Robust Observer Design with Combined Position and Mutual Inductance Estimation for Sensorless Variable Flux Reluctance Motor

Variable flux reluctance motor with dc field windings in stator (DC-VFRM) is a new rare-earth-free design for electric vehicles (EVs) owing to its robust rotor configuration and controllable excitation. This article deals with the estimation of rotor position and mutual inductance between armature and field windings in sensorless DC-VFRM drives. An adaptation law for the mutual inductance magnitude is proposed to augment a back-electromotive-force (back-EMF)-based observer. The augmented observer gains are designed based on the linearized model and stability conditions are derived. The impact of incorrect model parameters on steady-state position estimation errors is studied. A robust parameter design is proposed through the analysis of local stability, which maximizes the allowed model parameter uncertainty. Finally, the proposed observer is experimentally validated on a 12/10 DC-VFRM test platform, showing the stable operation under different operating conditions.