Optimal design of PM motors to achieve efficient flux weakening strategy in variable speed control applications

In this paper, two topologies of PM motors are studied and optimized to be suitable for direct drive propulsion of electric vehicle. Flux weakening strategy is used and optimal parameters of the motors are defined. The design of the machines is focused the quality of back EMF waveforms and external parameters. The first topology is a surface mounted motor (non-salient pole motor) with segmented magnets allowing a strong reduction of the harmonics. The second one is an inset motor (salient-pole motor) with an iron pole surface which is modified in order to reduce the harmonic content of the air-gap flux density. For both motors a special technique based on pulse width modulation is performed to achieve the harmonic reduction.