混合级联型多落点直流输电系统交流系统故障协调控制策略

混合级联型多落点直流输电系统整流侧为换相换流器（LCC），逆变侧为LCC和模块化多电平换流器（MMC）组串联的拓扑结构，可以有效抑制换相失败，具备大容量功率传输的优势。建立了单极混合级联型多落点直流输电系统，针对系统中LCC送受端交流故障引发的直流功率降低、逆变侧换相失败以及受端低端MMC子系统产生的功率反向问题进行了研究，提出了一种提升系统稳定性的协调控制策略。该策略通过改变逆变侧直流电压来维持交流系统故障后功率传输的稳定性，可防止受端MMC功率反送。PSCAD/EMTDC仿真结果验证了所提协调控制策略的有效性。

Fault Coordination Control Strategy of AC System in Hybrid Cascaded Multi-terminal HVDC System

The hybrid cascade multi-terminal HVDC transmission system adopts the topology structure which has commutation converter （LCC） on the rectifier side， modular multi-level converter （MMC） in series on the inverter side. The system which can effectively suppress commutation failure and has the advantage of large capacity power transmission. A single-level hybrid cascade multi-terminal HVDC transmission system is established. Aiming at DC power reduction caused by AC fault at LCC of rectifier and inverter， inverter commutation failure and power reverse generated by MMC subsystem，a coordinated control strategy is proposed to improve system stability. The stable transmission power of AC system after the fault is maintained by the change of DC voltage on the inverter side， MMC power reverse is prevented . The simulation result obtained in PSCAD/EMTDC shows the effectiveness of the proposed coordinated strategy.