Optimal design of PM motors for quasi-sinusoidal air-gap flux density

This paper presents an optimal design method for the rotor structure of permanent magnet synchronous motor by using Finite Element Method (FEM) combined with Pulse Width Modulation (PWM). The PWM technique is applied to the shape of the surface of the solid iron rotor and the magnets are buried. Calculation is straightforward and show that the radial air-gap flux density harmonics are eliminated leading to almost sinusoidal air-gap flux density. The well known Field Orientated Control (FOC) strategy is applied to control the machine. It is reinforced by a proper field weakening strategy for high speed applications. Simulation results on the entire speed range are satisfactory. In addition, analysis of the harmonics content of air-gap flux density, back-EMF and torque waveform is given and verifies the above claim.