I bob. Tadqiqotning nazariy asoslari Quyosh nergiyasidan foydalanish yo’llari
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Kirish I bob. Tadqiqotning nazariy asoslari Quyosh nergiyasidan foydalanish yo’llari O’zbekistonda quyosh energiyasidan foydalanish imkoniyatlari va muommolari Quyosh fotoelektr stansiyalari va ularning taxlili II bob. 2.1 Avtonom quyosh fotoelektr stansiyalari 2.2 Quyosh fotoelektr stansiyalarining istemolchilari va ularning yuklamalari 2.3 Fotoelektr tiziniming energiya samarorligi oshirish yo’llari 2.4 Avtonom quyosh fotoelektr stansiyalarida moslashuvchan boshqaruv tizimi https://uchitel.pro/%D0%BF%D0%BE%D1%81%D1%82%D0%BE%D1%8F%D0%BD%D0%BD%D1%8B%D0%B9-%D1%82%D0%BE%D0%BA/ http://www.matic.ru/clients/articles/harmonics-voltage-and-current-in-electrical-networks/ Content may be subject to copyright. Modelling and Power quality analysis of a Grid-connected Solar PV System S.V. Swarna Kumary*, V.Arangarajan Aman Maung Than Oo, GM Shafiullah, Alex Stojcevski School of engineering, Faculty of science Engineering and Built Environment Deakin University, Waurn Ponds e-mail: ssrungar@deakin.edu.au Abstract— Increased concern about global warming coupled with the escalating demand of energy has driven the conventional power system to be more reliable one by integrating Renewable Energies (RE) in to grid. Over the recent years, integration of solar PV forming a grid- connected PV is considered as one of the most promising technologies to the developed countries like Australia to meet the growing demand of energy. This rapid increase in grid connected photovoltaic (PV) systems has made the supply utilities concerned about the drastic effects that have to be considered on the distribution network in particular voltage fluctuations, harmonic distortions and the Power factor for sustainable power generation. However, irrespective of the fact that the utility grid can accommodate the variability of load or irregular solar irradiance, it is essential to study the impact of grid connected PV systems during higher penetration levels as the intermittent nature of solar PV adversely effects the grid characteristics in meeting the load demand. Hence, keeping this in track, this paper examines the grid-connected PV system considering a residential network of Geelong region (38◦.09' S and 144◦.21’ E) and explores the level of impacts considering summer load profile with a change in the level of integrations. Initially, a PV power system network model is developed in MATLAB/Simulink environment and the simulations are carried out to explore the impacts of solar PV penetration at low voltage distribution network considering power quality (PQ) issues such as voltage fluctuations, harmonics distortion at different load conditions. Keywords—Renewable energies, Grid connected PV, level of integration, MATLAB/Simulink I. INTRODUCTION Most of the world’s energy is derived from fossil fuels especially by burning coal as it has the substantial reserves of conventional resources. Now a days, generation of electricity via traditional methods is a challenging issue as it contributes to greenhouse gas (GHG) emissions and in fact the continuous usage of these fuels will outstrip the ability to produce them [1- 3].In addition to these facts, in developed countries like Australia the government has abandoned plans to shut down some of most dirtiest coal- fired power as part of the Contracts for Closure program (CFC) to cut down their GHG emissions which amount to about 1.5 % of GHG emissions, placing it among the top 20 polluting countries in the world. Hence, it is essential to use alternate energy sources for power generation to meet the growing demand and as well to conserve nature. In response to climatic change Australia is developing a suite of options aimed at delivering more efficient and sustainable low emission generations. Interest in and production of renewable energy in Australia has undergone substantial growth since 2006[4] and among the RE sources, solar PV has an unpredicted growth in power generation due to its reliability in power conversion and cost effectiveness [5]. This unpredicted growth in PV market mostly has been driven by the residential Grid connected PV systems-‘A source of emission free power generation’[6].Grid-connected photovoltaic (PV) power systems are energized by PV panels which are connected to the utility grid via an inverter can upload the excess energy to the grid during average or low peak demands. Grid connected PV systems reduces the line losses as the consumer power is generated close to the load demand. In addition, grid connected system benefits the utilities economically in delaying the line upgrades by means of peak load reduction [7]. However, integration of solar PV into grid has several impacts contributing to operational problems due to its intermittent nature. Integrating solar PV effects the functional operation of the power system network like load/frequency control, load following, unbalancing of voltage and current levels in the network and PQ issues including voltage disturbance, poor power factor, reactive power compensation flicker and harmonic distortions. Though integration issues/effects are not the major focus of this paper it is essential to study some of the effects of the Grid connected PV system that has to be analyzed for efficient power generation and distribution for sustainable energy flow [6, 8-10]. Keeping this in view, section II explains the effects of Grid connected PV systems on the distribution network. The main aim of this paper is to assess the effect of penetration levels of a grid connected PV system considering a residential low voltage distribution network in Geelong. This basic study will explore the impacts of PV integration on PQ at different solar irradiance levels and daily load demand based on the summer profile with a change in the level of PV integrations. Initially, a PV model is developed using MATLAB and simulations are analyzed considering different cases with reference to voltage and harmonic analysis. II. EFFECTS OF GRID CONNECTED PV SYSTEMS ON DISTRIBUTION NETWOK As per AS4777 standard, the nominal AC voltage of 230V at the point of supply in single phase line to neutral and 400 V in three phase line to line with a tolerance of 10% -6% and a frequency of 50Hz has to be maintained at low voltage distribution network side [11]. Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014 1
