Comparative Study of Magnet Temperature Estimation at Low Speeds Based on High-Frequency Resistance and Inductance

Interior permanent magnet synchronous motors have been widely used in electric vehicles. These motors employ Nd-Fe-B as the permanent magnet, which is vulnerable to temperature variations. Moreover, some features of Nd-Fe-B magnets are related to temperature, which can affect motor characteristics. Therefore, magnet temperature is an important parameter and methods for estimating it have been developed. In particular, a signal injection method has been developed for low-speed regions. In this method, two parameters are employed: high-frequency resistance and high-frequency inductance. In this paper, these two methods are compared to determine which parameter is more appropriate for estimations at low speeds and to reveal whether signal injection methods can be applied to the standstill condition. The comparison indicated that the high-frequency inductance-based method has a stronger correlation with the magnet temperature at low speed and standstill conditions than the high-frequency resistance-based method.