An AC-DC Coordinated Scheme for Cascaded Hybrid High-Voltage Direct Current to Suppress Wind Power Fluctuations

Given power fluctuations from near-land offshore wind farms, this article designs a coordinated control strategy for cascaded hybrid DC transmission. To suppress the frequency disturbances when wind power varies, supplementary active power control schemes are proposed, in which the coordinated DC voltage control strategy is also considered in order to keep DC voltage stable when the supplementary control prompts a voltage-sourced converter overload. Simultaneously, to further improve wind farm-side AC voltage stability, a dynamic limiter is added in the coordinated control, which can make a voltage-sourced converter release more reactive power when a fault happens. Thereby, the stability of DC-side voltage and active power and AC-side frequency and voltage can all be enhanced through the proposed coordinated scheme. Finally, the electromagnetic transient model of the hybrid high-voltage direct current with renewable power is established using PSCAD X4.6.2 software, and the simulation example is carried out with the model to verify the scheme proposed in this article.