Research Of Robust Repetitive Control On LCL-Type Grid-Tied Inverter

China has become the biggest contributor to the growth of renewable energy in the world,and distributed power generation has received extensive attention as the main way to develop renewable energy such as wind and solar energy.As an important energy conversion interface for distributed generation,grid-tied inverter is responsible for transforming DC power into high-quality AC power.In the current control of grid-tied inverter,the repetitive controller has become a research hotspot because of its superior steady-state performance,but it is difficult for the repetitive controller to maintain robust stability due to the change of system parameters and the uncertainty of power grid in actual operation.In this thesis,the LCL-type grid-tied inverter is taken as the research object.To deal with its poor dynamic capability and robustness,the robust control based on structural singular value theory is introduced into repetitive control,and the robust repetitive control strategy is proposed.First,some basic knowledge of robust repetitive control is introduced.For repetitive control,the internal model modification and object compensation are introduced from the point of view of stability.In order to improve the dynamic of repetitive control system,the compound repetitive control is composed of plug-in structure and PI control.Some basic knowledge of robust control is introduced,including uncertainty modeling,linear fractional transformation,μ theory and D-K iterative method.With introducing robust control to the repeat controller,the block diagram and design steps of the general robust repeat control strategy are presented.Secondly,the model of nominal model of LCL-type grid-tied inverter and the scheme of suppressing resonance are introduced,and the structure and design of module parameters of composite repeat controller of LCL-type grid-tied inverter based on passive damping of notch are given.In order to deal with the system parameter change and the weak grid,the structure uncertainty and the unstructured uncertainty are used to model the system parameter change and the weak grid respectively.On this basis,the robust repetitive control strategy of LCL-type grid-tied inverter based on μ theory is proposed,and the design steps and the parameter design basis of each block are given.To deal with the high order internal mode of repetitive control,the 5rd Padé approximation is used to reduce the order reduction error instead of conventional way.The order reduction method based on the least square method is selected to reduce the order of the high-order robust feedback controller.Finally,in order to verify the effectiveness of the robust repetitive control strategy of the LCL-type grid-tied inverter proposed in this paper,a 2kw inverter platform based on IPM and CPLD is constructed,and the experiments of the related stability and robust performance are carried out.The experimental results verify the effectiveness and robustness of the control strategy.