Abstract: A method is provided for controlling the concentration of nitrogen in a fuel cell stack. The method includes providing a fuel cell stack with cathode passages and anode passages including a valve in communication with the anode passages. The method further comprises selecting a maximum desired amount of nitrogen to be found in the fuel cell stack and calculating an actual amount of nitrogen in the fuel cell stack. Next, the method provides for comparing the maximum desired amount of nitrogen in the fuel cell stack to the actual amount of nitrogen in the fuel cell stack, and opening the valve if the actual amount of nitrogen in the fuel cell stack is greater than the maximum desired amount of nitrogen in the fuel cell stack. The method calculates the actual amount of nitrogen in the fuel cell stack based on an amount of nitrogen that enters the anode passages due to an age of the fuel cell stack.

Abstract: A device and method to regulate humidification in a cascaded fuel cell stack. The cascaded fuel cell stack includes individual fuel cells placed together in multiple groups. A recirculation loop is fluidly coupled to an anode flowpath to permit the recirculation of hydrogen or a related fuel. A controller and one or more sensors and flow manipulation devices cooperate with one another to selectively increase or decrease the flow of reactant in the recirculation loop in order to manage water levels in one or more of the anode, cathode or electrolyte layer disposed between the anode and cathode.

Abstract: Operating strategy for a fuel cell system controls the hydration level of the membranes in the fuel cells and achieves a desired operational performance. The membrane hydration level is managed by controlling the relative humidity of the cathode gas flowing through the cathode flow path. Targeted relative humidity set points for the cathode gas entering and exiting the cathode flow path are established based on the water vapor in the cathode gas. Temperature set points for the cathode gas to achieve the targeted relative humidity are established. The coolant supply subsystem is operated to cause the required cathode gas temperatures to be achieved.

Abstract: An apparatus and method for operating a fuel cell power system utilizing a low voltage power source and system power to power an airmover. The fuel cell power system uses a low voltage power source to power the airmover during start-up and transitions to using system power to power the airmover as the fuel cell stack increases its voltage output. During a shutdown operation the fuel cell power system transitions from using system power to using the low voltage power source to power the airmover enabling a purging operation to be performed. A controller coordinates the operation of the airmover between using the low voltage power source and using electrical power produced by the fuel cell stack to power the airmover.

Abstract: A fuel cell system that includes a fuel cell stack providing high voltage power. A tap is electrically coupled to the positive end of the stack to provide a positive voltage output terminal of the fuel cell stack, and a tap is electrically coupled to the negative end of the stack to provide a negative output terminal of the fuel cell stack. A low voltage tap is electrically coupled to one or more intermediate bipolar plates of the stack to provide low voltage power. Several intermediate taps can be electrically coupled to the bipolar plates, where a center intermediate tap is designated a reference potential tap. A switching network switches the several voltage potentials to provide an AC signal.

Abstract: A plurality of electrical current sensors for a set of fuel cell stacks in series independently measure electrical current in a fuel cell, and an acceptability status is determined for each electrical current sensor by independent comparison of each sensor measurement to the individual values of the other sensor measurements. A characteristic current measurement is derived from all electrical current sensors having an acceptability status which is trustworthy.

Abstract: Fuel cell parameters and limited electrochemical fuel cell sensors are used to calculate the concentration of diluting gas on the anode side of the fuel cell. The calculated concentration is then used to optimize fuel cell efficiency and/or stability by controlling the evacuation of diluted fuel from the anode side of the cell. In accordance with one embodiment of the present invention the dilution gas crossover rate of the membrane electrode assembly is calculated and the dilution gas concentration in the anode flow field is determined as a function of the crossover rate. The vent valve is opened when the dilution gas concentration in the anode flow field is above a high threshold value and is closed when the dilution gas concentration in the anode flow field is below a low threshold value.