Design of a 5 kW high output voltage series-parallel resonant DC-DC converter

This work presents a comprehensive procedure for designing a high output voltage series-parallel resonant DC-DC converter. The system output voltage control is by a combination of duty-cycle and switching frequency variation, where soft-switching is preserved over the entire operating range. The basic principle of operation of the converter is described and an analytical model is established which does provide a basis for the numerical calculation of the stresses on the power components. Furthermore, a control strategy for minimizing the no-load conduction losses is proposed and the transient behavior in case of load steps including output short-circuit is discussed based on digital simulations.

I. INTRODUCTION

The operation of high output voltage DC-DC converters is considerably affected by transformer non-idealities being caused by the large transformer turns ratio and/or large number of secondary turns. In particular, the leakage inductance and the secondary winding capacitance do take considerable influence on the converter behavior and do potentially reduce efficiency and reliability [1]. Therefore, converter topologies suitable for high-voltage applications should integrate the parasitics of the transformer into the circuit operation. Accordingly, series-parallel resonant converters are frequently employed for the realization of high output voltage DC-DC converter systems. However, the design of resonant converters is involved due to the large number of operating states occurring within a pulse period.