Development Of High Efficiency Single Phase Non-isolated Grid-connected Photovoltaic Inverter

With the deterioration of the worldwide energy problem, intensifying the developmentand utilization of renewable energy became a consensus around the world. Various methodscan be applied to utilize the solar energy. Photovoltaic grid-connected power generation is themost representative aspect among those methods and had gradually become the mainstream ofthe solar energy utilization. As the key component of the photovoltaic grid-connected powersystem, photovoltaic grid-connected inverter was widely studied. In this paper, the singlephase photovoltaic grid-connected power system was taken as the research object. Particularly,detailed analysis of the photovoltaic grid-connected inverter was carried out in order todevelop a DSP-based single phase non isolation grid-connected photovoltaic inverter.At the beginning, the background and prospect of photovoltaic grid-connected powergeneration were expounded in this paper. Then, from the perspective of national policy andthe market distribution, comparison of the photovoltaic inverter industry development indomestic and international was made. Besides, as the key technologies of the grid-connectedphotovoltaic power system, the Maximum Power Point Tracking (MPPT) technology and theinverter output current control strategies were analyzed systematically. Further, the systemhardware and software designs, including the main circuit design and its key componentsselection, control system circuit design and software design of the system, were elaborated.Finally, experimental program was carried out to verify the performance of the designednon-isolated photovoltaic grid-connected inverter.TTo improvethe energy utilization efficiency of the system, in-depth theoretical analysis of theMPPT technology in photovoltaic power generation technology was conducted. Based on thePerturbation and Observation (P&O) method, the impacts of control method and two-stagemain circuit structure on the MPPT control performance were progressively analyzed. Thenthe newly P&O method which combined the three-point judgment and the constant voltagecontrol method was put forward. To optimize the power quality of inverter output current,current control strategies including the grid-connected current control method, the DCcomponent elimination and the common mode current inhibition had been researched in detail.Deadbeat control method was taken as the inverter grid-connected control method to ensure real-time synchronization and low harmonic. The DC component elimination control strategythat based on the software compensation through the detection of the inverter output currentwas proposed. Common mode current inhibition strategy which focused on the capacitancefilter near common mode signal generating source and the output common-mode filter wasapplied to restrain the common mode interference in the non-isolated photovoltaicgrid-connected inverter.Based on the design concepts mentioned above, a1.5kW single phase non-isolatedgrid-connected photovoltaic inverter was successfully developed. Corresponding tests werecompleted and good experimental results were obtained. According to the experimentalresults, the proposed single phase non-isolated grid-connected photovoltaic inverter designwas feasible.