Research On Islanding Operation Characteristic And Identification Method Of Grid Connected Distributed Generation

In recent years, the scale of distributed generation system in the domestic and foreign develops rapidly, but its non planned outage islanding detection technology has always been difficult and hot spot in research. With the improvement of power users and industrial production etc. requirement of power quality, people pay more attention to the passive islanding detection technology, but in the detection techniques, islanding detection under power balance is always a difficulty, and the existing islanding detection technology can be found in islanding detection method must have characteristic of islanding and method that can identify the characteristics. So this paper islanding phenomenon power balanced state of the work was carried out the corresponding research on islanding detection technology for distributed generation islanding operation characteristic and identification method. So this paper, aiming at the islanding phenomenon under power balance, carries out the corresponding research work on islanding operation characteristics and identification methods of grid connected distributed generation in islanding detection technology.First of all, the basic issues of islanding is expounds. Starting from generating mechanisms of islanding effect, the necessary conditions of islanding is analyzed in detail, different detection standards of islanding effect are given. Then work principle and blind area distribution expression of the passive over/under pressure and the over /under frequency islanding detection method, and the commonly used active frequency drift and the power disturbance islanding detection method are analyzed.Secondly, according to the impedance characteristics before and after the distributed generation system and network islanding, the concept of real and virtual impedance is put forward, then combined with harmonic distortion of grid system, a kind of harmonic impedance characteristic function is constructed to research distributed islanding operation characteristic,at the same time the selection rule of characteristic quantity is given. Finally, by the simulation and the experiment, the islanding operation characteristics are further studied and analyzed, and thus the theoretical analysis is showed having some validity.At last, neural network is selected to detect and distinguish island phenomenon according to the extracted characteristic, which is good at identification and can overcome the shortcomings of the traditional threshold detection. Firstly, the algorithm of islanding detection identification methods which is based on the neural network is given. And also the basic principle of neural network and network structure selection are described. Then, the effect of islanding detection in single grid connected inverter and multi grid connected inverter are given by using of simulation. Finally, the identification method is tested through the experiment platform, and thus the islanding detection method is showed having recognition accurancy and feasibility.