Soft-start Optimized Strategies of MMC-HVDC with Overhead Lines Based on Full-Bridge Sub-modules

Abstract

Modular Multilevel Converter (MMC) based on full-bridge sub-modules(FB-MMC), which has advantages of outputting negative level, improving the utilization rate of DC voltage and having the capability of fast recovering DC short-circuit faults, can be applied to high voltage and large capacity MMC-HVDC system based on overhead lines. Based on the operation mechanism of FB-MMC, the charging characteristics of two kinds of charging modes including active charging and passive charging, are deeply analyzed , and corresponding soft-start strategies to be selected are given. Through theoretical and simulation comparison and analysis of performances of different soft-start strategies used in each kind of charging mode, the optimized soft-start strategies are proposed, which provide a theoretical basis for engineering design and application of high voltage and large capacity MMC-HVDC with overhead lines.