Research On Predictive Control Technology Of T-Type Three-Level Grid-Connected Inverter Based On LCL

There are two major issues that China’s sustainable development needs to solve urgently,one is environmental protection,and the other is energy demand.In recent years,new energy power generation has attracted more and more attention.As an interface device between distributed power generation and the grid,the control performance of inverters determines the power quality of new energy power generation.Research is of great significance.This paper establishes the continuous system mathematical model of the threephase T-type three-level grid-connected inverter based on the LCL filter in the threephase stationary coordinate system,the two-phase stationary coordinate system and the two-phase synchronous rotating coordinate system.In order to more accurately fit the hybrid system characteristics of the grid inverter at low switching frequencies,the mathematical model of the continuous system is improved,and the hybrid system model is derived.Moreover,on this basis,a high-precision discrete prediction mathematical model is derived.The following theoretical research use it as the basis.Aiming at the problems of high harmonic content and poor active damping effect of traditional LCL grid-connected inverter control methods,this paper proposes a multivariable predictive control strategy based on a high-precision discrete model.Capacitance voltage,grid side current,inverter side current,mid-point voltage difference,and switching frequency are added to the value function to achieve control objectives such as active damping,mid-point potential,improving grid-connected current quality,and reducing switching frequency.The two-step prediction delay compensation algorithm is introduced,and the design steps of the value function are given.Aiming at the difficulty of trying to adjust the weight coefficients of the multivariable predictive control algorithm,the switching frequency is not fixed,and the parameter drift of the LCL filter,this paper proposes a robust fixed-frequency segmented control strategy based on the prediction of a high-precision discrete model.Firstly,the value function segmented design method proposed in this paper is used to optimize the control,and then the parameter observer of the LCL filter is added to enhance the robustness of the control system.Finally,an improved switching sequence fixed-frequency control strategy is adopted to further reduce The harmonic content of the grid-connected current is fixed,the switching frequency is fixed,and the electromagnetic interference of the power board to the control board is reduced.Finally,MATLAB/Simulink software was used for simulation verification,and a20 k W three-phase T-type three-level grid-connected inverter prototype based on LCL filtering was built.The parameter design of the prototype and the selection process of hardware devices are given,and through experiments,the correctness and effectiveness of the theoretical analysis in this paper are verified.