- CVM multiple cell voltage monitors
- the method 30 of Figure 8 may function to prevent a fuel cell stack from outputting power and/or current to an associated load prior to the fuel cell stack reaching a desired operating temperature.
- the energy storage device power provides power to a balance of plant (BOP) and passively warms the fuel stack to a first operating temperature.
- the power provided from the BOP is proportionately switched away from the energy storage device and loaded onto the fuel cell stack based upon distribution of voltage measurements from a plurality of cell voltage monitors until the energy storage device is reliably offloaded.
- the BOP is powered with the fuel cell stack while recharging the energy storage device until the desired operating temperature of the fuel cell stack is reached, wherein upon reaching the desired operating temperature, power and/or current is output from the fuel cell stack to power the associated load.
- FIG. 9 Another exemplary method 40 for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device 18 in an aerospace power control system 10 is illustrated in Figure 9.
- the method includes monitoring voltage of each of a plurality of fuel cells that form a fuel cell stack (FC1 , FC2), wherein the fuel cell stack is providing power and/or current to an associated load (12) of the aircraft system.
- FC2 have an output voltage less than or greater a prescribed threshold of voltage output from one or more other fuel cells in the fuel cell stack.
- the controller is configured to deliver or cause to deliver power from and/or current from the energy storage device 18 to the associated load 12 if the output voltage is greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack.
- the method 40 may further include performing a remedial action on the one or more fuel cells having an output voltage greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack.
- a remedial action include shutting down the fuel completely, sending an alarm and/or other indication regarding the status of one or more fuel cells, for example.
- FIG. 10 Another exemplary method 60 for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device 18 in an aircraft system 10 is illustrated in Figure 10.
- the fuel cell stack (FC1 , FC2) is activated to provide power to a load 12.
- the method includes preventing a fuel cell stack (FC1 , FC2) from outputting power and/or current prior to the fuel cell stack reaching steady-state. If the fuel cell has not reached steady state, at block 66, output power and/or current from the energy storage device is provided to an associated load 12 of the aircraft system prior to the fuel cell stack reaching steady-state. If the fuel cell has reached steady state, the decision at block 64 is affirmative and signal control moves to block 68 where output power from the fuel cell stack is provided to the associated load and power and/or current provided from the energy storage device may be terminated.
- FIG 11 illustrates an exemplary method 70 in accordance with aspects of the present invention.
- the method 70 is directed for operating a fuel cell stack FC1 , FC2 in an aircraft system 10.
- the method includes monitoring electrical
- the data monitored may be stored in a memory 11 , which may take any suitable form.
- the electrical characteristics may be monitored by any current, voltage and/or power monitoring device.
- the memory 11 may be directly or indirectly coupled to the controller 14.
- the electrical characteristics associated with the fuel cell stack may be stored in memory 11.
- the data stored may be actual data from monitoring the fuel cell stack.
- the memory may also include reference data suitable for comparing with the stored electrical characteristics to determine health of the fuel cell stack.
- the health of the fuel cell stack may be determined in any desired way. For example, an algorithm that takes into account reference and monitored data may be used to determine health.
- the memory 11 may include reference data suitable for comparing with the monitored and stored electrical characteristics of the fuel cell stack to determine anomalous behavior associated with the fuel cell stack.
- the controller 14 calculates a maximum power the fuel cell stack is capable of supplying to an associated load 12 of the aircraft system.
- the maximum power may vary as a function of variation of electrical characteristics monitored over time.
- the controller 14 controls the maximum power and/or current the fuel cell stack is capable of supplying to an associated load based on the variation of electrical characteristics monitored over time.
- the health of the fuel cell stack may be determined in any desired way. For example, an algorithm that takes into account reference and monitored data may be used to determine health.
- the memory 11 may include reference data suitable for comparing with the monitored and stored electrical characteristics of the fuel cell stack to determine anomalous behavior associated with the fuel cell stack. For example, if the fuel cell stack is operating within a prescribed range based on the electrical characteristics monitored over time, the process flow continues to block 76.
- the method 70 further includes supplying power from an energy storage device 18.
- the energy storage device 18 may be any device capable of storing power and providing the power as needed by the aircraft system when the demand exceeds the capability of the fuel cell stack.
- the energy storage device may be a battery, a flywheel, a capacitor, etc.
- the functionality described in the above methods may be performed by one or more controllers.
- the controller is generally configured to make power available from the fuel cell stack (FC1 , FC2) and/or the energy storage device 18 to the associated load.
