Abstract—The issue of unintentional islanding in PV grid interconnection still remains as a challenge in grid-connected photovoltaic (PV) systems. This paper discusses the overview of popularly used anti-islanding detection methods, practically applied in PV grid-connected systems. Anti-islanding methods generally can be classified into four major groups, which include passive methods, active methods, hybrid methods and communication base methods. Active methods have been the preferred detection technique over the years due to very small non-detected zone (NDZ) in small scale distribution generation. Passive method is comparatively simpler than active method in terms of circuitry and operations. However, it suffers from large NDZ that significantly reduces its performance. Communication base methods inherit the advantages of active and passive methods with reduced drawbacks. Hybrid method which evolved from the combination of both active and passive methods has been proven to achieve accurate anti-islanding detection by many researchers. For each of the studied anti-islanding methods, the operation analysis is described while the advantages and disadvantages are compared and discussed. It is difficult to pinpoint a generic method for a specific application, because most of the methods discussed are governed by the nature of application and system dependent elements. This study concludes that the setup and operation cost is the vital factor for anti-islanding method selection in order to achieve minimal compromising between cost and system quality. Keywords—Active method, hybrid method, islanding detection, passive method, photovoltaic (PV), utility method I. INTRODUCTION VER the past decades, the rapid fall of the PV manufacturing cost has led to the fast development of PV energy system. This has made PV one of the most promising renewable energy resources in distributions generation (DG) [1]. In addition, solar energy is free and pollution free [2]. In grid-connected PV systems particularly, the connection of PV array and balance of system to the utility grid has to fulfill the technical requirement of interconnection from the utility grid. This is to ensure high power quality; substantial safety interaction and reliability of the utility are achieved. Therefore, abnormal operating conditions that could affect the grid-connected PV systems have to be prevented [3]. One of the major safety issues related is the challenge to avoid unintentional island mode of operation. An islanding mode is a condition in a DG which the energy resource continues to Wei Yee Teoh and Chee Wei Tan are with Department of Energy Conversion (ENCON), Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81300 Skudai, Johor, West Malaysia. (e-mail: weiyee@fkegraduate.utm.my, cheewei@fke.utm.my Tel: +6 07-5535768 Ext: 35768 ) supply to the local load even though the utility grid has been disconnected from the local load [3, 4]. Islanding mode of operation causes the utility grid to be disconnected from the DG in order to prevent any damage in the system. Under this condition, the grid is no longer servicing as a solid voltage and frequency reference. A general concept of islanding formation is illustrated in Fig. 1. During islanding mode, the utility circuit breaker is opened while the DG is still injecting power to supply the local load (the section between utility circuit breaker and the point of common coupling, PCC) [3, 4].This phenomenon occurs when utility suffers from unpredictable interruption of abnormality, such as voltage shut-down, short-circuit or equipment failure [5]. Fig. 1 An overview of islanding mode in a grid connected PV system There are two types of islanding modes, namely the intentional (planned) and the unintentional (unplanned) islanding [4, 6]. The purpose of intentional islanding is to sectionalize the utility system in order to create a power ‘island’ during an occurrence of disturbance. This is a common scenario especially for maintenance purposes. The local load in the created island will be supplied constantly by DG through a well-planned energy management until the utility is ready to be synchronized with the DG. Typically, intentional islanding is harmless to the power system because the problem can be solved during or after the grid disconnection [6]. However, unintentional islanding can create a severe impact to the power system stability due to the loss of grid synchronization. Consequently, this causes the DG to be out of the voltage and frequency references. This may damage the electrical devices and systems equipment in the islanded section. Another issue persists in the islanding mode whereby the technical workers may be placed under safety hazards as they may not be aware that the section is continuously powered by the DG. For this reason, anti-islanding control is essential in order to detect the islanding operation immediately. Wei Yee Teoh, Chee Wei Tan An Overview of Islanding Detection Methods in Photovoltaic Systems O World Academy of Science, Engineering and Technology Vol:5 2011-10-29 577 International Science Index Vol:5, No:10, 2011 waset.org/Publication/5748