AC Loss Analytic Method and Optimization of Litz Winding for High-Speed Electrical Machines

The high speed of the machine brings advantages, such as the improvement of the power density, but also has a significant effect on the ac loss of the winding. Compared to the commonly used round and flat wire, litz wire shows great performance on reducing the ac loss. However, the circulating current between the strands in litz wire cannot be ignored at high speed. Thus, it is necessary to study the circulating current loss of litz winding. This article proposed an analytical model to calculate the circulating current loss in litz winding, which takes the twisted process into consideration. First, the circulating current loss can be calculated based on the voltage and inductance obtained by sampling interpolation method. The calculation model takes the effect of the circulating current on the magnetic field in reverse into consideration. Second, taking doubly salient brushless dc (DSBLDC) generator as an example, the influence factors of litz winding structure parameters on circulating current loss are analyzed, which provides a basis for the design of machine winding. Finally, an experiment platform aiming to measure the circulating current loss is designed, proving the accuracy of the analytical model. And a 12/8 high-speed DSBLDC generator prototype with litz winding is designed for experimental verification.