Zero voltage switching assistance design for DC-DC series resonant converter with constant input current for wide load range

In under-sea dc power distribution systems, constant current feed is preferred over constant voltage feed for robustness against long distance cable impedance. The input voltage of each power converter module in a series connected dc power distribution system varies over a wide range as a function of the load power. This behavior brings unique challenges to maintaining zero voltage switching (ZVS) for series resonant converters (SRCs), making simple passive techniques impractical for applications with a wide load range. Hence, active ZVS assisting circuits are preferred to achieve ZVS over the resulting wide input voltage range. In this paper, design guidelines are provided for active ZVS assisting circuits in such systems. Limitation of active ZVS circuits and methods to overcome them are also presented. The analysis is verified by hardware testing of an SRC operating at 250 kHz from a constant input source of 1 A with regulated output current of 0.33 A, and a power level of 1 kW.