Fuel Cell Power Request Control Strategy

A fuel cell system for a hybrid fuel cell vehicle, said system comprising:

• a fuel cell stack responsive to a cathode air flow and an anode hydrogen gas flow;
• a compressor for providing the cathode air flow to the fuel cell stack;
• a first adder for adding an electric traction system power request signal from an electric traction system on the vehicle, an auxiliary power request signal from auxiliary power loads on the vehicle and a compressor power request signal that determines the speed of the compressor to provide a raw stack power request signal;
• a fuel cell stack controller generating a hydrogen flow rate signal for providing a desired hydrogen flow rate to the fuel cell stack, a desired air flow signal that is used to generate the compressor power request signal, and available stack current signal indicative of the current that is available from the fuel cell stack and an actual stack current signal indicative of the actual current being drawn from the fuel cell stack;
• a power request controller responsive to the actual stack current signal and the available stack current signal, and providing a power request reducing signal if the available stack current signal is greater than the actual stack current signal;
• a second adder for adding the power request reducing signal and the raw stack power request signal to generate a stack power request signal that is sent to the fuel cell stack controller so that the actual stack current signal and the available stack current signal are about equal;
• and
• a transient detector, said transient detector being responsive to the raw stack power request signal, said transient detector turning off the power request controller if the transient detector detects an up-power transient.

A method for preventing the current available from a fuel cell stack from exceeding the current actually being drawn from the fuel cell stack, said method comprising:

• determining the amount of current that the fuel cell stack can generate;
• determining the amount of current that is being drawn from the fuel cell stack;
• and
• reducing the amount of current that is available from the fuel cell stack if the amount of the amount of current available from the fuel cell stack exceeds the current being drawn from the fuel cell stack.