Research On Compound Control Strategy Of Linear Auto Disturbance Rejection And Repetitive Control For Three-level Grid-connected Inverter

The neutral point clamped(NPC)three-level grid-connected inverter is widely used in distributed grid because of its advantages of low withstand voltage and high output efficiency.However,the load or distributed power grid connected and off grid will affect the electrical parameters of the grid connected inverter,which will cause the output current quality of the grid-connected inverter to decline,instability,and even cause the system to collapse.Therefore,the compound control strategy of linear auto disturbance rejection control(LADRC)plus repetitive control of three-level grid-connected inverter is studied to improve the immunity and current quality of the three-level grid-connected inverter in this paper.First of all,on the basis of mastering the basic structure and working principle of LADRC,the first order LADRC based on the three-level grid-connected inverter is designed,and the mathematical model of three-level grid-connected inverter is established.The closed-loop system is analyzed,and the parameter range of the controller is designed.The correctness of the model and method in this paper is verified by Matlab simulation.The simulation results show that although LADRC has good dynamic performance,the control accuracy of the LADRC in a distributed power grid with harmonics is greatly reduced.Secondly,in view of the low accuracy of the LADRC,this paper proposes to compensate LADRC by repetitive controller,and then improve the output current accuracy of the system.Based on the analysis of the performance of the repetitive controller,the parameters of the repetitive controller are designed according to the harmonic characteristics of the output current of the grid-connected inverter in this paper,and the system simulation of LADRC plus repetitive control is completed.The simulation results show that the designed control scheme can effectively improve the output current quality of the grid-connected inverter.Finally,this paper presents a sensorless SiC MOSFET current detection scheme,and the effectiveness of the current detection scheme is verified through experiments.And the composite control grid-connected experiment of LADRC and repetitive control is completed on the three-level grid-connected inverter experimental platform with TMS320F28335 chip as the core,which verifies the feasibility and correctness of the research scheme in this paper.