Eddy Current Losses in Permanent Magnets of Inverter-Driven Synchronous Machines

Abstract:
This paper extends a semi-analytical factor-based method for predicting eddy current (EC) losses in permanent magnets (PMs) based on the results of 2-D magnetostatic finite element analysis (FEA) to include spatial field harmonics. To account for the impact of magnetic resistance on the reaction field, an approach based on the effective air-gap length is introduced in addition, which uses magnetostatic 2-D FEA as well. Taking into account inverter currents with substantial time harmonics, the study focuses on two machine topologies: a surface-mounted PM machine and a bar-type interior PM machine. Compared to both 3-D FEA results and a different semi-analytical calculation method based on the image theory, the extended factor-based method generally agrees, with different advantages and disadvantages. By employing this method, a deeper understanding of loss mechanisms is attained, providing valuable tools for loss analysis and loss reduction during the design process of PM machines. The presented calculation and visualization methods are integrated into an available FEA post-processing tool for advanced loss analysis.