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Abstract
An aircraft power control system and method including: a fuel cell stack formed from a plurality of fuel cells, wherein the fuel cell stack has a maximum power and/or current output to one or more aircraft systems based on power and/or current aggregated amongst the plurality of fuel cells; an energy storage device; a controller coupled to the fuel cell and the energy storage device, wherein the controller is configured to calculate the maximum power and/or current the fuel cell stack is capable of supplying to an associated load of the aircraft system; and the controller is configured to selectively receive additional power and/or current from the energy storage device when the associated load seeks an amount of power and/or power greater than the maximum power and/or current the fuel cell stack is capable of supplying.
Description
Title: AEROSPACE FUEL CELL POWER CONTROL SYSTEM
Technical Field
The present invention relates to an aerospace fuel cell power control system and, in particular, to a system and method for controlling operation of one or more fuel cells and/or fuel cell stacks using battery fill-in power in an aerospace vehicle.
Background
Fuel cell systems typically contain fuel cell stacks that comprise a number of individual fuel cells. The individual fuel cells and the stacks are usually supplied with reactant streams in parallel, with a hydrogen-containing fuel stream being supplied to the anode, and an oxidant stream, such as air or oxygen, being supplied to the cathode to produce an output power
A problem with conventional fuel cell control systems is they fail to prevent a fuel cell from delivering more power than the fuel cell's current capability, which may result in breakdown and failure of the fuel cell or the reduced power fuel cell is used to only partially power the load coupled to the fuel cell. This is especially problematic in an aerospace environment where safety is paramount. Summary
One aspect of the invention relates to a system including: an aerospace power control system including: a fuel cell stack formed from a plurality of fuel cells, wherein the fuel cell stack has a maximum power and/or current output based on power and/or current aggregated amongst the plurality of fuel cells; an energy storage device; and a controller coupled to the fuel cell and the energy storage device, wherein the controller is configured to calculate the maximum power and/or current the fuel cell stack is capable of supplying to an associated load; and the controller is configured to
selectively receive additional power and/or current from the energy storage device when the associated load seeks an amount of power and/or current greater than the
maximum power and/or current the fuel cell stack is capable of supplying.
Another aspect of the invention relates to the controller selecting the maximum power and/or current of the fuel cell stack is selected to prevent a cathode stoichiometry ratio associated with the fuel cell stack from falling below a prescribed value.
Another aspect of the invention relates to the fuel cell stack and the energy storage device is coupled in parallel to a direct current to direct current (DC-DC) converter that is coupled to the associated load.
Another aspect of the invention relates to the controller being configured to provide power to one or more aircraft systems.
Another aspect of the invention relates to the controller preventing an aggregate current output from the fuel cell stack exceeding a prescribed amount.
One aspect of the invention relates to a method for managing power output between a fuel cell stack and an energy storage device in an aerospace power control system, the method including: calculating a maximum power the fuel cell stack is capable of supplying to an associated load of the aerospace vehicle; monitoring output power of the fuel stack to the associated load; and selectively outputting additional power from the energy storage device when the associated load seeks an amount of power greater than the maximum power the fuel cell stack is capable of supplying to the associated load.
Another aspect of the invention relates to limiting power and/or current output from the fuel cell stack to a prescribed value, wherein the prescribed value is selected to prevent a cathode stoichiometry ratio associated with the fuel stack from falling below a prescribed value.
Another aspect of the invention relates to the additional power is provided to one or more aircraft systems.
One aspect of the invention relates to a method for managing power output between a fuel cell stack and an energy storage device in an aerospace power control system, the method including: monitoring voltage of each of a plurality of fuel cells that form a fuel cell stack, wherein the fuel cell stack is providing power and/or current to an associated load of the aircraft system; determining if one or more of the fuel cells have an output voltage less than or greater a prescribed threshold of voltage output from one or more other fuel cells in the fuel cell stack; receiving power from and/or current from
the energy storage device if the output voltage is greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack; and decreasing power and/or current from the fuel cell stack.
Another aspect of the invention relates to performing a remedial action on the one or more fuel cells having an output voltage greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack.
Another aspect of the invention relates to the energy storage device is provided to power one or more aircraft systems.
