基于MMC主动限流的VSC-HVDC双极短路故障控保协同策略

Collaborative Control and Protection Strategy for Bipolar Short-circuit Fault in VSC-HVDC Based on Active MMC Current Limiting

直流故障保护是柔性直流输电系统发展面临的主要挑战之一,利用模块化多电平换流器(MMC)的灵活控制实现限流已成为当前研究的热点。MMC的主动限流降低了故障电流变化率和故障电流幅值,易引起故障判断以及保护选择困难。文中以对称单极接线的柔性直流系统为研究对象,采用控保协同思想,将主动限流控制与故障识别相结合,提出了基于主动限流因子的故障区域识别与区分方法实现双极短路故障的区域识别与切除。首先,通过在MMC电流内环控制器中附加故障电流目标预设控制器,在故障发生后可快速跟踪故障电流的变化,自适应地调整MMC输出的直流电压将故障电流控制在预设目标参考值附近;其次,根据不同故障位置时故障电流目标预设控制器输出的限流因子快速确定故障区域。最后,在PSCAD/EMTDC中对四端柔性直流输电系统的不同故障场景进行了仿真分析,验证了所提控保协同策略的可行性和有效性。

DC fault protection is one of the main challenges faced by the development of flexible DC transmission systems,and the use of flexible control of modular multilevel converters(MMCs)to achieve current limiting has become a current research hotspot.The active current limiting of MMC reduces the rate of change and amplitude of fault current,which can lead to difficulties in fault diagnosis and protection selection.In this paper,a flexible DC transmission system with symmetrical single-pole connection is taken as the research object.Using the collaborative control and protection strategy and combining the active current limiting control and fault identification,the method for identifying and cutting off fault areas based on active current limiting factor is proposed to achieve the identification and removal of bipolar short-circuit fault areas.Firstly,by adding a fault current target preset controller to the MMC current inner loop controller,the variation of fault current can be quickly tracked after a fault occurs,and the DC voltage output by the MMC can be adaptively adjusted to control the fault current near the preset target reference value.Secondly,the fault area is quickly determined based on the current limiting factors output by the fault current target preset controller at different fault locations.Finally,simulation analysis is conducted in different fault scenarios of the four-terminal flexible DC transmission system in PSCAD/EMTDC,verifying the feasibility and effectiveness of the proposed collaborative control and protection strategy.