Permanent Magnets Aging in Variable Flux 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, penalizing the efficiency and increasing the risk of demagnetization. Variable Flux PMSMs (VF-PMSM) in which PMs are magnetized/demagnetized during normal operation of the drive have been proposed to avoid the use of flux weakening current. However, aging effects due to PM magnetization/demagnetization cycles have not thoroughly studied yet. This paper analyzes the variation of NdFeB PMs properties (i.e. magnetic, electric and thermal properties) resulting from magnetization/demagnetization cycles.(1)