Analysis and design of a 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. Presently 80 plus.org efficiency standards like “platinum” or “titanium” efficiency standards require power converters to meet high efficiency (>90%) from loads as low as 20% of full load. Zero-voltage switching is necessary for such highly efficient operation of the converter and also to ensure reduced EMI and 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, they increase the design complexity of the overall system. Moreover such techniques may suffer from increased circulating current losses 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 for three level DC-DC converter is proposed, analyzed and validated by experimental results. The proposed three level converter achieves ZVS even at no load, is able to 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.