New Precharge and Submodule Capacitor Voltage Balancing Topologies of Modular Multilevel Converter for VSC-HVDC Application

This paper presents two novel topologies on precharge and submodule capacitor voltage balancing schemes of Modular Multilevel Converter (MMC) for VSC-HVDC application respectively. Firstly, A traditional precharge process of MMC was modeled in PSCAD/EMTDC, its drawbacks were summarized and a novel topology was proposed based on submodules charged synchronously; Secondly, we analyzed the principles of a traditional submodule capacitor voltage balancing scheme, clarified its limitations and another novel topology based on the essential objectives of the balancing schemes was proposed. The topology is with Double DC Bus Bars, external DC voltage source and antiparallel thyristors. Detailed analysis and simulations indicated that the two topologies presented here not only can make up the drawbacks of the conventional schemes to a certain extent, but also have great potentiality in the application of VSC-HVDC projects in the future.