Research On Three Phase Photovoltaic Grid Connected Inverter System And Key Technologies

In today's world,the problems of resource shortage and environmental pollution are very prominent.Solar energy,as a new type of renewable energy,has the advantages of clean and pollution-free,so it has been focused on.The grid-connected photovoltaic system is the development trend in the future.The core component of the grid-connected system is the inverter,which is connected to the grid through filters.Aiming at the low efficiency and harmonic interference of photovoltaic grid-connected system,the key technologies of photovoltaic grid-connected system are studied.In this paper,LCL three-phase photovoltaic grid-connected inverter system as the object,the main research contents are as follows:(1)Determining the research program.Researching on the inverters in the PV gridconnected system,starting with the research process and development status of the inverters,the maximum power point tracking(MPPT)control technology,SVPWM technology and the grid-connected current control technology in the PVgrid-connected inverters are studied.(2)The mathematical model is researched and the parameter of LCL filter is designed.Based on the analysis of the topology and control mechanism of the LCL grid-connected inverter,the state equation of the filter in abc,?? and dq coordinates is derived,and the control parameters are designed and calculated.(3)The new MPPT control technology is studied.For single-stage photovoltaic grid-connected system,to have MPPT function,the typical MPPT methods are compared and analyzed.The control technology of constant voltage tracking method combined with conductance increment method is improved to track the maximum power point more quickly and accurately.Finally,it is verified on MATLAB/Simulink simulation platform.(4)The SVPWM technology in photovoltaic grid-connected inverters is studied.Starting from the basic principle of PWM modulation technology,the sectoral division,vector action time,switch duty ratio and mathematical theory of SVPWM technology are analyzed in detail.Modeling and Simulation on the platform of MATLAB/Simulink proves that the output current of photovoltaic grid-connected system and grid voltage can be realized in the same frequency and phase by using SVPWM modulation technology.(5)The compound current inner-loop control technology which combines quasiproportional resonance integral and deadbeat control is studied.This technology is based on LCL inverters.Based on this model,a three-phase photovoltaic grid-connected inverter simulation system with 50 kW output power is designed.The current inner loop control technology is simulated by MATLAB/Simulink platform.