Power Optimization And Grid-connected Control For Photovoltaic Array

With the rapid development of society and economy and faced with the increasinglysevere problems of power supply and environment pressures, we are forced to encourage andsupport the development and utilization of new energy resources and renewable energyresources to solve energy problem. As a new energy resource with the characteristics of widedistribution, easy accessibility and no pollution, solar energy has been given abroad attention.Photovoltaic (PV) power generation is the main kind of solar energy application, andoptimization of PV system and efficiency improvement of PV generation have been the hotresearch topic in the field of PV. This paper focuses on the power optimization of PV arraywhich involves the models and characteristics of PV array, power optimization of PV array,grid-connected control of PV system, design of PV grid-connected system, finally anexperimental platform is designed which is based on the previous theory study and simulationanalysis.Firstly, the basic model of PV cell is established to simulate its electrical characteristicsand module mismatch situations, then PV braches and array model are used to explore PVcharacteristics under partial shading conditions, which indicates that the PV arraycharacteristics are complicated and output power-voltage curve exhibits multiple localmaximum power points. Several conventional maximum power point tracking (MPPT)methods, which may lose effectiveness to track the global maximum power point (GP) underpartial shading conditions, are introduced. Moreover, two typical global maximum powerpoint tracking (GMPPT) methods are introduced. The section provides theory base.Secondly, based on the theory of series-parallel connection of electric circuit, the outputpower of the PV arrays branch under partial shading conditions is analyzed in detail. Amethod of power optimization design of series-voltage source for PV array under partiallyshaded conditions was presented. Furthermore, with voltage compensation to the branch,every branch in the array can operate on the maximum power point (MPP) condition to obtainthe maximum output power of the whole PV array, and then the method with series-voltagecompensation and the method without series-voltage compensation are comparativelysimulated and analyzed. The results show that the output power of the PV array under partialshading increases with the proposed method. The proposed method is easy to design inseries-parallel PV array and useful to practical application.Then, several PV grid-connected systems are introduced and the principle and design of Boost circuit are investigated in detail. As to voltage source inverter, current control methodand closed-loop controls of the system are introduced. The model of PV grid-connectedsystem with previous control method using MATLAB software is simulated to prove thecontrol feasibility.Finally, a2kW experimental platform of PV grid-connected system is designed whichinvolves design of main circuit parameters, inductance and sensing circuit and summary ofPCB plate making. Then the detailed processes of the main program, interrupt service routinesand the AD subprogram are proposed. The experimental results are analyzed at last.