基于联络通道电流检测的多馈入直流系统同时换相失败预防控制

受多馈入直流系统中各直流输电线路之间耦合特性影响，单一交流故障产生的谐波分量通过交流系统对多回直流线路进行干扰，易引发同时换相失败。基于换流器开关调制理论建立交流故障暂态过程中多馈入直流系统内谐波传变回路模型，分析谐波分量的产生机制和传变路径，分析交流故障导致多馈入直流系统发生同时换相失败的机理。将故障后多馈入直流系统内换相的动态演变过程划分为不同阶段，总结各阶段的换相特征发现，近端换流站发生换相失败后，通过交流侧联络通道扩散的故障电流分量引发同时换相失败的关键因素。提出基于联络通道电流检测的同时换相失败预防控制策略，通过检测联络通道异常电流使远端换流站对近端换流站发生的换相失败快速反应以减小发生同时换相失败的风险。以河南特高压多馈入直流系统为例进行仿真验证，仿真结果证明了所提控制策略的有效性。

Prevention control of concurrent commutation failure of multi-infeed DC system based on tie-line current detection

Due to the coupling characteristics among DC transmission lines in multi-infeed DC system, the harmonic components induced by an AC fault interfere with multiple DC lines through AC system, which easily leads to CCF(Concurrent Commutation Failure). The model of harmonics propagation circuit in the multi-infeed DC system during AC fault transient process is established based on converter switching modulation theory. The generation mechanism and propagation path of harmonic components are analyzed, and the mechanism of CCF caused by AC fault in multi-infeed DC system is deduced. The dynamic commutation process after the fault is divided into several stages, and the characteristics of each stage are concluded. It is found that the harmonic currents spreading through the tie-line in AC side can be a vital factor of CCF. A CCF prevention control strategy based on tie-line current detection is proposed, which makes the remote converter station react quickly to the commutation failure of local converter station by detecting the abnormal current of tie-line current to reduce the risk of CCF. Taking Henan multi-infeed UHVDC(Ultra High Voltage Direct Current) system as an example, the effectiveness of the proposed strategy is verified by the simulation results.