Setting-Less Nonunit Protection Method for DC Line Faults in VSC-MTdc Systems
Setting-Less Nonunit Protection Method for DC Line Faults in VSC-MTdc Systems
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DOI：
10.1109/tie.2021.3050380
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发表时间：
2022-01
影响因子：
7.7
通讯作者：
Chenhao Zhang;G. Song;A. Meliopoulos;Xinzhou Dong
中科院分区：
文献类型：
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作者：
Chenhao Zhang;G. Song;A. Meliopoulos;Xinzhou Dong
现有的单元化保护方案不可避免地需要整定，这在实际工程中是一个严重的问题。发生在不同断裂带上的断层会产生不同的等效模型，因此，可以通过识别断层与哪种等效模型匹配来确定断裂带。本文将“模型识别”思想引入到故障识别中，提出了一种“免整定”保护方法。首先，给出了后向外区、内区和前向外区发生故障时的Peterson等效电路。在此基础上，推导出相应的三种故障电压表达式，定义为三种故障模式。然后，利用这三种故障模式，采用Levenberg-MarQuardt最优逼近法对实测故障电压进行逼近。将最符合测量故障电压的故障模式识别为最终确定的故障模式，无需设置阈值即可进行故障识别。在PSCAD/EMTDC和实时数字仿真器等电力系统暂态过程中进行的大量试验研究表明，该方法适用于不同的多端直流系统，在不同的故障位置、不同的故障类型和高的故障阻抗下都是有效的。该方法对采样频率要求不高，对测量噪声具有较好的鲁棒性。
Existing nonunit protection schemes inevitably require setting, which is a serious problem in practical engineering. Faults occurred at different fault zones will result in different equivalent models, therefore, the fault zone can be determined by recognizing which equivalent model the fault fits well with. In this article, this “model recognition” idea is introduced in fault identification and a “setting-less” protection method is proposed. First, the Peterson equivalent circuits when faults occur at backward external zone, internal zone, and forward external zone are presented, respectively. Accordingly, the corresponding three fault voltage expressions are derived, which are defined as three fault modes. Then, the three fault modes are used to approximate the measured fault voltage using Levenberg-Marquardt optimal approximation method. The fault mode that best fits the measured fault voltage is recognized as the final determined fault mode, which is used for fault identification without setting threshold value. Numerous test studies carried out in Power Systems Computer Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC) and real-time digital simulator have demonstrated that the proposed method can be utilized for different multiterminal dc systems and is effective under different fault locations, different fault types, and high fault impedances. The proposed method does not require high sampling frequency and has good robustness against measuring noise.