AC Copper Losses Analysis of the Ironless Brushless DC Motor used in a Flywheel Energy Storage System

The purpose of this paper is to analyze ac copper losses of the ironless brushless dc machine (BLDCM) used in the flywheel energy storage system. The influence factors of the ac copper losses, such as the winding diameter, phase current, and machine speed, are analyzed. The research results show that the winding wire diameter has a huge effect on the ac losses in ironless BLDCM, and the shunt wound structure with multiple wires method can reduce winding ac losses effectively. However, due to induced voltage and impedance unbalance, additional circulating current losses are induced. For circulating current losses calculation, a winding circulating current equivalent calculation model is built. The circulating current losses are calculated by a simplified three-dimensional finite element method and the winding wires arrangement methods to reduce circulating current losses are explored. Three winding wires arrangements are compared and discussed. The results show that the ironless BLDCM using multiwires with suitable arrangements can reduce the copper losses.