Research On FCS-MPC Strategy Of Single-Phase Photovoltaic Inverter Parallel System

With the promotion of photovoltaic poverty alleviation in the 13 th Five-Year Plan and the promotion of photovoltaic and photovoltaic desertification control in the whole county during the 14 th Five-Year Plan,a breakthrough has been made in photovoltaic new energy power generation technology.However,a single photovoltaic power generation device can no longer meet the current demand due to its small capacity and low power.Therefore,the research on the control of the multi-inverter parallel system is of great significance.This thesis takes a single-phase photovoltaic inverter as the controlled object.A Finite Control Set Model Predictive Control(FCS-MPC)strategy is studied based on Mixed Logical Dynamical(MLD)modeling.The control study of a single inverter system is carried out first,and then the control of a parallel system of multiple inverters is further studied.The main research contents are as follows:(1)Through the research of traditional inverter grid-connected topology and multi-inverter connection mode,the non-isolated two-stage single-phase full-bridge inverter topology is selected as the control object.This thesis analyzes the current research status of inverter parallel technology and the control method of microgrid inverters;further studies the FCS-MPC strategy based on MLD modeling;analyzes the advantages of applying this method to inverter control.(2)MLD modeling and FCS-MPC strategy research for single-phase photovoltaic inverter system.In order to improve the grid-connected photovoltaic inverter power quality and meet the grid-connection requirements more quickly and accurately,MLD modeling and FCS-MPC are applied to one-phase photovoltaic inverter grid-connected systems.Firstly,the system is modeled according to the idea of hybrid logic dynamics.Then based on the model,a full-dimensional state observer is designed to estimate the output current,and phase-locked loop is used to phase-lock the grid voltage.Finally,a finite set model predictive controller is designed for control.The simulation results show that,compared with the traditional model predictive control based on the switching function model,the control strategy proposed in this dissertation not only solves the mixed integer quadratic programming problem existing in the traditional MPC,but also reduces the total harmonics distortion(THD)of the output current of the inverter circuit,improves the power quality of the inverter into the grid,and meets the grid connection requirements.(3)MLD modeling and FCS-MPC strategy research for single-phase photovoltaic multi-inverter parallel system.In order to improve the output voltage quality of the multi-inverter parallel system in the microgrid and suppress the circulating current between the inverters,the multi-inverter parallel system was modeled by MLD and the FCS-MPC controller was designed.Firstly,the multi-inverter parallel system is analyzed,and the hybrid logic dynamic model is established.Then take the parallel system of two inverters as an example to carry out the circulating current analysis.Finally,the objective function is established,the output voltage is controlled,and the circulating current is added as a constraint to the objective function value,which can not only solve the real-time changes of the control system by online optimization,but also effectively obtain higher tracking accuracy of the inverter output voltage and lower total harmonic distortion rate,suppress the circulating current between the inverters,and obtain a good dynamic response.