A Novel Segmented-Rotor Hybrid-Excited Synchronous Motor for Electric Vehicle Application

Permanent magnet AC (PMAC) motors are widely utilised in electric vehicles due to their high efficiency and power density. However, the major limitations of these motors are complex field weakening operation, limited constant power speed region, and reliance on costly and environmentally unfriendly rare-earth permanent magnets (PMs). In contrast, electrically excited synchronous motors offer solutions to these limitations. But their power density and efficiency are lower compared to PMAC motors. Hence, a motor combining both PMs and DC winding presents a promising solution. This paper introduces a novel segmented-rotor synchronous motor designed for electric vehicle application. It has permanent magnets and DC excited winding for field excitation. This machine is first of its kind in which path of magnet flux and DC field flux in rotor are separate and hence they can be considered parallel. In addition each rotor pole structure is hybridised. This results in segmented rotor structure, thus enhancing the power density. Flux distortion due to high current-loading is addressed by introducing a novel asymmetric pole-offset concept. Simulation studies using finite element method (FEM) are carried out to validate the proposed design and results are presented.