Design and Evaluation of a Short-Circuit Rotor-Ring for Enhanced Self-Sensing Capability in a Slotless PM Motor

Abstract

This paper deals with the design and evaluation of a short-circuit rotor-ring for enhanced self-sensing capability in a two-pole slotless permanent-magnet motor. High-frequency rotor anisotropy is enabled by adding a short-circuited rotor-ring. Optimal ring-dimensions are determined by parametric numerical studies. An effective high-frequency saliency of up to 1.8 is demonstrated. The steady-state estimation error is within $\pm$ 2 $^\circ$ , practically unaffected by current level (in contrast to slotted self-sensing electrical machinery) due to the large effective air-gap. The proposed observer performs properly also during dynamic load changes. Fall-times from 3000 to 0 r/min in less than 50 ms with negligible overshoot are demonstrated. Also parasitic effects, such as power losses, heating, and torque ripple are analyzed.