On-load Back-EMF Optimization Based on the Back-EMF MST Method and Parametric Optimization

Abstract This paper proposes an optimal design for a surface mounted permanent magnet synchronous machine (SM-PMSM) based on parametric optimization process to reduce the on-load Back-EMF distortions caused by an increase in the electromagnetic load and in the saturation. Unlike conventional methods described in the literature, the optimization approach proposed here accounts for the saturation effects, air gap flux density distribution and the evaluation of the on-load Back-EMF by means of finite element analysis, allied to the most recent on-load Back-EMF evaluation method, known as the Back-EMF MST (Maxwell stress tensor) method. Furthermore, the optimization process is performed considering either the machine's physical symmetry (based on pole numbers) and its nonevident symmetry (based on saturation effects and on the relevance of each tooth in the Back-EMF waveform), which is identified using the Back-EMF MST method. The proposed optimization process also analyzes different sets of variables based on symmetric and asymmetric tooth dimensions. The result is a machine with a reasonably improved design, higher average torque, lower torque ripple and smaller volume. In addition, the on-load Back-EMF is almost identical to the no-load one. Hence, the on-load cogging torque is almost identical to the no-load cogging torque.