MMC-HVDC双极故障条件下自适应限流控制策略

Adaptive current limiting control strategy for MMC-HVDCunder bipolar fault conditions

直流断路器(direct current circuit breaker,DCCB)广泛应用于柔直输电系统,其造价与开断电流密切相关。文中从减小断路器开断电流的角度出发,设计适用于半桥型模块化多电平换流器(modular multilevel converter,MMC)的自适应限流控制结构。在分析MMC直流侧短路电流特性的基础上,利用换流站输入阻抗幅值的变化反映其故障深度,定义换流站故障深度系数K f;将K f引入MMC控制结构,使其与桥臂电压参考值关联,提出针对MMC直流侧短路故障的自适应限流控制方法;在PSCAD/EMTDC平台搭建半桥型MMC柔直输电系统模型,模拟直流侧短路故障清除过程,验证限流控制的有效性。仿真结果表明:文中提出的限流控制方法可依据MMC不同故障深度,实现差异化限流控制,减小DCCB开断电流,提升故障清除速度。

Direct current circuit breakers(DCCBs)are extensively utilized in flexible DC transmission systems,with their cost being intricately related to the breaking current.An adaptive current-limiting control structure tailored for half-bridge modular multilevel converters(MMCs)has been developed with the aim of reducing the breaking current of circuit breakers.By examining the short-circuit current characteristics on DC side of MMC,the variation in the input impedance amplitude of the converter station is utilized to indicate the extent of the fault.The coefficient K f,which defines the fault depth of the converter station,is determined.K f is incorporated into the control structure of MMC to align it with the reference value of the bridge arm voltage.A proposed method for adaptive current limiting control addresses DC side short circuit fault of MMCs.The model of the half-bridge MMC flexible DC transmission system is created using power systems computer-aided design/electromagnetic transients including DC(PSCAD/EMTDC)platform to model the clearance of DC side short-circuit faults and validate the effectiveness of current limiting control.The simulation results demonstrate that the proposed adaptive current limiting control technique can effectively implement differentiated current limiting control depending on the diverse fault depths of MMC.The breaking current of DCCB is reduced and the fault clearing speed is improved by this approach.