Impact of machine magnetization state on permanent magnet losses in permanent magnet synchronous machines

Permanent magnet synchronous machines (PMSMs) operation above based speed is typically achieved by injecting negative d-axis current to produce flux weakening. However, this increases permanent magnet (PM) losses, reducing therefore the machine efficiency. Previous studies have reported that PM loss increase in flux weakening operation is due to the increase of the airgap flux harmonic content. These studies however did not consider PM properties variation with the MS due to magnetoresistive effect, which can also contribute to PM loss increase. This paper analyzes the variation of PM losses with the MS and flux weakening current. The impact of MS on the thermal behavior of the machine is also studied 1 .