International Journal of Electronics and Electrical Engineering Vol. 4, No. 3, June 2016 Harmonics Impact of Rooftop Photovoltaic Penetration Level on Low Voltage Distribution System Orawan Poosri and Chalie Charoenlarpnopparut Sirindhorn International Institute of Technology, Thammasat University, Bangkok, Thailand Email: orawan.poo@pea.co.th, chalie@siit.tu.ac.th Abstract—Integration of increasing penetration level of rooftop photovoltaic in the next few years may affect the quality of low voltage distribution system in Thailand. Harmonic current injected from rooftop PVs may cause harmonic problem and affect power quality of grid. Therefore, this research intends to study harmonic impact of rooftop photovoltaic penetration level on low voltage distribution system (400/230V) in urban area. DIgSILENT PowerFactory program is used to simulate and analyze the impact of rooftop PVs which connected in different penetration level and two scenarios of background system, such as balanced grid voltage, and polluted grid (with THDv). The result of simulated model shows that the total harmonic distortion voltage of the network is over the standard due to the amount of PVs with inverter (which has THDi<2%) connected to the system is more than 60% penetration of rated power of transformer. malfunction or may be damaged. The utility needs to study and analyze attentively the power quality issues for the optimization of the penetration rooftop PV in LV distribution network to minimize impact of rooftop PV. There are several papers interested in harmonics problem with PV systems [1]-[3]. They research some factors which can influence the harmonic distortion of the grid like radiance, environmental temperature, the control method of the inverter, the imbalance of three-phase grid, and the voltage harmonics of the grid. This paper uses two factors as system loading level and some harmonics of the grid (before PV will be connected to a network) for analyzing the effect to harmonic output of PVs. Index Terms—rooftop PV, distribution system, distributed generator, harmonics impact of rooftop PV A. Distribution System Model I. II. INTRODUCTION Currently, renewable energy resources as distributed generators in power systems are growing up in many countries around the world including Thailand due to rising fuel price, high electricity price and environment concerning. One of the most popular distributed generators is solar or Photovoltaic (PVs) power generator. In 2014, the government of Thailand encourages residential and commercial units to install rooftop PVs for producing and selling electricity through Feed-inTariff (FIT) which is proposed to attract many people for participating in this campaign. Grid connected PV systems use a power electronic inverter, which injects harmonic current into the power system, for changing DC to AC. However, the large amount of the rooftop penetration connected into Low Voltage (LV) distribution network, the large numbers of inverters which cause harmonic current injected into the grid also are massive in the network. The utility may face the important issue as the harmonics problem in residential network. Its disadvantage causes some electrical devices and the local equipment in the distribution network (like transformer, capacitor bank) Manuscript received April 16, 2015; revised September 24, 2015. ©2016 Int. J. Electron. Electr. Eng. doi: 10.18178/ijeee.4.3.221-225 221 SIMULATION SETUP PEA residential low voltage networks are composed of four wires with radial topology. It contains 250kVA Distribution Transformer (DTR) power rating which was connected in medium-voltage: low-voltage (22kV/400V). The secondary side of DTR has 3 feeders and there are 159 households) (71 single phase loads and 88 three phase loads) as shown in Fig. 1. B. Residential Load Profile and Daily Curve Power of Rooftop PV Power output of Rooftop PV and the loading curve of residential during 24 hours are shown in Fig. 2 and Fig. 3, respectively. C. Parameter of PV Size and connection type of PV Single phase PV sizes 3kW with 2 types of inverter as PV1 and PV2. PV1 is represented rooftop PV with inverter type 1 release THDi less than 2% PV2 is represented rooftop PV with inverter type 2 release THDi more than 5% Penetration level of Rooftop PV is the proportion of installed power solar rooftop with the rated power of transformer %PV Penetration = Total PowerPV Rated Power of TR International Journal of Electronics and Electrical Engineering Vol. 4, No. 3, June 2016 Figure 1. Single line diagram of PEA low voltage distribution system. TABLE I. %PV Penetration BUSES SELECTED FOR INSTALLATION OF ROOFTOP PV WITH 10, 20, …, 80% PV PENETRATION Bus with PV connected 10 20 Feeder1-bus17,18,19,20,21,22,23,24 30 Feeder1-bus17,18,19,20,21,22,23,24,25, 26,27 