Abstract: A system and method for quickly heating a fuel cell stack at fuel cell system start-up. The fuel cell system includes a three-way valve positioned in the anode exhaust that selectively directs the anode exhaust gases to the cathode input of the fuel cell stack so that hydrogen in the anode exhaust gas can be used to heat the fuel cell stack. During normal operation when the fuel cell stack is at the desired temperature, the three-way valve in the anode exhaust can be used to bleed nitrogen to the cathode exhaust.

Abstract: A system and method for putting a fuel cell system in a stand-by during a system idle condition to improve system fuel efficiency. The method can include diverting the cathode airflow around the stack, reducing an airflow output from a cathode compressor to a minimum allowable set-point, opening the stack contactors to disconnect the stack from the high voltage bus and electrically isolate the stack from the rest of the system, engaging an independent load to the stack, such as end cell heaters in the stack, to suppress stack voltage, maintaining a positive pressure in the anode side of the fuel cell stack and periodically bleeding the anode into the exhaust stream. When a system power request is made removing the idle condition, the system returns to normal operation by directing the airflow back to the cathode and opening the stack contactors when an open circuit voltage is attained.

Abstract: A method of controlling the relative humidity in an electrochemical conversion device comprises the steps of: providing a fuel cell stack comprising a plurality of fuel cells stackingly arranged, and at least one heater coupled to at least one end fuel cell; selecting a relative humidity setpoint for the at least one end cell; calculating an end cell membrane electrode assembly temperature setpoint using the relative humidity setpoint; calculating a heater temperature setpoint equal to the calculated end cell membrane electrode assembly temperature setpoint plus a computed temperature difference from the at least one end cell membrane electrode assembly to the heater; and adjusting the temperature of the end cell heater until it reaches the heater temperature setpoint and thereby achieves the relative humidity setpoint of the at least end cell membrane electrode assembly.

Abstract: A system and method for providing an anode exhaust gas bleed in a fuel cell system. The system provides a normal anode side bleed using first and second bleed valves if the first and second bleed valves are not blocked and the temperature of first and second split sub-stacks is greater than a predetermined temperature, provides a continuous anode side bleed using the bleed valves if the bleed valves are not blocked and the temperature of the sub-stacks is less than the predetermined temperature, provides a normal center anode bleed through the drain valve if the first or second bleed valve is blocked and the temperature of the sub-stacks is above the predetermined temperature and provides a continuous center anode side bleed through the drain valve if the first or second bleed valve is blocked and the temperature of the sub-stacks is below the predetermined temperature.

Abstract: A control strategy for removing nitrogen from the anode side of a fuel cell stack. The control strategy includes using a bleed valve to remove the nitrogen during the operation of the fuel cell stack until the stack ages to a point where the bleed valve is maintained open, but the concentration of nitrogen in the anode side of the stack continues to increase. Once the concentration of nitrogen in the anode side increases to a predetermined level, then a purge valve is opened in combination with the bleed valve to reduce the concentration of nitrogen. Once the nitrogen concentration is reduced below the level, then both valves are closed, and the sequence is repeated.

Abstract: A fuel cell system that employs a method for increasing stack power ramp up for high power up-transients by decoupling the build-up of stack current density from the cathode side pressure. The system gives the compressor power priority during the power up-transient to quickly provide the proper compressor speed, and therefore the proper air mass flow, for the desired current density of the fuel cell stack. The system also maintains the cathode side pressure of the stack low by keeping a cathode back-pressure valve open. By increasing the cathode input airflow rate to the proper level at the power up-transient, the current density of the stack will increase to the desired stack power level. Subsequently, the back-pressure valve is closed to increase the stack voltage to provide the total maximum power achievable by the stack.

Abstract: A system and method for limiting the amount of hydrogen being bled from an anode exhaust line. The method includes maintaining a pressure bias between an anode outlet and a cathode outlet of a fuel cell stack so that when an anode exhaust gas is bled from the anode exhaust line and mixed with the cathode exhaust gas, the concentration of hydrogen in the mixed gas is maintained below a predetermined percentage. The pressure bias is such that the anode exhaust gas has a higher gas pressure than the cathode exhaust gas.

