Review of flux-weakening in high performance vector controlled induction motor drives

This paper is a tutorial review of flux-weakening operation in high performance vector controlled induction motor drives (VCIM). Flux-weakening has become very important due to the enhanced benefits of high speed operation of many processes and due to the impending introduction of electrical vehicles with propulsion drives having a range of operational speed up to 14,000 r/min. All of these applications demand precision dynamic torque and speed control over the entire speed range. Flux-weakening control, though familiar in the pretext of low performance V/Hz type controllers, takes on complex proportions in the context of high performance vector controlled induction motor drives. Stator flux control emerges as the obvious candidate for high speed operation but is unsuitable or incompatible with indirect vector controllers. A hybrid combination of rotor flux linkages reference with the imposed voltage limit due to the limited DC link voltage is a very attractive alternative at this juncture for indirect VCIMs. This paper presents the fundamentals of flux weakening operation, presents the hybrid algorithm, critically reviews control algorithms for high performance flux-weakening and summarizes solution methodologies available for constant power operation over a wide speed range. In the process, an important solution for this problem in the form of coordinating the design of inverter-fed induction machines and control variables emerges in this paper.