Parasitic Capacitances in High Step Ratio Planar Transformers for Dual Active Bridge Converters: Cause and Effect

Planar transformers, favored for their high power density in bidirectional DC-DC power conversion applications, encounter challenges at higher frequencies and higher power levels due to increased stray capacitance. This issue is particularly pronounced with higher step ratios, where parasitic capacitance become more significant. In Dual Active Bridge (DAB) converters, such capacitance can cause elevated current ringing, especially on the high voltage (HV) side. To better understand the impact of stray capacitance in high step ratio planar transformers, it is essential to study this aspect with the help of designed prototypes featuring different winding structures. This article presents a comparative analysis of three different 5 kW, 1:29, 200 kHz prototypes to evaluate the cause and effect of parasitic capacitance at higher step ratios. By employing the vector fitting (VF) method, circuit parameters are extracted and simulated with their equivalent impedance models. Providing insights into minimizing the adverse effects of parasitic capacitance, the goal is to determine the optimal configuration for high power and high-frequency DAB converters.