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Research on the Impact of DC-line Fault Recovery Squences Control on AC Power Grid at HVDC Sending-end and Corresponding Mitigation Measures

DC-line fault recovery sequences (DFRS) are effective measures to improve the operational reliability of the HVDC transmission system, but these measures will also bring active power and reactive power impacts to the connected AC power grid. The paper first introduces the simulation model of the DC control system and the method to simulate the operation process of DFRS. Then combining with the DC control system model which is based on the actual project, the time domain simulation analysis is carried out to study the impact of the restart process on the AC power grid and the influence of the AC power grid strength and the initial firing angle of DFRS on the impact degree. On this basis, aiming at the risk that the low voltage ride through control function of nearby wind turbines may be triggered due to the low voltage on the sending-end power grid during the process of DFRS, an optimization strategy for DFRS is proposed. Finally, a simulation is performed based on the large-scale wind power grid connected Qishao UHVDC transmission system, and the effectiveness of the optimization strategy to improve the stable operation stability of the power grid is verified by the simulation results.