A Transformerless High-Voltage DC-DC Converter for DC grid Interconnection

Abstract

This paper presents a transformerless high-voltage DC-DC converter based on cascaded sub-modules. It is intended for interconnecting high-voltage or medium-voltage DC grids. The proposed DC-DC converter is composed by two phase legs, each of which consists of an upper arm and a lower arm with their middle nodes crossly connected through a branch of active sub-modules. By properly controlling the output voltage of the cross-connected branch, a trapezoidal AC current is induced to interact with the AC voltage components in upper and lower arm for rebalancing the power amongst converter arms. The features of modular design, single-stage power conversion and transformerless structure make the proposed DC-DC converter gain the outstanding merits of wide voltage ratio range, high system efficiency and light converter weight. A control scheme is also elaborated for guaranteeing the normal operation of the proposed DC-DC converter.

Existing System

Optimization.

Proposed System

This paper presents a transformerless high-voltage DC-DC converter. As compared to the prior arts, the proposal possesses at least one of the following merits 1) The avoidance of transformer and coupled inductor helps to reduce the size, weight and power loss of the overall system; 2) Single-stage configuration leads to the enhanced system efficiency; 3) Modular design enables the scalability to high-voltage rating. 4) Symmetric structure enables bidirectional power flow and continuous DC currents at both primary and secondary sides in steady state.

Architecture

Circuit Architecture