This paper presents a novel islanding prevention scheme of Grid-Connected PV Systems in Matlab/ Simulink based on monitoring the dc-link voltage of the PV inverter. A 100kW PV System equipped with islanding protection like frequency relays, a ROCOF relay, and respectively the proposed dc-link voltage relay are simulated under the conditions of islanding and the detection time for all these AI techniques are compared.
Islanding also known as loss of grid or Loss-of-Mains–LoM represents “a condition in that a portion of the power system that contains both load and distributed energy resources (DER) remains energized while isolated from the remainder of the power system”. Also, island represents a condition where a portion of an area electric power system (EPS) is energized solely by one or more local DER through the associated point of common coupling (PCC) while that portion of the area EPS is electrically separated from the rest of the area EPS. Development of sensitive and reliable AI protection is very important to encourage medium scale integration of DER into the electrical network and avoid unnecessary tripping of DER. The PV inverter design will be influenced by the power grid requirements, including the anti-islanding (AI) requirement which is considered the most technically challenging. One of the most challenging aspects of protection of DER is the sensitivity of islanding detection, which makes the system stable to external faults and frequency excursions. Islanding for PV Power Systems appears when the power grid is tripped and the inverter does not disconnect quickly enough and continues to operate with the local load. To perform islanding protection in some specific circumstances (impossibility of forming a stable island) it may be sufficient to use a combination of under/over frequency/voltage protection. In most cases, the islanding must be quickly detected and the PV System must be immediately disconnected from the power grid.
II. THE GRID CONNECTED PV SYSTEM AND ITS ISLANDING PREVENTION SYSTEM
The Simulink model of the 100kW Grid-Connected PV System is depicted in Fig.1. The PV Array, formed by330 SunPower modules provides in standard test conditions (STC) a maximum power of 100.7kW and 273.5V. The 100kW PV Array is connected to a 20kV power grid (Fig.2) with the main frequency of 50Hz through a 100kVA260V/20kV three-phase coupling transformer.
III. SIMULATION RESULTS OF ISLANDING CONDITIONS
The 100kW Grid-Connected PV Array from Fig. 1 is equipped with islanding protection methods like under/ over frequency relays, a ROCOF relay, and respectively the proposed dc-link voltage relay. This model is simulated using Simulink in various islanding scenarios. The islanding conditions occur in the studied network from Fig. 2 when the three- phase circuit breaker CB2 is opened at time (t) = 0.1 seconds (s). The circuit breaker CB2 disconnects the utility grid from the rest of the network during 150ms. As can be noted from Table I, the AI technique using dc link voltage relay has the fastest detection time. During islanding condition, the dc-link voltage decrease with the increase of the connected load. A small variation of inductive power does not influence much the detection time of the AI relays.
Detection Time Of Anti-Islanding Methods
Detection Time (s) of Anti-Islanding Relays
Local load greater than local
Local load matches with local generation
Local load less than local
The frequency relays have the limits of preset thresholds imposed by grid codes, leading to late detection of island conditions of PV systems. The detection times of islanding conditions of Grid-Connected PV System for the ROCOF relay are comparable with the detection times of frequency relays. The simulation results with detection time of different AI methods on various islanding scenarios of a PV System are depicted in Fig. 3
As it can be noted from Table and graphs, the AI technique using dc-link voltage relay has the fastest detection time. During islanding condition, the dc-link voltage decrease with the increase of the connected load. A small variation of inductive power does not influence much the detection time of the AI relays. System outfitted with islanding protection such as frequency relays, a ROCOF relay, and the proposed dc-link voltage relay are simulated under islanding conditions, and the detection time for all of these AI approaches is compared.
 Wang Chaoran, Xu An-fei, Shen Lei, “Research on islanding detection method in microgrid”, 3rd International Conference on Advanced Electronic Materials, Computers and Software Engineering (AEMCSE),2020.
 FarhatAra, Dr.JyotiShrivastava, “ANTI-Islanding in Grid Connected Solar Photovoltaic System”, International Journal of research in electronics and computer engineering, June 2019.
 P.K.Ganivada and P.Jena “Passive islanding detection Techniques using synchrophasors for inverter based distributed generator” Proceeding of the 2019 IEEE PES GTD Asia.