demands. Hence, it is essential to study the impacts to estimate the level of impact to maintain the As4777 standards. Following are some of the issues that have to be considered in analyzing the performance of any grid connected PV systems. A. Over Voltage/Reverse Flow Excess power generated by the solar PV should be properly accommodated by the grid for consistent power flow to avoid the worst case scenarios like power outage. For instance, the excess power generated by the solar PV during lower demands should export the active power to the grid which could result in over voltage or reverse power flow affecting the utility grid and household appliances leading to other safety and protection challenges. B. Voltage Fluctuations The intermitted nature of the solar PV is one of the reasons for voltage fluctuations in grid connected PV systems Irregular solar irradiance caused by the passing clouds, PV installation area, and the selected angle of incidences/reflections also plays a major role in driving the system to instability by means of voltage fluctuations. This irregular fluctuations causes voltage flicker /flicker
in the distribution network. C. Power factor Grid operated PV systems usually operate at unity power factor and the power produced by the PV units is active/real power. In addition to this active /real power supplied by the solar PV, the grid still has to still supply the reactive power. During this process the regular power flow of the system may have the adverse effect due to the insufficient reactive power and may decrease the power implying insufficient transmission. D. Harmonics Harmonic distortion is one of the major effect that has
Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014 2
A low voltage distribution transformer (DT) with star- delta configuration is considered in this network model. The DT specifications with respective to winding voltage ratio, impedance ratio, and transformer rated capacity are considered as 22 kV/400 V, 4.5%, and 100 KVA respectively. C. 2kv feeder G. Load Profile The Fig.2 depicts the typical residential daily load profile of particular area in Geelong. As per load profile, the daily peak load of each house is considered around 0.865 kW and similarly, minimum average load during sun shine hours is considered around 0.488 kW. Therefore considering 30 houses in each load group, the total peak load, and minimum average load for each load group is considered around 25.95 kW, and 14.64 kW respectively. A 22KV feeder is used between the utility source and the high voltage end of the transformer .The assumed length of the line per phase is 1000m and with respect to the positive sequence values of resistance, inductance, and capacitance of the line are considered to be 0.1153 Ω/km, 1.05 mH/km and 11.3 nF respectively. D. Solar PV power system H. Solar profile Fig. 2. Load profile. A PV system with a combination of three different groups of solar PV is used as a unique solar PV power system in analyzing the proposed model. The rated capacity of each group of solar PV system at Standard Test Condition (STC) is 31.9 kW. Each PV system consists of around 110 numbers of solar PV modules with configuration of 5 solar PV modules connected in series per string and 22 strings connected in parallel. The maximum voltage (Vmp), and maximum current (Imp) of each solar PV module is considered as 54.7 V and 5.58 A respectively. In each group of solar PV system, a Voltage Source Inverter (VSI) of rated capacity 50 KVA is considered with the implementation of current control scheme [12]. E. Low voltage (400 V) distribution feeder The above mentioned three solar PV groups are connected in low voltage distribution feeder with a length of 600 meters in distance. From the figure 1 it can be noticed that group 1 (solar PV 1) is connected very close to the transformer, group 2 (solar PV 2) is connected around 300 meters apart from first solar PV group, and similarly group 3 (solar PV 3) is connected around 300 meters apart from second PV group. The distribution feeder specification parameters are like; resistance 0.646 Ω/km, inductance 0.24 mH/km, and capacitance C=0.07 nF/km. F. Load group Three load groups are considered in this model and the maximum capacity of load in each group is assumed to be around 25.95 kW which is equivalent to residential load of 30 houses. As per daily solar irradiance level during summer days, for the selected location in Geelong, the daily maximum solar irradiance level is considered around 871.5 w/m2 at peak sun shine condition and similarly, a minimum average solar irradiance of 319.8w/m2 is considered for this study. IV.RESULTS AND DISCUSSION A study of voltage and harmonics analysis has been carried out for the developed PV power system network model considering different solar irradiance and different load conditions. Three different cases are used in analyzing the voltage scenario with respective to the PV integration in to the grid and two cases are considered in analyzing the Total Harmonic Distortion (THD). Case A: Voltage analysis with only Grid (without PV integration) The voltage analysis has been carried out in LV network at minimum average load condition (14.64 kW) for each load group. Initially, the simulation has been done by considering only grid connected system (without PV integration).Fig.3 clearly shows the behavior of voltage level at three different bus nodes A1, A2, and A3. From the simulation results it was observed that the voltage level at bus node A1, which is close to the distribution transformer is around 240V whereas the voltage at bus node A2, and A3 is observed as 232 V and 220 V respectively. From this voltage level graph it can be clearly stated that the voltage is in decreasing order from bus node A1 to A3. The reason behind the voltage drop is due to the increase in the impedance values with respective to the line distance length of line. . Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014 3
