Research On MPPT Grid-connected Control Of Three-phase Inverter Based On Quasi-Z Source

With the exhaustion of traditional fossil fuels and the increasingly severe environmental pollution situation,countries in the world have intensified efforts to develop and utilize new energy technologies.A variety of new energy power generation systems have made great progress.As a representative of new energy,solar energy has quickly become a new field that all countries are scrambling to expand due to its advantages such as unlimited reserves,green,zero pollution,safety and high efficiency,and at the same time provides a new path to solve the global energy crisis.Traditional MPPT(Maximum Power Point Tracking)cannot track the accurate Maximum Power Point in the presence of local shadow of photovoltaic array,which greatly affects the conversion efficiency of photovoltaic Power generation system.In order to improve the conversion efficiency of photovoltaic power generation system,it is necessary to carry out new research on the algorithm of maximum power point under local shadow.Because the traditional inverter is a two-stage inverter structure,in the DC-DC part,the system can only achieve a single voltage boost or buck,so the system reliability is poor,weak anti-electromagnetic interference ability.In this paper,the quasi-Z-source grid-connected photovoltaic inverter is used for research,which realizes the single-stage pressure lifting function and the voltage boosting and inverter function without inserting dead time,thus improving the reliability and efficiency of the system.In this paper,the mathematical model of photovoltaic cell(single exponential model,double exponential model,local shadow model)is first established,and its output I-U,P-U,power,current and voltage relationship characteristic graphs are obtained under different temperature and light conditions.Then the mathematical model of photovoltaic array is established based on the mathematical model of photovoltaic cell,and the output characteristics of photovoltaic array under different illumination intensity are analyzed.Disturbance were used respectively to observe(P&O),incremental conductance(INC),particle swarm optimization(PSO),variable step length conductance increment method to establish simulation model,through the simulation results to discuss ways of output characteristics,and through the different algorithms on the dc side of maximum power point tracking accuracy,speed,and the effectiveness of the algorithm to suppress oscillation as a condition of algorithm is selected.The control algorithm of MPPT was selected to keep the system stable at the maximum power point.The most important part of the grid-connected control technology of the quasi-Z source inverter is the setting of the control strategy.The quality of the control strategy will directly affect the stability of the grid-connected system.Set the network parameters when the Z-source inverter is working steady-state.A small signal model of impedance source in state space is constructed by aligning Z-source inverter.By analyzing the transient and steady state performance of the system,theoretical data support is provided for the setting of network parameters of the inverter and system control mode.The coupling relationship between duty ratio and modulation ratio is obtained by analyzing the relationship between duty ratio and grid-connected current as well as the relationship between modulation ratio and grid-side inductance.Direct axis and quadrator axis current PI control method is adopted to make the unit power factor of the quasi-Z source inverter meet the requirements of grid connection.Quasi-PR control technique is used to counteract network voltage interference in grid-side current control.Matlab/Simulink is used for three-phase grid-connection simulation.Through the simulation results,the effectiveness of grid-connection control is verified to ensure that the grid-connection current is in the same frequency and phase with the grid voltage,and the low harmonic operation of the system is maintained.