Active Power Limitation of Windfarm Generation Transmitted Through MMC-HVDC Systems

High-voltage DC systems based on modular multilevel converters (MMC-HVDC systems) are suitable for integrating power generation of renewable energy. However, once the transmission power exceeds the limitation, the system becomes unstable. This paper puts forward a way to figure out the power limitation. First, the equivalent circuit of sending-end system, which consists of renewable energy, the grid-connected inverter as well as the sending-end MMC, is established. Then, the power of the sending-system is calculated, and the maximum value of active power can be obtained. In addition, the qualitative explanation of the system instability mechanism is provided when the active power goes beyond the limitation. Finally, the transmission of renewable energy via modular multilevel converters (MMC-HVDC systems) is constructed on the PSCAD/EMTDC simulation platform. The calculation value of active power limitation is close to the simulation value, indicating the correctness of the analysis and calculation in this paper.