AC copper losses calculation of the ironless BLDCM used in a flywheel energy storage system

The purpose of this paper is to analyze the AC copper losses of the ironless brushless DC machine (BLDCM) used in the Flywheel Energy Storage System (FESS). The influence factors of the AC copper losses, such as the winding diameter, current and machine speed etc. are analyzed. The research results show that the winding diameter has a huge effect on the winding AC loss in ironless BLDCM, and the shunt wound structure with multiple wires method can reduce winding AC loss effectively. However, due to induced voltage and impedance unbalance, additional circulating current loss would be induced. For circulating current losses calculation, a winding circulating current equivalent calculation model is built. The circulating current losses are calculated by simplified 3D finite element method and the winding strand arrangement method to reduce circulating current loss is explored. Three strands arrangements are compared and discussed. The results show that the ironless BLDCM using multi-strands with suitable strands arrangements can reduce the copper loss.