A Novel Load Adaptive ZVS Auxiliary Circuit for PWM Three-Level DC-DC Converters

Three-level PWM dc-dc converters convert high dc voltage (>500 V) generally at the output of a three-phase ac-dc PWM rectifier in ac-dc converters to an isolated dc output voltage which can be used to power data center loads. Strict efficiency requirements at loads from 20% to 50% of full load of ac-dc converters for telecom applications have been introduced by energy star enforcing industries to improve efficiency of the dc-dc converter in an ac-dc converter powering data-center loads at those loads. High-efficiency requirements at low and mid loads in high switching frequency PWMdc-dc three-level converters implemented with MOSFETs can be achieved by reducing switching losses through optimized load adaptive ZVS for the entire load range. In this paper, a simple yet novel load adaptive ZVS auxiliary circuit for three-level converter is proposed for so that the resulting three-phase ac-dc converter can meet energy star platinum efficiency standard. The operation of the proposed dc-dc converter is described, analyzed, and validated by experimental results from an industrial prototype of a three-phase ac-dc converter comprising of a front-end three-phase boost PWM rectifier followed by the proposed converter.