Mid-high frequency suppression strategy based on damping control in offshore wind farms.

The interactive coupling between the AC submarine cable line in the MMC-HVDC(modular multilevel converter High Voltage Direct Current) grid-connected system and the fast dynamic control links such as wind turbine current control and MMC feedforward control is easy to cause medium-high frequency oscillation in the grid-connected system. Moreover, the traditional active damping control parameters are difficult to match and cannot adapt to all operating environments. To solve this problem, a high frequency stability enhancement control strategy based on active damping control for grid-connected systems is proposed. Firstly, the high frequency equivalent impedance model and the wide frequency impedance model on the AC side of MMC are established. Secondly, based on MMC side active damping control, the filter controller of AC voltage and current is introduced to improve it, and an improved active damping control strategy based on feedforward link is proposed. Finally, the effectiveness of the proposed strategy is verified by changing the cable parameters.