Derivation of an Optimal Winding Configuration for Minimizing the Effect of Winding Capacitances in a Two-winding High-frequency Transformer

To ensure reliable operation of medium/high-frequency (MF/HF) transformers, it is critical to avoid any close proximity among the switching and natural resonance frequencies. These series and parallel resonance frequencies are governed by the transformer parasitics, intrawinding and interwinding capacitances being among them. Therefore, it is desirable to minimize the winding capacitances of a MF/HF transformer and improve its circuit behavior at high frequency and/or high voltage operations. This paper investigates different winding schemes and layouts based on the relative positions of start and finish terminals in a layer/coil of a winding. Accordingly, the interwinding capacitance is modeled by incorporating the effects of layer-to-layer potential distributions that arise due to different coil connections and winding schemes. This study shows that while keeping the design parameters of a transformer same, the adverse effects of winding capacitance can be minimized by adopting to an optimal winding scheme and terminal layout. This shifts the series and parallel resonance frequencies towards high frequency of the frequency responses. Thereby, the resonance to operating frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> /f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">op</inf> ratio is improved, which diminishes the adverse impact of winding capacitances at high dv/dt. The theoretical analyses and choice of optimal winding scheme is verified using experimental results derived from MF transformers built using different winding schemes (wave and flyback) and tested with different combinations of terminal layouts.