Research On Grid-tied Inverter Based On Improved Repetitive Control Scheme

As the interface between the distributed power generation system and the power grid,the grid-tied inverters play an important role in safe running,stability,and high-quality operation of the distributed power generation system.Different control methods have appeared in recent years.Therefore,the methods of the harmonic suppression for the grid-tied inverters are studied in this thesis.It also deals with the system stability and parameter design.The robustness on system parameters' variation is analyzed and studied.According to the analysis results,an active damping technique based on zero-phase notch filter is optimized.Firstly,the theory,stability,and harmonic rejection of the conventional repetitive control are given,and then the performances of the cascade and parallel hybrid control schemes of RC and proportional integral(PI)control are analyzed.The advantages and disadvantages of two kinds of hybrid control method are compared from two aspects of the stability and the harmonic suppression characteristics,Secondly,a novel proportional integral multi-resonant control(PIMR)scheme is put forward for a grid-tied inverter,and the proposed PIMR control scheme is composed of a repetitive control(RC)in parallel with a proportional gain.Theoretical and stability analysis of PIMR in discrete domain have been given,and then a step-by-step systematic design procedure with consideration of the practical implementation aspects has also been provided.And the robustness of the controller is validated in the case of grid impedance change,which makes the system be stable within a certain range of parameter fluctuation.The simulation and experimental results have validated the feasibility and outstanding performance of the proposed control scheme.Thirdly,an active damping technique based on a fractional-order zero-phase notch filter is proposed to neutralize the resonance of LCL filter.The fractional-order zero-phase notch filter design process is given by using the Lagrangian FIR filter approximation method,and then is used in PIMR construction.The notch frequency of fractional-order zero-phase notch filter can exactly align with the resonant frequency of the LCL filter.The simulation and experimental results have validated the effects of the integer-order zero-phase notch filter and fractional-order zero-phase notch filter.