Frequency coupling control approach and stability analysis of sending and receiving-end power grids in MMC-HVDC systems

To avoid the negative impact of modular multilevel converter (MMC) based high voltage direct current (HVDC) systems partitioning on frequency stability, this paper proposes a frequency coupling control method for sending and receiving-ends, and analyzes the system stability after adopting this method. Firstly, for the receiving-end MMC station, a coupling additional control of DC voltage and AC frequency is proposed, mapping the AC frequency change to the DC voltage signal. Secondly, for the sending-end MMC station, the active power additional control is proposed, adjusting the active power command value with the sending-end frequency and DC voltage change. Then, the state-space model of AC/DC system is established to analyze the impact of frequency coupling control on system stability. Finally, the effectiveness of the frequency coupling control method and the correctness of the stability analysis results are verified in a modified IEEE 11-bus system.