PWM-based flux linkage and rotor temperature estimations for permanent magnet synchronous machines

Monitoring of rotor temperature in permanent magnet synchronous machines (PMSM) is of great significance as high temperatures can cause partial or even irreversible demagnetization of the permanent magnets. Rotor temperature measurement unfortunately is particularly difficult in practice, since it is difficult to access temperature sensors on a rotating shaft. Nevertheless, rotor temperature can be predicted indirectly with the information of rotor magnet flux linkage, as permanent magnet (PM) remanence decreases with rotor temperature. In this paper, a simple and relatively accurate method for online estimation of PM flux linkage is presented, based on the measurement of current response to the standard space-vector pulse width modulation (SV-PWM). This method uses the already-existing PWM voltage as the excitation signal in order to avoid of the need for additional signal injection. Knowledge of machine parameters, such as inductances which may vary due to saturation, is not required. The proposed methodology is experimentally verified and applied to rotor temperature prediction.