Abstract: A system for bleeding the anode side of first and second split fuel cell stacks in a fuel cell system that employs anode flow-shifting, where each split stack includes a bleed valve. The system determines that one or both of the bleed valves is stuck in an open position if there is flow through an orifice and a bleed has not been commanded. A shut-off valve is then used to provide the bleed if the cathode exhaust gas is able to dilute the hydrogen in the bled anode exhaust gas. An outlet valve between the first and second split stacks is used to bleed the anode exhaust gas if the cathode exhaust gas is not significant enough to dilute the hydrogen in the anode exhaust gas. If the first or second bleed valve is stuck in the closed position, then the outlet valve is used to provide the bleed.

Abstract: A method for improving fuel cell system reliability in the event of end cell heater failure in a fuel cell stack. The method includes detecting that an end cell heater has failed. If an end cell heater failure is detected, then the method performs one or more of setting a cooling fluid pump to a predetermined speed that drives a cooling fluid through cooling fluid flow channels in the fuel cell stack, limiting the output power of the fuel cell stack or the net power of the fuel cell system, limiting the maximum temperature of the cooling fluid flowing out of the stack, turning off stack anti-flooding algorithms that may be used to remove water from reactant gas flow channels in the stack, and turning off cathode stoichiometry adjustments for relative humidity control in response to water accumulating in cathode flow channels in the fuel cell stack.

Abstract: A fuel cell system is provided that includes a fuel cell stack and an air compressor in communication with a cathode inlet, a hydrogen source in communication with an anode inlet, and a start-up battery adapted to power the air compressor. The start-up battery is at least one of a low-voltage battery and a high-voltage battery. A pressure sensor is in communication with the air compressor and adapted to measure a compressor outlet pressure. A power conversion module is in electrical communication with the start-up battery and the air compressor. A controller is in communication with the power conversion module and adapted to set an air compressor speed based on an available electrical energy. A closed-loop method of operating the fuel cell system at start-up is also provided, wherein an anode purge is scheduled based on an air flow rate calculated from the compressor outlet pressure and the actual speed.

Abstract: A method for quickly and efficiently heating a fuel cell stack at system start-up. The method uses and prioritizes various stack heat sources based on their efficiency to heat the stack. A thermal set-point for heating the stack to the desired temperature is determined based on the ambient temperature and, the stack cooling fluid temperature. The set-point is then compared-to the stack heating provided by the heat sources that are operating through normal system start-up operation. If more heat is necessary to reach the set-point, the method may first charge a system battery using stack power where the load causes the fuel cell stack to heat up. If additional heating is still required, the method may then turn on a cooling fluid heater, then flow a small amount of hydrogen into the cathode inlet stream to provide combustion, and then increase the compressor load as needed.

Abstract: A fuel cell system is provided that includes a fuel cell stack and an air compressor in communication with a cathode inlet, a hydrogen source in communication with an anode inlet, and a start-up battery adapted to power the air compressor. The start-up battery is at least one of a low-voltage battery and a high-voltage battery. A power conversion module is in electrical communication with the start-up battery and the air compressor. The power conversion module is adapted to boost a voltage of the start-up battery as desired and power the air compressor at start-up. A controller is in communication with the power conversion module and is adapted to set an air compressor speed based on an available electrical energy. An open-loop method of operating the fuel cell system at start-up is also provided, wherein an anode purge is scheduled based on the available electrical energy from the battery.

Abstract: A method for providing a fast and reliable start-up of a fuel cell system. The method uses a stack voltage response to a load to assess if hydrogen and oxygen are being sufficiently distributed to all of the fuel cells by coupling an auxiliary load to the fuel cell stack until a predetermined minimum cell voltage has been reached or a first predetermined time period has elapsed. The method then determines whether a minimum cell voltage has dropped to a first predetermined voltage and, if so, reduces the maximum power allowed to be below the first predetermined voltage value, determines whether the minimum cell voltage in the stack is below a second predetermined voltage, or determines whether the minimum cell voltage drop rate is greater than a predetermined voltage drop rate. If none of these conditions are met, the method returns to loading the stack with system components.