One aspect of the invention relates to a method for managing power output between a fuel cell stack and an energy storage device in an aerospace power control system, the method including: preventing a fuel cell stack from outputting power and/or current prior to the fuel cell stack reaching steady-state; output power and/or current from the energy storage device to an associated load of the aircraft system prior to the fuel cell stack reaching steady-state; wherein, when the fuel cell stack reaches steady state, output power from the fuel cell stack is provided to the associated load and power and/or current provided from the energy storage device is terminated.
Another aspect of the invention relates to the energy is provided from an energy storage device to the associated load of the aircraft system prior to the fuel cell reaching steady state.
One aspect of the invention relates to a method for operating a fuel cell stack in an aircraft system, the method including: monitoring electrical characteristics associated with the fuel cell stack over time, wherein the fuel cell stack is a component of the aerospace power control system; calculating a maximum power the fuel cell stack is capable of supplying to an associated load of the aerospace power control system, wherein the maximum power varies as a function of variation of electrical characteristics monitored over time; controlling the maximum power and/or current the fuel cell stack is capable of supplying to an associated load based on the variation of electrical characteristics monitored over time.
Another aspect of the invention relates to including storing the electrical characteristics associated with the fuel cell stack in a memory.
Another aspect of the invention relates to the memory further including reference data suitable for comparing with the stored electrical characteristics to determine health of the fuel cell stack.
Another aspect of the invention relates the memory further includes reference data suitable for comparing with the stored electrical characteristics to determine anomalous behavior associated with the fuel cell stack.
Another aspect of the invention relates to further including supplying power from an energy storage device when the health of the fuel stack is outside a prescribed performance range.
Another aspect of the invention relates to the energy storage device being a battery, a flywheel, a capacitor and/or any other suitable device for storing energy.
One aspect of the invention relates to a method for starting a fuel cell stack in cold temperatures with an energy storage device, the method including: preventing a fuel cell stack from outputting power and/or current to an associated load prior to the fuel cell stack reaching steady-state; initiating the fuel stack, wherein the energy storage device warms the fuel cell stack by progressive electrical loading of the fuel cell stack by actively managing the fuel cell stack using a plurality of cell voltage monitors, wherein one of the cell voltage monitors is at a level below other cell voltage monitors, the fuel cell stack is unloaded and the energy storage device is used to power the associated load; and outputing power and/or current from the energy storage device to an associated load prior to the fuel cell stack reaching steady-state; wherein, when the fuel cell stack reaches steady state, output power from the fuel cell stack is provided to the associated load and power and/or current provided from the energy storage device is terminated.
One aspect of the invention relates to a method for starting a fuel cell stack in cold temperatures with an energy storage device, the method including: preventing a fuel cell stack from outputting power and/or current to an associated load prior to the fuel cell stack reaching a desired operating temperature; wherein the energy storage device power provides power to a balance of plant and passively warms the fuel stack to a first operating temperature; and power provided from the balance of plant is proportionately switched away from the energy storage device and loaded onto the fuel
cell stack based upon distribution of voltage measurements from a plurality of cell voltage monitors until the energy storage device is reliably offloaded; and powering the balance of plant with fuel cell stack while recharging the energy storage device until the desired operating temperature of the fuel cell stack is reached, wherein upon reaching the desired operating temperature, power and/or current is output from the fuel cell stack to power the associated load.
The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings. Brief Description of the Figures
Figure 1 is a block schematic drawing of an exemplary system in accordance with aspects of the present invention.
Figure 2 is a block schematic diagram illustrating a current limitation process based on chemistry of the Proton Exchange Member and abundance of hb and O2 reactancts.
Figure 3 is a block schematic drawing of an exemplary system in accordance with aspects of the present invention pertaining to calculated current limitations.
Figure 4 is a block schematic drawing of an exemplary system in accordance with aspects of the present invention illustrating battery augmentation at the point of current regulation.
Figure 5 is a graphical representation of the polarization curve illustrating the relationship between fuel cell voltage and current density.
Figure 6 is another exemplary polarization curve illustrating various flow rates.
Figures 7A-7D are exemplary graphical representations that illustrate poor voltage triggering voltage-based fill-in.
Figure 8 is a block schematic drawing illustrating an exemplary system in accordance with aspects of the present invention.
Figures 9-11 are exemplary methods in accordance with aspects of the present invention.
Description of the Preferred Embodiments
The following description of the preferred embodiments of the invention is not intended to limit the invention to these preferred embodiments, but should be considered illustrative to enable a person skilled in the art to make and use the claimed invention.
