Improved Adaptive Sliding-Mode Observer Based Position Sensorless Control for Variable Flux Memory Machines

This article focuses on the position sensorless control for variable flux memory machine (VFMM) of which the magnetization state (MS) can be flexibly changed by applying a d-axis current pulse to achieve the so-called MS manipulation. First, the unique challenges in VFMM sensorless control are in depth analyzed and summarized based on the experimental results. An improved adaptive sliding-mode observer (SMO) and an improved phase-locked loop (PLL) are then proposed. Specifically, a newly developed dq-axis voltage pulse injection method is employed to accurately measure the dq-axis inductances of VFMM during MS manipulations and update them into SMO to increase its convergence speed. An adaptive law is proposed for tuning sliding-mode gains to obtain satisfying estimation performance of SMO under different conditions of speed and MS. In addition, to enhance the position tracking performance against the position estimation error resulted from MS manipulation or speed change, an improved PLL is structured, whose bandwidth can be adaptively adjusted by using fuzzy logic control. Finally, the feasibility and effectiveness of the proposed sensorless control strategy are verified through experimental measurements on a hybrid magnetic circuit VFMM prototype.