A system which enables fuel cells to be activated at a working point of
high energy conversion efficiency. A control unit calculates a required
output of an inverter from an input accelerator travel. The control unit
specifies an output electric current-output voltage characteristic
corresponding to a gas flow rate, obtains a point of highest energy
conversion efficiency on the specified characteristic to specify the
point as a working point of fuel cells, and computes an output electric
power of the fuel cells at the specified working point. The control unit
determines an output voltage required to a battery, based on a difference
between the calculated required output of the inverter and the computed
output electric power of the fuel cells and a state of charge of the
battery. The control unit controls a DC-DC converter and regulates the
output voltage of the DC-DC converter, so as to cause the battery to
generate the output voltage thus determined. The control unit
subsequently controls the inverter, so as to cause a motor to consume
electric power corresponding to the required output.