Method of operating a fuel cell system with integrated feedback control

Abstract

A recirculating reagent fuel-cell includes an ion-exchange membrane interposed between an anode and cathode anode to form a membrane/electrode assembly (MEA), the MEA interposed between a fuel gas diffusion layer and an air (oxidant gas) diffusion layer. An air and fuel flow network are provided having an input portion for supplying reagent and an output portion for removing reagent after electrochemical reaction. At least one of the air flow network and fuel flow network includes a recirculation loop, the recirculation loop feeding back a portion of the fuel or air after electrochemical reaction to their respective input portion. The air flow network can include a water vapor condenser where water formed on the cathodes in proportion to the external load on the fuel cell stack is extracted and the fuel flow network can include an evaporator, where water is fed to the evaporator in the fuel feed loop from the condenser of the air feed loop.

1 . A method of operating a PEM fuel cell, which comprises the following steps: 
 providing a fuel flow to an anode side of the fuel cell;    providing an air flow to a cathode side of the fuel cell;    recirculating a portion of the air flow, after reaction thereof at the anode side, from an output to an input of the cathode side; and    selectively pressurizing the fuel flow and the air flow, with a length of a pulse period and a duty cycle of increased pressure within the pulse period adjusted to an instantaneous power requirement of the fuel cell.    
     
     
         2 . The method according to  claim 1 , which comprises recirculating a portion of the fuel flow, after incomplete reaction at the cathode side.  
     
     
         3 . The method according to  claim 2 , which further comprises transferring water generated at the cathode side into the recirculated portion of the fuel flow to humidify the fuel flow.  
     
     
         4 . The method according to  claim 1 , which comprises setting the fuel flow and the air flow as a time-varying mass flow, the mass flow varying with a load on the fuel cell.  
     
     
         5 . The method according to  claim 4 , wherein the time-varying mass flow is operative across all loads on the fuel cell.  
     
     
         6 . The method according to  claim 4 , wherein the time-varying mass flow comprises discrete pulses.  
     
     
         7 . The method according to  claim 4 , which comprises time-synchronizing the mass flow of the fuel flow with the mass flow of the air flow.  
     
     
         8 . The method according to  claim 1 , which comprises providing the air flow with a jet pump, and inducing recirculation in the recirculation loop with the jet pump.  
     
     
         9 . The method according to  claim 8 , which comprises feeding recirculated air from the output on the anode side to a suction input of the jet pump, mixing the recirculated air flow portion with a fresh air flow portion in the jet pump, and feeding the mixed air flow to the anode side of the fuel cell.  
     
     
         10 . The method according to  claim 1 , which comprises inducing pressure variations with a pressure sensor-controlled two-position pressure regulator having a first, fully open position and a second, fully closed position.  
     
     
         11 . The method according to  claim 10 , wherein the pressure regulator is a directly controlled by hydrogen consumption two-positional pressure regulator in the fuel feed network, and a slave pressure regulator connected in the air feed network and controlled by the pressure regulator in the fuel feed network.  
     
     
         12 . A method of operating a PEM fuel cell system, which comprises: 
 providing a membrane/electrode assembly (MEA) including a proton exchange membrane (polymer electrolyte membrane, PEM) between an anode chamber with an anode and a cathode chamber with a cathode;    supplying fuel to the anode chamber through a hydrogen supply network connected to supply hydrogen fuel to the anode;    varying a pressure in a feed portion of the hydrogen supply network, under control of a fuel pressure regulator, with a duration of a pressure cycle and a duration of a pressure pulse within the cycle adjusted in dependence on a magnitude of a fuel cell output requirement;    supplying air to the cathode chamber through an air supply network connected to supply air to the cathode;    varying a pressure in a feed portion of the air supply network, under control of an air pressure regulator, and synchronizing the air pressure regulator with the fuel pressure regulator.    
     
     
         13 . The method according to  claim 12 , which comprises measuring a pressure in the hydrogen supply network in a master measuring chamber of a hydrogen supply pressure regulator, communicating via a feedback line in the hydrogen recirculation loop, and slaving an air supply regulator to the hydrogen supply pressure regulator, for synchronizing the pressure cycles and pulses at the anode with the pressure cycles and pulses at the cathode.  
     
     
         14 . The method according to  claim 12 , which comprises: 
 pumping the fuel in the hydrogen supply network with a fuel jet pump having an inducing nozzle and a suction input communicating with an anode output of the anode chamber;    varying the pressure in the feed portion of the hydrogen supply network with a two-position pulse-generating hydrogen supply pressure regulator having a hydrogen input and a hydrogen output communicating with the inducing nozzle of the fuel jet pump;    selectively setting the regulator to a first, at least substantially closed position and a second, at least substantially open position for feeding hydrogen to an input of the anode chamber with pulse-fluctuating pressure; and    pumping the air with an air jet pump having an input receiving air from an air supply and a suction input communicating with a cathode output of the cathode chamber; and    setting a pressure in the air supply network with a differential air supply regulator having an input area communicating with the air supply and an output area communicating with an inducing nozzle of the air jet pump.