Feeder2-bus11,21,24,25,34,70,91,93,95, 96,108,112,113,119 Feeder1-bus17,18,19,20,21,22,23,24,25, 26,27 Feeder2-bus21,34,70,108,112,113 40 Feeder1-bus17,18,19,20,21,22,23,24,25, 26,27 Feeder2-bus11,21,24,25,34,54,55,70,85,89, 90,91,92,93,94,95,96,97,108,112,113,119 50 Feeder1-bus17,18,19,20,21,22,23,24,25, 26,27 Feeder2-bus11,21,24,25,34,36,46,47,48,49, 50,51,52,53,54,55,70,85,89,90,91,92,93,94,95,96,9 7,108,112,113,119 60 Feeder1-bus17,18,19,20,21,22,23,24,25, 26,27 Feeder2-bus11,21,24, 25,34,36,46,47,48,49, 50,51,52,53,54,55,70,85,89,90,91,92,93,94,95,96,9 7,103,104,105,106,107,108,109,110,111,112,113,1 19 70 80 Figure 2. Daily output power of rooftop PV. Figure 3. Dialy load profile of household. Rooftop PVs will be installed to distribution system with 10, 20, 30, 50, 60, 70, and 80% PV Penetration. Nodes connected with PV are shown in Table I. Feeder1-bus17,18,19,20,21,22,23,24,25, 26,27 Feeder2-bus11,21,24,25,34,36,46,47,48,49, 50,51,52,53,54,55,69,70,71,72,85,89,90,91,92,93,9 4,95,96,97,98,99,100,101,102,103,104, 105,106,107,108,109,110,111,112,113,119 D. Simulated Scenarios Scenario 1: It assumes that the distribution system is balanced and without harmonics in the grid. Scenario 2: It assumes that the grid (without PV installation) has some harmonics making the Total Harmonic Distortion voltage (THDv) is nearly 2%. Case study are 4 cases as: Case 1. PV1 is installed in scenario 1 with 10% to 80% PV penetration Case 2. PV1 is installed in scenario 2 with 10% to 80% PV penetration Feeder1-bus17,18,19,20,21,22,23,24,25, 26,27 Feeder2-bus11,21,24, 25,34,36,46,47,48,49, 50,51,52,53,54,55,69,70,71,72,73,74,75,76,77,78,8 5,89,90,91,92,93,94,95,96,97,98,99,100,101,102,1 03,104,105,106,107,108,109,110, 111,112,113,119 Feeder3-bus21,51,88 ©2016 Int. J. Electron. Electr. Eng. 222 International Journal of Electronics and Electrical Engineering Vol. 4, No. 3, June 2016 limitation of THDi at PCC are shown in Table III and Table IV. Case 3. PV2 is installed in scenario 1 with 10% to 80% PV penetration Case 4. PV2 is installed in scenario 2 with 10% to 80% PV penetration All cases are considered at loading level, 25%, 50% and 80% of rated power transformer. I 2 I3 I4 2 THDi (%) 2 2 100 (1) 100 (2) I1 V2 V3 V4 2 THDv (%) E. Standard Harmonics Limitation Total Harmonic Distortion (THD): The ratio of RootSum-Square (RMS) of the harmonic component and RMS of the fundamental component in the percentage as the total harmonic distortion current (THDi) and the total harmonic distortion voltage (THDv) in (1) and (2) respectively. Ref. [4], [5] the limitation of THDv at Point of common coupling (PCC) are shown in Table II and the 2 2 V1 TABLE II. HARMONICS VOLTAGE LIMITATION PEA recommendation (PRC-PQG-01/1998) IEEE Std. 519-1992 THDv less than 5% Odd less than 4% Even less than 2% THDv less than 5% Individual THD less than 3% TABLE III. PEA RECOMMENDATION HARMONIC CURRENT LIMITS FOR CUSTOMERS AT POINT OF COMMON COUPLING (PRC-PQG-01/1998) Harmonic order 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 0.4kV 48 34 22 56 11 40 9 8 7 19 6 16 5 5 5 6 4 6 Current limitation (A, rms) at PCC 11 and 22kV 22, 24 and 33kV 69kV 115kV and more 13 11 8.5 5 8 7 5.9 4 6 5 4.3 3 10 9 7.3 4 4 4 3.3 2 8 6 4.9 3 3 3 2.3 1 3 2 1.6 1 3 2 1.6 1 7 6 4.9 3 2 2 1.6 1 6 5 4.3 3 2 2 1.6 1 2 1 1 1 2 1 1 1 2 2 1.6 1 1 1 1 1 1 1 1 1 TABLE IV. IEEE STD. 519-1992 HARMONIC CURRENT LIMITS Current Distortion Limits for General Distribution Systems (120V Through 69000V) Maximum Harmonic Current Distortion in Percent of IL Individual Harmonic Order (Odd Harmonics) ISC/IL <11 11≤h<17 17≤h<23 23≤h<35 35≤h TDD <20* 4.0 2.0 1.5 0.6 0.3 5.0 20<50 7.0 3.5 2.5 1.0 0.5 8.0 50<100 10.0 4.5 4.0 1.5 0.7 12.0 100<1000 12.0 5.5 5.0 2.0 1.0 15.0 >1000 15.0 7.0 6.0 2.5 1.4 20.0 Even harmonics are limited to 25% of the odd harmonic limits above. Current distortions that result in a dc offset, e.g. half-wave converters, are not allowed. *All power generation equipment is limited to these values of current distortion, regardless of actual ISC/IL. where ISC = maximum short-circuit current at PCC. IL = maximum demand load current (fundamental frequency component) at PCC. TDD = Total demand distortion (RSS), harmonic current distortion in % of maximum demand load current (15 or 30 min demand). PCC = Point of common coupling. III. loading is changed to 80%, the trend of THDv in system is the same. When PV penetration integrated to the network is more, the total harmonic distortion voltage of buses on the network is higher as Fig. 5(a) and Fig. 5(b). When the large number of PVs are connected to the polluted grid (with total harmonic distortion voltage about 2%), harmonics background in system and TEST RESULT When PV1 (THDi<2%) were connected to system more than with 60% PV Penetration in Case 1 and 2, the