A Power Self-Balanced High Step-Down Medium Voltage DC Converter With Expandable Soft-Switching Range

Abstract

This paper proposed a power self-balanced high step-down medium voltage dc converter with expandable soft-switching range. The proposed one features the input voltage self-balance of each submodule and the current self-balance of each MOSFET, due to the sub-modules transmitting the same power through LC-coupled branches. The LC-coupled branch provides multiple direct AC power paths from medium voltage input to load, eliminating the losses caused by conventional multi-stage transmission. Each submodule of the proposed converter is a soft-switching unit that uses an auxiliary inductor to achieve soft switching, which reduces the resonant current and facilitates the expansion of the number of modules, without redesigning the transformer, instead of the conventional resonant converter that reduces the transformer magnetizing inductance to achieve soft-switching. Moreover, an auxiliary power supply scheme for the proposed converter is provided, which is used to solve the problem of difficult startup of the medium voltage DC converter, where the negative impedance characteristics of the series-connected auxiliary power supply are suppressed without the need for lossy voltage sharing resistors. A prototype with 1kV dc input and 100V/1kW output is built to verify the feasibility of the proposed topology.