柔性高压直流环网直流侧故障保护策略研究

Studies on DC Fault Protection Strategies for MMC Based HVDC Grid

直流故障保护问题是当前高压直流电网发展过程中所面临的关键技术问题之一。针对直流断路器在应用于高压直流电网故障保护时,可能面临直流故障发展迅速且有时难以区分的问题,该文研究了基于直流断路器附加电感的直流电网故障保护策略及其附加电感值的选取方法。通过对四端直流环网的直流极间短路故障特性进行分析,提出了由附加电感电压和模块化多电平换流器直流侧电压组合而成的直流断路器动作判据。由于该判据中所涉及参数都由本地测量实现,它具有不依赖于异地信号实时通信的特点。通过在Matlab/Simulink仿真平台上建立的四端直流环网模型所进行的仿真分析表明:该故障保护策略可以"有选择"地准确隔离故障线路或母线,并保证非故障部分在故障扰动后维持正常运行工况,且其不受故障位置、功率反转、控制方式和短路电阻的影响,并在不同结构的直流电网中具有较好的通用性。

DC fault protection is one of the key technologies in the development of HVDC grid. In view of the DC circuit breaker(DCCB) based HVDC grid fault protection method, this paper first studies the DC grid fault protection strategies based on DCCB's auxiliary inductor and the selection method of auxiliary inductor for DCCB. Then DC pole-to-pole short circuit fault characteristics were analyzed through a 4-terminal meshed HVDC grid. On this basis, this paper proposed the operating criteria of DCCB by using the combination of auxiliary inductor voltage and MMC DC voltage. In particular, all these criteria are measured by local measurements and independent of the real-time communication system. Finally, a model of 4-terminal meshed HVDC grid is built on Matlab/Simulink simulation platform, and the simulation results showed the fault protection strategy can selectively isolate faulty lines and buses, and ensure the healthy part can maintain normal operation. Also, the proposed strategy is not affected by fault location, power reversal, operation mode and short-circuit resistance, having a good versatility in HVDC grids with different structure.