Research On Key Technologies Of Grid-connected PV Inverter

With the aggravation of energy shortage and environmental damage,distributed photovoltaic power generation has attracted the attention of scholars and experts from all over the world.However,the large-scale development of distributed photovoltaic power generation faces some technical problems,such as low energy conversion efficiency,power quality fluctuation,unstable security performance and so on.Under the existing technical conditions,inverter control is the key to improve the conversion efficiency and power quality of photovoltaic grid-connected power generation system.In this paper,the threephase LCL photovoltaic grid-connected inverter is taken as the research object,and its maximum power point tracking control,LCL filter damping control and grid-connected control are deeply studied.The main research contents are as follows:The photovoltaic module is modeled,and the electrical characteristics of photovoltaic cells under actual working conditions are obtained.The advantages and disadvantages of traditional MPPT control are compared and analyzed.In view of the fact that the traditional conductance increment method can’t accurately track the maximum power point in local shadow environment,a photovoltaic MPPT algorithm using cuckoo search combined with variable step conductance increment method is proposed,and the accuracy of this method is demonstrated by simulation analysis.The LCL three-phase photovoltaic grid-connected inverter is modeled,its model in,and coordinate system is deduced,and the parameters of LCL filter are redesigned.Aiming at the natural resonance peak of LCL filter,the damping control is analyzed,and the active damping control with double feedback of grid-side current and capacitor current is proposed,and the effectiveness of this method is verified.Aiming at the problems of poor dynamic response of traditional controllers in gridconnected inverters,harmonic disturbance of current and inability to realize optimal tracking of alternating current,a method of controlling voltage with fuzzy PI and controlling current with discrete QPR and RCDBC is proposed.In view of the problem that the traditional DSOGI-PLL can’t correctly decouple the positive and negative sequence components and harmonic components of voltage under non-ideal voltage,and can’t realize synchronization,by using the improved DSOGI-PLL phase-locked loop technology,the DC filtering structure and frequency feedback link are introduced.The simulation analysis proves that the proposed method can improve the suppression ability of harmonic current,and can accurately phase-lock and realize the unity power factor grid connection.In order to further verify the effectiveness and practicability of the proposed method,an experimental platform of photovoltaic grid-connected inverter system was built.The overall structure,hardware design and software design of the system are introduced.The hardware design of the system includes the design of sampling,driving and protection circuits,and the software design of the system includes the design of the main circuit and interrupt subroutine.Finally,the grid-connected voltage and current are analyzed,and the effectiveness and practicability of the control method proposed in this paper are demonstrated.