Novel Magnetization State Control Method Utilizing d-Axis Current to Eliminate Unintentional Demagnetization of Low-Coercive Force PM for Variable Flux Memory Machine

This paper proposes a novel magnetization state (MS) control method to eliminate the unintentional demagnetization (UD) of low-coercive force permanent magnet (PM) for variable flux memory machine (VFMM). In the proposed method, the amplitude of demagnetization
d
-axis current pulse is determined from a look-up table with the relationship between the demagnetization
d
-axis current pulse and the intersections of torque-speed curves under different MSs, and subsequently used as the condition for the MS manipulation. A PM flux linkage observer is adopted to monitor the UD all the time and the amplitude of
d
-axis current is controlled without exceeding the amplitude of the demand demagnetization
d
-axis current pulse to avoid the UD in the whole speed range. The inverter nonlinearity is compensated to improve the estimation accuracy of the PM flux linkage. The experiment validation is conducted on a hybrid magnet memory machine system to illustrate the UD issue and to verify the PM flux linkage estimation method and the proposed MS control method.