Research On Control Strategy Of LCL Grid-connected Inverter Based On LADRC

New energy is widely used in the power supply chain due to its features of cleanliness,high utilization rate and sustainable use.Decentralized new energy sources typically form distributed generation system that interact with the grid via grid-connected inverter while providing local power.A large number of new energy units in the grid provide considerable power,but affect the performance of the grid,easy to form a weak grid environment,and introduce grid voltage harmonics.During the development of grid-connection technology,LCL inverter is widely used because of its low consumption and strong filtering.However,the problems still exist:on the one hand,the resonance caused by LCL filter needs to be solved;on the other hand,the influence of grid impedance and harmonics on the inverter current needs to be suppressed.In this paper,the application of LADRC in the control of LCL grid-connected inverter is studied.The main contents are as follows.Firstly,according to the topological structure of LCL three-phase grid-connected inverter,the mathematical model in dq coordinate system is established,and the parameters of LCL filter are reasonably designed.On this basis,the advantages and disadvantages of existing damping methods are analyzed for the resonance problem of LCL grid-connected inverter.Secondly,according to the principle of ADRC and the order of system,a third-order LADRC controller is designed for LCL inverter,and the system control block diagram and closed-loop transfer function in dq coordinate system are derived.On this basis,this paper analyzes the influence of LADRC control parameters on the tracking performance,the resonance suppression ability and stability of the system through frequency domain method.It is concluded that LADRC can effectively suppress resonance,but the stability margin of system is insufficient.Therefore,this paper introduces a damping method based on capacitive current feedback to improve the robustness of the system,calculates the parameter range satisfying the stability margin requirements by Matlab.And the effectiveness of LADRC control strategy is verified through simulation,which has better performance than PI control.Then,on the basis of LADRC control strategy,this paper establishes the impedance model of the system.deduces the output impedance expression of the inverter,and gives the stability conditions and the principle of harmonic suppression of the system in the weak grid.Based on this,this paper analyzes the influence of control parameters on system performance,and optimizes the parameters by simulation.Finally,this paper designs an output impedance correction method based on the observation feedback,which improves the output impedance of the inverter by extracting feedback from the interior of LADRC controller,so that the system has better harmonic suppression ability and stability in the weak grid,and the effectiveness of the impedance correction method is verified by simulation.The corrected LCL grid-connected inverter has a better ability to suppress major grid harmonics,and can adapt to a wide range of changes in the grid impedance.