Improved MPPT Function-Integrated Grid-connected Photovoltaic Inverter System Research And Design

Photovoltaic power generation steps into Large-scale development stage with numbers of grid-connected photovoltaic power plants. Photovoltaic power generation will occupy an important position in the future energy supply system. Thus the grid photovoltaic technologies become an important research content in recent years.This paper analyzes the characteristics of the PV array and the MPPT control the U-I of the basic principles, briefly sis of several major classical MPPT control strategy and the current major improvements research work about them. Considering the characteristic of the relation between dl/dU+I/U and Umodify(the deviation between the instantaneous value of system output voltage and the value of maximum power point voltage) for PV systems, this paper proposed an auto-adapted step size incremental conductance MPPT method based on segmented numerical approximation. We built the PV system model with the solar cell block and the MPPT controller using Matlab2009. Then, we used that model to emulate the tracking effectiveness of this algorithm when the illumination intensity changed sharply between500(W/m2) and1000(W/m2). The result showed that, compared with the conventional fixed step size method, the proposed approach can effectively improve the tracking speed and accuracy simultaneously. AS compared with other more complex methods, such as the gradient iteration solution and intelligent control method, the proposed approach is simpler and easier to implement. Then, this paper analyzes the relationship between the electrical vectors of grid-connected photovoltaic systems in grid-connected work condition to study the basic inverter control principles. Study the main grid-connected photovoltaic systems architecture and inverter topology and related impact on MPPT and grid-connected inverter control system. Based on grid-connected PV systems mathematical model in different coordinate systems, this paper focus on feedforward compensation-based decoupling inverter control strategy. Then studies the network side inverter implementing MPPT-based control strategy and the DC/DC converter implementing MPPT-based control strategy, and compare their advantages and disadvantages respectively. By building the PV array engineering simulation model, this paper studies the DC/DC converter implementing MPPT-based control strategy grid-connected photovoltaic system. The simulation results verify its good performance in MPPT and grid-connected inverter control.This paper describes several typical DC current injection suppression methods, analysis the applicability of them in grid-connected PV system based on LCL-filter. Considering the characteristics of PR and PI controllers, propose a grid-connected inverter DC injection suppression technology based on PR&PI integrated control strategy, effectively eliminating the DC component in grid current. Using Matlab/Simulink to implement simulation study, simulation results verify the effectiveness of this program.With a certain12.5MW photovoltaic power plant project, this paper briefly discusses the basic principle for photovoltaic power plant feasibility studies and planning studies. On the basis of completed feasibility study, this paper completes the access system design work for this12.5MW photovoltaic power plant.