Research On Maximum Power Point Track Of Photovoltaic System Based On Shadow Effect

Shortage of traditional fossil energy and environmental issues are becoming moreand more seriously, in this case, the research about new energy technology becomes ahot topic. Solar energy, as a clean、non-polluting renewable energy, has become themost potential for development of new energy, Photovoltaic(PV) power generation, asthe most effective way to use solar energy, has been concerned widely in theinternational community.On the situation of uneven illumination, PV array will occur hot spot phenomena,even PV cell will be burned. To multiply bypass diode on both ends of PV module is thecommon solution, however, the bypass diode will change the electrical characteristics ofPV module, e.g., PV array’s V-P characteristic curve will appear multi-peak undershading conditions, in this case, the normal maximum power point tracking(MPPT)algorithm is inefficient and even complete failure.In this paper, output characteristics of PV array on the situation of unevenillumination are investigated, as well as, a suitable MPPT algorithm under shadingconditions is designed. Firstly, the reason that results in V-I multi-knee and V-Pmulti-peak by bypass diode is analyzed, with the help of equivalent mathematicalmodel of PV cell, the conclusion that V-I characteristic will have N knee shapes and V-Pcharacteristic will have N peaks is derived, and is verified by simulation. In the nextplace, the distribution of local peak point of PV array under shading conditions isanalyzed, the prediction equation of a certain peak point position is deduced andverified by simulation.Once more, some common unimodal and multimodal MPPTalgorithms are analyzed, focus on the analysis of particle swarm algorithm and geneticalgorithm what are both global optimization algorithms and point out the limitationsthat they apply to the MPPT of PV cell, the bimodal MPPT algorithm is designed bycombining theory analysis and the feasibility of the algorithm is verified through thesimulation. Finally, a test platform of MPPT is built and write a program based on TI’sDSP(TMS320F2812).The most outstanding characteristic of bimodal MPPT algorithm designed in this paper is anticipation function and capability of rapid positioning, the algorithm iscompatible with the unimodal MPPT algorithm and is different with general globaloptimization algorithm that will still search widely under unimodal condition. Thesimulation result shows the algorithm can track the global maximum power pointaccurately under the condition of uniform and uneven illumination intensity. In theexisting test platform, also can track the maximum power point accurately under theuniform illumination intensity condition, but the test platform remains to be perfectunder uneven illumination intensity condition.