特高压混合级联系统受端交流故障问题分析

受端混合级联直流输电系统具有经济性高、灵活性强等诸多优势，应用前景十分广泛。当其受端VSC发生交流系统故障时，换流阀功率输送能力减弱，此时，整流站功率持续输出会加剧直流侧的功率盈余，造成VSC换流器电压急剧升高。故障结束后，系统需要较长时间恢复功率正常输送，严重影响系统的正常运行和稳定性。针对特高压混合级联系统受端换流器发生交流故障时直流侧过电压问题及故障结束后的功率恢复问题，提出了电压-功率协同控制策略及基于受端交流电压变化的交流低压限流控制策略。最后采用真实控制保护装置搭建基于RTDS仿真系统的硬件在环仿真平台，验证了所提策略的可行性。

Analysis of AC faults in the receiving-end of a hybrid cascaded multi-terminal HVDC system

The receiving-end hybrid cascaded multi-terminal HVDC system has a wide range of application scenarios because of its economy, flexibility and many other advantages. When an AC system failure occurs in receiving-end of an inverter VSC station, the power transmission capacity of the VSC is weakened, and during the fault, the continuous output power of the rectifier station will aggravate the power surplus on the DC side, resulting in a sharp increase in VSC converter voltage. After the failure, the system takes a long time to restore power to normal delivery, seriously affecting the normal operation and stability of the system. Aiming at the problem of overvoltage on the DC side and the power recovery problem when the AC fault occurs in the receiving end converter of the hybrid cascaded multi-terminal HVDC system, this paper proposes a voltage-power coordinated control strategy and an AC low voltage based on the change of the receiving end AC voltage. It uses real control and protection devices to build a hardware-in-the-loop simulation platform based on the RTDS simulation system, which verifies the feasibility of the proposed strategy. This work is supported by the Major Science and Technology Project of Henan Province: Research on Key Technologies and Equipment Development of VSC-UHVDC Power Transmission (No. 191110210900).