PWM-based Flux linkage estimation for permanent magnet synchronous machines

Monitoring of rotor temperature in permanent magnet synchronous machines (PMSM) is of great importance as high temperature could cause partial or even irreversible demagnetisation of the permanent magnets (PMs). 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 obtained indirectly with the information of rotor magnet flux linkage, as PM remanence decreases with rotor temperature. Here, 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 any form of signal injection which produces undesirable disturbance to the system. Knowledge of machine parameters, such as inductances which may vary due to saturation, is not required. The proposed methodology has been verified in real-time simulation.