Abstract: A method for triggering an anode bleed from split fuel cell stacks in a fuel cell system that employs anode flow-shifting. The method requests the bleed if any one of three different conditions are met. Those conditions include that the concentration of nitrogen in the anode side of the split stacks is above a predetermined percentage, the voltage spread between the maximum cell voltage and the minimum cell voltage of two fuel cells in the split stacks is greater than a predetermined spread voltage and the absolute value of the difference between the overall voltage of the two split stacks is greater than a predetermined voltage. The concentration of nitrogen in the anode can be determined in any suitable manner, such as by a nitrogen cross-over model or a sensor.

Abstract: A temperature control system and method for a fuel cell stack cooling system is disclosed. The temperature control system includes a coolant circulation line for circulating a coolant to and from a fuel cell stack. A coolant pump is provided in the coolant circulation line, and a pump ?P sensor is provided in fluid communication with the coolant circulation line on inlet and outlet sides of the coolant pump. The pump ?P sensor measures a change in pump pressure between the inlet and outlet sides of the coolant pump. A pump map is provided having correlated values of pump speed, change in pump pressure and coolant flow rate for correlating the coolant flow rate with the pump speed and the change in pump pressure to attain a desired coolant flow rate for optimum fuel stack cooling.

Abstract: A method for controlling a fuel cell system, capable of quickly detecting the pressure rise caused by a faulted open anode injector, reducing pressure in the fuel cell stack when the fault occurs, and taking remedial action to allow continued operation of the fuel cell stack, and militate against a walk-home incident.

Abstract: A fuel cell system that increases stack stability by reducing the amount of liquid water droplets at the anode input of a fuel cell stack in the system. Re-circulated anode exhaust gas from the fuel cell stack and fresh hydrogen gas are sent to an anode heat exchanger so that both the fresh hydrogen gas and the re-circulated anode exhaust gas are heated to reduce the formation of water droplets in the anode input gas. Further, a portion of the heated cooling fluid directly from the fuel cell stack is sent to the heat exchanger to heat the fresh hydrogen gas and the re-circulation hydrogen before the cooling fluid is sent to an isolation heat exchanger to have its temperature reduced.

Abstract: A method of controlling the relative humidity in an electrochemical conversion device comprises the steps of: providing a fuel cell stack comprising a plurality of fuel cells stackingly arranged, and at least one heater coupled to at least one end fuel cell; selecting a relative humidity setpoint for the at least one end cell; calculating an end cell membrane electrode assembly temperature setpoint using the relative humidity setpoint; calculating a heater temperature setpoint equal to the calculated end cell membrane electrode assembly temperature setpoint plus a computed temperature difference from the at least one end cell membrane electrode assembly to the heater; and adjusting the temperature of the end cell heater until it reaches the heater temperature setpoint and thereby achieves the relative humidity setpoint of the at least end cell membrane electrode assembly.

Abstract: A fuel cell system that employs a method for increasing stack power ramp up for high power up-transients by decoupling the build-up of stack current density from the cathode side pressure. The system gives the compressor power priority during the power up-transient to quickly provide the proper compressor speed, and therefore the proper air mass flow, for the desired current density of the fuel cell stack. The system also maintains the cathode side pressure of the stack low by keeping a cathode back-pressure valve open. By increasing the cathode input airflow rate to the proper level at the power up-transient, the current density of the stack will increase to the desired stack power level. Subsequently, the back-pressure valve is closed to increase the stack voltage to provide the total maximum power achievable by the stack.

Abstract: A fuel cell system that controls an anode exhaust gas bleed during power up-transients. The fuel cell system includes a by-pass valve that allows compressor air to by-pass the fuel cell stack and be directly emitted into the cathode exhaust gas stream. The system detects a power up-transient by monitoring the rate of closing of the by-pass valve and the rate of change of an increase in the compressor airflow set-point. If these parameters pass a certain threshold, then the system determines that a power up-transient is occurring, and prevents an anode exhaust gas bleed for a predetermined period of time. If cathode pulsing is occurring where power up-transients come one after another, then the system will continuously reset the time period for preventing the anode exhaust gas bleed until a second time limit is reached, where the bleed is then forced.