Research On LCL-type Grid-connected Inverters Control System

Today,with the gradual depletion of fossil fuels and environmental pollution,the use of renewable energy including solar energy and wind energy has become a key breakthrough in changing today's energy crisis.Grid-connected power generation is the main form of renewable energy development,and the grid-connected inverter is the middle bridge between new energy and grid,which is to convert energy from new energy sources into standard AC power of grid.Based on the topological structure of grid-connected current and capacitive current double closed-loop control for LCL-type grid-connected inverter,the paper selects the high-order LCL filter to filter out the large number of high-frequency harmonic components of the grid-connected inverter arm output voltage.The method of capacitive current feedback active damping to suppress the inherent resonance peak is introduced to ensure the stablity of grid-connected inverter system.The paper uses visualization algorithm to analyze and deduce the parameters of PI regulator,which provides the theoretical and design basis for the PI regulator.The research work of this paper is as follows:Firstly,the paper establishes the topology of LCL-type grid-connected inverter system,analyses the principle of bipolar SPWM pulse width modulation,and discusses the similarity between single phase and three-phase grid-connected system in circuit structure and principle to make the theoretical basis of unified design for grid-connected inverter.According to the technical indicators of grid-connected inverter system operation,the parameters of LCL filter are designed.Secondly,the LCL-type grid-connected inverter system is mathematically modeled to analyze and deduce the double closed-loop transfer function of the grid-connected system.The Bode diagrams of LCL-type grid-connected inverter system resolved by Matlab are to verify the effect of capacitive feedback active damping on the harmonic resonance peak.The parameters of grid-connected current PI regulator are designed by using the visualization algorithm and visualized by the frequency domain and time domain performance indexs.This method can obtain theoptimal PI parameter field without repeating parameters.Then,The paper describes the three kinds of three-phase grid-connected current control methods with the LCL filter.And the grid-connected current dq control method is used to simulate experiment.the simulation platforms of LCL-type single-phase and three-phase grid-connected inverter system have been built through Matlab/ Simulink.The numerical PI values are selected to simulate the waveforms and analysis the system performances,such as the harmonic content,full-load and half-loaded static characteristic and so on.The rationality and feasibility of the double closed-loop control for grid-connected inverter system are proved theoretically.Finally,the hardware system based on DSP-TMS320F2812 and the software system of HDSP-XDS510 USB have been designed,and the experimental prototypes of LCL-type single-phase 3kW and three-phase 9kW grid-connected inverter are built.The experimental results verify the validity of the above theoretical analysis and the effectiveness of the visualization algorithm design.