Design And Research Of LCL Photovoltaic Grid-connected Inverter

As a bridge between solar energy and power grid system,grid connected inverter system is the key core of photoelectric conversion,which requires high grid connected efficiency and power quality.However,Grid connected efficiency and power quality are affected by the actual grid connected power and current distortion rate.An effective control strategy is very important.In this paper,two-stage photovoltaic grid connected inverter is used as the model to improve the traditional MPPT control and inverter grid connected control strategy,and on this basis,An 2kW grid connected experimental platform is designed for experimental research and verification.The main contents include:1.According to the project idea and experimental requirements,the two-stage grid-connected structure is taken as the research object.At the same time,the paper select the LCL inverter after analyzing and comparing the typical inverter topology.Then,the mathematical model of photovoltaic cells,boost circuit and LCL inverter is built according to the topology,then analyzing the advantages and disadvantages of the control strategy in each coordinate system.2.Then,based on the principle of boost circuit,the traditional MPPT control strategy is discussed.It is found that the system will oscillate at the maximum power point and not track to the actual maximum power point after the uneven illumination.Therefore,the paper presents an adaptive step size disturbance observation algorithm of constant parameter function.It can effectively reduce the system vibration through adaptive step size,constant parameter function can re plan the working point of the system and work at the actual maximum power point after the variable illumination.Finally,it is verified in the MATLAB simulation model The effectiveness of the control strategy is discussed.3.Then combining with the inverter mathematical model,the paper discusses the resonance peak problem of LCL filter.After deducing the working principle of the traditional active damping method,modifying the feedback function of the capacitance current and combineing the grid current and the capacitance current feedback into a single feedback loop,the results of Bode diagram is analyzed that the method basically retains the inhibition effect of the traditional active damping method and simplifies the parameter setting Constant and current feedback loop.Finally,a single current feedback multiple PR control strategy is used to reduce the harmonic content of grid current,and the feasibility of this method is verified by simulation in MATLAB.4.Finally,according to the technical requirements of the 600 kW grid connected photovoltaic power generation system of the school enterprise project,a 2kW photovoltaic power generation system verification platform is designed.The paper select the device model and design the main circuit diagram.According to the control requirements,the sampling circuit,the driving circuit and the software program design on the DSP are completed successively.The 2kW experiment platform is built in the laboratory,and the signals of sampling circuit and driving circuit are tested respectively.Finally,the effectiveness of the control strategy proposed in this paper is verified by experiments.