Torque-Speed Characteristics of Induction Machine and Hybrid Permanent Magnet Assisted Synchronous Reluctance Machine for Electric Vehicle Application

This thesis describes an investigation into two types of electrical machines for EV/HEV applications, i.e. induction machine (IM) and permanent magnet assisted synchronous reluctance machine (PMA-SynRM). Both are low-cost due to no or less usage of NdFeB permanent magnet (PM), compared with interior PM (IPM) machines. IM is investigated with particular reference to its maximum torque/power-speed characteristic. Firstly, an analytical method based on dq-axis reference frame to obtain the maximum torque/power-speed characteristic is developed and validated by experiments. Then, the influences of some design parameters on the flux-weakening performance are investigated, such as the ratio of leakage to mutual inductance, stator and rotor resistances, and iron saturation, etc. In addition, the influences of some physical parameters on the torque/power-speed characteristic are investigated, including split ratio, number of stator/rotor slots per pole per phase, length of airgap, number of pole pairs and stator/rotor slot area, etc. Finally, the difference in maximum torque/power-speed characteristics between motor and generator modes is described, and how the design parameters influence the difference is investigated. For PMA-SynRM, a novel hybrid-PM assisted SynRM is proposed, which utilizes both ferrite and NdFeB PMs. The design process is presented and the electromagnetic performance and material cost are analyzed and discussed. The analyzed electromagnetic performances include electromagnetic torque, flux density, back electromotive force (EMF), torque/power-speed characteristic, power factor, torque ripple, cogging torque and demagnetization, etc. Finally, the electromagnetic performances and material costs of IM and hybrid-PM assisted SynRM are compared with those of IPM, respectively, including torque capability per Ampere, torque/power-speed characteristic, power factor, torque ripple and efficiency map, etc.