Patent ID: 8896178

Claim:
A synchronous motor drive system comprising a synchronous motor and a drive device for driving the synchronous motor, the synchronous motor including: a rotor having a plurality of magnetic poles located circumferentially of the rotor at equally spaced intervals; a stator having an annular stator yoke and a plurality of stator teeth located circumferentially on the stator yoke at equally spaced intervals, each stator tooth in one or more pairs of two adjacent stator teeth having a slit formed at a tip thereof; a plurality of main coils each wound around a different one of the stator teeth in concentrated winding; and one or more sub-coils each wound between a different pair of the one or more pairs through the slits, wherein the drive device is configured to separately control electric current supplied to the main coils and electric current supplied to the sub-coils, and supplies electric current only to the main coils when a requested torque is less than a predetermined value and to both the main coils and the sub-coils when the requested torque is equal to or greater than the predetermined value.