Design of a 5-phase permanent magnet brushless DC motor for automobiles

Permanent magnet (PM) brushless DC motors (BDCM) have been increasingly used in automobiles due to their light weight, small size, high efficiency, high reliability, variable speed operation and good dynamic performance. This paper presents the design and development of a 5-phase BDCM for automobiles. Both the analytical method and finite element method (FEM) were used. The analytical method based on generalized electrical machine theory was applied to the preliminary design of the BDCM in conjunction with the empirical method. The model of the BDCM, along with those of the motor controller and load, was developed for simulation studies. The FEM was used to calculate electromagnetic torque due to PM-current interaction, torque ripple due to reluctance variation of teeth and slots, average airgap flux density, maximum flux densities in the rotor and stator, self-inductances, mutual inductances, and back-emf waveforms. A range of geometrical variations was investigated by the authors for the BDCM design. The 5-phase BDCM was developed based on the design and has been in mass production for automobiles. The test waveforms are presented in this paper to offer a comparison with those obtained using the analytical and FEM methods.