Variable flux machine torque estimation and pulsating torque mitigation during magnetization state manipulation

This paper focuses on dynamic control, under loaded conditions, of the magnetization state of suitably designed variable flux (VF) permanent magnet (PM) machines. Such VF-PM machines have been shown to achieve low loss operation over a wide range of load and speed. For this type of machine, the PM flux linkage varies during the magnetization manipulation process. Published magnetization techniques have occurred at zero load conditions and thus did not generate torque pulsations. However, under loaded conditions, the existing methods would produce unwanted torque pulsation. This paper proposes a parameter insensitive method to solve this issue. This method generates a decoupling current command which is calculated from accurately estimated stator flux linkage. Accurate flux estimation, i.e. insensitive to inductance saturation and PM flux linkage variation (e.g. temperature or magnetization level) is achieved by using the voltage disturbance estimated by a closed-loop stator current vector observer. In both simulations and experiments, it is shown that even during magnetization processes under loaded conditions, the flux can be estimated correctly and smooth torque output can be achieved.