Evolution of Classical 1-D Based Models and Improved Approach for the Characterization of Litz Wire Losses

Prediction of Litz wire losses is a challenging endeavor in the design of high frequency transformers. Although many analytical approaches of varying complexity can be found in literature, classical 1-D based models are the norm in the analysis of wide design spaces. Even then, an important degree of uncertainty exists around the accuracy of the 1-D models. After a critical review of these models and an analysis of their application in Litz wire loss prediction, a new model is proposed which tries to address some of the concerns and limitations of the existing approaches. The models are evaluated against 2-D finite element simulations in many different conditions to ensure the models correctly consider the impact of different parameters. Experimental results are presented to demonstrate the accuracy of the new approach at very high frequencies and high amounts of strands using four prototypes with different Litz wires, designed to correctly match the conditions inherent to any 1-D model.