Active Flux Based Advanced Encoderless AC Drives: A Tutorial Review

“Active flux” is an alternative unitary concept for the control of practically all ac drives. As aligned to rotor d-axis (for synchronous and flux-modulation machines) and to rotor flux axis for induction machines, “active flux” is a physical/technical concept that turns all travelling field physically salient electric ac machines into a functionally nonsalient model. As its position is independent of load torque (for known machine parameters) it leads to notable simplifications in encoderless advanced control of ac drives. This tutorial review summarizes the fundamentals of the “active flux” concept as applied to practically all ac machines and the progress from 2008 to today with sample literature results. It also introduces in draft the theory of applying “active flux” to MTPA, MaxCosFi, maximum torque per flux (MTPF) integrated into smooth control of ac drives, for constant and variable magnetic saturation, with promising recent results for a reluctance synchronous motor drive. Weighting “active flux” merits and demerits and offering new workfronts in its application the article is hoped to assist in producing even better ac motor/generator drives in the future.