THDv of buses exceed the limitation (must less than 5%). For PV2 (THDi>5%) were installed less than 40% PV Penetration, THDv of buses still be in standard. Comparing Fig. 4(a) and Fig. 4(b) when the network ©2016 Int. J. Electron. Electr. Eng. 223 International Journal of Electronics and Electrical Engineering Vol. 4, No. 3, June 2016 harmonics from PV inverters are making THD of the network higher as Fig. 6(a), Fig. 6(b). As Fig. 6(c), none of PVs were connected on feeder 3 while PV penetration installed on feeder 1 and 2 is from 10% to 70%. It causes to increase THDv of buses on feeder 3. (a) (a) (b) (b) Figure 4. (a) %THDv in system when PVs were connected to grid with 10-80% PV penetration in case 1-4 and network loading is 50%, (b) %THDv in system when PVs were connected to grid with 10-80% PV penetration in case 1-4 and network loading is 80%. (c) Figure 6. (a) %THDv at buses on feeder 1 when PVs were connected to grid with 50% PV penetration and network loading 50% in case 1-4 , (b) %THDv at buses on feeder 2 when PVs were connected to grid with 50% PV penetration and network loading 50% in case 1-4, (c) %THDv on feeder 3 when PVs were connected to grid with 10-80% PV penetration in case 1-4. IV. CONCLUSION This paper studies harmonics impact of rooftop PV with inverter 2 type (which has THDi<2% and >5% in PV1 and PV2 respectively). Although THDi of PV inverter is less than 2%, it is possible to face the THDv of buses in system exceed the limitation if PVs were connected to grid with higher 60% to 80% penetration of the rated power of the distribution transformer. Considering system loading level at 25%, 50%, and 80%, it has an effect on to THD of system slightly. Besides, harmonics background in network should be measured and taken into account before high penetration PV will be integrated to LV network. When PVs were connected to the polluted grid, both THDi of PV inverter and harmonics background may affect THD of network to increase or higher the standard. (a) ACKNOWLEDGMENT This study was supported by the Provincial Electricity Authority (PEA), Thailand under the Smart Grid Scholarship Program at SIIT, Thammasat University, Thailand. (b) Figure 5. (a) %THDv at buses on feeder 2 when PVs were connected to grid with 10-80% PV penetration, (b) %THDv at buses on feeder 3 when PVs were connected to grid with 10-80% PV penetration. ©2016 Int. J. Electron. Electr. Eng. 224 International Journal of Electronics and Electrical Engineering Vol. 4, No. 3, June 2016 Sirindhorn International Institute of Technology Thammasat University (SIIT) Master Degree Scholarship. She is currently a student of Master degree in engineering technology field of Sirindhorn International Institute of Technology (SIIT), Thammasat University. REFERENCES [1] [2] [3] [4] [5] R. Torquato, F. C. L. Trindade, and W. Freitas, “Analysis of the harmonic distortion impact of photovoltaic generation in Brazilian residential networks,” presented at the 16th IEEE International Conference on Harmonics and Quality of Power, Bucharest, Romania, May 25-28, 2014. K. Dartawan, R. Austria, H. Le, and M. Suehiro, “Harmonic issues that limit solar photovoltaic generation on distribution circuits,” presented at World Renewable Energy Forum, Denver, Colorado, May 13-17, 2012. X. Y. Zhao and S. Y. Liu, “A research of harmonics for multiple PV inverters in grid-connected,” presented at Asia-Pacific Power and Energy Engineering Conference, Shanghai, China, March 2729, 2012. Harmonic Regulations for the Commercial and Industrial (Thailand), PRC-PQG-01/1998. IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems, IEEE Std. 519-1992. Chalie Charoenlarpnopparut obtained B.ENG. (1st Class Honor) in Electrical Engineering, Chulalongkorn University, Bangkok, Thailand and M.S. and Ph.D. in Electrical Engineering, The Pennsylvania State University, University Park, PA, USA. He is currently an Associate Professor and Assistant Director for General Administration, Bangkadi Campus in Sirindhorn International Institute of Technology Thammasat University (SIIT). He has received many Teaching Award and Outstanding Teacher both at SIIT and Thammasat University. His research interest include Multidimensional systems and signal processing, Robust control, Image processing, Wavelet and filter bank, Signal processing for communication, Convolutional code design. Orawan Poosri obtained B.ENG degree in Electrical Engineering and M.SC degree in Information Technology from King Mongkut's University of Technology Thonburi, Bangkok, Thailand in 2006 and 2012. Since 2008 to 2013, she has worked as an engineer at Provincial Electricity Authority Central Area 3 (Nakhon Pathom Province), Thailand. Since 2013, she has received Provincial Electricity Authority (PEA) ©2016 Int. J. Electron. Electr. Eng. 225