Research On Two-stage Three-phase Photovoltaic Grid-Connected Control Method

Photovoltaic power generation as a green and clean energy conversion mode has been widely studied in the context of "dual carbon".Two-stage photovoltaic parallel power generation has attracted much attention in the market due to its high conversion efficiency and flexible configuration.The front stage completes boosting and MPPT work through DC/DC circuits,and the latter stage completes inversion and grid connection through three-phase inverters.In the DC/DC circuit of the previous stage,the average switching model is used to model and analyze the boost circuit.The traditional disturbance observation method is limited by the step size,and cannot take into account the optimization time and the stability of the output voltage.This nonlinear output characteristic will aggravate the harmonics of the grid-connected current.According to the photovoltaic power generation characteristic curve,the improved disturbance observation method introduces multiple steps on the basis of a single step,which improves the conversion efficiency while improving the stability of the system output voltage and reducing the harmonics of the grid-connected injection current.In the post-stage,the working principle of the inverter circuit is analyzed,the mathematical model of the post-stage circuit is derived,and the control algorithm is summarized and improved.The output characteristics and control requirements of H-bridge,NPC and FC inverters are analyzed.The working characteristics of L,LC and LCL filter are summarized;Designed a phase-locked loop based on a single synchronous coordinate system;Designed based on PI control of the double closed-loop control system,the traditional PI controller cannot meet the control requirements of the nonlinear system,the introduction of fuzzy PID controller to optimize the control of the outer ring,according to the input of the system,dynamic adjustment of parameters,and then get better control effect.Finally,based on the above research,the MPPT and grid-connected simulations were completed in Matlab/Simulink,and the experiments were completed on the TMS320F28335 experimental platform,and the above theoretical rationality and correctness can be obtained through simulation and experimental results.In the previous simulation experiment,it is verified that the improved algorithm can improve the stability of the output voltage and improve the output efficiency of the photovoltaic system.In the later simulation experiments,the improvement of the grid-connected current and voltage harmonics by the improved algorithm is verified.