Novel Structure of Ferrite-Magnet Motor Based on New Criteria for Reluctance Torque Utility

Abstract

A novel structure for a ferrite-magnet motor was derived from new criteria for the utility of reluctance torque, based on the permanent magnet (PM) flux linkage of the stator phase windings, the current, and the direct- and quadrature-axis inductance. Through both theoretical consideration and experiments, a motor with large PM flux linkage is shown to utilize little reluctance torque even if the salient-pole ratio is over 3.0. The proposed criteria help clarify the properties inherent in different motors and also indicate that selecting a rotor geometry with less saliency can improve efficiency. Results are given for two types of 6-pole ferrite-magnet motors with output power of 0.2 kW, a rated rotation number of 1080 min−1, and Y connection.