Application Research Of Improved Hybrid Islanding Detection Method In Z-Source Inverter Photovoltaic Grid-Connected System

The grid-connected inverter is the core of the photovoltaic grid-connected power generation system.The Z-source inverter can reduce the chopper circuit and realize the buck-boost function,which increases the reliability and flexibility of the system,its application is more and more extensive.In the photovoltaic grid-connected power generation system,the occurrence of the islanding effect will bring safety problems and even affect the normal operation of the system.Therefore,the research on the islanding detection method has important practical significance.In this paper,the photovoltaic grid-connected power generation system based on Z-source inverter is taken as the research object,and the islanding detection method is further studied.Firstly,aiming at the shortcomings of the input current and the large voltage stress in the basic Z-source inverter topology,a modified Z-source inverter topology is analyzed in detail,the advantages are verified by simulation and are more suitable for photovoltaic power generation systems.Secondly,the control strategy of the whole photovoltaic grid-connected system is analyzed.Based on the analysis of the output characteristics of photovoltaic cells,two maximum power point tracking algorithms are introduced.The photovoltaic grid-connected system is simulated by MATLAB/Simulink.It shows that the control method works well and can obtain stable output.Then,the related problems of islanding detection are studied.The principle and detection standard of islanding effect are analyzed.Several common detection methods are analyzed and verified by simulation,and their advantages and disadvantages are summarized.Aiming at the problem that the load properties existing in the traditional Sandia frequency shift method have an influence on the detection results,an improved Sandia frequency shift method is proposed.Aiming at the problem that the single active detection method has a great influence on the power quality,an improved hybrid detection method is proposed.The effectiveness of the improved hybrid model is verified by changing the load parameters in the simulation model.Finally,an experimental platform for photovoltaic grid-connected systems was designed.Hardware design includes device selection,main circuit design,auxiliary circuit design,etc.And Software design including main program design,subprogram design are completed separately.The experimental platform of photovoltaic grid-connected system based on improved Z-source inverter was built.The experiment of grid-connected experiment and islanding test was carried out,and the experimental results were analyzed.The experimental results show that the improved algorithm of island detection has good performance,achieves the expected detection effect,and has applicable value.