Research On Photovoltaic-grid System And Control Strategy

The environmental pollution and energy crisis has become one of the most challengingproblems in today’s social.solar energy with its rich resources, clean pollution-freeadvantages is under the attention of human being, its application is more and more widely,especially the research and development of solar photovoltaic grid-connected system.through the theoretical analysis and modeling simulation. The maximum power tracking ofthe photovoltaic (pv) grid system and control methods are studied.Finishing the followingworks:Firstly, the research from the photovoltaic system composition, which contains circuittopology structure, filtering circuit model and the grid system control mode, is studied.mathematical model of three-phase grid inverter state space based on the LCL filte isbuilt.The equation of state of the order number by9order turns to6order throughcoordinate transformation, which reduces the design difficulty of inverter controller.Secondly, all kinds of maximum power tracking (MPPT) algorithm is got a detailedcomparison and analysis. the common methods to maximum power tracking containpersistence pressure method, disturbance observation method, the incremental conductancemethod and intelligent algorithm, in this thesis, an improved algorithm of variable steplength conductance increment method is put forward based on constant pressure methodand incremental conductance method.Established the maximum power tracking simulationcircuit model, the simulation experiment results show the improved algorithm is correct.Thirdly, the control strategies of photovoltaic (pv) grid systems are analyzed, mainlyresearch and design the repetitive control method based on the principle of endometrium.By far the most commonly used control strategy is PI control, however, PI control has somedisadvantages, when using PI control system, the output current and voltage waveform infirst few cycle oscillation is relatively large, after the system is stable, it is still has a lot ofharmonic, it has a certain influence on grid voltage. Therefore, an method is put forwardbased on the combination of PI control and repetitive control algorithm, and through theanalysis of simulation results, the system is verify and feasibility.