Battery "fill-in" control for a fuel cell stack is triggered and metered by a family of computations. These computations predict the fuel cell stack's instantaneous capability to deliver power, current and voltage to prevent the fuel cell from exceeding this limit. Thus, the present invention takes an observational-based understanding (e.g., when a step load (dl/dt), battery fill-in is needed) to a model-based understanding (e.g., battery fill-in is necessary when the fuel cell computations indicate that the fuel cell and/or fuel cell stack cannot provide more than a certain power (e.g., X kilowatts (kW) that is required by the load).
Referring to Figure 1 , an exemplary aerospace power control system 10 is illustrated. In this system, two fuel cell stacks (FC1 and FC2) are illustrated. In this example, the optimal fuel cell stack voltage is approximately: 150 Volts at maximum load and 240 Volts at minimum load. A fuel cell stack operating at partial load is susceptible to voltage drops when a large electrical load instantaneously appears. During transient power demand, the relatively slow changing air stream will cause the fuel cell stack (FC1 , FC2) to be dragged away from its "Ohmic" region and crash. This results in fuel cell damage and shutdown may occur. As designed, the DC/DC converter is designed to produce +/-270 voltage until the fuel cell stack has been dragged down to 130 Volts, after which it will cease to convert. In all but full load the low voltage will result in the fuel cell stack (FC1 , FC2) being well out of its intended "Ohmic" region. Fuel cell damage and shutdown may occur. A person of ordinary skill in the art will readily appreciate that the above voltages and voltage ranges are exemplary in nature and not intended to limit the scope of the present invention.
The present invention seeks to design robustness against fuel cell voltage drop (potentially resulting in fuel cell stack driven into shutdown) during large power transients. In such cases, a load 12 can be added to the fuel cell without warning, and produce shutdowns from voltage dips. As used herein, the load 12 may be any type of
electrical load from one or more aircraft systems. Exemplary aircraft systems include cockpit controls, communication systems, air systems, connecting linkages, engine controls, and operating mechanisms to control an aircraft's speed, direction and altitude in flight, etc.
To prevent unwanted stack voltage dips (due to imperfect air delivery/hydrogen delivery/humidity control/contamination/aged stack, etc), it is desirable to design the DC/DC converter (HVDC01) to limit conversion (in kW or current limit) based on a command from the system controller 14, as illustrated in Figure 1. The controller 14 computes the capability in kW (or current limit) of the stack based on airflow, fuel, humidity, pressure, temperature etc. Under this scenario, HVDC01 will only convert at the fuel cell stack's full capacity (kW) when the compressor and injectors are ready to handle the load, and not before. Under most scenarios, HVDC01 will limit its
conversion to less than its rated power. HVDC01 will be commanded to convert only what the stack is capable of delivering at a given point in time. If an aircraft or a component of an aircraft instantaneously draws a larger load than the fuel cell stack can accommodate, the result will be that the electrical bus 16 will start to go low. This "lower voltage" is the trigger for the other DC/DC converter to start drawing power from the energy storage device 18.
The energy storage device 18 may be a battery, a flywheel, a capacitor and/or any other suitable device for storing energy. In one embodiment, the energy storage device 18 is a 144 V lead acid battery, which is used to augment the HVDC01. The energy storage device 18 generally needs to step-in before the fuel cell stack output voltage drops below a prescribed voltage. In one embodiment, the energy storage device 18 steps in preemptively at the moment (or with a nominal latency delay) that the system controller 14 calculates that the air and fuel cannot satisfy the electrical demand. This allows for the fuel cell controller to catch up to the electrical loads giving time for compressor to spool, fuel to be delivered, etc.
There are two general types of triggers to initiate battery fill-in: 1) Fuel Cell Capability based Triggers; and 2) Voltage based Triggers.
1. FUEL CELL CAPABILITY BASED TRIGGERS
A fuel cell stack's ability to produce power and current is calculated based upon fuel cell operating conditions, primarily airflow and hydrogen (H2) supply. The
instantaneous current (dl/dt) draw against the fuel cell is actively managed to prevent the fuel cell from exceeding its calculated limit. This "limit" controls the fuel cells cathode stoichiometry ratio from falling below a predetermined floor. Active prevention may occur by commanding current limits to the multiple DC/DC converters that draw power from the fuel cell. In general, a power budget is determined, and allocated to each of the DC/DC converters in a manner not to overtax the fuel cell.
