Abstract: A system and method for determining the maximum allowed stack current limit rate for a fuel cell stack that considers cell voltage. The method includes estimating a fuel cell stack voltage based on a fuel cell resistance value, stack variables and a current request signal. The fuel cell resistance value can be modeled based on stack temperature and stack relative humidity. The stack variables can include exchange current density and mass transfer coefficient. The method then uses the estimated fuel cell voltage and a look-up table based on estimated voltage to determine a current rate limit value for changing the current of the stack. The method then adds the current rate limit value and the current request signal to obtain the current set-point.

Abstract: A fuel cell system is disclosed, wherein the fuel cell system is heated by a fluid during a starting operation to mitigate against vapor condensation and ice formation in a fuel cell assembly and to decrease a warm up time of the fuel cell system.

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 fuel cell system that employs a method for determining the potential that a freeze condition will exist after the system is shut-down based on predetermined input, such as ambient temperature, geographical location, user usage profile, date, weather reports, etc. If the system determines that a freeze condition is probable, then the system initiates a purge shut-down of the fuel cell system where water is purged out of the reactant gas flow channels. If the system determines that a freeze condition is unlikely, then it will initiate a normal shut-down procedure without purging the flow channels. The system will then periodically determine if the conditions have changed, and will initiate the purge if a freeze condition subsequently becomes probable.

Abstract: A fuel cell system is disclosed that employs a humidifier and an oxygen sensor for measuring the oxygen concentration in the cathode exhaust gas from the fuel cell stack to determine a system diagnostic, such as a fluid leak from or across the humidifier.

Abstract: A method for purging water from a fuel cell stack at fuel cell system shutdown. The method includes determining a stack water generation request to control the rate of drying of membranes in the stack and determining a cathode catalytic heating water generation request. A maximum charge a battery in the fuel cell system can accept is also determined. An ancillary power request for powering components of the fuel cell system during shutdown is determined. The method allocates how much of the water generation request will be fulfilled by operating the fuel cell stack to charge the battery and to provide the power needed for the ancillary power request, and how much of the water generation request will be fulfilled by cathode catalytic heating that produces water and heat in a cathode side of the fuel cell stack.

Abstract: A self-learning assisted hybrid vehicle system that includes a main power source for providing power to the vehicle, a supplemental power source for providing supplemental power for providing power to the vehicle and an electric motor or other mechanical system for driving the vehicle. The system also includes a self-learning controls unit that receives and stores information from a plurality of inputs associated with the vehicle. The self-learning controls unit uses the information to make predictions about future driving conditions of the vehicle to efficiently utilize the power sources of the hybrid vehicle.

Abstract: A valve for a fuel cell system includes a valve housing having a valve seat formed therein. The valve seat includes an orifice formed therein to permit a fluid to flow through the valve housing. A movable member is disposed in the valve housing and is movable between an open position and a closed position. The movable member includes a first end having an elongate portion and a generally conical shaped base. At least a portion of the base is disposed in the orifice of the valve seat when the movable member is in the closed position to militate against a formation of ice across the orifice of the valve seat.

Abstract: A method for performing a plausibility check of a fuel cell stack anode side pressure sensor to determine whether the pressure sensor is providing an accurate measurement. Prior to system start-up when a cathode side compressor is not providing cathode air to a fuel cell stack, and the cathode side of the stack is at ambient pressure, a pressure measurement from a differential pressure sensor between the anode side and the cathode side of the fuel cell stack is provided. The differential pressure sensor reading is added to a pressure measurement from an ambient pressure sensor, where the sum should be about the same as the pressure measurement from the anode side pressure sensor if the anode side pressure sensor is operating properly.

Abstract: A method of operating a fuel cell system comprising a fuel cell and a compressor that provides air to the fuel cell. The method comprises sensing a temperature indicative of the temperature of a fuel cell, providing a restriction in an air flow path to the fuel cell when the sensed temperature is below a threshold, and increasing the speed of the compressor to provide a desired air flow to the fuel cell. In at least some implementations, increasing the speed of the compressor increases the power drawn from the fuel cell to power the compressor and helps to increase the heat of the fuel cell. The increased speed of the compressor can also result in warmer air flow from the compressor that can further increase the temperature of the system components.

Abstract: A process for controlling the length of a purge and the purge rate of a fuel cell stack at system shut-down so as to provide the desired amount of stack humidity. The membrane humidification is measured at system shut-down by a high frequency resistance sensor that detects membrane humidification and provides the measurement to a controller. The controller controls the compressor that provides cathode input air to the fuel cell stack so that the time of the purge and the flow rate of the purge provide a desired membrane humidity for the next start-up.

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 self-learning assisted hybrid vehicle system that includes a main power source for providing power to the vehicle, a supplemental power source for providing supplemental power for providing power to the vehicle and an electric motor or other mechanical system for driving the vehicle. The system also includes a self-learning controls unit that receives and stores information from a plurality of inputs associated with the vehicle. The self-learning controls unit uses the information to make predictions about future driving conditions of the vehicle to efficiently utilize the power sources of the hybrid vehicle.

Abstract: A method for shutting down a fuel cell system including operating a fuel cell stack. the method includes providing an increased cathode air flow so as to dry fuel cell membranes in the stack until a first desired level of high frequency resistance is achieved, rehydrating the cell membranes of the stack until a second desired level of high frequency resistance is achieved, and operating the stack with a decreased cathode input relative humidity until a third desired level of high frequency resistance is achieved.

Abstract: A system and method for determining the maximum allowed stack current limit rate for a fuel cell stack that considers cell voltage. The method includes estimating a fuel cell stack voltage based on a fuel cell resistance value, stack variables and a current request signal. The fuel cell resistance value can be modeled based on stack temperature and stack relative humidity. The stack variables can include exchange current density and mass transfer coefficient. The method then uses the estimated fuel cell voltage and a look-up table based on estimated voltage to determine a current rate limit value for changing the current of the stack. The method then adds the current rate limit value and the current request signal to obtain the current set-point.

Abstract: A purge valve for a split fuel cell stack design that prevents a direct flow path between the anode sides of the split stacks. The purge valve includes an inlet port that receives purge air from a compressor, a first outlet port in fluid communication with the anode side of one of the split stacks and a second outlet port in fluid communication with the anode side of the other split stack. A spring biased shaft maintains a diaphragm in a closed position to close off the flow channels between the inlet port and the first outlet port, the inlet port and the second outlet port and the first and second outlet ports during normal fuel cell operation. A hole is provided through the diaphragm to provide pressure equalization in the chamber.

Abstract: A fuel cell system that employs a two-position valve at the cathode exhaust gas output for controlling the pressure within the fuel cell stack to control the stack relative humidity. In one embodiment, the two-position valve is switchable between a fully open and a fully closed position, where the valve is opened when the fuel cell system is operating at a low operation temperature and the valve is closed when the fuel cell system is operating at a high operation temperature. A fixed restriction valve is provided in parallel with the two-position valve so that when the two-position valve is fully closed, the proper amount of pressure is provided at the cathode output. In another embodiment, the two-position valve employs sized leak paths so that when the two-position valve is in the closed position, the cathode exhaust gas can still flow through.

Abstract: A method for performing a plausibility check of a fuel cell stack anode side pressure sensor to determine whether the pressure sensor is providing an accurate measurement. Prior to system start-up when a cathode side compressor is not providing cathode air to a fuel cell stack, and the cathode side of the stack is at ambient pressure, a pressure measurement from a differential pressure sensor between the anode side and the cathode side of the fuel cell stack is provided. The differential pressure sensor reading is added to a pressure measurement from an ambient pressure sensor, where the sum should be about the same as the pressure measurement from the anode side pressure sensor if the anode side pressure sensor is operating properly.

Abstract: A method for controlling the pressure within a fuel cell stack to control the stack relative humidity. In one embodiment, a two-position valve receiving the cathode exhaust is switchable between a fully open and a fully closed position, where the valve is opened when the fuel cell system is operating at a low operation temperature and the valve is closed when the fuel cell system is operating at a high operation temperature. A fixed restriction valve is provided in parallel with the two-position valve so that when the two-position valve is fully closed, the proper amount of pressure is provided at the cathode output. In another embodiment, the two-position valve employs leak paths so that when the two-position valve is in the closed position, the cathode exhaust gas can still flow through.

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.