Permanent magnet temperature estimation in PMSMs using pulsating high frequency current injection

The injection of a high frequency signal in the stator via inverter has been shown to be a viable option to estimate the magnet temperature in PMSMs. The variation of the magnet resistance with temperature is reflected in the stator high frequency resistance, which can be measured from the resulting current when a high frequency voltage is injected. However, this method is sensitive to d and q-axis inductances (L_d and L_q) variations as well as to the machine speed. In addition, it is only suitable for SPMSMs, being inadequate for IPMSMs. In this paper, the use of a pulsating high frequency current injection in the d-axis of the machine for temperature estimation purposes is proposed. The proposed method will be shown to be insensitive to the speed, L_q and L_d variations. Furthermore, it can be used with both SPMSMs and IPMSMs¹.