As illustrated in Figure 2, each fuel cell (FC1 , FC2) includes an anode 20 and a cathode 22 separated by an electrolyte 24. Each oxygen module reacts to produce four (4) electrons of electrical current (at a stoichiometry ratio=1). Airflow sensors in FC1 and FC2 determine how much oxygen is available. The governing control law provides that the total current leaving the fuel cell is limited by the multiple DC/DC converters (sum total orchestrated by master controller). Software control prevents the
stoichiometry ratio from going below a minimum floor. For example a fuel cell stack crash may occurs at a stoichiometry ratio <1.4. Likewise, the availability of hydrogen for Proton Exchange is calculated in software by pressure and flow abundance. Electrical limiting within the plurality of DC/DC converters occurs when insufficient hydrogen is present to supply the electrical load.
Referring to Figure 3, two fuel cell stacks (FC1 and FC2) are shown. Each fuel cell stack can be "throttled" to prevent consumers in aggregate ( + 1 n = i) from over withdrawing current from their respective stack. As illustrated in Figure 1 , both fuel cell stacks (FC1 and FC2) are coupled to a communication channel, which is configured to provide current limit signals to the DC/DC converters 32 associated with each fuel cell stack. The remaining energy is stored in the balance of plant (BOP) 33 (Figure 4).
Referring to Figure 4, the energy storage device 18 is operatively coupled to the fuel cell stacks (FC1 , FC2) to provide fill-in power. That is, when the load coupled to the fuel cell stack (FC1 , FC2) attempts to use more energy than available by the fuel cell stack; the energy storage device 18 is configured to provide the needed power. The fill- in power combines with the fuel cell power to fulfill all electrical loads.
Accordingly, this invention prevents the fuel cell stack (FC1 , FC2) from being driven beyond its "Ohmic region" and into the undesirable "transport loss region" of the polarization curve, illustrated in Figure 5. The multiple facets of the control scheme prevent the fuel cell stack from crashing resulting in fuel cell system reset.
Referring to Figure 6, a distinct polarization curve is illustrated for each different reactive air system (e.g., a compressor pushing air through the fuel cell) over various flow rates. The airflow is controlled such that the device is operating in the middle portion of the graph (e.g., not in the "concentration over-potential" or "transport loss" regions of the graph). A person having ordinary skill in the art will readily appreciate that the polarization curves illustrated in Figure 6 are exemplary in nature and not intended to limit the scope of the present invention.
2. VOLTAGE BASED TRIGGERS
In additional to the "fuel cell capability calculation" triggering fill-in power, other triggers for energy storage device intervention may also be desirable:
· CVM anomalies (cell voltage monitor) rather than creating shutdowns in traditional fuel cell systems, instead result in power fill-in.
• Fuel cell stack undervoltage determined by the existing load also triggers power fill-in. These voltage triggered fill-ins not only protect the stack from crashing, but allow the MFFCS system to continue operating under adverse conditions with occasional fixed short bursts of battery fill-in.
• More robust operation against adverse conditions can be achieved. Adverse conditions include:
stack degradation;
intermittent contamination;
imperfect air delivery;
contamination in Hydrogen;
poor humidity control;
poor temperature control;
sensor delay, drift, and inaccuracy;
some catalyst deterioration;
random variation;
other unforeseen events;
Since all these phenomenon result in poor fuel cell voltage, short bursts power fill-in will prevent the fuel cell crash as long as irregular events are intermittent in nature.
Figures 7A-7D illustrate various examples of anomalous fuel cell behavior, which voltage triggering and "voltage based" power fill-in is designed to abate. Figure 7A illustrates the effect of Cathode pressure loss on the voltage- current graph of a typical fuel cell. The upper graph illustrates higher pressure (P2) than the lower graph (low pressure (P1). A step loss in pressure resulting in a downward step voltage will trigger battery fill-in.
Figure 7B illustrates voltage (V) and power (W) plotted over current density for the balance of load, age of 2000 hours and age of 5000 hours. As can be seen from the graphs, with increased time, there is a downward translation (e.g., decreased voltage output) associated with the operational time of the fuel cell.
Figure 7C illustrates voltage (V) and power (W) plotted over current density age at 2000 hours and age at 5000 hours. Degradation is observed where the Ohmic losses have increased over time.
Figure 7D illustrates voltage (V) and power (W) plotted over current density age at 2000 hours and age at 5000 hours. Observed is anomalous behavior or malfunction causing a limit to gas diffusion layer capability, or potentially a limited availability of fuel cell reactancts.
