Current Control Strategy Of Single-phase Grid-connected Inverter Based On Robust Repetitive Control

The repetitive controller（RC）has good fundamental signal tracking and harmonic signal suppression capabilities.However,repetitive control requires high accuracy in system modeling and is not robust enough in the case of grid frequency fluctuations or weak grids.Considering the robust controller’s insensitivity to changes in system parameters,a composite control strategy based on robust repetition is proposed.First,the single-phase LCL grid-connected inverter is modeled and the parameters of the LCL filter are designed.The damping strategy for the single-phase LCL-type gridconnected inverter is also discussed.Second,the repetition controller is designed as the main controller of the current controller with priority.The RC is analyzed based on the internal model principle,while the repetitive controller structure is optimized and the parameters of the repetitive controller are designed using Proportional integral multiple resonant repetitive control（PIMR）.The design flow of a robust controller based on the hybrid S/SK problem is then given,and a new Robust proportional-integral multiple resonant repetitive control（RPIMR）is formed by combining the robust controller with the repetitive controller.The stability analysis of this control system is given.The results show that the dynamic response of the RPIMR is not as good as that of the PIMR controller,but the RPIMR has a lower dynamic response when the frequency fluctuates.The Simulink simulation also considers the case of a weak grid and presents the steady-state analysis of the output current of the RPIMR and the PIMR in the case of a weak grid,which further confirms that the RPIMR has better robustness than the PIMR.It is further demonstrated that the RPIMR has better robustness than the PIMR and can guarantee an output current THD of less than 3% in the case of weak grid and grid frequency fluctuations.In the experimental part,the schematic diagram of the hardware design of the LCL-type grid-connected inverter experimental platform and the selection of components is presented.A grid-connected inverter system based on TMS320F28335 as the main control chip is built.The software design adopts MATLAB/Simulink code generation for fast engineering code construction.The experimental analysis of the robust repetitive controller and the transient and steady-state analysis of the repetitive controller at 50 Hz are carried out to verify the feasibility and effectiveness of the proposed control strategy.