Oscillation Risk Assessment for a Dual-infeed MMC-HVDC System Using Impedance Network Modeling and Aggregation

As the modular multilevel converter based high voltage direct current (MMC-HVDC) technology is increasingly applied, the inverter buses of multiple MMC-HVDC links may be in close proximity, complicating the system oscillation issues. Conventional methods may fail to adequately assess the stability of such complex AC-DC systems. To fill this gap, this paper develops an oscillation risk assessment method for dual-infeed MMC-HVDC systems. An impedance network model including AC/DC networks’ impedances and MMCs’ three-port impedances is established, reflecting the AC and DC side dynamics and their coupling interactions. Besides, a calculation method for MMC's DC/AC-port equivalent impedances is proposed. Further, the impedance model aggregation and oscillatory mode analysis are presented. The effectiveness of the proposed method is verified by simulations.