Optimal Design of Permanent Magnet Motors to Improve Field-Weakening Performances in Variable Speed Drives

Two motors are studied and optimized for transportation applications. The objective is to design motors whose external model is well suited for conventional vector control. Hence, in the design procedure, the emphasis is on the back-electromotive force (EMF) waveforms and external parameters. The first topology is a surface-mounted (nonsalient pole) motor with segmented magnets reducing significantly selected harmonics. The second is an inset magnet type (salient pole) motor with surface poles particularly shaped to reduce the harmonic content of the air gap flux density. For both motors, the principle of pulse width modulation is used for the harmonic reduction in the design process. The interest of these motors lies in the sinusoidal waveform of their back EMF allowing a simple vector control even at field-weakening region for high speeds.