Fuel cell system

Abstract

An IR resistance of each of unit cells is measured, and a highest unit cell voltage as a threshold voltage is set based on the IR resistance and load current. The setting of the highest unit cell voltage uses map data that approximates current-voltage characteristics of a unit cell when the fuel gas is insufficiently supplied. In that case, the highest unit cell voltage is determined based on the voltage with respect to the load current obtained from the map data, and the IR loss calculated from the IR resistance and the load current. This highest unit cell voltage is compared with the measured unit cell voltage. If the unit cell voltage is below the highest unit cell voltage, the power generation of the fuel cell is stopped or restrained.

1 . (canceled) 
     
     
         2 . A fuel cell system comprising:
 a unit cell that generates electric power by an electrochemical reaction between a fuel gas supplied to an anode of the unit cell and an oxidant gas supplied to a cathode of the unit cell;   a fuel cell that is formed with the unit cell;   a voltage measurement device that measures a voltage of the unit cell;   a power generation controller that performs a voltage recovery process when the voltage of the unit cell is below a predetermined threshold voltage;   a cell temperature measurement device that measures a temperature of the unit cell; and   a threshold voltage setting device programmed to set the predetermined threshold voltage based on the measured temperature of the unit cell   wherein the threshold voltage setting device stores map data that predicts a temperature dependency of an IR resistance of the unit cell, and sets the predetermined threshold voltage based on an IR loss calculated from a load current and the IR resistance with respect to the cell temperature obtained from the map data.   
     
     
         3 . The fuel cell system according to  claim 2 , further comprising oxidant gas supply controller that supplies the oxidant gas to the fuel cell less than an amount of the oxidant gas, which is determined based on the load current. 
     
     
         4 . The fuel cell system according to  claim 2 , further comprising:
 a time measuring portion programmed to measure the time after the unit cell voltage has dropped below a predetermined threshold voltage and that determines if the elapsed time has exceeded a permissible time.   
     
     
         5 . The fuel cell system according to  claim 2 , wherein the power generation controller stops a power generation of the fuel cell when the voltage of the unit cell becomes lower than a predetermined threshold voltage. 
     
     
         6 . The fuel cell system according to  claim 2 , wherein the fuel cell is formed by connecting a plurality of the unit cell in series.