Abstract
With the high penetration of photovoltaic systems, the interaction between grid-tied inverters and line impedances results in harmonic resonance at point of common coupling (PCC) in high-power photovoltaic (PV) plants. Thus far, most publications have reported about this issue from a theoretical perspective, and there is no field verification in a real PV plant. To fill this gap, field waveforms are captured in a high-power PV plant to figure out the mechanism of the harmonic resonance phenomenon. This paper, for the first time, presents a nonlinear self-oscillation concept to clarify the mechanism of the harmonic resonance in a high-power PV plant. The field harmonic measurement of a grid-tied PV plant is carried out. The analysis of harmonic spectra and current distributions in a photovoltaic plant shows that these harmonic characteristics are different from the signals generated by the resonances of PV inverter output filters. The correlation of frequency, phase sequence and amplitude show that the different harmonics at PCC are generated by the same source inside PV inverters. Based on the comparison of PCC harmonics with periodic steady-state outputs of nonlinear systems, the nonlinear self-oscillation concept is proposed to clarify the mechanism of the harmonic resonance in a high-power PV plant. The tests in field and signal analysis verify the effectiveness of the proposed method and solution.
Highlights
Due to fossil fuel depletion and environmental pollution around the world, the development of renewable energy, such as wind and photovoltaic, has attracted much attention [1,2,3,4]
It is proposed that the inter-harmonics at point of common coupling (PCC) of PV plant in field were generated by nonlinear
This paper has proposed the nonlinear self-oscillation concept to clarify the mechanism of the harmonic resonance in a real high-power PV plant
Summary
Due to fossil fuel depletion and environmental pollution around the world, the development of renewable energy, such as wind and photovoltaic, has attracted much attention [1,2,3,4]. The distributed generation (DG) systems based on renewable energy can be connected in parallel with each other to form a micro-grid. The analysis of field data of photovoltaic (PV) plants indicates that the harmonics at point of common coupling (PCC) in weak grid can exist stably for a long time and the line impedances of low-voltage power distribution systems cannot be ignored [5]. Harmonics in micro-grid may cause abnormality of distribution system and even damage of power facilities, further reducing power quality and even causing the shutdown of PV inverters [6]. With the high penetration of nonlinear power electronics devices, the impact harmonic resonance between inverters and grid is more complicated. Many studies are only implemented for a single power electronic equipment and single renewable energy
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