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Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014 4
Fig. 6. THD analysis at bus node A3. Fig. 7. THD analysis at bus node A1. Case E: Harmonic analysis at minimum solar irradiance with peak load The THD analysis is also carried out at minimum solar irradiance (319.8 W/m2) and peak load (25.95 kW) conditions. Fig 8.and Fig 9. shows the harmonic analysis results and from the results it can be seen that the THD values of voltage and current harmonics at bus node A3 is around 2.26% and 2.91% whereas at bus node A1 it is around 1.18% and 1.35% respectively. The results clearly indicate that the THD values are higher at far end of the feeder (bus node A3) as compared to transformer near bus node A1.From the above two cases it can be clearly stated that THD values of current and voltage distortions at minimum solar irradiation condition is less compared to maximum PV generation condition with peak load. Fig. 8 .THD analysis at bus node A3. Fig. 9 .THD analysis at bus node A1. Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 September – 1 October 2014 5
harmonic injection in the low voltage distribution network with the integration of solar PV systems. From the voltage analysis results the following conclusions are drawn. Considering case‘A’ it can be seen that the voltage level at far end of the feeder (bus node A3) is less as compared to bus node which is near to the distribution transformer. The level of drop in the voltage level at far end of the feeder depends on the distribution network length or distance and impedance level. From the case ‘B’ results it can be stated that there is significant voltage rise at far end bus node feeder as compared to other bus nodes due to reverse power flow with excessive PV generation from solar PV group at minimum load condition. Case ‘C’ results concludes that the voltage level at far end feeder of bus node is less as compared to other bus nodes, which is mimicking case ‘A’ results. From the THD analysis results the following conclusions are drawn. At maximum PV generation as well as at minimum PV generation considering peak load condition it can be observed that the level of harmonics of voltage and current harmonics are high at far end feeder of bus node as compared to bus node near distribution transformer. The only difference is that the THD values of current and voltage harmonics are in reduced level at minimum solar PV generation as compared with the maximum solar PV generation condition. This is due to cumulative contribution of harmonics from more number of PV inverters used during maximum solar PV generation conditions. However irrespective of the case selected, the maximum voltage deviation and the harmonics are within the tolerance level as per the AS777 standard. This research study will be helpful for utilities and customers in future to estimate the level of impacts of PQ factors in distribution network while integrating large scale PV in to the network. In this context, future work will extended this analysis to investigate the model with storage under higher penetrations and lower load demands to optimize the provision of power from PV system and support the network for sustainable energy generation and distribution. REFERENCES [1] T. ABBASI and A. SA, Renewable energy sources their impact on global warming and pollution: PHI Learning Pvt. Ltd., 2010 [2] M. Jefferson, "Sustainable energy development performance and prospects," Renewable energy, vol. 31, pp. 571-582, 2006 [3] N. Panwar, S. Kaushik, and S. Kothari, "Role of renewable energy sources in environmental protection: a review," Renewable and Sustainable Energy Reviews, vol. 15, pp. 1513- 1524, 2011. [4] M. Diesendorf, "How can a “competitive” market for electricity be made compatible with the reduction of greenhouse gas emissions" Ecological Economics, vol. 17, pp. 33-48, 1996. [5] G.Chicco, J. Schlabbach, and F.Spertino, "Experimental assessment of the waveform distortion in grid-connected photovoltaic installations," Solar Energy, vol. 83, pp. 1026- 1039, 2009. [6] S.Lewis, "Analysis and management of the impacts of a high penetration of photovoltaic systems in an electricity distribution network," in Innovative Smart Grid Technologies Asia (ISGT), 2011 IEEE PES, 2011, pp. 1-7. [7] K.Kontogiannis, G. Vokas, S. Nanou, and S. Papathanassiou, "Power Quality Field Measurements on PV Inverters," Power, vol. 2, 2013. [8] M.Chikh, A. Mahrane, T. Kacim, and A. Mina, "Impact analysis of the integration of PV system in utility distribution. Case study: Multi- technologies photovoltaic pilot plant at UDES, Algeria." [9] W.Tayati and G. Pack, "Renewable Energy Penetration Limits for Isolated Remote Area Power Systems." [10] V. BARBU, G. Chicco, F. Corona, N. GOLOVANOV, and F. Spertino, "Impact of a Photo voltaic plant connected to the MV Network on harmonic distortion: an Experimental assessment, “Scientific Bulletin- "Polytechnical" University Of Buchartest Series C Electrical Engg and Computer Science, vol. 75, pp. 179-194, 2013. [11] B. Noone, "PV Integartion On Australian Distribution Network," 2013 [12] S. Ali, N. Pearsall, and G. Putrus, "Impact of High penetration level of grid-connected Photovoltaic systems on the UK low voltage distribution network," in International Conference on Renewable Energies and Power quality, 2012, pp. 1-4. https://www.researchgate.net/publication/286651421_Modelling_and_power_quality_analysis_of_a_grid-connected_solar_PV_system Download 45.85 Kb. Do'stlaringiz bilan baham: 
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