The Effect of Stator/Rotor Bifurcations on a PMaSynRM Torque Ripple

In the operation of PMaSynRM, the generated torque ripple can lead to the production of acoustic noise and vibration. It is important to take this into consideration to minimize any potential negative effects on the systems, especially in electric vehicle applications. The study investigates the torque produced by a PMaSynRM and highlights the effect of geometry bifurcation on torque ripple and average torque. This paper presents a motor design with different bifurcation shapes of stators, such as the circle, triangle, and gear shapes, and the rotor, which can be trapezium or triangle-shaped. Eleven design patterns with different width and height were analyzed for each one, and the performance of the motor in different patterns were compared and the best one was selected based on the 2D finite element method FEM. The simulation results indicated that when the stator teeth notch is circular in shape and the rotor pole groove is trapezium-shaped, the electromagnetic torque is reduced by 5.27%, and the torque ripple is minimized by 63.58% compared to the base design.

I. Introduction

Permanent magnet (PM) machines are commonly used in electric vehicle (EV) applications for several reasons, including their high power density, high efficiency, and ability to operate over a wide speed range [1]. However, they are expensive because they require the high volume of rare earth magnets. Permanent Magnet-assisted Synchronous Reluctance (PMaSynRM) machines are an alternative to tackle this problem that combines the advantages of both permanent magnets and low-cost reluctance motors technology. It has gained significant attention in the past decade, especially for EV applications, due to their ability to achieve good electromagnetic performance while minimizing the use of rare earth materials but suffering from relatively high torque ripples. This is primarily due to the predominant reliance on reluctance torque, which can result in variations in torque output during operation. Torque ripple can affect the smoothness of motor operation and may require additional control strategies to mitigate [2]. Those ripples can lead to undesired mechanical vibrations and noises which cause premature aging of bearings. These obstacles can have an influence on the comfort and stability of high-performance electric vehicles. To address the torque ripple issue, researchers and engineers have been working on various techniques and control algorithms. These approaches aim to optimize the design and control of PMaSynRM to reduce torque fluctuations and improve overall performance [2, 3].