Research And Design Of Independent Photovoltaic Control System On MPPT Under Partical Shading

With the depletion of traditional energy sources and the adverse impact on the environment,renewable clean energy has attracted much attention.Solar energy is a renewable and clean energy source.Solar power generation has become an important part of the world's energy.However,solar cells have a low photoelectric conversion rate.Most photovoltaic power generation systems adopt the MPPT technology to get higer output power.This thesis mainly studies the MPPT technology of independent photovoltaic power generation system,the charge-discharge control strategy of the battery and designs a charge-discharge controller with MPPT function.Multiple power points occur when PV arrays are partially shaded due to environmental factors.At this time,the traditional MPPT algorithm fails.To solve these problems,the working principle and mathematical model of solar cells are first studied,and then the MATLAB/Simulink is used to build the simulation model of photovoltaic array and research the output P-U and I-U curve of the PV array.In the independent photovoltaic control technology,the duty cycle of the DC/DC circuit is usually used to achieve the MPPT technology,so under the partial shading a simulation analysis of the P-D curve of the PV array based on the BUCK circuit is carried out.In addition,through the study of battery charging characteristics and the advantages and disadvantages of common battery charging strategies,a three-phase charging strategy using MPPT charging,constant voltage charging and floating charge charging is adopted.By analyzing the advantages and disadvantages of the traditional MPPT algorithm and Particle Swarm Optimization algorithm,the particle swarm optimization algorithm is improved,and a composite control strategy combining the improved PSO algorithm with adaptive step size disturbance are adopted.For conventional particle swarm optimization algorithm,the search speed is slow,the initial position of the particles is not easy to determine,and it is easy to fall into local extremum.This thesis designs a fixed boundary population particle position initialization method and a segmentation maximum step size strategy to improve the performance of the algorithm;for the problem of power loss caused by the single particle swarm algorithm under the illumination gradual change,the adaptive step size disturbance observation method was introduced to ensure that the output power is stable at the global maximum power point.The simulation results show that the improved MPPT control algorithm in this thesis can track the global extremum more quickly and stably than the conventional PSO algorithm under the partial shading.The commonly used DC/DC topology is analyzed,and the hardware and software design of the independent photovoltaic charge-discharge controller are described in detail.The design of hardware circuit mainly includes charging circuit,power tube driving circuit,main control circuit,sampling circuit and LED constant current driving circuit,etc;software program design mainly includes system main program,sampling filter program,charging control program and LED constant current control program,etc;The controller hardware designed in this thesis is low cost and has strong scalability.The designed independent photovoltaic charge-discharge controller was tested and analyzed.Firstly,each module of the controller is debugged to ensure that it can work.The constant current charging program,constant voltage charging program,MPPT algorithm and LED driver are tested separately.Test results show that the controller basically meets the design requirements.