Zero-Voltage-Switching Auxiliary Circuit for Minimized Inductance Requirement in Series-Resonant DC/DC Converter Systems

Abstract

For power electronic converter systems, the cost and the size of the magnetic components are typically limiting factors when it comes to overall production costs and power density. This especially holds for soft-switching high-frequency applications, where a resonant discharge of the output capacitances of the semiconductors relies on sufficient amount of energy stored in the main magnetic components, i.e., inductors or transformers, yielding a substantial increase in their volumes. In this article, an alternative solution is introduced, where a small auxiliary circuit is used to ensure soft-switching of the power transistors, whereby the aforementioned volume of the main magnetic components can be significantly reduced. The proposed auxiliary circuit provides zero-voltage-switching conditions independent of the applied voltages, the switching frequency, and the output power level, without significantly increasing the circuit complexity or the control effort. The new concept is first analyzed based on simple analytical calculations and circuit simulations, and is then experimentally verified by means of hardware demonstrators related to a 3.6-kW 250-500V/250-500V series-resonant dc/dc converter application. Finally, it is shown that the auxiliary circuit can also be used to precharge the output capacitor of a converter system, which allows to further reduce the size of the main magnetic components.