Sensorless Control of Variable Flux Memory Machines Based on Improved Extended EMF Model and Adaptive Extended State Observer

The sensorless control of variable flux memory machine (VFMM) is very challenging since its flux regulation is achieved through magnetization state (MS) manipulation by applying a short
d
-axis current pulse. This article proposes a novel sensorless control strategy for VFMM based on an improved extended electromagnetic force (EEMF) model and adaptive extended state observer (ESO). Firstly, the conventional EEMF model is improved for VFMM by incorporating the derivative term of PM flux linkage to eliminate the position estimation error caused by the unique MS manipulation. Based on the improved model, two ESOs with an adaptive bandwidth are designed to accurately estimate the αβ-axis EEMFs over a wide speed range. Specifically, an adaptive tuning scheme is proposed to online adjust the bandwidth of ESOs considering both normal operations at different MSs and MS manipulations. Then, the finite element method (FEM) is utilized to obtain the required information for EEMF model and adaptive ESOs, including the PM flux linkage and its derivative during MS manipulations. Finally, the feasibility and effectiveness of the proposed sensorless control strategy are verified through both simulation and experimental measurements on a hybrid magnetic circuit VFMM (HMC-VFMM) prototype.