A Four-Capacitor Model for Interprimary-Winding Capacitances Analysis in the Input-Series Transformer-Integration Converters

The input-series transformer-integration (ISTI) converters are suitable for the high-input voltage multiple-output applications. In these converters, interprimary-winding capacitances are the unique stray capacitances of the integrated transformer, and energy influences of these capacitances cannot be ignored in the high-voltage applications. In order to analyze energy influences of the interprimary-winding capacitances, in this article, a four-capacitor model is proposed to represent these capacitances within arbitrary two primary windings of the integrated transformer. Based on the proposed model, energy varying of the interprimary-winding capacitances is analyzed in detail during each switching period. Furthermore, estimation of the four lumped capacitors is discussed. Finally, three different integrated transformers are designed for a 1-kV/60-W laboratory-made flyback ISTI converter, and validity of the proposed model is verified through the simulating and the experimental comparisons of these integrated transformers.