张北柔性直流电网换流阀故障穿越策略与保护定值优化

不同于以往端对端柔性直流工程，应用直流断路器的柔性直流电网要求直流线路故障时换流站可实现故障穿越。文中以张北柔性直流电网工程为背景，首先，建立了直流线路故障时换流阀暂态电流的数学模型；然后，基于传统阀控过流保护策略，分别提出了保证换流阀故障穿越能力的定值设计方法和保证换流阀安全性的定值设计方法，解决了传统的阀控过流保护策略无法兼顾直流线路故障下换流阀的故障穿越能力要求和站内故障时换流阀的安全性要求的问题；最后，提出了基于分桥臂闭锁的新型阀控过流保护策略，并设计了详细的动作时序。在PSCAD中搭建张北柔性直流电网仿真模型，验证了所建立数学模型的准确性和所提出策略的有效性。

Fault Ride-through Strategy and Protection Setting Optimization of Converter Valve for Zhangbei VSC-HVDC Grid

Different from the previous point-to-point voltage source converter based high voltage direct current(VSC-HVDC)project, the converter in a DC grid based on DC breakers is required to ride through a DC fault. Based on the Zhangbei DC grid project, a mathematical model is established to calculate the transient current of the valve when a DC line fault occurs. Then the methods of designing the setting values to guarantee the fault ride-through ability and the safety of the valve are proposed based on the traditional valve overcurrent protection, which solves the problem that the traditional valve overcurrent protection is not able to guarantee the fault ride-through ability and the safety of the valve at the same time. Finally, a novel fault ride-through strategy based on independent arm blocking is proposed, and a detailed time sequence is designed. A simulation model of the Zhangbei VSC-HVDC grid based on PSCAD is established and the accuracy of the established model and the efficiency of the proposed strategy are verified.