Investigating the Size of Permanent Magnets to Maximize the LSPMSM’s Efficiency

Line-start permanent magnet synchronous motors (LSPMSMs) have advantages such as high efficiency (HE) and line-starting capability, making them increasingly desirable for drive systems aimed at energy conservation. For LSPMSMs, the thickness of the permanent magnet (PM) significantly affects the operational parameters and, in particular, efficiency of the motor. This paper aims to determine the characteristics of d-axis magnetizing inductance Lmd of the LSPMSM as the PM size changes, thereby evaluating the efficiency and operational parameters of the LSPMSM. The research results for a 2.2 kW LSPMSM with 4 poles indicate that when the thickness of the magnet varies from 4.0 mm to 6.0 mm, the Lmd values obtained from the FEM model align closely with those calculated analytically, with an error of no more than 10%. Additionally, the study also reveals the existence of an optimal magnet thickness for the LSPMSM to achieve the best efficiency. Simulation results show that the motor reaches a maximum efficiency of ηmax.FEA=0.9 with an optimal thickness of lm=5.5mm, and experimental validation on a prototype achieved ηmax.test=0.895, resulting in an error of 1.2%. Furthermore, the research indicates that as the thickness increases, the starting characteristics deteriorate, and the vibration of the LSPMSM increases. Both experimental and simulation results are consistent, affirming the accuracy of the research findings.