Research On The Control Method Of Single-phase PV Grid-connected System

In order to solve the shortage of traditional energy and its environmental problems, theworld is looking for a new kind of green renewable energy. Solar energy is paid more andmore attention with its characteristics of resource unlimited, clean and so on. The photovoltaicgrid-connected power generation system is becoming a hot research spot. This thesis focuseson the research of the two-stage single-phase photovoltaic grid-connected power generationsystem, doing an in-depth study of the maximum power point tracking method and thegrid-connected control method.Firstly, the thesis overviews the control strategy of photovoltaic grid-connected powergeneration system, and research the structure of the boost circuit and the inverter circuit of thebipolar type grid-connected inverter system. Single-phase full bridge inverter main circuit ofvoltage type current control method and bipolar SPWM modulation is determined and theparameters of main circuit are design.Secondly, establishing the simulation model of photovoltaic cells, its outputcharacteristics and the maximum power point tracking methods are analyzed. Considering theproblem of conventional perturbation and observation method, a variable step perturbationand observation method is used. The algorithm obtains the working point of photovoltaic cellsby judging current differential, so as to determine the disturbance of the next time step.Then, the mathematical model of grid-connected inverter is established and analyzed.Grid-connected control strategy adopts double loop control strategy, which voltage outer loopused to stabilize the DC bus voltage and current inner loop to realize the grid current control.The current loop uses the triangular wave control mode, which adopts proportion resonantcontrol as the controller. In view of the influence of grid voltage on grid current, the gridvoltage feed-forward compensation is designed.Finally, the variable step perturbation and observation method and grid-connectioncontrol method is simulated by MATLAB. The simulation results verify the variable stepperturbation and observation method can track the maximum power point quickly andaccurately. And the simulation results also show that grid-connected current conform to thegrid-connected requirements and the DC bus voltage can be stabilized in the reference value.