Patent ID: 7682719

Claim:
A fuel cell system comprising: a fuel cell stack providing output power at a particular current density; and a power controller for controlling the output power of the fuel cell stack, said power controller storing a reference polarization curve that defines the current/voltage relationship of the fuel cell stack, said power controller revising the reference polarization curve to match an actual polarization curve of the stack over time when the stack current density is below a predetermined threshold by changing a first adaptation value and revising the reference polarization curve to match the actual polarization curve of the stack when the stack current density is above a predetermined threshold by changing a second adaptation value; wherein the first adaptation value defines an absolute voltage difference between the predicted average cell voltage of fuel cells in the stack and the average cell voltage of the reference polarization curve for a particular stack current density, and the second adaptation value defines a current dependent voltage difference between the predicted average cell voltage of fuel cells in the stack and the average cell voltage of the reference polarization curve for a articular stack current density.