Optimized Design of Full-Bridge Modular Multilevel Converter With Low Energy Storage Requirements for HVdc Transmission System

Abstract

Modular multilevel converter (MMC) is a well-proved circuit topology in voltage-source converter-based high voltage direct current (VSC-HVdc) transmission systems. As is known, the conventional half-bridge submodule (HBSM)-based MMC-HVdc is not suitable for overhead line transmission applications. In addition, high energy storage requirements, i.e., large capacitance is inevitable. The conventional design of the full-bridge submodule (FBSM)-based MMC usually does not utilize the negative voltage state of FBSM in normal operation. Considering the same dc voltage as with the HBSM case and utilizing the negative voltage state of the FBSM, this paper presents the design method of the power transmission capability of a single FBSM. Meanwhile, an optimized energy storage capacitance design method of the FBSM is proposed. With this method, the capacitance of FBSM can be reduced significantly. The correctness and effectiveness of the proposed method is verified by the simulation of a ±160 kV VSC-HVdc MMC and the comparison results of the dc short fault blocking and ride through capability are also provided.