Research On Islanding Detection Method Of Grid Connected Power Generation System

With the rapid development of photovoltaic power generation and wind power generation technology,the penetration rate of distributed grid connected generation system based on renewable energy is increasing year by year.Distributed grid connected generation system improves the flexibility and reliability of power supply,but it will also produce islanding effect,which poses a serious harm to electrical equipment and personal safety.Therefore,the distributed grid connected generation system must have the ability of anti islanding.Therefore,it is of great significance to study a fast and reliable anti islanding strategy.In this paper,the islanding detection method of grid connected power generation system is studied.The main research contents are as follows:The relationship between the mismatch degree of active power and reactive power before and after islanding and the amplitude and frequency of voltage after islanding is obtained by formula derivation,thus explaining the mechanism of islanding.The relevant islanding detection standards are introduced.The principles of common islanding detection methods are analyzed,and the advantages and disadvantages of various detection methods are summarized.In this paper,the description methods of non detection zone are systematically described,and their advantages and disadvantages are analyzed.Finally,the inverter topology and its control principle are introduced.The above work has laid a solid foundation for the improvement of the islanding detection method.The principle of active frequency shift islanding detection method with load impedance angle feedback(method A)is analyzed.Considering that method A needs to detect the impedance angle of the local load and the load power can be calculated according to the impedance angle,it can be judged whether the load is in the non detection zone of the passive detection method.This paper presents a hybrid detection method which combines OVP/UVP and OFP/UFP method with method A.The proposed method takes the calculated load power into the non detection zone discriminant of passive method to judge whether the load is in the non detection zone of passive method.If it is in the non detection zone,method A is used for islanding detection,otherwise passive detection method is used.Compared with method A,the proposed method not only eliminates the non detection zone completely,but also reduces the impact on power quality to the greatest extent.The simulation results based on Matlab/Simulink verify the effectiveness and superiority of the proposed method.An improved active phase shifting method(method B)is introduced.Aiming at the problem that method B can not take into account the detection speed and power quality,this paper adopts an improved active phase shifting method,and the positive feedback coefficient is fuzzy optimized according to the frequency offset and its change rate.The improved method and method B are compared and analyzed in terms of detection speed and non detection zone.Compared with method B,the improved method has faster detection speed and smaller non detection zone.The simulation results based on MATLAB / Simulink verify the effectiveness and superiority of the improved method.