Design And Implementation Of Photovoltaic Inverter

The energy crisis has become a common crisis around the world,and the traditional fossil energy represented by oil and coal has been unable to meet the needs of today's social development.Many renewable energy sources,solar energy has attracted extensive attention from all over the world because of its advantages of huge reserves,no pollution,no consumption and safety.The grid-connected photovoltaic inverter converts the direct current of solar cells into alternating current and sends it to the power grid.The former dc-dc circuit can realize the Maximum Power Point Tracking(MPPT)of solar cell array while boosting voltage,so as to achieve the Maximum effective use of energy.The back-stage dc-ac inverter circuit inverts the DC bus voltage of the front stage into an AC current of the same frequency and phase as the grid voltage.In this paper,the photovoltaic grid-connected inverter system is taken as the research object,and the topology structure,MPPT,hardware and software design of the inverter are studied in depth.On this basis,a 5kW dual-stage photovoltaic grid-connected inverter prototype has be designed.Firstly,the commonly used MPPT algorithm including voltage fixing method,disturbance observation method and conductance increment method is introduced,and the latter two methods are simulated and verified.The response time and steady-state error of conductance increment method are relatively good,but the step size setting is complicated.Therefore,this paper proposes an improved MPPT control strategy of variable step size.This paper introduces the principle of the improved conductance increment method of variable step size from two aspects of step size adjustment coefficient and initial disturbance step size setting,and builds the simulation model of photovoltaic system in MATLAB/SIMULINK simulation software.The simulation results show that the improved variable step size algorithm can effectively improve the dynamic response speed of the photovoltaic system under the condition of dramatic changes in light intensity,while maintaining a high steady-state tracking accuracy.Then,the software and hardware of the grid-connected photovoltaic system have been designed to realize the 5kW photovoltaic system experimental platform controlled by DSP(TMS320F28035),and the experimental verification has been carried out.The experimental results show that the improved variable step size algorithm can effectively improve the dynamic response speed of the photovoltaic system under the condition of dramatic changes in light intensity,while maintaining a high steady-state tracking accuracy.In addition,the proposed algorithm has a relatively simple control logic and a small amount of computation,which can be realized conveniently by DSP,and has a good application prospect in photovoltaic inverter system.