Permanent Magnets Aging in Variable Flux Permanent Magnet Synchronous Machines

Permanent magnet synchronous machines (PMSMs) operation above base speed is typically achieved by injecting negative d-axis current to produce flux weakening. However, this mode of operation increases copper, stator/rotor core, and permanent magnet (PM) losses, penalizing the efficiency and increasing the risk of demagnetization. Variable flux PMSMs in which PMs are magnetized/demagnetized during normal operation of the machine have been proposed to avoid the use of flux weakening current. However, PM aging due to magnetization/demagnetization cycles has not been thoroughly studied yet. This article analyzes the variation of NdFeB, SmCo, and AlNiCo PMs properties, including magnetic, electric, and thermal, resulting from magnetization/demagnetization cycles.