Islanding Detection Technology For Micro-grid Of Multi-distributed Generators

Recently, with the rapid development of new energy technologies, distributedgenerators, such as photovoltaic, wind turbine, battery, are widely connected to thegrid system, formatting a large number of distribution networks with high penetrateand double directions of power flow. The active distribution networks have changedthe conventional power flow and fault characteristic, creating many new challenges,in which the anti-islanding protection is one of key issues. At present, thedevelopment trend of anti-islanding protection is to integrate protection into theinverter and it can be divided into passive protection and active protection.Constant power output control strategy is commonly used in distributed powergrid, when the system disconnect from the main network, there will be a powershortfall, the amplitude value and frequency of the system voltage will shift. Passiveislanding detection is to detect island operation by measuring the amplitude andfrequency of the voltage state. With good stability as well as the advantages of a smallamount of calculation, frequency measurement algorithm based on Fourier transformhas been the most widely used in the frequency measurement field. However, theFourier algorithm, due to the disadvantage of spectrum leakage, fences effect, as wellas the time lag, is difficult to adapt to the requirements of islanding detection.Therefore, this paper does a in-depth analysis and discussion about the application ofalgorithm basing on Kalman filter.The fundamental purpose of the active islanding detection method is to minimizeor eliminate the non-detection zone of passive islanding detection, while minimizingthe impact on the grid power quality. Relatively speaking, the power disturbancedetection method is a simple and practical method. In practical applications, thepower disturbance method faces two problems: the select of disturbance value and thesynchronization issues. Basing on the equivalent circuit of the island system, thispaper analyzes the intrinsic relationship between the voltage amplitude and activepower, frequency and reactive power, and analyzes the intrinsic relationshipquantified combining with the concept of load quality factor and load resonantfrequency,. In addition, this paper presents the voltage harmonic sudden change as thepick-up condition of active islanding detection, which solves the synchronization problem of power disturbances. Finally, a simulation model of micro-grid system isbuilt in Simulink, verifying the correctness of theoretical analysis as well as thevalidity disturbance detection method based on reactive power.