An exemplary method 30 for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device 18 in an aerospace power control system 10 is illustrated in Figure 8. At block 32, the method 30 includes a controller 14 (or other device) calculating a maximum power the fuel cell stack (FC1 , FC2) is capable of supplying to an associated load 12 to one or more aircraft systems of an aerospace vehicle.
At block 34, the output power of the fuel stack to the associated load is monitored. Monitoring may be performed in any desired manner using conventional current monitoring and/or voltage monitoring devices.
At block 36, additional power is selectively output from the energy storage device to the associated load 12 when the associated load 12 seeks an amount of power greater than the maximum power the fuel cell stack (FC1 , FC2) is capable of supplying to the associated load 12.
The method 30 may optionally include limiting power and/or current output from the fuel cell stack (FC1 , FC2) to a prescribed value, wherein the prescribed value is selected to prevent a cathode stoichiometry ratio associated with the fuel stack from falling below a prescribed value.
The solution for a cold starting fuel cell may involve a current limit from the master controller 14 being set to 0 A, which triggers power fill-in from the energy storage device. For example, for cold start warm-up, the BOP's current limits are set to zero, forcing battery operation. The fuel cell stack is progressively un-throttled as temperature permit, minimizing the total battery draw for the warm-up process. During start-up of a fuel cell in cold temperatures, the energy storage device is used to externally and passively warm the system before a fuel cell start-up routine is attempted. To encourage a start-up without excessive water condensation and shock loading cycles, a progressive gentle electrical loading of the fuel cell is done by actively managing that the voltage of the multiple cell voltage monitors (CVM) to stay tight within a nominal distribution. When a single CVM monitor strays lower than the rest, this triggers the control system to retreat to back to fill-in power provided by the energy storage device and unload the fuel cell. The process is retried again until successful loading has occurred. This achieves the best cold start performance in terms of the critical battery cold cranking capacity in Amp-Hours.).
The method 30 of Figure 8 may function to prevent a fuel cell stack from outputting power and/or current to an associated load prior to the fuel cell stack reaching a desired operating temperature. The energy storage device power provides power to a balance of plant (BOP) and passively warms the fuel stack to a first operating temperature. The power provided from the BOP is proportionately switched away from the energy storage device and loaded onto the fuel cell stack based upon distribution of voltage measurements from a plurality of cell voltage monitors until the energy storage device is reliably offloaded. The BOP is powered with the fuel cell stack
while recharging the energy storage device until the desired operating temperature of the fuel cell stack is reached, wherein upon reaching the desired operating temperature, power and/or current is output from the fuel cell stack to power the associated load.
Another exemplary method 40 for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device 18 in an aerospace power control system 10 is illustrated in Figure 9. At block 42, the method includes monitoring voltage of each of a plurality of fuel cells that form a fuel cell stack (FC1 , FC2), wherein the fuel cell stack is providing power and/or current to an associated load (12) of the aircraft system.
At block 44, a determination is made as to if one or more of the fuel cells (FC1 ,
FC2) have an output voltage less than or greater a prescribed threshold of voltage output from one or more other fuel cells in the fuel cell stack.
At block 46, the controller is configured to deliver or cause to deliver power from and/or current from the energy storage device 18 to the associated load 12 if the output voltage is greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack.
At block 48 power and/or current is decreased from the fuel cell stack.
The method 40 may further include performing a remedial action on the one or more fuel cells having an output voltage greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack. Such a remedial action include shutting down the fuel completely, sending an alarm and/or other indication regarding the status of one or more fuel cells, for example.
Another exemplary method 60 for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device 18 in an aircraft system 10 is illustrated in Figure 10. At block 62, the fuel cell stack (FC1 , FC2) is activated to provide power to a load 12. At block 62, the method includes preventing a fuel cell stack (FC1 , FC2) from outputting power and/or current prior to the fuel cell stack reaching steady-state. If the fuel cell has not reached steady state, at block 66, output power and/or current from the energy storage device is provided to an associated load 12 of the aircraft system prior to the fuel cell stack reaching steady-state.
If the fuel cell has reached steady state, the decision at block 64 is affirmative and signal control moves to block 68 where output power from the fuel cell stack is provided to the associated load and power and/or current provided from the energy storage device may be terminated.
Figure 11 illustrates an exemplary method 70 in accordance with aspects of the present invention. The method 70 is directed for operating a fuel cell stack FC1 , FC2 in an aircraft system 10. At block 72, the method includes monitoring electrical
characteristics associated with the fuel cell stack over time, wherein the fuel cell stack is a component of the aircraft system. The data monitored may be stored in a memory 11 , which may take any suitable form. The electrical characteristics may be monitored by any current, voltage and/or power monitoring device.
