Patent ID: 8040089

Claim:
A drive device for a synchronous electric motor that includes a stator coil having a plurality of windings, which are connected together to form a star connection and generate a rotating magnetic field upon energization thereof with electric current supplied from a power supply device to rotate a rotor of the synchronous electric motor, the drive device comprising: an inverter circuit that includes a plurality of arm pairs, which are connected in parallel between a cathode bus bar and an anode bus bar, wherein each of the plurality of arm pairs is adapted to connect with a corresponding one of the plurality of windings and includes an upper arm and a lower arm, which are connected in series between the cathode bus bar and the anode bus bar and have an upper arm switching element and a lower arm switching element, respectively; a capacitor that is connected to the inverter circuit; a control means for executing a switching operation of the upper arm switching elements and the lower arm switching elements of the plurality of arm pairs by obtaining and supplying a control signal to each corresponding one of the upper arm switching elements and the lower arm switching elements of the plurality of arm pairs through use of a selected modulation scheme that is selected from a plurality of modulation schemes, each of which is set to charge the capacitor with a corresponding charge amount that differs from that of any other one of the plurality of modulation schemes, so that the rotating magnetic flied is generated at the stator coil according to an output state of the capacitor and an output state of the power supply device, wherein the capacitor is charged with the electric current, which flows from the stator coil to the capacitor while bypassing each corresponding one of the upper arm switching elements and the lower arm switching elements of the plurality of arm pairs upon the execution of the switching operation of the upper arm switching elements and the lower arm switching elements of the plurality of arm pairs by the control means; a power supply state sensing means for sensing the output state of the power supply device; and a deciding means for deciding which one of the plurality of the modulation schemes is used as the selected modulation scheme based on a sensed value of the power supply state sensing means, wherein the charge amount of the capacitor is adjusted according to the output state of the power supply device upon the execution of the switching operation of the upper arm switching elements and the lower arm switching elements of the plurality of arm pairs by the control means according to the control signal obtained with the selected modulation scheme.