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 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 temperature control system and method for a fuel cell stack cooling system is disclosed. The temperature control system includes a coolant circulation line for circulating a coolant to and from a fuel cell stack. A coolant pump is provided in the coolant circulation line, and a pump ?P sensor is provided in fluid communication with the coolant circulation line on inlet and outlet sides of the coolant pump. The pump ?P sensor measures a change in pump pressure between the inlet and outlet sides of the coolant pump. A pump map is provided having correlated values of pump speed, change in pump pressure and coolant flow rate for correlating the coolant flow rate with the pump speed and the change in pump pressure to attain a desired coolant flow rate for optimum fuel stack cooling.

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: An airflow control system and method for a fuel cell includes a compressor that supplies air to a storage chamber for storing the air. Fuel cell subsystems are connected to the air storage chamber. Each of the fuel cell subsystems includes a flow controller and flow sensor. A sensor measures air pressure in the storage chamber. A controller polls the flow controllers of the fuel cell subsystems for a minimum required air pressure for the fuel cell subsystems. The controller selects a highest minimum required air pressure. The controller controls the compressor to provide the highest minimum required pressure in the air storage chamber. The air storage chamber includes tubing, a manifold or both.

Abstract: A fuel cell system that employs an oxygen sensor for measuring the oxygen concentration in the cathode exhaust gas from the fuel cell stack. A controller provides a signal that drives a compressor providing air to a cathode input of the stack so that the compressor provides the desired oxygen to achieve the desired cathode lambda. In one embodiment, the fuel cell system also employs an airflow meter that measures the amount of air being applied to the compressor. The controller compares the oxygen input applied to the stack to the oxygen output from the stack for diagnostic purposes, such as determining the presence of leaks. A temperature sensor can be employed to measure the temperature of the cathode exhaust and a pressure sensor can be employed to measure the pressure of the cathode exhaust to compensate for water vapor in the cathode exhaust.

Abstract: The present invention is a method of operating a fuel cell stack and system that minimizes the potential for having a large pressure differential between the anode and cathode flow fields and a low relative humidity occurrence within the cathode flow fields. This is accomplished by tempering the downward transient in power demand seen by the fuel cell stack. The downward transient in power demand on the fuel cell stack is tempered by reducing the rate at which the power generated by the fuel cell stack is decreased and providing the excess power generated by the fuel cell stack to other parasitic components of the fuel cell system.

Abstract: A mechanization of a fuel cell system and a method of operating the same is provided which simplifies the start-up of the fuel cell system. The fuel cell system can be started up without using any battery derived high voltage power to drive a high voltage compressor. The present invention provides for the use of a low voltage blower to provide oxygen to the cathode side of the fuel cell stack to enable start-up of the fuel cell stack without the initial use of a high voltage compressor. The low voltage blower can be powered by a low voltage power source and/or the voltage produced by the fuel cell stack.

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 fuel cell generation system employing a load following algorithm that provides the desired output power from the fuel cell on demand. The system includes a draw current sensor that measures the current drawn from the fuel cell used to satisfy the system load demands. The load following algorithm uses the measured draw current to identify the proper amount of fuel and air to meet the load demands, and then provides a buffer of extra fuel and air to the fuel cell so if the load demand suddenly increases, the fuel cell is able to immediately produce the extra output power. As the current drawn from the fuel cell changes in response to changing load demands, the load following algorithm causes the amount of fuel and air being applied to the fuel cell stack to increase and decrease so that the buffer of extra fuel and air is maintained substantially constant.

Abstract: Hydrogen in a fuel cell is vented and purged with a fail-closed valve using stored energy (e.g. from a capacitor) when a diagnostic parameter is outside of an acceptable operating range. The valve closes after the stored energy has depleted. A safety switch in the relay circuit of the solenoid switch (or solenoid valve) is also grounded in computer-implemented shutdowns. Benefits from the invention include use of air-compatible catalysts, minimized parasitic losses to power output, minimized contamination of fuel cell internal surfaces after venting, minimized risk of explosive mixture buildup, and efficient operation.