Experimental Assessment and Mathematical Modeling of a Self-Excited Wound Rotor Synchronous Motor With Multiphase Stator Design

Wound rotor synchronous motors (WRSMs) are emerging as a compelling alternative to permanent magnet (PM) motors in the context of electric vehicles, offering magnet-less operation and cost-effectiveness. Various techniques exist to excite the field system of synchronous motors, each presenting drawbacks. This paper investigates a self-excitation technique based on a multi-phase stator design that autonomously energizes the field winding, eliminating the need for external excitation systems or rotating transformers, thus reducing motor weight and size. The multi-phase stator generates two distinct magnetomotive force (MMF) components: a dominant flux component responsible for torque production and a harmonic component crucial for field winding excitation. Independent control of both flux components is achieved by regulating the decoupled αβ and xy sequence current components, respectively. The paper presents the mathematical modeling and steady-state equivalent circuit for this topology. Extensive testing determines the motor parameters, analyzes the relationship between xy current and field current, and examines the effects of mechanical loading and speed variations on the field current. An improved Field Oriented Control (FOC) strategy is proposed to compensate for the effects of mechanical loading due to cross-coupling between the two subspaces caused by various nonidealities. An experimental setup employing a five-phase stator is developed to validate the proposed control methodology.