Influence of Phase Magnetic Couplings on Phase Current Characteristics of Multiphase BLDC Machines With Overlapping Phase Windings

Abstract

Multiphase brushless dc (BLDC) machines are implemented in electric and hybrid electric vehicle applications due to their high torque/power density, good fault tolerance capability, and low torque ripple. Moreover, the per-phase converter rating can be reduced by increasing the phase number. However, the number of magnetic couplings between phases increases with the phase number, and these magnetic couplings can have an important influence on the machine performance. Therefore, they need to be considered in simulation models and their effect should be considered in control algorithms. Accordingly, the objective of this paper is to analyze the effect of magnetic phase couplings on the performance of multiphase BLDC machines with an overlapping phase winding configuration. First, a detailed electric machine model, in which the machine parameters that are determined by 2-D finite-element method analysis are implemented, is developed. Using this model, the influence of mutual inductances on phase current characteristics with pulse amplitude modulation (PAM) and pulsewidth modulation (PWM) controls is investigated. In addition, a novel PAM-based control strategy, in which the effect of phase mutual inductances is considered, is proposed and analyzed. After demonstrating the influence of mutual inductances on phase current characteristics, the dependence of mutual inductances on the winding configuration is studied. Finally, experimental results with the PAM control and the new PAM-based control are used to validate the simulation results.