A Study On Island Detection And Partition Of Grid-connected DG System

With the development of distributed generation system, island effects may bringabout serious results to the operation of system and the safety of the workers. Therefore,the grid-connected inverter must own the function of anti-islanding protection.This paper introduces the principle of island effects, and classifies the existing islanddetection methods. Based on the analysis of the shortage of traditional island detectionmethod, this paper proposes an island detection method which combined the phaseaberration and voltage-active/frequency-reactive algorithm. This method improves thespeed of island detection and reduces the influence of power quality, it can also erasenon-detection zone.Generally speaking, island detection method usually judges the island based on thevoltage and the change of frequency. This paper combines voltage-active andfrequency-reactive algorithms, and monitors the change of output voltage ofgrid-connected inverter and the change of frequency. If one of the variable exceeds thethreshold value, we can get the conclusion that island is happen. Therefore, this detectionmethod is more accurate than others.Island partition is a control mode of looking for reasonable solution column point, itis a comprehensive topic, it comes down to stable operation of the electric system andwhole contents of protective relaying. The traditional search method can not adapt to thering structure of distribution network and can not distinguish the grade of the load, thispaper proposes island partition method for distributed generation system based on primalgorithm, and the issue of islanding is transformed into obtaining the minimal spanningtree of the connected graph. According to the actual situation of island, this paper dividesthe load into important load and normal load, and combines off-line backup path andonline load research. This method not only ensures the power supply of important load,but also ensures the power supply of the normal load, forming DG Island.This paper applies Matlab to built island detection emulation model which verifiesthe availability of the detection method. The analysis of the algorithm proves rationality and accuracy of the prim algorithm.