In a multiple power
source system of the present invention that has an
inverter connected to a
reactance, such as three-phase coils in a motor, a
high voltage battery is connected with a
low voltage battery via one
transistor (Tr2) and one
diode (D2) included in the
inverter and one phase coil (U-phase coil) of the three-phase motor. The
transistor Tr2 is turned on to make the
electric current flow from the
low voltage battery to the U-phase coil. The
transistor Tr2 is subsequently turned off at a preset timing, so that the
electric energy accumulated in the
reactance, that is, the U-phase coil, flows through the
diode D1 into the
high voltage battery and thereby charges the
high voltage battery. This arrangement enables the charging process from the
low voltage battery to the
high voltage battery without any complicated circuit structure for the
voltage step-up. The three-phase motor may be unipolar driven with transistors connected to one side of the
inverter. The arrangement of the present invention does not require any complicated structure, which undesirably increases the size of the multiple power
source system, in order to ensure mutual supplement of the
electric energy between electric systems having a large difference in
voltage, for example, an electric
system for driving a
hybrid vehicle and an electric
system for its
control circuit.