The memory 11 may be directly or indirectly coupled to the controller 14. The electrical characteristics associated with the fuel cell stack may be stored in memory 11. The data stored may be actual data from monitoring the fuel cell stack. In addition, the memory may also include reference data suitable for comparing with the stored electrical characteristics to determine health of the fuel cell stack. The health of the fuel cell stack may be determined in any desired way. For example, an algorithm that takes into account reference and monitored data may be used to determine health. In another embodiment, the memory 11 may include reference data suitable for comparing with the monitored and stored electrical characteristics of the fuel cell stack to determine anomalous behavior associated with the fuel cell stack.
At block 74, the controller 14 (or other processing device) calculates a maximum power the fuel cell stack is capable of supplying to an associated load 12 of the aircraft system. As discussed above, the maximum power may vary as a function of variation of electrical characteristics monitored over time.
At block 76, the controller 14 controls the maximum power and/or current the fuel cell stack is capable of supplying to an associated load based on the variation of electrical characteristics monitored over time.
At block 78, a determination is made as to the health of the fuel cell stack. As stated above, the health of the fuel cell stack may be determined in any desired way. For example, an algorithm that takes into account reference and monitored data may be
used to determine health. In another embodiment, the memory 11 may include reference data suitable for comparing with the monitored and stored electrical characteristics of the fuel cell stack to determine anomalous behavior associated with the fuel cell stack. For example, if the fuel cell stack is operating within a prescribed range based on the electrical characteristics monitored over time, the process flow continues to block 76.
If a determination is made at block 78 that the fuel cell stack is operating outside of the prescribed range, at block 80 the the method 70 further includes supplying power from an energy storage device 18. As stated above, the energy storage device 18 may be any device capable of storing power and providing the power as needed by the aircraft system when the demand exceeds the capability of the fuel cell stack. For example, the energy storage device may be a battery, a flywheel, a capacitor, etc.
The functionality described in the above methods may be performed by one or more controllers. The controller is generally configured to make power available from the fuel cell stack (FC1 , FC2) and/or the energy storage device 18 to the associated load.
This concept of coordinated fuel cell (FC1 , FC2) and battery 18 control has the following benefits:
1) coordinate power of a fuel cell stack with battery augmentation in a technically elegant modeled based manner;
2) increases system robustness by eliminating fuel cell "stack crashing" by preventing the fuel cell from entering into its undesirable "transport loss" region, which would damage the fuel cell;
3) reduces fuel cell stack degradation by protecting the fuel cell stack from electrical transient shock loads;
4) increased operational robustness by periodic power fill-in on stack under-voltage and Cell Voltage Monitor (CVM) anomalies;
5) prevents the fuel cell from being pulled below the predetermined cathode stoichiometric "floor" ratio during transient electrical loading;
6) provides robustness against random variation via detection of abnormal voltages triggering power fill-in to prevent fuel cell crash;
7) allows consistent fuel cell power by compensating for fuel cell anomalies with variable power fill-in;
8) precise transient control of a fuel cell's cathode stoichiometry ratio necessary for generating fuel tank inerting gas, which is done by the addition of rapid throttling of electrical current instead of relying solely on the response of the air compressor.
Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, parts, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
Claims
1. An aerospace power control system (10) comprising:
a fuel cell stack (FC1, FC2) formed from a plurality of fuel cells, wherein the fuel cell stack has a maximum power and/or current output based on power and/or current aggregated amongst the plurality of fuel cells;
an energy storage device (18);
a controller (14) coupled to the plurality of fuel cells and the energy storage device, wherein the controller is configured to calculate the maximum power and/or current the fuel cell stack is capable of supplying to an associated load (12); and the controller is configured to selectively receive additional power and/or current from the energy storage device when the associated load seeks an amount of power and/or power greater than the maximum power and/or current the fuel cell stack is capable of supplying.
2. The system of claim 1 , wherein the controller selects the maximum power and/or current of the fuel cell stack is selected to prevent a cathode stoichiometry ratio associated with the fuel cell stack from falling below a prescribed value and protect the fuel cell stack when the associated load draws more power than the capacity of the fuel cell stack.
3. The system of any one of claims 1-2, wherein the fuel cell stack and the energy storage device is coupled in parallel to a direct current to direct current (DC-DC) converter (32) that is coupled to the associated load.
