A Shared Capacitor-Based H-Bridge Modular Multilevel DC-DC Converter

Abstract

Conventional Modular Multilevel Converter (MMC) is considered a promising candidate in the industry in high-voltage and high-power applications. However, in DC-DC operation, the capacitor voltages suffer a great deal of unbalance which results in a failure in the DC operation. In literature, a shared capacitor approach was presented for dual MMC-based AC drive systems to ensure limited capacitor voltages ripples during low-/zero-frequency operation. In the shared capacitor approach, every two adjacent submodules (SMs) in opposite legs share a common capacitor with a special arrangement of switching devices. In this paper, the shared capacitor approach has been adopted to produce a modular DC-DC converter, which is intended to be used in HVDC applications such as supplying a DC load or connecting DC-grids of different voltage levels. The proposed converter is a single-stage transformer-less converter, which consists of two legs and is characterized by a low number of very diminished capacitors in the combined SMs. Also, the proposed converter offers low current stresses and bidirectional power flow capability. The proposed architecture illustration and its control algorithm are provided in detail. Simulation results are provided to validate the performance of the proposed converter.