Abstract—More PV systems have been connected to the electrical network each year. As the number of PV systems increases, some issues affecting grid operations have been identified. This paper studied the impacts related to changes in solar irradiance on a distribution/sub-transmission network, considering variations due to moving clouds and daily cycles. Using MATLAB/Simulink software, a solar farm of 30 MWp was built and then implemented to a test network. From simulations, it has been determined that irradiance changes can have a significant impact on the grid by causing voltage fluctuations outside the allowable thresholds. This work discussed some local control strategies and grid reinforcements to mitigate the negative effects of the irradiance changes on the grid. Keywords—Utility-scale PV systems, reactive power control, solar irradiance, voltage fluctuation. I. INTRODUCTION HE global cumulative capacity of photovoltaic (PV) generation has increased exponentially in the last ten years, reaching 178 GW in 2014 [1]. In the following years, the number of PV systems will continue to increase and PV cumulative capacity will likely exceed 400 GW worldwide by 2020 with China, Germany, USA and Japan as major markets [2]. In Brazil, the growth of PVs has not followed the international trend. By October 2015, PV systems contributed to only 0.02% of the total electric generation in the country [3]. However, the electricity market operator (CCEE) announced thirty-one new solar farms with an overall capacity of 889 MWp by 2017. These projects will be mainly located in the states of Bahia (14 projects) and São Paulo (9 projects). Moreover, twenty-nine of them will have a capacity of 30 MWp [4]. The increasing number of PV systems connected to the electrical network has caused impacts on grid operations. According to [5], when PV generation exceeds the local load of a distribution network, reverse-power-flows occur toward upstream voltage levels resulting in voltage rises. Moreover, uncertainty and variability of PV power can affect the operation of the grid regarding voltage regulation. These issues are related to changes in solar irradiance due to daily cycles and meteorological phenomena, such as moving clouds C.F.T. Montenegro, L.F.N. Lourenço, M.B.C. Salles and R.M. Monaro are with the Department of Electric Energy and Automation of the Polytechnic School of the University of Sao Paulo, SP, Brazil (phone: +5511 3091 5533; e-mails: cristiantomo@usp.br, lfnlourenco@usp.br, mausalles@usp.br, monaro@usp.br). [6]. Research presented in [6] shows the effect of irradiance changes on a real-life network with a rooftop PV system. It finds that moving clouds can cause voltage fluctuations outside the allowable thresholds depending on the network loading. In utility-scale PV systems, as projected in Brazil, solar production is concentrated in a limited geographic region. Thus, it is very likely to lose a considerable amount of PV power by cloud coverage, potentially affecting the operation of the grid. Mitigating voltage fluctuations due to PV generation is studied in [7], it proposes control strategies that allow PV systems to inject or absorb reactive power using PV inverters. This can help to reduce voltage variations caused by changes in solar irradiance levels. This paper analyzes the effect of solar irradiance changes on the operation of a distribution/sub-transmission network with a utility-scale PV system. It has been modeled a solar farm with a capacity of 30 MWp in accordance with the discussed projects that are underway in Brazil. Alternatives to mitigate the negative effects on voltage regulation have been investigated. They are related with reactive power compensation by the PV system and grid reinforcements. This work is structured as follows: Section II includes a 30 MWp solar farm model, corresponding to one of the 29 new projects under construction in Brazil and presents the test network; Section III presents the disturbances in power output that may occur due to variations in solar irradiance levels and control strategies considered in this paper; Section IV presents the results and their discussion and, finally, Section V presents the conclusions. II. TEST SYSTEM A. Solar Farm The solar farm modeled in this work is composed of twenty identical PV systems of 1.5 MWp connected in parallel. The model (Fig. 1) is based on [8] and contains a PV generator, voltage source converter (VSC), current based control with a DC voltage loop, maximum power point tracker (MPPT) and a phase-locked loop (PLL). Each system is connected to a 12.47 kV grid at the point of common coupling (PCC) through a RL filter and a wye-delta transformer. The value of 1.5 MWp was chosen according to inverter stations available in the market. PV system parameters have been summarized in Table I. Dynamic Performance Analysis of Distribution/ Sub-Transmission Networks with High Penetration of PV Generation Cristian F.T. Montenegro, Luís F. N. Lourenço, Maurício B. C. Salles, Renato M. Monaro T World Academy of Science, Engineering and Technology International Journal of Computer and Systems Engineering Vol:10, No:6, 2016 806 International Scholarly and Scientific Research & Innovation 10(6) 2016 ISNI:0000000091950263 Open Science Index, Computer and Systems Engineering Vol:10, No:6, 2016 publications.waset.org/10004842/pdf