Abstract: A method for determining membrane humidification by determining the membrane protonic resistance of a fuel cell stack at humidified conditions, and normalizing the base resistance of the fuel cell stack against the base resistance of a reference fuel cell stack.

Abstract: A method and an apparatus to adapt the performance of a cathode humidification unit as a membrane in a fuel cell stack degrades over time. An algorithm compares a sensed humidity profile of the fuel cell stack and model humidity profile of a cathode humidification unit model to calculate a new degradation factor. The cathode humidification unit model uses the degradation factor in the performance of the cathode humidification unit.

Abstract: A method for reconditioning a fuel cell stack. The method includes periodically increasing the relative humidity level of the cathode input airflow to the stack to saturate the cell membrane electrode assemblies to be greater than the relative humidity levels during normal stack operating conditions. The method also includes providing hydrogen to the anode side of the fuel cell stack at system shut down while the membrane electrode assemblies are saturated without stack loads being applied so that the hydrogen crosses the cell membranes to the cathode side and reacts with oxygen to reduce stack contaminants.

Abstract: A system and method for operating a fuel cell stack of a fuel cell system in a vehicle when an error in cathode air flow rate is detected. The system and method include estimating a cathode air flow rate and detecting an error in the estimated cathode air flow rate. The system and method also include utilizing high frequency resistance measurements from a high frequency resistance sensor to control a relative humidity of the fuel cell stack when the error in the estimated cathode air flow rate has been detected.

Abstract: A system and method that monitor the rate of a voltage drop of fuel cells in a fuel cell stack to determine whether the voltage drop is a result of cathode reactant starvation or anode reactant starvation. The method looks at a falling voltage of a fuel cell to determine whether the rate of the fall in voltage indicates that hydrogen starvation of the anode of the fuel cell is occurring. The method also looks at the actual voltage of the fuel cell that is falling to determine whether it is a below a predetermined minimum voltage threshold also indicating that hydrogen starvation of the anode of the fuel cell is occurring. If hydrogen starvation is occurring, the method performs power limiting of the fuel cell stack either based on the rate or the voltage level.

Abstract: A system and method for determining if an RH sensor that measures the relative humidity of cathode inlet air provided to a fuel cell stack or an HFR circuit that measures stack water content is operating properly. The method provides the cathode inlet air through a WVT unit that increases the water content of the cathode inlet air. The method uses a water buffer model for determining the water content of the fuel cell stack based on inputs from a plurality of system components and revises a water transfer model using the HFR humidification signal or the RH signal to correct for WVT unit degradation. The method determines whether the RH sensor or the HFR circuit is operating properly, such as by determining if the HFR humidification signal is increasing at a rate that is faster than what the stack water content is able to increase.

Abstract: A method for providing calibration synchronization pulses in a pulse width modulation (PWM) signal including fuel cell voltage measurement pulses. The method includes providing a sequence of voltage signals representative of the voltage of the fuel cells in a fuel cell group, where the sequence of voltage signals are provided in the order of the position of the fuel cells in the group. The method also includes providing a sequence of calibration pulses and combining the sequence of voltage signals and the sequence of calibration pulses so that the calibration pulses are provided before a voltage signal of a first cell in the group. The method modulates the combined sequence of the voltage signals and the calibration pulses using an inverted saw tooth wave to provide the PWM signal, where a width of the pulses representing the voltage signals are proportional to a width of the pulses representing the calibration pulses.

Abstract: A system and method for selectively operating a fuel cell stack in response to loss of a voltage signal from one or more fuel cells in the stack. If the voltage signal from the one or more fuel cells is lost, the method performs one or more remedial actions to cause the fuel cell stack to operate in a more stack safe condition. The method then determines whether the cell or cells whose voltage signal is lost was healthy, such as operating above a predetermined voltage threshold, prior to the voltage signal being lost. If the cell voltage signal was above the voltage threshold, then the fuel cell stack is operated normally under the remedial actions, and if the voltage signal is below the voltage threshold, then the fuel cell stack is operated in a power limitation mode.

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 system and method for increasing the temperature of a fuel cell stack quickly, especially at cold stack start-up. The method includes determining whether the fuel cell stack is below a first predetermined temperature threshold, and, if so, starting a cooling fluid flow through the stack and engaging a shorting circuit across the stack to short circuit the stack and cause the stack to operate inefficiently. The method then determines a desired heating rate of the fuel cell stack and calculates a cathode airflow to the fuel cell stack based on the desired heating rate. The method reduces the flow of cathode air to the stack if a minimum cell voltage is below a predetermined minimum cell voltage threshold and disengages the shorting circuit and applies vehicle loads to the stack when the stack temperature reaches a predetermined second temperature threshold.

