Three-Level ZCS Converter Suitable for Medium Voltage DC Distribution Network

A novel three-level zero-current-switching (ZCS) converter, operating in discontinuous current mode, is proposed for the application of distributed photovoltaic power accessing the medium voltage dc distribution network. The proposed converter is composed of a traditional neutral point clamped (NPC) three-level (TL) circuit and an auxiliary circuit, owning 6 switches and 2 transformers. By controlling the auxiliary circuit with Pulse width modulation (PWM), ZCS can be reached for the basic TL circuit, which delivers most of the power, with the switching loss of the converter remarkably reduced. The influence of turn's ratio the auxiliary transformer on the switch current is discussed in detail, and the parameters design principles are put forward, which is verified with PLECS simulation results. Finally, a prototype of 300 V-1500 V/1500W is built to verify the performance of the proposed converter.