Study on Main Circuit Configuration and Control Modes for a New LCC-MMC Hybrid HVDC System

This paper proposes a new hybrid HVDC system with the line-commutated converter (LCC) at the rectifier side and LCC and the modular multilevel converters (MMC) connected in series at the inverter side, where multiple MMCs are connected in parallel. Firstly, two receiver connection modes are discussed, including centralized access and distributed access. The simulation results show that distributed access is helpful to reduce the interaction between the inverter-side LCC and MMC under the receiving-end AC faults. Then, two control modes of parallel-connected MMCs are proposed and compared, which include the fixed DC voltage control and the fixed active power control. The simulation results show that the fixed DC voltage control helps the system recover quickly after the MMC AC-side fault, and the DC current balance control can eliminate the unbalanced current distribution caused by the potential deviation of device parameters.