Abstract: A method for providing calibration and synchronization pulses in a pulse width modulation (PWM) signal including cell voltage measurement pulses, where the calibration pulses are four calibration pulses having a pattern of a narrow width high voltage pulse followed by a wide width low voltage pulse followed by a narrow width high voltage pulse followed by a wide width low voltage pulse that has a very low probability of occurring in a practical fuel cell system. The method modulates a combined sequence of the voltage measurement signals and the calibration pulses using an inverted saw tooth wave to provide the PWM signal, where a width of the pulses representing the voltage signals are proportional to a width of the pulses representing the calibration pulses.

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: The present disclosure relates to systems and methods that may be used to predict a performance metric of a fuel cell. A system consistent with the present disclosure may include sensors in communication with the fuel cell stack, a performance metric prediction system, and a control system. The performance metric prediction system may determine a current density based on inputs provided by the sensors at a plurality of time periods, calculate a first parameter while the current density is below a lower threshold, and calculate a second parameter while the current density is above an upper threshold. The first parameter and the second parameter may be used to selectively adjust a fuel cell polarization curve over time. Based upon the polarization curve, a performance metric of the fuel cell stack may be predicted. The control system may implement a control action based upon the performance metric.

Abstract: A method and an apparatus to adapt the performance of a cathode humidification unit as a membrane in a fuel cell stack degrades over time. An algorithm compares a sensed humidity profile of the fuel cell stack and model humidity profile of a cathode humidification unit model to calculate a new degradation factor. The cathode humidification unit model uses the degradation factor in the performance of the cathode humidification unit.

Abstract: The present disclosure relates to systems and methods that may be used to predict a performance metric of a fuel cell. A system consistent with the present disclosure may include sensors in communication with the fuel cell stack, a performance metric prediction system, and a control system. The performance metric prediction system may determine a current density based on inputs provided by the sensors at a plurality of time periods, calculate a first parameter while the current density is below a lower threshold, and calculate a second parameter while the current density is above an upper threshold. The first parameter and the second parameter may be used to selectively adjust a fuel cell polarization curve over time. Based upon the polarization curve, a performance metric of the fuel cell stack may be predicted. The control system may implement a control action based upon the performance metric.

Abstract: A system and method for operating a fuel cell stack of a fuel cell system in a vehicle when an error in cathode air flow rate is detected. The system and method include estimating a cathode air flow rate and detecting an error in the estimated cathode air flow rate. The system and method also include utilizing high frequency resistance measurements from a high frequency resistance sensor to control a relative humidity of the fuel cell stack when the error in the estimated cathode air flow rate has been detected.

Abstract: A system and method that monitor the rate of a voltage drop of fuel cells in a fuel cell stack to determine whether the voltage drop is a result of cathode reactant starvation or anode reactant starvation. The method looks at a falling voltage of a fuel cell to determine whether the rate of the fall in voltage indicates that hydrogen starvation of the anode of the fuel cell is occurring. The method also looks at the actual voltage of the fuel cell that is falling to determine whether it is a below a predetermined minimum voltage threshold also indicating that hydrogen starvation of the anode of the fuel cell is occurring. If hydrogen starvation is occurring, the method performs power limiting of the fuel cell stack either based on the rate or the voltage level.

Abstract: A system and method for determining if an RH sensor that measures the relative humidity of cathode inlet air provided to a fuel cell stack or an HFR circuit that measures stack water content is operating properly. The method provides the cathode inlet air through a WVT unit that increases the water content of the cathode inlet air. The method uses a water buffer model for determining the water content of the fuel cell stack based on inputs from a plurality of system components and revises a water transfer model using the HFR humidification signal or the RH signal to correct for WVT unit degradation. The method determines whether the RH sensor or the HFR circuit is operating properly, such as by determining if the HFR humidification signal is increasing at a rate that is faster than what the stack water content is able to increase.

Abstract: A system and method for selectively operating a fuel cell stack in response to loss of a voltage signal from one or more fuel cells in the stack. If the voltage signal from the one or more fuel cells is lost, the method performs one or more remedial actions to cause the fuel cell stack to operate in a more stack safe condition. The method then determines whether the cell or cells whose voltage signal is lost was healthy, such as operating above a predetermined voltage threshold, prior to the voltage signal being lost. If the cell voltage signal was above the voltage threshold, then the fuel cell stack is operated normally under the remedial actions, and if the voltage signal is below the voltage threshold, then the fuel cell stack is operated in a power limitation mode.

Abstract: A method for determining membrane humidification by determining the membrane protonic resistance of a fuel cell stack at humidified conditions, and normalizing the base resistance of the fuel cell stack against the base resistance of a reference fuel cell stack.