Torque Ripple Minimization in Interior PM Machines using FEM and Multiple Reference Frames

Pulsating torque exists in interior permanent magnet (IPM) machines due to non-sinusoidal flux density distribution around the air-gap. These torque pulsations are reflected as speed ripple, noise and vibration, which degrade the IPM drive performance and should be minimized. Firstly, the paper proposes a mathematical model of IPM machine that takes into account space harmonics of inductances and flux linkages related to permanent magnets as a function of rotor position. The space harmonics are analyzed by the 2D finite-element method (FEM) and the motor parameters of the model are determined. Then, the pulsating torque is compensated by generating an inverse torque component through the stator current, and this procedure to predetermine the adequate current reference is based on maximum torque per ampere characteristic (MTPA). Because of the periodic nature of torque ripple, this paper presents a current control scheme that solves bandwidth limits of conventional PI controllers by means of multiple reference frames. Two different motor structures have been studied and verification for them is given