Control method for fuel cell system

The present invention relates to a control method for a fuel cell system. The purpose of the present invention is to provide a control method for a fuel cell system, which allows an exact air supply to a fuel cell stack, thereby avoiding the occurrences of flooding and dry-out in the fuel cell stack. In addition, another purpose of the present invention is to provide the control method for a fuel cell system, which can minimizes unnecessary and excessive air supply, thereby reducing energy consumption in driving an air blower and improving fuel efficiency of a fuel cell vehicle. To this end, the control method for a fuel cell system comprises the steps of: calculating a fuel cell demand current using a driver demand current calculated from a driver demand torque; calculating a target flow rate 1 of air to be supplied to a fuel cell stack using the fuel cell demand current and a target stoichiometric ratio (SR) of air; compensating the target flow rate 1 using the target SR; calculating an RPM command value of an air blower based on a compensated target flow rate 2 and the amount of air currently measured and subsequently controlling an operation of the air blower based on the calculated RPM command value. [Reference numerals] (A1) Accelerator pedal input from driver; (A2,C2) Vehicle speed; (BB) Measurement signal; (C1) Required torque from driver; (C3) Vehicle speed; (C4) Bus stage voltage; (D1) Motor/Inverter efficiency; (D2) Battery assist current; (D3) Vehicle accessories required current; (D4) BOP required current; (EE) Estimated value of Internal RH of stack; (FF,II,K2,NN) Target SR; (G1) Required current 1 for fuel cell; (G2) Compensation current for abnormal cell voltage of fuel cell; (G3) Responsive controlling compensation current when fuel cell restarts; (HH,L2,RR) Air flow; (J1) Air flow based current limit for fuel cell; (J2) Maximum current limit for fuel cell; (K1) Required current 2 for fuel cell; (L1) Current of fuel cell; (MM) Target flow 1; (OO) Calculated SR; (PP) Final current limit for fuel cell; (QQ) Target flow 2; (SS) RPM command value for air blower