Influence of Magnetoresistance and Temperature on Permanent Magnet Condition Estimation Methods Using High-Frequency Signal Injection

Torque production capability of permanent magnet synchronous machines (PMSMs) depends on the permanent magnet (PM) magnetization state (MS). MS is a function of PM initial magnetization level, which decreases as temperature increases. Furthermore, excessive PM temperature can produce irreversible PM demagnetization. PM MS and temperature measurement/estimation is therefore important both for torque control and monitoring purposes. The injection of a high-frequency (HF) signal in the stator windings has been shown to be a viable option for temperature and MS estimation. This technique estimates the PM temperature or/and MS from the variation of the stator reflected PM HF resistance. However, since PM HF resistance is affected by both PM temperature and MS due to magnetoresistive effect, separating both effects is not trivial. This paper studies the effect of magnetoresistance and temperature on the PM resistivity, the target being twofold: to understand how temperature and MS estimation methods interfere with each other, and to further use this knowledge for the development of methods to be able to estimate the magnet temperature and MS simultaneously.