Research On Islanding Of Distributed Generation System

Distributed generation is the main developmental direction of the electrical industry. As the number of Distributed Generation (DG) systems manifold increasingly in grid,especially the grid-connected equipment that based renewable energy gain in popularity in distributed generation systems, the probability of islanding in utility networks increased, the risk associated with unintentional islanding must be taken into account.Research on islanding related problems has been conducted for over twenty years,but most of them have focused on anti-islanding protection and test of grid connected inverter system.In this paper,islanding of distributed generation system is studied comprehensively and systematically, the definition and elementary issues of islanding are described,anti-islanding schemes are presented and their relative effectiveness is determined using phase criterion and non-detection zone(NDZ),and anti-islanding test is discussed. Furthermore, because it can be desirable to permit islanding to increase customer reliability, and this is often done where the DG provides backup power to the facility where it is installed,this paper describe briefly intentional islanding of microgrid.The main research contents of this paper include:1. The mechanism of islanding is analyzed, the probability and the risk associated with unintentional islanding is discussed.2. The Communication-Based anti-islanding techniques and the local detection schemes of DG systems are discussed,and the active methods and the passive methods in local detection schemes are described in detail.3. The NDZ is regarded as performance index to evaluate anti-islanding methods' effectiveness in this paper,and is described quantificationally by using phase criterion and Matlab simulation.4. To validate the anti-islanding protection function of grid-connected devices, the anti-islanding test procedure is summarized on the basis of IEEE Std. 1547.1, and the islanding test circuit is designed for the small-scale wind/solar/battery hybrid power system which equipped with sandia frequency shift (SFS) method.The experimental results indicate: The SFS. active anti-islanding algorithm can detect islanding effectively and appears to provide a good compromise between islanding detection effectiveness, output power quality, and system transientresponse effects.