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AC Loss Analysis and Measurement of a Hybrid Transposed Hairpin Winding for EV Traction Machines

Abstract:

To address the problem of high-frequency ac loss of hairpin winding, a hybrid transposed hairpin winding (HTHW) scheme, which combines flat wire and litz wire, is proposed. The HTHW can effectively reduce the high-frequency ac loss, while maintaining a relatively high slot fill factor. In this article, the ac loss generation mechanism under high-frequency excitation is first analyzed. Then, based on the field-circuit-coupled finite element method, the current density distribution, and ac loss of hairpin winding with different transposed topologies are calculated and compared. Finally, an experimental platform enabling direct measurement of hairpin winding loss is built to verify the simulation. The simulation and experimental results show that the ac loss of the proposed HTHW is much lower than that of the traditional hairpin winding, for medium to high running frequency. In our case, the ac and dc resistance ratio of the presented HTHW is 2.12 at the frequency of 1200 Hz, contrasting that of the ratio of traditional hairpin winding, which is 10.2.