Analysis of unbalanced magnetic pull of permanent magnet assisted synchronous reluctance motor based on uneven axial temperature distribution of magnets

Abstract

This paper discusses the effect of uneven axial magnet temperature of permanent magnet assisted synchronous reluctance motor (PMa-SynRM) on unbalanced magnetic pull (UMP). The loss generated in stator and rotor contribute to temperature rise in the motor. Commonly, radial direction thermal analysis has been done while assuming constant temperature in axial direction of a machine. However, the uneven temperature distribution of magnet in axial direction can substantially generate uneven magnetization. This uneven magnetization can cause an unbalanced magnetic pull in the motor. For analysis of axial direction uneven magnetization, 3-D model of a 3Kw, 1800 rpm, 5 phase PMa-SynRM has been developed. From finite element analysis (FEA), loss data of 3-D model has been calculated. This information have been used as inputs for the thermal analysis in axial direction. By applying thermal model of PMa-SynRM in thermal analysis, uneven magnet temperature distribution has been clearly observed and analyzed. This temperature distribution of magnet has been manually fed back to the 3-D FEA model to assess the performance. Comparison of radial force between constant and uneven temperature of magnets in axial direction showed noticeable difference which can cause UMP. Experimental results of axial temperature also showed good matching with simulation results.