基于改进子模块的MMC-HVDC直流侧故障隔离研究

Research on Fault Isolation of MMC-HVDC DC Side Based on Improved Sub-Module

架空线路场合下的高压直流输电系统(HVDC)故障率较高。当前,混合式直流断路器存在容量小、成本高等问题,使得具备故障自清除能力的子模块成为解决系统直流侧故障的最佳解决方案,但上述方案使用了更多电力电子器件,带来了损耗增大,投资成本增加等问题。为此提出一种新型混合方式的模块化多电平换流器(MMC)子模块拓扑结构,在不影响自清除故障能力的前提下减少了所需电力电子器件,提高其经济性和直流侧故障隔离性能。首先给出了将新型子模块与传统半桥子模块在桥臂中合理搭配的设计方案;其次,探究了改进型拓扑结构极对极短路故障穿越机理及子模块构建的经济性性优化方法。最后,基于PSCAD/EMTDC平台搭建了双端MMC-HVDC模型,对提出的子模块性能及其混合型MMC性能进行仿真验证。结果表明,提出的改进子模块及相应的混合型MMC可快速阻断故障电流,具备良好直流故障隔离能力,且具有更好的经济性,在实际工程中上具有良好的应用前景。

The high-voltage direct current transmission system(HVDC)has a high failure rate in the case of overhead lines.At present,the hybrid DC circuit breaker has the problems of small capacity and high cost,which makes the sub-module with fault self-clearing capability the best solution to solve the DC side fault of the system.However,this solution uses more power electronic devices,which brings Loss increases,investment costs increase and other issues.To this end,this paper proposes a new hybrid modular multi-level converter(MMC)sub-module topology,which reduces the required power electronic devices without affecting the self-clearing fault capability,and improves its economy and DC side fault isolation performance.The paper firstly presented the design scheme of reasonably collocating the new sub-module with the traditional half-bridge sub-module in the bridge arm.Secondly,the pole-to-pole short-circuit fault ride-through mechanism of the improved topology and the economic optimization of the sub-module construction were discussed.Finally,a double-ended MMC-HVDC model was built based on the PSCAD/EMTDC platform,and the performance of the proposed sub-module and its hybrid MMC were simulated and verified.The results show that the proposed improved sub-module and the corresponding hybrid MMC can quickly block the fault current,have good DC fault isolation ability,better economy,and a good application prospect in practical engineering.