柔性直流输电系统新型故障重启方法

摘要

The overhead-line based DC transmission is becoming the developing trend of flexible DC transmission because of the breakthrough of the converter-based DC fault isolating technique.The probability of nonpermanent faults on the overhead line is very large, thus the restart scheme should be configured to increase the supply reliability.However, the conventional restart scheme will lead to the second overcurrent or overvoltage damages, which is detrimental to the safe operation of the system.This paper proposes a novel restart scheme, which makes the converter operate as an uncontrolled rectifier, then the fault property can be determined according to the current characteristic of the DC line.Compared with the conventional restart scheme, the overcurrent and overvoltage problems during the restarting period could be avoided effectively.Finally, cases in point are used via the PSCAD/EMTDC to verify the feasibility and superiority of the proposed restart scheme.%换流器自清除技术的逐渐成熟使得基于架空线路输电成为柔性直流输电的发展趋势.架空线路输电时瞬时性故障概率较大,因此需配置有效的重启方法确定是否应该恢复系统的正常运行.传统的柔性直流输电系统重启方法因重启于永久性故障时会对系统造成二次过流、过压危害,不利于系统的安全可靠运行.提出了一种具有低电流、低电压危害的新型重启方法,在故障性质判断期间将换流器运行于不控整流方式,通过判断电流的有无,实现故障性质的判断.这种方法在重启于永久性故障时能够有效避免对系统的二次过流冲击,也不会产生二次过电压.最后,在PSCAD/EMTDC仿真平台上搭建了两端模块化多电平换流器型直流系统,通过仿真测试验证了所设计重启方法的可行性和优越性.