Analytical model of electromagnetic torque of surface PM motors considering current harmonicsin electric vehicles

Abstract

The modeling of the magnetic field, as well as the amplitude prediction and source analysis of torque ripple, are the theoretical basis to reduce the vibration and noise of electric motors. An analytical model of electromagnetic torque of surface permanent magnet motors considering current harmonics, which is capable of purely analytical calculation and theoretical analysis, is proposed in this paper. The open-circuit magnetic field solution considering the stator slot is performed by using the analytical conformal mapping along the deformed solving path, allowing more accurate prediction of the cogging torque. The armature reaction field is derived under any current condition with current harmonics. So far, the analytical model of electromagnetic torque is established, and the purely analytical calculation of torque value and the theoretical analysis of torque ripple characteristics are implemented in an 8-pole-24-slot surface permanent magnet motor used for the propulsion of light electric vehicles. The generation mechanism of constant torque and torque ripple is clarified both under sinusoidal current and harmonic current. Furthermore, the effect of the stator skew slot on the motor torque is well explained to demonstrate the utility of the proposed model. It is found that the skew slot is almost ineffective in mitigating the torque ripple caused by current harmonics.