Nowadays, using Distributed Generators (DGs) is attractive to industries and customers due to their easy installation capability and economic design. Distributed Energy Resources (DERs) are available in different sizes and technologies including solar cells, wind turbines, synchronous generators. Regarding the widespread use of DGs and their growing influences on power grids, the issues and problems that arise from DGs integration to the grid should be noticed more seriously. Islanding issue will be of more concern with extending the penetration of DERs. Islanding is a situation when one or more of the DERs continue to energize the portion of the system that has been separated from the main grid. Reliable and fast detection of islanding is required for protection of sensitive loads and also safety and security issues. According to related standards, anti-islanding schemes shall detect the formation of an island and isolate DERs in less than two seconds. Utilizing any of these schemes has its own advantages and drawbacks and proposing a fast and reliable method which does not negatively affects power quality is still appealing and challenging. The scope of this thesis is to investigate the islanding detection methods which are based on dynamic response of synchronous DGs. For this purpose, two catagories of methods are considered. One catagory includes active methods that change synchronous DGs conventional active and reactive controller which leads to instability in islanding situation without adverse effect on the stable performance of the system in grid-connected mode. The other includes methods that provide islanding detection by means of measuring the electrical parameters of the system and extracting their behavioral indicators following islanding and non-islandong disturbances. In this thesis, a systematic procedure for designing of synchronous DGs active anti-islanding protection is proposed and based on it, suitable changes on active and reactive power control loops are applied. So that the new proposed method improves detection time and undesirable effects on synchronous DGs performance in grid-connected mode in comparison to previous works. In addition, a boosted Hilbert-Huang Transform (bHHT) method for signal processing and analysis of dynamic response of synchronous DGs is proposed. So, based on this method and by proposing suitable indicators, islanding situation can be discriminated from other non-islanding situations. Both proposed methods are better than the previous ones in terms of anti-islanding protection criteria. Also they are more suitable in practical situaions, e.g. when motors load penetration is high in the grid. This thesis also proposes a hybrid islanding detection method with combining these two methods that results in a more comprehensive and powerful scheme for islanding detection. Designing and analyzing of proposed methods and dynamic modeling of the test systems conducted in PSCAD environment and using MATLAB software. Keywords: DERs islanding, active anti-islanding protection, detection based on dynamic behavior of synchronous DG, synchronous DG controllers, processing of synchronous DG output signals