Fast rotor loss calculations in fractional-slot permanent magnet machines

Abstract

Permanent magnet machines with fractional slot windings are popular because of their shorter end windings, low cost and ease of manufacturing. On the other hand, fractional slot machines have higher eddy current losses in the rotor magnets and sleeve. An accurate calculation of these losses usually involves a time-stepped finite-element analysis with moving rotor, which is time consuming. This paper compares different methods of evaluating these losses using finite element analysis based on their time-cost. The models are mainly divided into two types: time-domain and frequency-domain models. The paper proposes an equivalent frequency-domain analysis in the stator frame for rotor loss calculations, using the Lorentz force term. This method yields similar results to the time-stepped finite element model with a significant time saving. The time saving can be significant in a machine optimization study.