Grid-forming Control of VSC-HVDC Systems Connecting Asynchronous Power Grids

Interconnecting asynchronous power grids with the VSC-HVDC transmission is an important trend. To enhance the weak grid operation performance and grid frequency response capability of the VSC-HVDC system, a novel grid-forming without using the phase-locked-loop is applied in both ends of the VSC-HVDC system. The DC voltage-Active power droop-based grid-synchronization method is utilized. With the proposed method, the sending and the receiving end MMCs perform like a synchronous motor and a synchronous generator, respectively. When the frequency changes in either grid, the system can automatically response to it and change the active power transmission by VSC-HVDC to achieve primary frequency regulation and active frequency support. Finally, the validity of the dual-end grid-forming control is verified based on the simulations in PSCAD/EMTDC.