Research on Key Technology Points for MMC-HVDC System

Abstract:
With the sustainable development of renewable energy, there is a high demand for the high voltage direct current (HVDC) transmission over long distances. The HVDC system based on modular multilevel converter (MMC) technology has obvious advantages. This paper researches basic topology and typical control strategies for the MMC-HVDC system. Decoupled inner current loopand outer power loop are applied. Circulatingcurrent results in high power loss forsemiconductor devices. Therefore, the circulatingcurrent suppressing controller (CCSC) is adoptedfor better performance. By building themathematical model, simulations are developed inPSCAD/EMTDC to prove a strong dynamicresponse of the MMC-HVDC facing severetransient conditions. Limitations of controlstrategies are also revealed.