Electric Field and Parasitic Capacitance Analysis for HF Transformers with Coaxial Winding Arrangements

Electric field and voltage distribution analysis play an important role in designing optimal DC-DC converters. Parasitic parameters, especially interwinding and intra-winding capacitances in high frequency (HF) transformers, hugely influence the performance and efficiency of isolated converters. In this paper, electric field, voltage distribution, and insulation coordination are analyzed for a high frequency transformer with coaxial windings. Also, parasitic capacitances such as interwinding and intra-winding capacitances are calculated. Coaxial windings show a robust magnetic coupling and low leakage inductance, which make them suitable for many applications that need low eddy current and copper loss. Hence, a comprehensive analysis on the electric field and capacitive behavior of the high frequency transformers with coaxial windings is very helpful for industrializing them. In this paper, a 2kW HF transformer with voltage level of 400V/400V at frequency of 5 kHz is designed and analyzed for isolated DC-DC converter applications. For analyzing the field distributions and finding the parameters, numerical method is used. Also, the mathematical procedure of finding parameters with finite element method (FEM) is explained. The design method and the analysis procedure used in this paper can later be used for designing optimal isolated DC-DC converters or integrating parasitic parameters in resonant tank circuits for achieving zero voltage switching (ZVS) and zero current switching (ZCS). Especially for converters including silicon carbide (SiC) and gallium nitride (GaN) switches.