International Journal of Power Electronics and Drive System (IJPEDS) Vol. 9, No. 2, June 2018, pp. 478~494 ISSN: 2088-8694, DOI: 10.11591/ijpeds.v9.i2.pp478-494  478 Journal homepage: http://iaescore.com/journals/index.php/IJPEDS Review of DC Offset Compensation Techniques for Grid Connected Inverters Ahmed Omar 1 , Adel El-Rfaey 2 , Mona Fouad Moussa 3 , Yasser Gaber Dessouky 4 Department of Electrical Engineering, Arab Academy for Science, Technology and Maritime Transport, Egypt Article Info ABSTRACT Article history: Received Dec 16, 2017 Revised Jan 18, 2018 Accepted Feb 2, 2018 Limitations of DC injection into the AC network is an important operational requirement for grid connected photovoltaic systems. There is one way to ensure that this issue needs a power transformer as a connection to the AC network. However, this solution adds cost, volume, mass, and power losses. Ideally there shouldn't be any DC at the output of the inverter, but practically, a small amount of DC current is present. Therefore, in this paper there are techniques for the DC offset elimination are proposed. Some have drawbacks which was treated by another technique. Also there are best solutions for eliminating DC offset as in section 17, and 18 as it explains how to reduce the DC offset in a transformerless operation with reducing the power losses, mass and the cost effect.. Keyword: DC offset compensation techniques Grid connected inverters Copyright © 2018 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Ahmed Omar, Department of Electrical Engineering, Arab Academy for Science, Technology and Maritime Transport, Alexandria Desert Rd, Giza Governorate, Egypt. Email: ahmedomr_eg@hotmail.com 1. INTRODUCTION Power quality is an essential issue for the combination of grid connected inverters. The issues identified to DC current injection in inverter based distributed generation have been generally overlooked, in spite of developing concerns regarding its impact on distribution system components. One of the most extreme issues brought on by DC current injection is saturation of the distribution transformers bringing about waveform distortion, excessive losses, overheating and dimensioned life expectancy. In addition, it also may cause mistakes in some of the measurement and protective relays systems [1]. An acceptable source of DC current injection into the grid emerges from the semiconductor circuits in inverter frameworks. The presence of undesirable DC current components in the output currents of such frameworks can be ascribed to several factors such as pulse width modulation signals, non-linearity of the switching devices, and the drift in the voltage and current measurement sensors used to give feedback signals for the control frameworks. A number of rules and standards are forced to limit the effect of DC current injection into the grid [2], [3]. Among these principles and proposals are rules to restrain the allowable amount of DC current injection into the distribution network. They vary from country to country. For instance, British standard limits DC injection to 20mA for distributed generation with stage streams beneath 16A rms [4]. In IEEE standard 'IEEE 929-2000' the DC limits is 0.5% of the inverter rated current [5]. The DC current injection in the Australian standard AS4777.2 should not exceed 0.5% of the inverter rated output current or 5mA, which is the greater [6]. Various methods have been proposed to prevent or minimize DC current injection by grid-connected inverters in photovoltaic systems. This paper presents a review on the issue of the DC offset and how to overcome it with different methods through existing techniques that have been submitted to limit DC current injection into the distribution network as will be illustrated in each section. section 1 is the Introduction, section 2 presents the isolation transformer