4. The system of any one of claims 1-3, wherein the controller is configured to provide power to one or more aircraft systems.
5. The system of any one of claims 1-4, wherein the controller prevents an aggregate current output from the fuel cell stack exceeding a prescribed amount.
6. A method for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device (18) in an aerospace power control system (10), the method comprising:
calculating a maximum power the fuel cell stack is capable of supplying to an associated load (12) of an aerospace vehicle;
monitoring output power of the fuel stack to the associated load;
selectively outputting additional power from the energy storage device when the associated load seeks an amount of power greater than the maximum power the fuel cell stack is capable of supplying to the associated load.
7. The method of claim 6, further including limiting power and/or current output from the fuel cell stack to a prescribed value, wherein the prescribed value is selected to prevent a cathode stoichiometry ratio associated with the fuel stack from falling below a prescribed value.
8. The method of any one of claims 6-7, wherein the additional power is provided to one or more aircraft systems.
9. A method for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device (18) in an aerospace power control system (10), the method comprising:
monitoring voltage of each of a plurality of fuel cells that form a fuel cell stack, wherein the fuel cell stack is providing power and/or current to an associated load (12) of the aircraft system;
determining if one or more of the fuel cells have an output voltage less than or greater a prescribed threshold of voltage output from one or more other fuel cells in the fuel cell stack;
receiving power from and/or current from the energy storage device if the output voltage is greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack; and
decreasing power and/or current from the fuel cell stack.
10. The method of claim 9, further including performing a remedial action on the one or more fuel cells having an output voltage greater than or less than the prescribed threshold of voltage output from the one or more other fuel cells in the fuel stack.
11. The method of any one of claims 9-10, wherein the energy storage device is provided to power one or more aircraft systems.
12. A method for managing power output between a fuel cell stack (FC1 , FC2) and an energy storage device (18) in an aircraft system (10), the method comprising: preventing a fuel cell stack from outputting power and/or current prior to the fuel cell stack reaching steady-state;
output power and/or current from the energy storage device to an associated load (12) of the aircraft system prior to the fuel cell stack reaching steady-state;
wherein, when the fuel cell stack reaches steady state, output power from the fuel cell stack is provided to the associated load and power and/or current provided from the energy storage device is terminated.
13. The method of claim 12, wherein energy is provided from an energy storage device to the associated load of the aircraft system prior to the fuel cell reaching steady state.
14. A method for operating a fuel cell stack (FC1 , FC2) in an aircraft system (10), the method comprising:
monitoring electrical characteristics associated with the fuel cell stack over time, wherein the fuel cell stack is a component of the aircraft system;
calculating a maximum power the fuel cell stack is capable of supplying to an associated load (12) of the aircraft system, wherein the maximum power varies as a function of variation of electrical characteristics monitored over time; and
controlling the maximum power and/or current the fuel cell stack is capable of supplying to an associated load based on the variation of electrical characteristics monitored over time.
15. The method of claim 14, wherein further including storing the electrical characteristics associated with the fuel cell stack in a memory.
16. The method of claim 15, wherein the memory further includes reference data suitable for comparing with the stored electrical characteristics to determine health of the fuel cell stack.
17. The method of any one of claims 14-16, wherein the memory further includes reference data suitable for comparing with the stored electrical characteristics to determine anomalous behavior associated with the fuel cell stack.
18. The method of any one of claims 14-17, further including supplying power from an energy storage device when the health of the fuel stack is outside a prescribed performance range.
19. The method of any one of claims 14-18, wherein the energy storage device is one selected from a group of a battery, a flywheel, and a capacitor.
20. A method for starting a fuel cell stack in cold temperatures with an energy storage device, the method comprising: preventing a fuel cell stack from outputting power and/or current to an associated load prior to the fuel cell stack reaching a desired operating temperature; wherein the energy storage device power provides power to a balance of plant and passively warms the fuel stack to a first operating temperature; and power provided from the balance of plant is proportionately switched away from the energy storage device and loaded onto the fuel cell stack based upon distribution of voltage
measurements from a plurality of cell voltage monitors until the energy storage device reliably offloaded; and powering the balance of plant with fuel cell stack while recharging the energy storage device until the desired operating temperature of the fuel cell stack is reached, wherein upon reaching the desired operating temperature, power and/or current is output from the fuel cell stack to power the associated load.
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US201361821260P | 2013-05-09 | 2013-05-09 | |
US61/821,260 | 2013-05-09 |
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