适用于MMC直流电网的源网配合式电容型直流断路器

Source-network Coordination Type DC Circuit Breaker Based on Pre-charged Capacitors for MMC DC Grid

为充分发挥模块化多电平换流器(modularmultilevel converters,MMC)的控制能力,解决直流断路器(direct current circuit breaker,DCCB)开断电流和开断速度要求高、造价昂贵等问题,文中提出一种适用于MMC直流电网的源网配合式电容型DCCB。预充电电容是该DCCB最主要的部分,安装于每条直流出线上。所提DCCB利用MMC主动调压控制策略,在故障期间自适应调节子模块投入数量,使换流器直流出口电压与预充电电容电压相等,从而为快速机械开关提供低电压、零电流分断条件。文中详细介绍所提DCCB的拓扑结构、MMC主动调压控制原理、所提DCCB工作原理及其控制时序,并给出所提DCCB元件参数的设计方法。最后,在PSCAD/EMTDC中搭建四端MMC柔性直流电网模型,通过仿真及对比验证该方案的有效性。

In order to give full play to the control ability of modular multi-level converters(MMC)and solve the problems of high breaking current and breaking speed and high cost of DC circuit breakers(DCCB),this paper proposed a sourcenetwork coordination type DCCB based on pre-charged capacitors for MMC DC grid.Installed on each DC outlet line,the pre-charged capacitor is the most important part of the DCCB.The proposed DCCB used the MMC active-voltageregulation control strategy to adaptively adjust the number of sub-module inputs during the fault period to make the DC outlet voltage of the converter equal to the pre-charged capacitor voltage,thereby providing zero voltage and zero current for fast mechanical switching Breaking conditions.This paper introduced the proposed DCCB topology,MMC active-voltage-regulation control principle,the proposed DCCB working principle and control sequence in detail,and gave the DCCB component parameter design method.Finally,a four terminal MMC DC grid model was built in PSCAD/EMTDC.The effectiveness of the proposed DCCB was verified by simulation and comparison.