Abstract: A method for starting a cold or frozen fuel cell stack as efficiently and quickly as possible in a vehicle application is based upon a state of charge of a first power source such as a high voltage battery. Power flow between the first power source and fuel cell system is coordinated in conjunction with a specific load schedule and parallel control algorithms to minimize the start time required and optimize system warm-up.

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 method for starting a cold or frozen fuel cell stack as efficiently and quickly as possible in a vehicle application is based upon a state of charge of a first power source such as a high voltage battery. Power flow between the first power source and fuel cell system is coordinated in conjunction with a specific load schedule and parallel control algorithms to minimize the start time required and optimize system warm-up.

Abstract: A method for starting a cold or frozen fuel cell stack as efficiently and quickly as possible in a vehicle application is based upon a state of charge of a first power source such as a high voltage battery. Power flow between the first power source and fuel cell system is coordinated in conjunction with a specific load schedule and parallel control algorithms to minimize the start time required and optimize system warm-up.

Abstract: A method for managing fuel cell power increases in a fuel cell system using an air flow feedback delay. The method comprises the steps of determining a required air mass flow rate at a predetermined point in the fuel cell system, determining an actual air mass flow at a predetermined point in the fuel cell system, calculating an air flow feedback delay as a function of the required air mass flow rate and the actual air mass flow, and delaying an external circuit from increasing current draw from the fuel cell stack by the magnitude of the air flow feedback delay.

Abstract: A system and method for determining when to trigger reconditioning of a fuel cell stack and when to disable the reconditioning of the fuel cell stack. In one embodiment, the stack reconditioning is triggered when a maximum stack power estimation falls below a first predetermined power threshold. The reconditioning of the stack can be disabled so it is not performed when the trigger occurs if the reconditioning process does not raise the maximum power estimation above a second predetermined power threshold or the time from one reconditioning trigger to a next reconditioning trigger is less than a predetermined time threshold, or both.

Abstract: A fuel cell system that employs end cell heaters in the end cells of a fuel cell stack in the fuel cell system that consistently maintain the temperature of the end cells above the operating temperature of the stack so as to reduce water in the end cells. In one embodiment, the temperature of the end cells is maintained within the range of 80° C.-85° C. across the entire output power range of the fuel cell stack. In accordance with another embodiment of the invention, the end cells are electrically coupled in series, and the control signal for controlling the end cells heaters is selected to heat the warmest end cell to the desired temperature.

Abstract: A method for providing an accurate time that a fuel cell system has been shut-down so that the gas constituents in the anode and cathode side of the fuel cell stack can be known for an efficient next system start-up sequence. The method uses two timers, a stand-by timer that provides a time count for how long the fuel cell system has been off, but the vehicle ignition is still on, and a shut-off timer that provides a time count of how long the vehicle ignition has been off. The two time counts are added to give a complete time count of how long the fuel cell stack has been shut-down.

Abstract: A fuel cell system that employs a technique for nitrogen bleeding. The fuel cell system includes a fuel cell stack having a first sub-stack and a second sub-stack, where the hydrogen gas flow is flow-shifted between the sub-stacks. A first nitrogen bleed valve is provided in an anode gas input line coupled to the first sub-stack and a second nitrogen bleed valve is provided in an anode gas input line coupled to the second sub-stack. When the first sub-stack is receiving the anode gas, and a nitrogen bleed is requested, the first bleed valve is closed and the second bleed valve is opened to provide the nitrogen bleeding. When the second sub-stack is receiving the anode gas, and a nitrogen bleed is requested, the second bleed valve is closed and the first bleed valve is opened to provide the nitrogen bleed.

Abstract: A method for reducing the probability of an air/hydrogen front in a fuel cell stack is disclosed that includes closing anode valves for an anode side of the fuel cell stack to permit a desired quantity of hydrogen to be left in the anode side upon shutdown and determining a schedule to inject hydrogen during the time the fuel cell stack is shutdown. The pressure on an anode input line is determined and a discrete amount of hydrogen is injected into the anode side of the stack according to the determined schedule by opening anode input line valves based on the determined pressure along the anode input line so as to inject the hydrogen into the anode side of the stack.

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 method for determining whether a fuel cell stack is overheating. The method measures the temperature of end cells in the stack using end cell temperature sensors, and calculates an average end cell temperature based on the end cell temperature measurements. The method also measures the temperature of a cooling fluid being output from the fuel cell stack. The method determines if any of the measured end cell temperatures are outlying by comparing each end cell temperature measurement to the average. The method determines that the cooling fluid outlet temperature sensor has possibly failed if the cooling fluid outlet temperature is greater than the average end cell temperature and the cooling fluid outlet temperature minus the average end cell temperature is greater than a predetermined temperature value.

Abstract: A system and method for determining when to trigger reconditioning of a fuel cell stack and when to disable the reconditioning of the fuel cell stack. In one embodiment, the stack reconditioning is triggered when a maximum stack power estimation falls below a first predetermined power threshold. The reconditioning of the stack can be disabled so it is not performed when the trigger occurs if the reconditioning process does not raise the maximum power estimation above a second predetermined power threshold or the time from one reconditioning trigger to a next reconditioning trigger is less than a predetermined time threshold, or both.

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 reducing the probability of an air/hydrogen front in a fuel cell stack is disclosed that includes closing anode valves for an anode side of the fuel cell stack to permit a desired quantity of hydrogen to be left in the anode side upon shutdown and determining a schedule to inject hydrogen during the time the fuel cell stack is shutdown. The pressure on an anode input line is determined and a discrete amount of hydrogen is injected into the anode side of the stack according to the determined schedule by opening anode input line valves based on the determined pressure along the anode input line so as to inject the hydrogen into the anode side of the stack.

Abstract: A system and method for limiting the output current of a fuel cell stack as the stack degrades overtime. A look-up table identifies a predetermined voltage set-point for stack current density. A first comparator provides a voltage difference signal between the set-point and the stack voltage. The voltage difference signal is provided to a controller, such as a proportional-integral controller, that provides a current limiting signal. The current limiting signal and a current request signal are provided to a second comparator that selects which signal will be used to limit the maximum output current of the stack. A polarization curve estimator estimates parameters of the stack that will change over the life of the stack. The parameters are provided to a gain scheduler that provides gains to the controller that are based on where in the life of the stack it is currently operating.

Abstract: A method for managing fuel cell power increases in a fuel cell system using an air flow feedback delay. The method comprises the steps of determining a required air mass flow rate at a predetermined point in the fuel cell system, determining an actual air mass flow at a predetermined point in the fuel cell system, calculating an air flow feedback delay as a function of the required air mass flow rate and the actual air mass flow, and delaying an external circuit from increasing current draw from the fuel cell stack by the magnitude of the air flow feedback delay.

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 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: A method for managing fuel cell power increases in a fuel cell system using an air flow feedback delay. The method comprises the steps of determining a required air mass flow rate at a predetermined point in the fuel cell system, determining an actual air mass flow at a predetermined point in the fuel cell system, calculating an air flow feedback delay as a function of the required air mass flow rate and the actual air mass flow, and delaying an external circuit from increasing current draw from the fuel cell stack by the magnitude of the air flow feedback delay.