Hydrogen supply method for fuel cell system

A hydrogen supply method for a fuel cell system, for supplying hydrogen according to a state of the fuel cell system when the fuel cell system is started, the hydrogen supply method comprising steps of:

• (a) measuring a stop time period which elapses until the fuel cell system is started after the fuel cell system is stopped;
• (b) determining whether a reaction time period consumed to complete a reaction of residual hydrogen and residual oxygen residing in a fuel cell stack since the fuel system is stopped is not more than the stop time period;
• (c) when it is determined in the step (b) that the stop time period is less than the reaction time period, closing a purge valve that is able to discharge gases accommodated in an anode from the anode and supplying at the same time hydrogen to the anode such that an internal pressure of the anode becomes a predetermined first target pressure;
• (d) before the step (b), measuring the internal pressure of the anode;
• (e) determining whether the internal pressure of the anode measured in the step (d) is less than a predetermined abnormal pressure;
• (f) when it is determined in the step (e) that the internal pressure is not less than the predetermined abnormal pressure, opening the purge valve and supplying at the same time hydrogen to the anode such that the internal pressure of the anode becomes a predetermined maximum allowable pressure;
• (g) when it is determined in the step (e) that the internal pressure of the anode is less than the predetermined abnormal pressure, determining whether a cross-over time period, for which residual gases residing in the fuel cell stack cross over through a polymer electrolyte membrane and the anode and the cathode is in pressure equilibrium after the fuel cell system is stopped, is not less than the stop time period;
• (h) when it is determined in the step (g) that the stop time period is less than the cross-over time period, estimating partial pressures of remaining gases, excluding the hydrogen, of the gases accommodated in the anode with reference to the internal pressure of the anode measured in (d);
• and
• (i) closing the purge valve and supplying at the same time an amount of the hydrogen corresponding to the partial pressures of the remaining gases estimated in the step (h) to the anode.