Research On Harmonic Current And Resonance Suppression Strategy Of Single-phase Grid-connected Converter

Grid-connected converter plays an important role in electricity conversion.However,the grid-connected harmonic current caused by the dead-time effect of converter switch tube and the DC side ripple voltage,the resonance phenomenon caused by the filter threaten seriously the safe operation of the power grid.Therefore,this thesis analyzes the generation mechanism of harmonic currents and resonance of grid-connected converter.The corresponding harmonic currents and resonance suppression strategies are studied.Firstly,the mathematical model of the single-phase grid-connected converter is established.Then it analyzes the mechanism of the dead-time effect caused by the switch tube and the harmonic current caused by the secondary ripple voltage on the DC side.The multi-quasi-resonant controller graded compensation method is given to suppress the harmonic current caused by the dead-time effect.A voltage loop optimization strategy based on the lead-lag compensation notch filter is designed,which suppresses effectively the third harmonic current caused by the secondary ripple voltage on the DC side through the feedback loop.The open-loop cut-off frequency of the system is widened,and the response speed is faster.Secondly,it analyzes the resonance phenomenon caused by the LCL filter for high frequency harmonic current suppression.Under the condition of weak power grid,the limitation of using single-loop control method to suppress resonance is explained.A resonant suppression strategy based on capacitive current voltage proportional control(CCVP)active damping is given,which suppress effectively the resonance phenomenon and improve the robustness of the system.A analysis method of virtual resistance characteristic factors extraction is proposed.The CCVP active damping proportional coefficient is designed by the Nyquist stability criterion.A design example of LCL filter and CCVP active damping proportional coefficient is given.The given resonance suppression strategy has good robustness when the filter parameters and grid impedance change.The resonance suppression strategy has good dynamic characteristics when the load changes.Finally,Matlab simulation platform and experiment platform for a single-phase gridconnected converter are built to verify harmonic current and resonance suppression methods proposed in this thesis.It is verified that the multi-quasi-resonant controller graded compensation method and the voltage loop optimization strategy based on the lead-lag compensation notch filter can suppress effectively harmonic current.The the resonance suppression strategy based on CCVP active damping can suppress effectively the resonance phenomenon caused by the LCL filter.