Study On Maximum Power Point Tracking Of Partially Shaded Photovoltaic System

Photovoltaic Power Generation is a very important kind of applications of solar energy, it is acknowledged to be the most development prospects of all the kinds of the new energy and renewable energy sources. It has great significance both for improving the engineering level of Photovoltaic Power Generation and constructing security structure of the energy sources.On the situation of uneven illumination, if photovoltaic array has overtopped temperature, there would be the phenomena named hot spot effect. The usual solution of this problem is multiplying bypass diode. This solution can prevent the photovoltaic battery to be breakdown, but it would lower the efficiency of generating electricity in a photovoltaic system, and diode can't be controlled. During the situation of uneven illumination, the output current-voltage curve of the PV system will appear echelonment, and there would be many local peaks in its P-V curve. When the external environments changed, the traditional mathematical model and tracing method of the unimodal maximum power point would fail. So, it's necessary to construct a new kind topological structure of photovoltaic power system and develop a new kind of control arithmetic to find the maximum power point, adjust the peak power output and improve the generating efficiency of the photovoltaic power system.Based on the studying of domestic and foreign literature, this thesis present a new kind of topological structure which with integrated converter and a kind of improved Particle Swarm Optimization (PSO) was used to research control technology of photovoltaic power system under the situation of uneven illumination. In this paper, the electrical characteristic and the maximum power point tracing of photovoltaic cells were analysis, and deeply study on the topological structure and operating principle of the integrated converter, and particularly analysis control method of the integrated converter constituted by multi- modules to make every photovoltaic cell work in their maximum power point. A kind of method named PSO with Extended Memory (PSOEM) is proposed. Compared with the standard PSO, PSOEM has better performances in global optimization and multivariable optimization in the situation of multi-modal function. It is used in the photovoltaic array maximum power tracing control under the situation of uneven illumination, and solve the problem of multi-peak optimization in partial shading. On the basis of the mathematical model and control strategy, Using Matlab/Simulink to do simulation experiments of the system constituted by two modules under different shading conditions. The overall performance of this control strategy is checked by this simulation experiments. Test results shows that compared with the solution by multiplying bypass diode, this method has superiority in improving output power of photovoltaic array , the feasibility and effectiveness of this proposed method is proved.