AC Copper Loss Reduction in Electrical Machines through Winding Transposition of Rectangular Bundle with Compressed Conductors

This paper introduces an innovative novel winding structure optimization method, aiming to mitigate AC copper losses and preserve high copper fill factor in electrical machines simultaneously. By combining a rapid circulating current loss calculation method and finite element analysis (FEA), both the circulating current loss and eddy current loss are simultaneously suppressed in the winding composed of rectangular bundles with compressed conductors, leading to an effective reduction on overall AC copper loss. The FEA results demonstrate that the proposed winding structure can achieve a ratio of AC-to-DC copper loss of active length as low as 0.05 at 1000 Hz. Based on the calculation results, a motorette (composed of winding, stator and rotor core) was fabricated, achieving 47% copper fill factor in a parallel-tooth slot and restricting the AC-to-DC copper loss ratio of active length to 0.13 at 800 Hz and 0.27 at 1000 Hz, respectively. Compared with Litz wire, the proposed winding demonstrates improvements in copper fill factor and limited compromise in AC copper loss suppression ability below 1000 Hz, thereby beneficial to power density enhancements in electrical machines.