A novel three-level DC-DC converter with load adaptive ZVS auxiliary circuit

Multi-level converters are widely used to convert high voltage DC (typically above 500V) to an isolated DC output voltage that may vary from 12V to 300V, depending on the application. Typical applications can range from network server power supplies to battery chargers for purely electric vehicles. Almost all these industrial applications require the converter to operate from no load to full load. Zero-voltage switching is necessary for the efficient operation of the converter as it ensures reduced EMI, reduced switching losses and the proper operation of the switching devices. Most conventional ZVS techniques for multi-level converters fail to achieve ZVS typically below 50% of full load, while some ZVS techniques are able to do so, but they increase the design complexity of the overall system. Moreover such techniques may suffer from increased circulating current loess at certain load ranges (typically at high loads) thus offsetting the gain in efficiency achieved through ZVS. In this paper a simple yet novel ZVS auxiliary circuit that achieves ZVS even at no load, can optimize the circulating auxiliary circuit current necessary for ZVS as a function of load, thus maximize the efficiency of the converter for all load conditions, is proposed, analyzed and validated by experimental results.