混合直流输电系统直流故障处理策略比较分析

基于电网换相换流器(line commutated converter,LCC)以及模块化多电平换流器(modular multilevel converter,M M C))的混合型高压直流输电技术是实现远距离大容量输电的有效技术手段。为了快速清除直流短路故障,主要有2种实现方法:一是逆变侧换流器采用具有直流故障自清除能力的子模块,如全桥型子模块及箝位双子模块;二是在逆变侧直流出口加装大功率二极管以切断故障后的电流流通通路。该文通过研究不同直流故障处理策略的物理机理及控制流程,对其可行性及适用性进行深入研究。通过在PSCAD/EMTDC中搭建典型模型,考察直流故障下的系统响应特性,对不同处理策略下的系统暂态特性进行综合比较。最后,对基于全桥型子模块的不闭锁穿越式直流故障处理策略进行了仿真验证,仿真结果表明此种策略不适用于真双极直流系统,无法实现直流短路故障的有效清除。

Analysis and Comparison of DC Fault Handling Strategies for Hybrid HVDC System

The hybrid high voltage direct current (hybrid HVDC) transmission system based on line commutated converter (LCC) and modular multilevel converter (MMC) is a feasible solution for long distance bulk power transmission.In order to handle the DC short-circuit fault,two kinds of methods can be adopted.The first one is to use the sub-modules (SMs) which have the capability of DC-fault clearance in inverter side converter,such as full-bridge SMs and clamp-double SMs.The second one is to arrange high-power diode at the MMC DC port to cut off the current flow path after the fault.Through analyzing the physical mechanism and control flow of different DC fault handling strategies,this paper studies its feasibility and applicability.The typical testing system is built in PSCAD/EMTDC,the system response under DC fault is investigated,and the system` transient characteristics under different strategies are compared.In addition,the non-block DC-fault-handling strategy based on full-bridge SMs is simulated and verified.The results show that this kind of solution is not suitable for the bipolar HVDC system and the DC fault current can not be blocked thoroughly.