Fuel cell system and its startup control

#This invention relates to a fuel cell system, and more particularly to startup control when a fuel cell system is started from a low temperature state.

#A fuel cell system transforms the energy of fuel, directly into electrical energy. In the fuel cell system disclosed by JP8-106914A published by the Japanese Patent Office in 1996, in a pair of electrodes provided on either side of a membrane electrode, fuel gas containing hydrogen is supplied to the anode and an oxidizing agent gas containing oxygen is supplied to the cathode. Electrical energy is then extracted from the electrodes, using the electrochemical reactions produced on the surface of the membrane electrode, i.e.,

#anode reaction: H2→2H++2e−

#FIG. 1 is a block diagram of a fuel cell system relating to this invention.

#FIG. 2 is a flowchart showing the startup processing of the fuel cell system.

#FIG. 3 is a flowchart showing the startup processing taking the humidification state of a membrane electrode into consideration.

#Referring to FIG. 1 of the drawings, a fuel cell system relating to this invention is provided with a fuel cell stack 1 comprising plural cells c1, c2, . . . , cn, pressure sensors 5, 6, 7, a cooling water pump 12, a cooling water tank 13, a heat exchanger 14 and a controller 16. A temperature sensor 15 for measuring the internal temperature Tsin of the fuel cell stack 1 is installed inside the fuel cell stack 1. Measurement signals from these sensors are input into the controller 16.

#Pressure sensors 5, 6, 7 measure the pressure in an air passage 8 which supplies air, a cooling water passage 9 which supplies cooling water and a fuel gas passage 10 which supplies fuel gas to the fuel cell stack 1, in the vicinity of the inlet to the fuel cell stack 1.

#The controller 16 comprises one, two or more microprocessors, a memory and an input/output interface. The controller 16 calculates a pressure difference ΔP between the cooling water passage 9 and electrodes, a cathode 2 and anode 3 at the inlet of the fuel cell stack 1, from the signals from the pressure sensors 5, 6, 7. When the system is started, the controller 16 determines a pressure Pcw of cooling water according to the internal temperature Tsin of the fuel cell stack 1 detected by the temperature sensor 15, and controls the opening of a pressure reducing valve 11 and the rotation speed of the cooling water pump 12 so that a determined cooling water pressure Pcw is realized.