Maximum Power Point Tracking And Grid Connected Control Method For Photovoltaic Power Generation System

With the development of photovoltaic (PV) power generation technology, photovoltaic grid-connected system is widely used.But as the environment of PV system is becoming more and more complicated, and it bring many complex problems for the stability of the PV cells’ output and the grid-connected. The research object of this paper is the PV grid-connected system, and the research purpose is in order to bring the maximized and the optimized electric energy, carrying out theoretical analysis and simulation study.Firstly, this paper system atically elaborated the research background, and then draw out three major part in PV grid-connected system:PV cell modeling, Maximum Power Point Tracking, Grid-connected control.This paper aims at the three main parts, and carries out the research contentsas follows:(1) Based on the detailed analysis of the physical characteristics and the mathematical model of PV cells, using Matlab/Simulink to build a common engineering model, analyzing the relationship between the cells’output characteristic of external factors; Then, the principle of the multi peak of the P-U characteristic curve of the PV array under local shading is analyzed.At the same time the Multi peak of PV array model is set up, and the distribution law is simulated and analyzed.(2) Analysis of the control principle of MPPT and introduction of the tracking methods of several commonly used maximum power point.At the same time, the implementation strategy of P & O and INC is analyzed, and the simulation model of each sub module is established, and compare the tracking performance. In view of the two defects of P & O method, a variable step size disturbance observer based on power prediction is adopted to improve the dynamic response speed and stability of the control method.(3) For the problem of multi peak of PV array in the case of partial shade, analysis of the advantages and disadvantages of Particle Swarm Optimization algorithm (PSO) that is applied to the MPPT control, using an adaptive learning factor PSO.Compared with the traditional INC, this algorithm not only retains the advantages of the basic PSO, but also has a faster convergence speed, higher accuracy, accurately track the global MPP of PV generation system under local shading condition and stabilize it.(4) In the single-phase PV grid-connected system,Two-stage grid connected power generation system based on Boost converter is established, Using a based on grid voltage feed-forward compensation of SPWM current control strategy of grid connected control. The simulation results show that the system dynamic performance is good. Not only achieve the MPPT of PV but also achieve unity power factor.(5) In the three-phase PV grid-connected system, through the grid inverter, the mathematical model under the stationary reference frame transform coordinate to get the mathematical model under rotating reference frame, establishing the Three-phase grid inverter discrete mathematical model based on SVPWM current deadbeat control is separately applied the Deadbeat Control to the active current and the reactive current, and the result shows that the harmonics of grid-connected current can still meet the requirements of the grid connected.