Research On Micro Photovoltaic Grid-Connected Inverter And Islanding Detection Technology

Since walked into the 21 century,energy loss and environmental pollution became the two difficulties of economic and social development all around the world.In order to protect the ecological environment and promote global economy,the exploitation and use of renewable and clean energy was drawing more and more attention.As a kind of pollution-free green energy,the traditional energy has been replaced by the solar energy gradually.Thus,the grid-connected photovoltaic power generation will be developed rapidly.The topologies of micro grid-connected photovoltaic inverter was deeply studied on the thesis.The topology and working principle of the interleaved active-clamp flyback were introduced and analyzed especially for micro grid-connected photovoltaic inverter.Then the small signal mathematics model was constructed for this inverter.On this basis,the control strategy and islanding detection techniques of the micro grid-connected photovoltaic inverter were deeply studied.Firstly,the sorts and topologies of micro grid-connected photovoltaic inverter were analyzed and compared on the thesis,advantages and drawbacks of different topologies were proposed and a topology of the inverter was chosen for research.Secondly,the control strategy of micro grid-connected photovoltaic inverter was introduced and analyzed.At the same time,the standards and system models of islanding detection technology were studied and the concepts and hazards were analyzed.Based on the analysis of normal islanding detection theory,an active islanding detection method with positive feedback of voltage frequency absolute was proposed for analysis of the none-detected zone and then the model was simulated.Simulation results show that the new method not only could detect the island phenomenon quickly and accurately,but also had a good power quality.Based on the overall design and the islanding detection technology,the complete design of micro grid-connected photovoltaic inverter was presented.The hardware of active-clamp fly-back staggered grid inverter was designed such as main circuit,drive circuit,sampling circuit and so on.Then the software design of the system was also given,such as system status,main program,sampling program,zero-cross detection program,islanding detection program and so on.Finally,the grid experiment of the micro grid-connected photovoltaic inverter was done to show the grid connected waveforms.Experimental results show that THD of grid-connected current of the micro photovoltaic grid-connected inverter had reached the national standard and the proposed system was stable and reliable.