Patent ID: 7144646

Claim:
A control circuit for a fuel cell system having a fuel cell stack and a battery, the control circuit comprising: a series pass element electrically coupleable between at least a portion of the fuel cell stack and a portion of the battery; and a regulating circuit for linearly regulating current through the series pass element in response to a greater of a battery charging current error, a battery voltage error and a stack current error wherein the regulating circuit comprises: a battery charging current error integrator having a first input coupled to receive a battery charging current signal proportional to a battery charging current, a second input coupled to receive a battery charging current limit signal proportional to a battery charging current limit, and an output to supply a battery charging current error signal proportional to a difference between the battery charging current and the battery charging current limit; a battery voltage error integrator having a first input coupled to receive a battery voltage signal proportional to a battery voltage, a second input coupled to receive a battery voltage limit signal proportional to a battery voltage limit, and an output to supply a battery voltage error signal proportional to a difference between the battery voltage and the battery voltage limit; a stack current error integrator having a first input coupled to receive a stack current signal proportional to a stack current, a second input coupled to receive a stack current limit signal proportional to a stack current limit, and an output to supply a stack current error signal proportional to a difference between the stack current and the stack current limit; and an OR circuit coupled to the output of each of the error integrators to select a greater one of the error signals from the error integrators.