Evaluation of the Rotor Mechanical Stresses and Electromagnetic Parameters of a Permanent Magnet Electric Machine

Abstract

Electric machines with permanent magnets incorporated into the rotor have broad prospects for use in applications characterized by an increased rotational speed of the electromechanical converter. The method of placing permanent magnets on the electromechanical converter’s rotating part has an essential influence on the rotor mechanical strength and the machine’s electromagnetic performance. The article discusses ways to reduce mechanical stresses in the synchronous machine rotor with V-shaped permanent magnets. Preliminary assessment of stresses was made using a simplified analytical model. Based on the obtained results, configuration options for permanent magnets and rotor pole pieces were selected. A distribution pattern of mechanical loads on the external and internal saturation bridges was obtained using a finite element analysis, which refines and confirms the approximate analytical results. The rotor design has been optimized with respect to the criterion of achieving the minimum of maximal stresses in the saturation bridges. The angle between permanent magnets on the pole and the fillet radius at the permanent magnet to pole piece junction locations are chosen as independent parameters. The proposed solutions have been verified from the viewpoint of ensuring the required magnetic induction value in the gap, and the angular characteristics have been calculated. Based on the obtained theoretical study results, a prototype synchronous motor with a rotor containing V-shaped permanent magnets has been designed and manufactured, and its tests have been carried out.