Improvement of large scale solar installation model for ground current analysis M. García-Gracia a , N. El Halabi a, * , H.M. Khodr b , Jose Fco Sanz a a CIRCE, Center of Research for Energy Resources and Consumption, C/Maria de Luna 3, 50018 Zaragoza, Spain b GECAD – Knowledge Engineering and Decision-Support Research Center of the Polytechnic Institute of Porto, Portugal article info Article history: Received 27 January 2010 Received in revised form 26 April 2010 Accepted 29 April 2010 Available online 31 May 2010 Keywords: PV installation modeling Ground currents Grounding couplings Large-scale solar installation Current distortion Leakage impedance abstract Application of a simplified PV model to large-scale PV installations neglects the current distortion, poten- tial rise and losses in the system as consequence of the capacitive coupling inside the dc electric circuit. These capacitive couplings represent a leakage impedance loop for the capacitive currents imposed by the high frequency switching performance of power converters. This paper proposes a suitable method to reproduce these harmonic currents injected not only into the grid, but also into the dc circuit of the PV installation. The capacitive coupling proposed of PV modules with ground is modeled as a parallel resistance and capacitor arrangement which leads to an accurate approximation to the real operation response of the PV installation. Results obtained are compared with those of simplified models of PV installations used in literature. An experimental validation of the proposed model was performed with field measurements obtained from an existing 1 MW PV installation. Simulation results are presented together with solutions based on the proposed model to minimize the capacitive ground current in this PV installation for meeting typical power quality regulations concerning to the harmonic distortion and safety conditions and to optimize the efficiency of the installation. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Renewable energy systems are being considered as promising generation sources to cover the continuously increasing demand of energy and to improve reliability of electric power systems [1,2]. In particular, photovoltaic (PV) solar energy has become sig- nificant and attractive due to their availability and compatibility with typical demand curves of distribution networks. However, the extensive dimension required for PV installations leads to develop optimum sizing methods to guarantee the lowest invest- ment with full use of PV arrays, so that the installation can work at the optimum conditions in terms of investment and power sys- tem reliability [3]. In small scale PV installations, the performance of the installation strongly depends on manufactured modules [4]. Otherwise, for large-scale PV installations, electrical parameters, such as the capacitive coupling with grounding systems, become significant because of the high frequency current imposed by the power converters and can affect considerably the behavior of the plant. Based on field measurements, it has been noticed the impor- tance of modeling the PV array with capacitive coupling with the grounding system, to accurately simulate the dc and ac compo- nents of the current waveform measured in the installation. This capacitive coupling is part of the electric circuit consisting of the PV arrays, cables capacitive couplings, ac filter elements and the grid impedance, and its effect is being appreciated in most large- scale PV plants. Due to this capacitive coupling between PV modules and earth, potential differences imposed by switching actions of the converter inject a capacitive ground current [5,6] which can cause significant electromagnetic interferences, grid current distortion, losses in the system, high noise level in the installation and unsafe conditions for work [7,8]. Several PV installation analysis are presented in literature [4,9–11], where most theoretical analysis and experimental verifi- cations have been performed for small scale PV installations with- out considering ground coupling. Converter models and topologies also have been studied [2,12], but without considering the amount of losses produced by the capacitive circuit that appears due to the switching actions. Simplified PV installation models, presented in [13–15], have been evaluated for small scale installations, however the applica- tion of these models to large scale installations neglects the current distortion and losses as consequence of capacitive coupling. In [16], the total conversion losses of a 3 MW PV installation have been studied considering reflection losses, low radiation and shadow losses, temperature losses, auxiliary losses, array losses and con- verters losses. The latter two factors sum a total of 10% of the rated power where part of these losses is due to the capacitive coupling that was neglected in [11]. The paper proposes an improved model for large-scale PV installations that details the capacitive coupling of the electric 0306-2619/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2010.04.031 * Corresponding author. Tel.: +34 976761923 ; fax: +34 976762226. E-mail address: nabileh@unizar.es (N. El Halabi). Applied Energy 87 (2010) 3467–3474 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy