Adaptive Full-Order Observer for Sensorless Variable Flux Reluctance Motor Drives Considering Field-Current Adjustability and Stator Resistance Mismatch

Variable reluctance motors with direct-current field windings in stator (DC-VFRM) offer advantages such as simple rotor structure and no rare earth. Moreover, sensorless control with an adaptive full-order observer (AFO) can further reduce system costs and improve reliability. However, DC-VFRM has an adjustable field current, and more significant variations in stator resistance caused by factors such as temperature changes. If not handled properly, inappropriate field current and inaccurate stator resistance will result in position estimation error and instability. To solve these problems, a robust AFO considering field-current adjustability and stator resistance mismatch is designed. First, an improved AFO structure and gain design criteria considering different field-current amplitudes are given. In addition, a stator resistance adaptation is used to enhance AFO. The decoupling conditions and gain analytical solution of the enhanced AFO are derived. Then, a field-current control strategy is also proposed to improve the stability of AFO and reduce the position estimation error. Finally, the proposed method is carried on a 12/10 DC-VFRM experimental platform, demonstrating its ability to accurately identify stator resistance and improve position estimation accuracy, meanwhile achieving stable operation under different field currents.