Research On Islanding Detection For Three-phase Grid-connected Inverter

The distributed generation system will operate independently with the local load if the grid failure fails to supply power to the local load. This state is called islanding. The islanding will cause serious damage to electric equipment and maintenance personnel.Hence, the grid-connected inverter, as the interface between distributed generation units and grid must have the ability of detecting islanding. The key point of the research of the islanding detection is how to eliminate the Non-Detecting Zone and reduce the impact of the islanding algorithm on the grid. By taking three-phase grid-connected inverter as the target, a further study of islanding detection on the basis of the predecessors is discussed in this paper.Research on the operation of Grid-connected three-phase inverter is the basis study of the islanding detection. Because of the LCL filter,the active damping based on capacitor voltage feedback control is added to the system to solve the problem of resonance which cased by the LCL filter. The mathematical model of the system is established in order to get the accurate capacitance voltage feedback coefficient and the current of inverter control loop parameters. Lastly,the control method and the design results are verified by simulation and experiments.The keystone of this research is to accelerate the islanding detection and reduce the impact of islanding detection method on the grid. The islanding detection algorithm based on reactive current control makes the frequencu offset by the reactive current is the same as that of the active current.Then,the frequency can exceed the detection threshold quickly The quantitative analysis for islanding detection was carried to make it as far as possible to reduce the impact on the grid based on the Non-Detecting Zone.The islanding detection method does not inject harmonics to the grid and almost no impact on the grid.Finally, the islanding detection of the single inverter and multiple inverter are verified through the MATLAB/Simulink.Finally, Experimental verification of the proposed method is carried out on the experimental platform of three phase inverter. The experimental results show that thedetection method based on reactive current control has no non-detection zone(NDZ), and does not inject harmonics into the grid.