Research On Control Strategy Of Photovoltaic Grid Inverter

With the rapid development of the world economy,the problem of energy shortage and environmental degradation has become an urgent problem.In the face of these challenges,countries around the world are vigorously developing new energy technologies.Due to the characteristics of rich solar energy storage and green environmental protection,it has been developed by countries all over the world,photovoltaic power generation technology is one of the ways to effectively use solar energy.In order to improve the utilization rate of solar energy and the quality of grid connected current,this paper takes the two-stage photovoltaic power generation system as the research object,and studies the control of the two key technologies: control of the front-stage photovoltaic maximum power point tracking(MPPT)and resonance suppression of the post-stage inverter grid connected current.Firstly,the two-stage photovoltaic power generation system is introduced.The basic structure of two-stage photovoltaic power generation system is analyzed;the mathematical model of photovoltaic cell under normal working condition is established,and the output characteristic curve of photovoltaic cell under different temperature and light conditions is obtained through simulation;the basic principle of the maximum power point tracking of the front-stage is analyzed;the mathematical model of LCL grid connected inverter under three coordinate systems is established,which provide a basis for later research.Secondly,in order to solve the problems of slow tracking speed and power oscillation in the front-stage of PV maximum power point tracking control,the active disturbance rejection control(ADRC)is proposed.The shortcomings of PID control and the composition and principle of ADRC are analyzed,and the stability of nonlinear ADRC is analyzed.The mathematical model of maximum power point tracking based on Boost circuit is established.The coupling among photovoltaic output voltage,current and load voltage is regarded as the internal disturbance of the system,and the nonlinear ADRC is designed to decouple it.In order to verify the effectiveness of the proposed method,the ADRC is added to the traditional perturbation and observation method for comparison.The simulation results show that the proposed method can improve the tracking speed of the maximum power point,effectively reduce the power oscillation,and improve the utilization of solar energy.Finally,in order to avoid additional sensors and save cost,the control strategy of grid current feedback active damping is proposed.However,when using this control strategy,the second-order differential signal of the grid current is extracted by difference method,which is easy to introduce noise and amplify it,affecting the system performance and grid current quality.In order to overcome this problem,grid current feedback active damping base on the tracking differentiator is proposed.The noise amplification effect of differential method is analyzed,and the tracking differentiator is introduced;grid current feedback link and the parameters of LCL invert are designed,and stability of LCL inverter are analyzed;the third-order tracking differentiator is designed to improve the grid current feedback method.The improved control strategy based on differential tracking and the traditional grid current feedback control strategy are compared by MATLAB simulation.The simulation results show that the improved method is better than the difference method in steady-state,dynamic characteristics and anti-noise characteristics,and has a good engineering application prospect.