基于改进过压限制器和ACDTS的混联半波长系统故障保护策略

交直流混联半波长输电系统的暂态特性与常规的混联系统存在着很大差异。当混联系统半波长沿线发生不对称故障时，直流系统会受到沿线工频过电压和过电流的冲击。文章详细分析了混联系统半波长沿线故障的传播过程，研究了故障传播耦合机理。针对直流侧过电压问题，提出了在直流母线侧加装改进过压限制器，增设辅助限压通道，分级抑制直流侧过电压，并降低单个通道的电流值，提高了系统保护的限压水平；另一方面，对于直流侧过电流问题，提出了在换流站接口端并联接入双向晶闸管，实现交流系统等效三相短接，隔离交流侧母线馈入的故障过电流，确保换流站设备及线路的安全性。最后利用仿真验证了两种保护策略的可行性。

Research on the coupling mechanism and protection strategy of AC side short circuit fault in hybrid half-wavelength system

The transient characteristics of AC/DC hybrid half-wavelength transmission system is quite different from conventional hybrid system. When an asymmetric fault occurs along the half-wavelength line of the hybrid system, not only will the power-frequency overvoltage be formed along the line, but also the dc side will be impacted by over-voltage and over-current. In view of the above phenomenon, this paper analyzes the propagation process of the fault along the half-wavelength line of the hybrid system in detail, and studies the coupling mechanism of fault propagation. In order to suppress the influence of fault effectively, an improved over-voltage limiter is installed on the dc bus and a bi-directional thyristor is connected in parallel at the interface of the converter station to cut off the fault propagation channel. Finally, the simulation model of AC/DC hybrid half-wavelength system was built on the PSCAD simulation platform, and the voltage and current changes before and after the system protection were compared to verify the feasibility of the protection strategy.