Research On Current Control Based On Three-level LCL Photovoltaic Grid-connected Inverter

With the expansion of the world energy crisis and the gradual deterioration of environment,human beings have an increasing demand for the development and utilization of new energy sources.Solar photovoltaic is attracting more and more attention due to its advantages such as wide distribution,abundant reserves,high efficiency and cleanness.In order to make the solar photovoltaic power generation system be efficiently,cleanly and friendly gird-connected,Control strategy for gird-connected of photovoltaic inverter should be further studied.Model Predictive Control(MPC)has the advantages of intuitive concept,flexible control,fast dynamic response,and easy implementation through digitalization,it is a better control method currently.Therefore,this paper study the model predictive control of the classical Neutral Point Clamped(NPC)three-level topology.First,the basic working principle and mathematical model of NPC three-phase three-level inverter are summarized.Based on the NPC three-level topology,the relationship between the switching action combination of the three-level inverter and the output voltage is analyzed;the mathematical model based on the LCL filter in the?? coordinate system is established to lay the foundation for the design of the subsequent model predictive control system;The working-sector decision method of the space vector modulation(SVPWM),the action time of each voltage vector and the sequence of switching actions in the carrier period are given.Secondly,the neutral point imbalance problem of NPC three-level inverter is studied.For the neutral point potential imbalance problem of NPC type three-phase three-level inverter,the balance factor method is given to control the potential balance of the neutral point.The proposed algorithm based on the model predictive control cost function to balance the DC side capacitor voltage can effectively suppress the fluctuation of the neutral point potential.Finally,the cost function of model predictive control is established and the simulation is carried out for analysis.Based on the basic principle of model predictive control,the discrete-time model and cost function of the inverter in the ?? coordinate system are established and the simulation model of the inverter system is built in Matlab/Simulink software.By changing the weight coefficient in the cost function,it is easy to control the grid-connected current,suppress the neutral point potential imbalance and reduce the switching frequency.The simulation results verify the superiority of the model predictive control in the grid-connected inverter control.