摘要
基于架空线路的柔性直流电网多发瞬时性故障,重合闸是提高系统供电可靠性的必要手段,但容易造成系统二次过流和过压危害,严重影响系统安全运行。文中首先提出了一种简单、有效的重合闸限流电阻计算方法,通过估计桥臂最大电流来建立限流电阻和桥臂电流之间的约束关系,从而将桥臂电流限制在一定过流水平,减少重合闸期间换流站的闭锁时间。然后,分析了换流站端口过电压的产生原因,并提出了一种由晶闸管和吸能电阻构成的限压电路。该电路并联在桥臂电抗两端,能够在直流断路器动作时刻为桥臂电抗提供额外的电流通路,有效抑制系统的暂态过电压。最后,基于PSCAD软件搭建一个三端环形测试系统,大量仿真结果证明了所提方法的有效性。
Temporary faults often occur on overhead transmission lines of flexible DC grid, so reclosing scheme is the key measurment to inprove the reliability of power supply. However, reclosing may result in overcurrent and overvoltage again, and thus influence the safe operation of the system. A simple and effective calculation of the reclosing current limiting resistance is first proposed. The constraint relation between the arm current and current limiting resistance is established by estimating the maximum arm current, so the overcurrent in the bridge arm of the converter can be limited to a reasonable level and the converter blocking time can be avoided during reclosing. Then, the cause of overvoltage across the converter is analyzed, and a novel voltage limiting circuit, which composed of a thyristor and energy absorption resistance is proposed, which is in parallel with the arm reactor and can provide additional current path for arm reactor when the DC circuit breaker trips. Consequently, the transient overvoltage of the system can be prevented effectively. At last, a three-terminal DC test system with ring topology is modeled in PSCAD software, and a large number of simulation results verify the effectiveness of the proposed method.
引文
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