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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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

Received: 07 August 2024

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TM615

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	Lu Geye
	Zheng Dayong
	Lin Qiuqiong
	Yin Zheng
	Zhang Pinjia

Cite this article:

Lu Geye,Zheng Dayong,Lin Qiuqiong等. CM Impedance Characteristics Analysis and Equipment Condition Diagnosis in Photovoltaic Grid-Connected System based on Leakage Current[J]. Transactions of China Electrotechnical Society, 0, (): 250426-.

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