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 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 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 detection method for enabling gas composition observation during fuel cell system start-up is described. In one embodiment, the method includes initiating a flow of hydrogen to the anode to pressurize the anode; opening an anode flow valve; determining if an anode pressure exceeds an anode pressure threshold; enabling anode flow set point detection after a first predetermined time if the anode pressure exceeds the anode pressure threshold; monitoring an anode flow set point using the anode flow set point detection; determining if the anode flow set point exceeds an anode flow set point threshold; and closing the anode flow valve after a second predetermined time if the anode flow set point exceeds the anode flow set point threshold.

Abstract: A system and method for reducing the frequency of stack stand-by mode events, if necessary, as a fuel cell stack ages and experiences lower performance. The method determines an irreversible voltage loss of the fuel cell stack at predetermined time intervals and determines a stack voltage degradation variable based on the irreversible voltage loss. The method also determines if the stack voltage degradation variable indicates that the fuel cell stack will not meet predetermined stack end-of-life voltage requirements and calculates a maximum allowed voltage degradation rate of the fuel cell stack. The method calculates a maximum number of stand-by mode events per unit time that can be allowed to prevent the stack from exceeding the maximum allowed degradation rate and controls the number of stand-by mode events based on the calculated maximum number of stand-by mode events.

Abstract: A system and method for reducing the frequency of stack stand-by mode events, if necessary, as a fuel cell stack ages and experiences lower performance. The method determines an irreversible voltage loss of the fuel cell stack at predetermined time intervals and determines a stack voltage degradation variable based on the irreversible voltage loss. The method also determines if the stack voltage degradation variable indicates that the fuel cell stack will not meet predetermined stack end-of-life voltage requirements and calculates a maximum allowed voltage degradation rate of the fuel cell stack. The method calculates a maximum number of stand-by mode events per unit time that can be allowed to prevent the stack from exceeding the maximum allowed degradation rate and controls the number of stand-by mode events based on the calculated maximum number of stand-by mode events.

Abstract: A method for operating a fuel cell stack where electrical energy from regenerative braking is used to operate system loads instead of using fuel cell stack power to conserve hydrogen. A fuel cell stack and an ultracapacitor are electrically coupled to a high voltage electrical bus. A by-pass line is provided around a blocking diode including a by-pass contactor. A stack contactor is provided to disconnect the fuel cell stack from the electrical bus. A stand-by mode request is made if the voltage at a node proximate to the blocking diode closest to the ultracapacitor is higher than the voltage at a node proximate to the blocking diode closest to the fuel cell stack. Steps are then made to electrically prepare the high voltage electrical bus. Then, the stack contactor is opened and the by-pass contactor is closed to allow the regenerate braking energy to power the system loads.

Abstract: A remedial method for starting a fuel cell system is described. The method includes determining if the remedial method is required; providing air to an exhaust of a fuel cell stack; setting a hydrogen flow rate to an anode side of the fuel cell stack; providing a predetermined volume of hydrogen to the anode side of the fuel cell at the hydrogen flow rate; providing a predetermined volume of air to a cathode side of the fuel cell stack after the predetermined volume of hydrogen has been provided to the anode side while continuing to provide air to the exhaust of the fuel cell stack and hydrogen to the anode side of the fuel cell stack; determining if a stack voltage is stable after the predetermined volume of air has been provided to the cathode side; and closing the anode outlet valve after the stack voltage is stable.

Abstract: Methods and systems of reducing the start-up time for a fuel cell are described. One method of reducing the start-up time includes: concurrently supporting load requests for the fuel cell and stabilizing the voltage of the fuel cell; wherein stabilizing the voltage of the fuel cell comprises: providing a flow of hydrogen to the fuel cell and opening an anode valve, wherein the hydrogen flow continues for predetermined volume or a predetermined time; and ending voltage stabilization after the predetermined volume or predetermined time is exceeded while continuing to support load requests for the fuel cell.

Abstract: A fuel cell system that controls the speed of the compressor providing cathode air to a fuel cell stack just after a system start-up procedure has ended so as to reduce the chance that the compressor current draw will cause a stack quick stop. The method includes recognizing a command for high compressor speed just after the system start-up procedure ends, where the stack is in the run state, and instead of providing a step change in the compressor command, ramping up the compressor speed so that the current draw from the compressor does not spike.

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 system and method for improving fuel cell system start-up reliability. The method includes determining if the resistance of the membranes in a fuel cell stack is too high, where the reliability of system start-up will be reduced, and if so, providing one or more remedial actions to help ensure that the start-up is more reliable. In one embodiment, the system and method determine that the fuel cell membranes are to dry based on whether a high frequency measurement of the fuel cell stack exceeds a predetermined HFR threshold. If the HFR threshold has been exceeded, a special start-up procedure is used that increases the reliability that the start-up will be successful using the remedial actions, such as reducing cathode airflow and turning on stack end cell heaters.

