Research on control strategy of LCC-MMC hybrid HVDC system

A new hybrid HVDC system is investigated to synthetically utilize the advantages of line commutated converter based HVDC (LCC-HVDC) and modular multilevel converter based HVDC (MMC-HVDC). The rectifier of the system adopts LCC, the inverter is composed by LCC in series with the MMC unit, and the MMC unit is composed of multiple MMCs in parallel. The mathematical model of the hybrid HVDC system is deduced and the coordinated control strategy between the rectifier and the inverter is designed. In PSCAD/EMTDC simulation environment, typical transient conditions such as start-up, AC system fault, DC overhead line fault and converter fault of the hybrid HVDC system are analyzed. The simulation results show that the system has good dynamic performance under various conditions.