Control of Non-conventional Synchronous Motors

Chapter 8

Variable Reluctance Machines: Modeling and Control ¹

8.1. Introduction

The term “variable reluctance machine” (VRM) covers a very large range of devices directly or indirectly using the variation of the air-gap permeance to convert electromechanical energy. Different topologies, associated with specific supply modes, have been designed, studied and tested to fulfill the specifications of various applications with very variable performances. Although the majority of structures have not (yet) moved beyond the prototype, two families − synchronous reluctance or synchro-reluctant machines (Synchrel) and the switched reluctance machines (SRM) − have very interesting performances and potentials. The latter already being well established in industry [MUL 99].

The rotors of these two families of machines are devoid of all sources of magnetomotive force (permanent magnets and supplied winding). Only the stator supports polyphase winding (concentrated for SRM and generally distributed for Synchrel). This gives them an undeniable robustness and genuine advantages for high-speed applications. In both cases, synchronous operation can be obtained when their supplies are supervised by an appropriate control. The performances obtained are then comparable, or even greater in some cases, to that of induction machines of the same volume [STA 93].

These machines are not devoid of defects. Thus, the principal drawback of Synchrel machines lies in their power factor, which is relatively ...