Abstract: A system and method for correcting a large fuel cell voltage spread for a split sub-stack fuel cell system. The system includes a hydrogen source that provides hydrogen to each split sub-stack and bleed valves for bleeding the anode side of the sub-stacks. The system also includes a voltage measuring device for measuring the voltage of each cell in the split sub-stacks. The system provides two levels for correcting a large stack voltage spread problem. The first level includes sending fresh hydrogen to the weak sub-stack well before a normal reactive bleed would occur, and the second level includes sending fresh hydrogen to the weak sub-stack and opening the bleed valve of the other sub-stack when the cell voltage spread is close to stack failure.

Abstract: A method for operating a fuel cell stack where electrical energy from regenerative braking is used to operate system loads instead of using fuel cell stack power to conserve hydrogen. A fuel cell stack and an ultracapacitor are electrically coupled to a high voltage electrical bus. A by-pass line is provided around a blocking diode including a by-pass contactor. A stack contactor is provided to disconnect the fuel cell stack from the electrical bus. A stand-by mode request is made if the voltage at a node proximate to the blocking diode closest to the ultracapacitor is higher than the voltage at a node proximate to the blocking diode closest to the fuel cell stack. Steps are then made to electrically prepare the high voltage electrical bus. Then, the stack contactor is opened and the by-pass contactor is closed to allow the regenerate braking energy to power the system loads.

Abstract: A system and method for putting a fuel cell vehicle system into a stand-by mode where there is little or no power being consumed, the quantity of fuel being used is minimal and the fuel cell system is able to quickly recover from the mode. The method includes determining whether predetermined stand-by mode vehicle level entrance criteria have been satisfied at a vehicle control level and predetermined stand-by mode fuel cell level entrance criteria have been satisfied for a fuel cell system control level, and putting the vehicle in the stand-by mode if both the vehicle level entrance criteria and the fuel cell level entrance criteria have been satisfied. The method exits the stand-by mode if predetermined vehicle level exit criteria have been satisfied or predetermined fuel cell level exit criteria have been satisfied.

Abstract: Methods and systems of reducing the start-up time for a fuel cell are described. One method of reducing the start-up time includes: concurrently supporting load requests for the fuel cell and stabilizing the voltage of the fuel cell; wherein stabilizing the voltage of the fuel cell comprises: providing a flow of hydrogen to the fuel cell and opening an anode valve, wherein the hydrogen flow continues for predetermined volume or a predetermined time; and ending voltage stabilization after the predetermined volume or predetermined time is exceeded while continuing to support load requests for the fuel cell.

Abstract: A detection method for enabling gas composition observation during fuel cell system start-up is described. In one embodiment, the method includes initiating a flow of hydrogen to the anode to pressurize the anode; opening an anode flow valve; determining if an anode pressure exceeds an anode pressure threshold; enabling anode flow set point detection after a first predetermined time if the anode pressure exceeds the anode pressure threshold; monitoring an anode flow set point using the anode flow set point detection; determining if the anode flow set point exceeds an anode flow set point threshold; and closing the anode flow valve after a second predetermined time if the anode flow set point exceeds the anode flow set point threshold.

Abstract: A remedial method for starting a fuel cell system is described. The method includes determining if the remedial method is required; providing air to an exhaust of a fuel cell stack; setting a hydrogen flow rate to an anode side of the fuel cell stack; providing a predetermined volume of hydrogen to the anode side of the fuel cell at the hydrogen flow rate; providing a predetermined volume of air to a cathode side of the fuel cell stack after the predetermined volume of hydrogen has been provided to the anode side while continuing to provide air to the exhaust of the fuel cell stack and hydrogen to the anode side of the fuel cell stack; determining if a stack voltage is stable after the predetermined volume of air has been provided to the cathode side; and closing the anode outlet valve after the stack voltage is stable.

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 system and method for correcting a large fuel cell voltage spread for a split sub-stack fuel cell system. The system includes a hydrogen source that provides hydrogen to each split sub-stack and bleed valves for bleeding the anode side of the sub-stacks. The system also includes a voltage measuring device for measuring the voltage of each cell in the split sub-stacks. The system provides two levels for correcting a large stack voltage spread problem. The first level includes sending fresh hydrogen to the weak sub-stack well before a normal reactive bleed would occur, and the second level includes sending fresh hydrogen to the weak sub-stack and opening the bleed valve of the other sub-stack when the cell voltage spread is close to stack failure.