Novel polyphase multipole square-wave permanent magnet motor drive for electric vehicles

Abstract

A novel high power density permanent magnet (PM) motor drive for electric vehicles (EVs) is proposed. The motor is a polyphase multipole square-wave PM motor, which can be classified as a kind of PM brushless dc motor. The distinct features of the proposed motor as compared with that of the conventional PM brushless dc motor lie in that: firstly, the multipole magnetic circuit arrangement enables the minimization of magnetic yoke, resulting in the reduction of motor volume and weight; secondly, the coil span is purposely designed to be equal to one slot pitch, thus saving in copper used; thirdly, by using 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; finally, 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. Therefore, as the proposed motor drive possesses distinct advantages of high power density, high efficiency and superior dynamic performance, it is very suitable for EV applications. A prototype of 5-phase 22-pole 5-kW motor drive has been designed for an experimental EV.