Patent ID: 8173311

Claim:
A fuel cell system comprising: at least one fuel cell comprising an anode, a cathode and an electrolyte disposed between said anode and said cathode; an anode flowpath configured to convey a first reactant to said anode; a cathode flowpath configured to convey a second reactant to said cathode; a cooling loop in thermal communication with at least one of said anode flowpath and said cathode flowpath; at least one pump fluidly coupled to said cathode flowpath; at least one valve fluidly disposed in said cathode flowpath; a plurality of sensors coupled to said cathode flowpath such that upon passage of said second reactant adjacent said plurality of sensors, said plurality of sensors generate a signal corresponding to said second reactant, said plurality of sensors comprising at least one mass flow sensor, at least one temperature sensor and at least one pressure sensor to sense at least one of a temperature, a pressure, and a stoichiometry associated with said second reactant; and a controller signally coupled to said plurality of sensors and configured to operate at least one of said pump and said valve in response to changes in a desired relative humidity of said second reactant in said cathode flowpath in order to maintain said desired relative humidity within a prescribed range, said desired relative humidity selected independent of said temperature, said pressure, and said stoichiometry, said controller configured to correlate at least one of a temperature setpoint based on a desired stoichiometry and an optimum pressure, a pressure setpoint based on a temperature, and a stoichiometry setpoint based on said desired stoichiometry established therein to an operating condition of said system such that said maintaining said relative humidity is substantially achieved while keeping said pressure and temperature setpoints operably decoupled from one another in order to avoid windup oscillations in said system while also minimizing said stoichimetry setpoint at said operating condition.