Influence of magnetoresistance and temperature on permanent magnet condition estimation methods using high frequency signal injection

Abstract

Torque production capability of permanent magnet synchronous machines (PMSMs) depends on the permanent magnets (PM) magnetization state (MS). MS is a function of PM initial magnetization level, decreasing 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 as well. The injection of a high frequency (HF) signal in the stator of windings has been shown to be a viable option for temperature and MS estimation. This technique estimates 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, development of methods able to separate both effects would be highly relevant. With this purpose, this paper studies the effect of magnetoresistance and temperature on the PM resistivity. The target of this study is twofold: a better understanding of how temperature estimation and MS estimate methods can interfere with each other, and the development of methods able to estimate the magnet temperature and MS simultaneously.1