基于漏电流的光伏并网系统共模阻抗特性分析与装备状态诊断

doi:10.19595/j.cnki.1000-6753.tces.241409

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摘要

漏电流是表征光伏发电与并网系统健康状况最直观有效的特征量之一。漏电单元测量结果涵盖了交、直流侧各装备对地状态老化情况,尚不能完成独立诊断。本文构建了基于漏电流的系统级宽频共模阻抗模型,揭示了光伏阵列对地漏电状态、连接电缆和升压器对地绝缘老化状态对宽频共模阻抗特性的影响机理,映射了漏电流幅频特性与各装备对地等效电容的量化关系。根据工程应用中量测单元配置要求,提出了一种基于漏电流的系统共模阻抗模型与利用方法,实现了交、直流侧对地健康状态的解耦分析与独立诊断。在线测试结果表明,直流侧对地寄生电容计算误差小于4 %,交流侧主设备对地绝缘等效电容计算误差小于2 %。

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	陆格野
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关键词 ：光伏发电, 漏电流, 特征谐波, 共模阻抗, 状态诊断

Abstract：

Photovoltaic (PV) power generation is expected to be a major energy source in the future. However, the first batch of globally installed PV assets has now entered the late stage of their service life, with increasing frequency of faults and growing prominence of operation and maintenance issues.The leakage current is an effective indicator for the health condition of PV power generation and grid-connected system. It is challenging to realize online condition diagnosis of equipment on both AC and DC sides. The core innovation of this paper is the proposal of a common-mode (CM) impedance model of PV power generation and grid-connected systems and the leakage-current-based utilization method for decoupled analysis and independent diagnosis of the grounding conditions of equipment on AC and DC sides.
First, since the PV grid-connected inverter can generate characteristic harmonics in output voltage, the online diagnosis mechanism of equipment ground-wall (GW) condition is investigated using CM characteristic harmonic components. The leakage current path of equipment in PV system is analyzed. The leakage current not only flows in the parasitic capacitance of PV panel to the ground, but also flows in the GW branches of AC equipment, which reflects the coupling effect between AC and DC sides.
Second, the CM equivalent circuit of PV system is built. There are four parts, namely the equivalent capacitance of PV array to the ground, the equivalent electrical parameters of LCL filter, the GW insulating capacitances of cable and transformer. Once the electrical parameter is changed, the measuring result i_meais affected. In other words, i_mea can reflect not only the leak state of PV array but also the GW ageing condition of AC equipment. The changes of frequency-amplitude curves can indicate the grounding conditions of equipment on both AC and DC sides. Besides, the ratio of Icm mea and Icm 1, defined as relation H₁, is proposed. H₁is clarified with effects by the change of Zcm ac but nothing to do with the leak state of PV array.
Third, the leakage-current-based diagnosis strategy is proposed to realize the decoupling and independent diagnosis of equipment conditions on AC and DC sides. The ratio H₁ at f_c has nothing to do with the leak state of PV array but can only reflect the change of GW insulating ageing condition on AC side. Two broadband CM impedance spectra (Zcm ac and Zcm sys) can be calculated and their linear segments can be used to calculate the total equivalent GW insulating capacitances of cable and transformer.
Fourth, the simulation and online experiments are conducted to validate the proposed method effectiveness. The conclusions are drawn. For one thing, Zcm sys and Zcm ac in linear segment can quantify the leak state of PV array and the GW insulating ageing condition of AC equipment, respectively. Online experiments show that the diagnosis error of each side is less than 2 % and 4 %, respectively. For another, H₁ can avoid the effect of leak state of PV array but can significantly decrease with the GW insulating ageing condition of AC equipment. Hence, since the effect on the measured leakage current is decoupled, independent diagnosis of PV array and equipment on AC and DC sides is enabled based on the proposed method in this paper.

Key words： Photovoltaic power generation leakage current characteristic harmonics CM impedance condition diagnosis

收稿日期: 2024-08-07

PACS:

TM615

基金资助:

中央高校基本科研业务费专项资金（2024XKRC033）和国家自然科学基金（52207208,52307063）资助项目

通讯作者: 陆格野女,1993年生,副教授,硕士生导师,研究方向为新能源系统与装置状态监测与故障诊断。E-mail：gylu@bjtu.edu.cn

作者简介: 郑大勇男,1994年生,博士,副教授,研究方向为电气设备状态在线监测。E-mail：10283@bjtu.edu.cn

引用本文:

陆格野, 郑大勇, 林秋琼, 尹政, 张品佳. 基于漏电流的光伏并网系统共模阻抗特性分析与装备状态诊断[J]. 电工技术学报, 0, (): 250426-. Lu Geye, Zheng Dayong, Lin Qiuqiong, Yin Zheng, Zhang Pinjia. CM Impedance Characteristics Analysis and Equipment Condition Diagnosis in Photovoltaic Grid-Connected System based on Leakage Current. Transactions of China Electrotechnical Society, 0, (): 250426-.

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