Research On Islanding Detection And Experiment For Grid-connected Distributed Generation

Due to the exhaustion of fossil energy,more serious environmental problem and the defects of large power grid,more and more equipments of distributed generation are connected to power grid system.While distributed generation system is expanding constantly,the power supply system will cause some serious problems,due to interruption of large power grid,such as unplanned islanding operation.This kind of operation mode will cause great harm to power equipments and operators,so the research of islanding detection is of great significance.In this paper,the basic issues of islanding detection,operation principles of common islanding detection methods and their improvements will be studied deeply.Accurate,effective detection and trying not to affect the power quality are standards of good islanding detection methods.Based on the analysis of common detection methods(remote islanding detection,passive islanding detection,active islanding detection),this paper finds out their advantages and disadvantages as well as their applications.Aiming at the deficiency of traditional detection methods,this paper proposes a new method of compound positive feedback detection.In this method,different positive feedback control arithmetics are added to detections of voltage and frequency.This avoids failing to detect,due to detection of single parameter.Meanwhile,this paper takes d axis component of voltage and frequency as control disturbances,which reduces the effects of positive feedback control on normal power quality.This method can improve accuracy of detection and reduce effect of normal power quality.This paper studies on the control model of grid-connected inverters.This system uses double loop control and designs the voltage and current loop PI regulator.Through building simulation model in Matlab/Simulink environment,the results verify the effectiveness and reasonableness of the proposed detection method.In the end of this paper,the three-phase grid connected inverters are used as the experimental platform of detection system to study on islanding detection.Meanwhile,the hardware and software are designed.The designs of hardware include the parameter design of LCL grid-connected filter,selection of filter capacitor at the DC side,selection of power switch tube,drive current,control circuit,AC voltage and current sampling circuit,over-current protection circuit and so on.The software is the design of Composite positive feedback detection method.The rationality of the parameter selection and the correctness of the proposed method are verified by analysis of the experiment.