Comparison of optimal design and performance of PM machines having non-overlapping windings and different rotor topologies

Abstract

This paper investigates the influence of machine's parameters on the design and optimisation of permanent magnet (PM) brushless ac machines having three different rotors, viz. surface PM (SPM), I-shaped interior PM (IPM-I) and V-shaped interior PM (IPM-V), and with non-overlapping double/single layer windings. The IPM-V angle δ between two magnet pieces within a pole was found to have a significant impact on the optimum split ratio. Smaller values of angle δ have smaller optimal split ratios and higher torque. However, for torque per magnet volume, a global optimal split ratio and angle δ can be found within limits. Increasing the magnet thickness for interior PM machines results in a decrease in the magnet width due to geometric limitations and hence there exists an optimal magnet thickness for maximum torque, which is obvious in IPM-V machines. Comparison reveals that the IPM-I machine presents the widest constant power-speed region due to its larger d-axis inductance and low back-EMF. Single layer windings produce larger average torque and d-axis inductance, hence wider power-speed range operation, however exhibits larger torque ripples. (7 pages)