A novel high power density permanent magnet (PM) motor drive for electric vehicles (EVs) is proposed. The motor is a polyphase multiple square-wave PM motor, which can be classified as a kind of PM brushless DC motor. The features of the proposed motor as compared with those of the conventional PM brushless DC motor. The multipole magnetic circuit arrangement permits the minimization of magnetic yoke, resulting in the reduction of motor volume and weight. The coil span is purposely designed to be equal to one slot pitch, thus saving in copper used. By using a fractional number of slots per pole per phase, the arrangement of numbers of poles and slots is so unique that the magnetic force between stator and rotor at any rotating position is uniform, hence eliminating the cogging torque which usually occurs in PM motors. The motor can be controlled to operate at constant torque region and constant power region with field weakening. Thus, both high starting torque and high cruising speed can be achieved.
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