Optimum geometry for torque ripple minimization of permanent magnet motor by the finite element method

There has recently been considerable interest in using the permanent magnet synchronous motor for vehicle propulsion systems but the major problem is torque ripple which causes increased undesirable acoustic noise. As a function of the rotor position, the torque produced by these machines has a pulsating component in addition to the dc component. The torque waveform and, thus, the frequency content of the waveform can be influenced by several factors in the motor design and construction. This paper addresses the various factors that influence the torque waveshape. It is shown that the flux, the basic induced electromotive force (EMF) waveshape, and the geometry of the motor are key factors in determining the torque waveshape. For that purpose, four sinusoidal wave-form motor configurations were investigated and analyzed to extract the data (flux, flux density and EMF) needed to predict the torque produced by a given geometry at any position of rotor. Hence the static torque curve can be constructed and torque ripple can be found. Finite element method has been conducted to obtain the torque waveform and the other electromagnetic characteristics of the motor.