 C.Y.Chan, Tiger K.Y call and Simon K.K Ng “An Impact study of ROCOF Relays for islanding detection” IET Advances in Power System control, Operation & Maintenance (APSCOM) Hongkong 2015.
 B. Ponmudi and G. Balasubramanian, “Performance Comparison of different Passive Methods for the Detection Of Islanding Condition in Grid Connected PV System” , ARPN Journal of Engineering and Applied Sciences, 2018.
 PukarMahat, Zhe Chen and BirgitteBak-Jensen, “Review of Islanding Detection Methods for Distributed Generation”, DRPT, Nanjing China, 2018.
 Xuesong Zhou, Mao Liu, Youjie Ma and ZhiqiangGao, “An Overview of Photovoltaic System”, IEEE 2018.
 Shambhu B. Jinjala, BhavarthN.Vaidya, “Analysis of Active and Passive Method for Islanding Detection of 3-phase Grid Connected PV System”, IEEE, 2018.
 L B Sun, Z S Wu and K K Yan. “Application of Islanding Detection and Classification of PowerQuality Disturbance in Hybrid Energy System”, 2018 Asia Conference on Energy and Environment Engineering, 2018.
 Abhishek Sharma, Dr. Sunitha R., “Unintentional Islanding Detection in Microgrid”, International Conference on Energy, Communication, Data Analytics and Soft Computing (ICECDS-2017).
 Ravi Raj, Mande Praveen, “Survey of Islanding Detection Techniques for Grid Connected Photovoltaic Inverters”, International Journal of Computer Science and Network, Volume 6, Issue 1, February 2017.
 Manish Parihar, M.K. Bhaskar, Dharmendra Jain, Digvijay Sarvate, Deepak Bohra.\"Voltage Stability Analysis of Power System using Power World Simulator\", Volume 5, Issue XI, International Journal for Research in Applied Science and Engineering Technology (IJRASET) Page No: 2508-2515, ISSN : 2321-9653, http://doi.org/10.22214/ijraset.2018.11371.
 Ruchika, Pankaj Gupta, D. K. Jain and R. S. Bhatia, “Islanding detection technique for a Distributed Generation with Perfectly Matched Load condition”, International conference on Computing, Communication and Automation (ICCCA), pp. 1503-1506,2017.
 Dong Xie ,DajinZang ,PengGao ,Minmin Xiang ,Lu Yang, “Research on Islanding Detection Technology for Multi Grid-Connected Inverters”, IEEE, 2017.
 Lu Yu, Dahai Zhang1, Jinghan He, “Active Islanding Detection Method for Multi- Inverter in Power Distribution System”, IEEE, 2017.
 Pankaj Gupta, D.K. Jain, S. Bhatia and Ruchika, “A Review of Islanding Detection Techniques forGrid Connected Distributed Generation”, International Conference on Emerging Trends in Engineering Innovations and Technology Management, 2017.
 Y. Pavani B. Ramesh, “Islanding Detection of DG And Improvement of Stability by using Inverter Control Scheme”, International Journal of Science Technology & Engineering, November 2017.
 Manish Parihar, M.K. Bhaskar \"Review of Power System Blackout\" International Journal of Research and Innovation in Applied Science -IJRIAS vol.3 issue 6 June 2018, pp.08-13 URL: https://www.rsisinternational.org/journals/ijrias/DigitalLibrary/Vol.3&Issue6/08-13.pdf.
 45. Oihane ABARRATEGUI, Inmaculada ZAMORA, DunixeMarene LARRUSKAIN, “Comparative analysis of islanding detection methods in networks with DG”, International Conference on Electricity Distribution Vienna, 21-24 May 2007.
 46. Khalil El-Arroudi, GezaJoos and Innocent Kamwa, “Intelligent-Based Approach to IslandingDetection in Distributed Generation”,IEEE TRANSACTIONS ON POWER DELIVERY · MAY 2007.
 47. Sung-Il JangandKwang-Ho Kim, “An Islanding Detection Method for Distributed Generations Using Voltage Unbalance and Total Harmonic Distortion of Current”, IEEE TRANSACTIONS ON POWER DELIVERY, 2004.
 Guo-Kiang Hung, Chih-Chang Chang, and Chern-Lin Chen, “Automatic Phase-Shift Method for IslandingDetection of Grid-Connected Photovoltaic Inverters”, IEEE Transactionson Energy Conversion, Vol.18, No.1,2003.