A Reactive Power Coordinated Control Strategy for Sending-end of Hybrid Cascaded UHVDC System With Grid-connected Large-scale Wind Power

With the continued increase of the proportion of renewable energy generation, the strength of the sending power grid in UHVDC transmission system is weakened and poor voltage quality might exist in AC system at the sending end. To improve the voltage quality of the weak AC system located at the sending end, based on the hybrid cascaded UHVDC system with grid-connected large-scale wind power , a reactive power coordinated control strategy, in which the filter and the modular multilevel converter (abbr. MMC) were coordinately participated into the voltage regulation of power grid sending end, was proposed. The operating characteristic of this cascaded DC system, the principle of reactive power control of the filter and the factors impacting the reactive power supporting ability of MMC under different operating condition were respectively analyzed. In allusion to the insufficient reactive power supporting capacity of MMC for weak AC system under the overloaded operating condition, an adaptive DC voltage control strategy for MMC, which could adjust DC voltage of MMC according to the active power transmitted by MMC to expand the reactive power limit of MMC, was put forward. Results of simulation example show that the proposed reactive power coordinated control strategy can effectively support the voltage of weak AC system located at the sending end and the voltage quality of the AC system can be also improved.