Impact of Machine Magnetization State on Permanent Magnet Losses in Permanent Magnet Synchronous Machines

Negative d-axis current injection used in interior permanent magnet synchronous machines (PMSMs) weakens the permanent magnets' (PMs) flux, eventually increasing the PMs losses and reduces, therefore, the machine efficiency. Several studies have reported that the increase in the air gap flux harmonic content as the primary reason for the PM losses increase in flux weakening operation, disregarding PM properties variation with the magnetization state (MS) due to PM magnetoresistive effect. This paper analyzes the variation of PM losses with the MS and flux weakening current, the target being threefold: a better understanding of PM losses production mechanisms; to analyze the impact of MS on the thermal behavior of the machine; use this knowledge to improve the machine design.