Analysis of local demagnetization in magnet for PM-assisted synchronous reluctance motors

This digest investigates the demagnetization risk of permanent magnet-assisted synchronous reluctance machines (PMa-SynRM). PMa-SynRM is often designed with multilayer PMs/flux barriers to increase saliency and reluctance torque. Weaker or less PM (than that for IPM motor) is embedded into the rotor of PMa-SynRM, which can be demagnetized during high-performance operation (e.g., high armature reaction or current phase advance control). Demagnetization possibility of PM depends on factors such as temperature, armature current and design operating points and mostly occurs combining some of the above factors. The temperature distribution across the PM can be different and the operating points at different locations in the PM can also vary. This very likely causes local demagnetization within a PM. This work proposes a method to evaluate the demagnetization risk within a PM for all the PM layers of PMa-SynRM rotors. A model based on the magnetic circuit is first developed to calculate the operating points across the PM at the no-load and loaded condition. The magnet temperature distribution is then estimated with a commercial software. With the temperature and loaded operating points ofthe PM, the risk of local demagnetization can be predicted. This is validated using finite element analysis. From the analysis, a design method that can avoid demagnetization is then proposed. Experimental studies are conducted to validate the simulations.