Research On Islanding Detection Method Of Three-phase Photovoltaic Grid-connected Inverter

The double challenge of energy crisis and environmental pollution forces people to seek and develop new clean energy sources.Solar energy as an inexhaustible and renewable clean energy is received much attention and rapid development.Photovoltaic power generation technology is an important form of solar energy utilization,it converts solar energy directly to electrical energy.As more and more photovoltaic power generation systems are connected to the power grid,islanding effect is greatly received great attention.Islanding may cause serious harm to system equipment and person.Therefore,it is important practical significance to study islanding effect and its detection methods.Firstly introduced the background and significance of photovoltaic power generation technology,and then the topological structure of three-phase photovoltaic grid-connected inverter,control strategy and phase locked loop technology are described.At the same time,the concept,the harm and the detection method of the island are introduced.Aiming at the traditional passive and active islanding detection methods have none-detection zone,a new active islanding detection method is proposed,which is called active low-frequency drift(ALFD)method and it has carried on analysis.According to the control characteristics of three-phase photovoltaic grid-connected inverter,a vector control system based on grid voltage orientation is designed,and select the mathematical model in the synchronous rotating coordinate system,then closed loop dynamic is designed to ensure the system could run stably.About the research of ALFD method,this paper introduced the ALFD method used in single-phase photovoltaic grid-connected inverter principle and engineering realization.On this basis,the principle and engineering realization of the ALFD method applied in three-phase photovoltaic grid-connected inverter is introduced in detail.At the same time,the implementation strategy of ALFD which is applied in three-phase photovoltaic grid-connected inverter carried out intensive syudy.Then,the software and hardware system of three-phase photovoltaic grid-connected inverter system is designed,and the working principle of the system structure and control circuit is introduced.At the same time,the principle and digital realization of SVPWM algorithm in three-phase coordinate system is studied,the instruction current generation module is designed.Then discretization and digital realization of the regulator.Finally,simulation and experimental research are carried out on the main design content.The results of simulation and experiment show that the digital realization method of SVPWM is effective.The system stability design of three-phase photovoltaic grid-connected inverter is reasonable and effective.The application of ALFD method in three-phase photovoltaic grid-connected inverter is feasible and can quickly detect the occurrence of the islanding.The ALFD method is applied to three-phase photovoltaic grid-connected inverter,which has the advantages of no blind zone,small current distortion and easy to implement.In order to prevent the occurrence of the islanding,it provides a new way of thinking,which has valuable research value and wide application prospect.