Research On MPPT And Grid-connected Control Of Stand-alone PV Microgrid System

PV generation system consists of Stand-alone, Grid-connected and Multi-mode systems.Among them, Stand-alone PV generation has the following advantages: the least energytransformational, the most immediate, the best economical etc, but there are also manyproblems to be solved itself: the mutations of external conditions such as light intensity andtemperature have a great influence on the output power of photovoltaic cells; in some place ofsufficient sunshine, excess energy stored in the battery will be wasted. A kind ofgrid-connected controllers was designed specially for Stand-alone PV generation system,which can achieve "plug and play" feature for additional energy output, it can help to improvethe flexibility of energy transmission of stand-alone PV generation system. Hence, theresearch on maximum power point tracking technology and grid-connected control forStand-alone PV generation system have certain theoretical significance.This thesis will launch the research from following several aspects: maximum powerpoint tracking technology, the mathematical model of grid-connected controller andgrid-connected control strategy. On the basis of equivalent circuit of photovoltaic cells, withthe consideration of light intensity and temperature and other external conditions on theoutput power of photovoltaic cells, mathematical model of the photovoltaic cell wasestablished. According to the topology structure of inverter, which can complete energyconversion, mathematical model was derived.Based on the principle of maximum power point tracking, for the conventionalperturbation and observation method is difficult to get a higher response speed andsteady-state performance, an improved perturbation and observation method was proposed,which can rapidly track the maximum power point of requirements, and maintain stability.Finally set up model for simulation analysis, the results verify the accuracy of the algorithm.The structure and working principle of grid-connected controller are analyzed, accordingto its topology structure, transient and steady state mathematical model are established,parallel and series sides control models were derived with dq transformation. On the basis ofparallel and series sides control models of grid-connected controller, grid-connected controlstrategy and control parameters were designed. Grid-connected simulation model was built inMatlab/Simulink, two kinds of simulations that directely connecting grid and connecting gridwith grid-connected controller were simulated and contrasted, the results prove that thegrid-connected controller can smoothly and fastly achieve the "plug and play" feature ofstand-alone PV generation system.