Comparative Study on Torque Ripple Reduction Techniques for an Automotive Permanent Magnet Motor without Skew

Abstract

Permanent magnet motors are a good choice for Electric Vehicles (EV) due to their high power density and efficiency. Additionally, reducing torque ripple is important to ensure comfortable and silent vehicles. To achieve this, the step-skewing of the rotor is the most commonly adopted choice. However, stepskewing complicates the rotor manufacturing process, increasing its time and costs. Therefore, in this article, different alternatives to step-skewing are analysed for an EV motor, which are pole span optimisation, sinusoidal airgap, pole shifting, and magnetic slot wedges. The different methods are compared, and the results indicate that no single torque ripple reduction technique can reduce torque ripple below 10 % in all the working points. Thus, the proposed alternatives are combined, and the combination of pole shifting together with span optimisation is identified as the optimal solution. The results show that torque ripple is reduced to below 10 % in all the working points, while the average torque meets the application requirements.