Research on the Resonance Analysis of Clustered Grid-connected Distributed Photovoltaic System based on the Wavelet Decomposition

Abstract

The coupling interaction between multiple grid-connected inverters, inverters and grid in the clustered grid-connected distributed photovoltaic (PV) system can cause series and parallel harmonic resonance in the grid. The power quality of grid is seriously affected. Therefore, the resonance problem of the clustered grid-connected distributed PV is urgent to be studied. Aiming at this problem, a resonance analysis model of clustered grid-connected distributed PV system is established in this paper. Besides, the resonance problem of clustered grid-connected distributed PV system during its operation is analyzed. Moreover, a fast resonance detection method based on Wavelet Decomposition is proposed. Finally, simulations verify the effectiveness of the proposed method for the resonance problem of the clustered grid-connected distributed PV system. Introduction In recent years, the global energy crisis and environmental problems have become increasingly serious. Renewable energy such as photovoltaic (PV) is getting more and more attention. PV grid-connected system is becoming more widely used with the continuous reduction of the cost of PV cells [1]. In distribution network, the types of distributed generations and nonlinear wavy loads are complex. Particularly, the output power of wind turbines and PV cells is fluctuant, random, and intermittent, which often leads to the power unbalance between source and load in the distribution network. In addition, a large number of harmonics and inter harmonics are generated because of extensive application of a large amount of electric power electronic equipments. As mentioned above, resonance and other power quality problems are becoming more complex and prominent in the distribution network [2, 3]. Therefore, the research of resonance in the clustered grid-connected distributed PV system has important theoretical value and urgent practical significance. Distributed PV sources are connected to distribution network via inverters, which may cause multiple power quality problems in the grid, such as voltage and current harmonics, voltage sag, voltage swell, voltage interruption, voltage fluctuation and flicker, voltage and current imbalanced component and resonance. A large number of distributed PVs are connected in the distribution network, so the harmonic and resonance of the distribution network must have various spectrums. At the same time, the voltage fluctuation and flicker signal in the network are random and dynamic non-stationary signals [4]. As for resonance disturbance detection of clustered grid-connected distributed PV system, it is needed to propose a detection method to analyze not only the harmonic and resonance signal, but also the nonlinear and non-stationary signals. The closed-loop control of both voltage-source converter (VSC) and current-source converter (CSC) systems with LC filters is investigated in [5], with a focus being put on the damping of LC resonance. Paper [6] designs a virtual harmonic resistance based active damping method to mitigate the resonances. And paper [7] presents that compared with traditional Fourier transform and short-time Fourier transform (STFT), the Wavelet Decomposition has the time-frequency local characteristic and it is adaptive. Therefore, the Wavelet Decomposition method is suitable for the resonance disturbance detection of clustered grid-connected distributed PV system. 3rd International Conference on Machinery, Materials and Information Technology Applications (ICMMITA 2015) © 2015. The authors Published by Atlantis Press 1064 In this paper, a simple introduction of the clustered grid-connected distributed PV system is presented. Application principle of Wavelet Decomposition in the clustered grid-connected distributed PV system is briefly introduced. Wavelet Decomposition algorithm is used to detect and analyze the resonant voltage and resonant current problem in the clustered grid-connected distributed PV system. Simulations are carried out in MATLAB/ SIMULINK. Resonance Analysis of Clustered Grid-connected Distributed PV System A. Structure of clustered grid-connected distributed PV system Fig.1 shows the grid-connected PV power generation system. Grid-connected distributed PV units or distributed generations n are connected to the point of common coupling (PCC) through the line i . And it is connected to the distribution network whose internal impedance is g Z [8]. Distribution network