Transformer´s capacitance effect on the operation of triangular-current shaped soft-switched converters

This paper addresses the effect of the isolating transformer parasitic capacitor in soft switched converter topologies that apply triangular inductor current. When a transformer is included in the circuit, it will not only add (leakage) inductance to the converter but will also add capacitance. This capacitance will cause a partial resonance behavior and therefore may alter the voltage transfer ratio of the converter. The objective of this study was to analyze the effect of this capacitance on the behavior of Triangular Current Shaped (TCS) soft-switched converters. The isolated TCS converter was analyzed and the theoretical results were verified by simulations and experimentally at a 1kW power level. The analysis show that the transformer´s capacitance boosts the voltage gain of the converter, changes the shape of the inductor current and hence modifies the RMS value of the current. It was found though, that by proper design the RMS current (for same power level) may in fact be reduced and consequently, will result in lower conduction losses as compared to the case with no capacitor.