Research on Coordinated Reactive Power Control Strategy for Hybrid Cascaded UHVDC Transmission System at Sending End

In the current hybrid cascaded UHVDC transmission system, the coordination between the line commutated converter (LCC) and the voltage source converter (VSC) is insufficient in terms of reactive power control. To fully utilize the VSC's capabilities in reactive power compensation and harmonic suppression, two kinds of coordinated strategy are proposed in this paper. Firstly, a coordinated reactive power control strategy of the VSC aimed at reducing tap changer operations of the LCC's transformer is proposed. Additionally, to prevent the problems such as degradation of filtering performance and power runback caused by the unavailability of certain AC filters, this paper introduces a strategy that leverages the VSC and shunt capacitors to replace the function of the unavailable filter. In the end, a simulation system based on RTDS and real control devices is built for the hybrid cascaded UHVDC transmission system studied in this paper and the simulation results prove the validity of the proposed control strategies.