Photovoltaic Cell Model And Its Maximum Power Point Tracking Under Shading Conditions

A complete photovoltaic power generation system is mainly composed of photovoltaic cells,MPPT controller,DC-DC inverter and load.The output power of the photovoltaic cell is affected by the ambient temperature and the light intensity.The output power of the photovoltaic cell is affected by the ambient temperature and the light intensity and the MPPT algorithm affects the output performance of photovoltaic system.Secondly,the output of photovoltaic power generation systems under shading conditions is more complicated.The output of cells is also affected by the connection mode of the photovoltaic cells.The conventional MPPT algorithm cannot accurately track the multi-peak global maximum power point.In order to improve the overall efficiency of the photovoltaic power generation system,the following studies have been done for the applicability of the photovoltaic cell engineering model,the advantages and disadvantages of the traditional maximum power point algorithm,and the application of the MPPT intelligent algorithm for photovoltaic components under shading conditions:According to the single exponential diode current output equation of photovoltaic cell,the output performances of two monolithic simplified photovoltaic cell models and two photovoltaic series cell assembly models under shading conditions were studied.Firstly,the results show that the two models can reproduce the experimental results accurately,but the theoretical and experimental errors of the two models increase obviously with the bias voltage rising.The reason is that the characteristics of the cell have changed completely under high bias,and the battery properties cannot be described by the characteristics of an ideal constant current source and an ideal diode.Secondly,for a single photovoltaic cell engineering model,the study found that the index model as a whole is superior to the simplified model and more suitable for the photovoltaic power generation characteristics;The reason lies in two aspects.On the one hand,the exponential model takes into account the influence of light intensity on current and voltage.On the other hand,the exponential model considers the four temperature coefficients of short-circuit current,open-circuit voltage,maximum power point current and voltage.For shading PV module models,any one of the models is in good agreement with the experimental data,but there are obvious errors.The reason is that both models are obtained under simplification.Under non-uniform illumination,the working state of the cell is not affected by the simple analysis due to the influence of the bypass diode.Finally,from the root-mean-square error analysis,the four-parameter model is superior to the power law model.The reason may be that the four-parameter model considers factors that are more comprehensive.By analyzing the output characteristics of photovoltaic cells,several conventional maximum power point algorithms and their improved algorithms are studied,and a photovoltaic power generation system model is established through Matlab/Simulink to achieve maximum power point tracking.First,the basic maximum power point algorithm perturbation observation method and its improved theoretical model of perturbation observation method were established through research,and the maximum power point tracking of the two algorithms was realized.As a result,it was found that the perturbation observation method improved its step size at the maximum power point,and the tracking speed and accuracy were better than the normal disturbance observation method.Secondly,the conductivity increment model was established,and an improved conductance increment method was built on the basis of the conductance increment method.The improved conductance increment method uses a varying step size to track the maximum power point,which is 0 near the maximum power point.The incremental step conductance method determines the maximum power point based on the conductance characteristics of the photovoltaic cell itself,so it can accurately find the maximum power point.Its tracking effect is better than the general conductance increment method.By studying the output characteristics of tandem photovoltaic modules under shaded conditions,an adaptive inertial weighted particle swarm algorithm was designed for maximum power point tracking based on the basic particle swarm optimization algorithm.The algorithm achieves the maximum power point tracking of the multi-peak output power of photovoltaic cell modules under shaded conditions.Through the simulation verification of the two PV modules under different shading conditions,the algorithm’s ability to track the maximum power of multi-peak output is proved.This research has certain reference value for the application of intelligent algorithm in the maximum power point tracking of photovoltaic cell components under shading conditions.