Power management method using feedback current bias for simultaneously controlling low cells and overall stack voltage

Abstract

A method for controlling the current output from a fuel cell stack to prevent the stack voltage or the minimum fuel cell voltage from dropping below predetermined voltage set-points. The method for the stack voltage control includes determining whether the stack voltage has dropped to the predetermined voltage set-point, and if so, capturing and holding the actual stack current at that point as the maximum allowed stack current. If the stack voltage continues to fall below the voltage set-point, then the voltage set-point is subtracted from the actual voltage to get a positive error signal. Controller gains are then multiplied by the error signal to reduce the current allowed from the stack to drive the error signal to zero, and increase the stack voltage. The method for the minimum fuel cell voltage operates in the same manner, but with different values.