联接变是衔接交直流系统的桥梁,对其故障特性的分析是构建保护方案的重要基础。然而,双馈风电经柔直送出系统中整流侧联接变发生故障时,机侧短路电流呈现出频偏和弱馈故障特性,而阀侧短路电流不仅含有大量谐波,在不同的控制策略下还存在幅值差异、相角差异,甚至会出现断流的情况。如此复杂的故障特性给联接变的差动保护正确动作带来十分严峻的挑战。为此,该文以联接变阀侧发生最为常见的单相接地故障为例,分析双馈风电场柔直送出系统联接变风电场侧及阀侧短路电流故障特性及致使差动保护性能降低的原因。在此基础上,提出分别利用形态学滤波分解及同步挤压小波变换对换变流两侧电流进行处理,并以处理后的两侧电流轨迹图斜率为判据,对区内外故障和涌流进行识别的保护方案。最后,基于PSCAD/EMTDC的仿真结果表明：所提出的方案能很好地对风电联接变区内外故障和涌流进行识别,在不同影响因素条件下该方案也具有良好的适用性。
Abstract
VSC-HVDC interfacetransformer is a bridge connecting AC and DC systems, the analysis of its fault characteristics is critical for protection scheme. However, when MMC of wind farm side （WFMMC） fault occurs in the VSC-HVDC interfacetransformer in double fed induction generators （DFIG） wind farms for voltage source converter based high voltage direct current （VSC-HVDC） transmission, the short-circuit current of DFIG side shows the characteristics of frequency offset and weak feed. The short-circuit current of WFMMC side not only contains a large amount of harmonic, but also amplitude difference, phase difference, and even disconnection under different control strategies. Such complex fault characteristics bring extremely high requirements and severe challenges to the appropriate operation of VSC-HVDC interfacetransformer differential protection. Therefore, this paper selects the most common single-phase grounding fault on the converter transformer WFMMC side for case studies, which analyzes the fault characteristics of short-circuit current on the DFIG wind farms side and WFMMC side. Meanwhile, the reasons for the decline of differential protection performance is also discussed. On this basis, this work proposes a protection scheme to process the currents on both sides of the VSC-HVDC interfacetransformer by using morphological filter decomposition and synchrosqueezed wavelet transforms. Besides, the internal or external faults are identified based on the slope of the current trajectory drawn by processed current. Finally, the simulation results based on PSCAD show that the proposed scheme can identify the faults and inrush currents rapidly and accurately, meanwhile, the scheme also shows good applicability under different influencing.
关键词
风力发电 /
联接变压器 /
双馈风力发电机 /
形态学滤波分解 /
同步挤压小波变换 /
电流二维轨迹
Key words
wind power /
VSC-HVDC interfacetransformer /
doubly-fed induction generator /
morphological decomposition /
synchronous wavelet transform /
two dimensional current trajectory
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基金
国家自然科学基金（52037003）; 云南省重大专项（202002AF080001）
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