Bidirectional DC-DC converter plays an important role in distributed power generation system due to it is necessary to control the power flow between energy storage devices and DC bus. The conventional phase-shifted dual-active-bridge (PS-DAB) converter inherits simple control, symmetrical stricture, and zero voltage switching (ZVS). However, large dv/dt will be created when applied in a high voltage range. Modular multi-level DC transformer (MMDC) originates in the modular multi-level converter (MMC) and dual active bridge (DAB). The MMDC topology can be obtained via displacing the power devices in the primary side of DAB with series-connected submodules. A vital issue to ensure MMDC is operating in a stable state is balancing the capacitor voltage of each submodule in the arm. A capacitor voltage balance method is proposed in this paper. The operating principle is reassigning the gate signals of higher capacitor voltage submodules (SMs) to lower capacitor voltage SMs. According to the simulation results, the capacitor voltage has different outputs. The N+1 level change of each N-SMs- arm balanced when the MMDC starts, which means that EMI and dv/dt are reduced in the transformer pressure.
title : Analysis and design of Modular Multi-level DC/DC Converter author : Xu Han, Huiqing Wen