Research On The Method Of Harmonic Suppression In LCL-type Photovoltaic Grid-connected Inverter

With the intensification of energy crisis and environment pollution problem,grid-connected photovoltaic power generation technology has received wide attention and rapid development.The gird-connected inverter is used as the energy interface of photovoltaic power and the AC grid.It has a major impact on the output power quality.The grid-connected current quality has been made clear requirements by related industry in order to prevent output current harmonics to pollute the AC grid.Therefore,harmonic suppression method of grid-connected inverter has become a hot research topic.In this paper,based on photovoltaic LCL grid-connected inverter as the research object,the suppression methods of low order harmonic and DC injection are studied.The research has important significance of the realization of low THD of grid-connected current and large-scale grid-connected photovoltaic power supply.Firstly,the effect of large-scale grid-connected photovoltaic power supplies on power system was introduced and the problem of harmonic was mainly analyzed.The status of harmonic suppression method of grid-connected inverter was reviewed.Then the grid-connected inverter main circuit topology and the mechanism of generating current harmonics caused by SPWM modulation,inverter dead-time effect,power grid voltage distortion,instruction current signal error,DC injection were analyzed in details.Secondly,a novel dead-time elimination and compensation method based on full analysis of the feature of the grid-connected inverter and zero-current clamping phenomenon is presented to eliminate the dead-time effect of grid-tied inverter.In comparison with traditional dead-time elimination and compensation methods,the proposed method can better restrain the output voltage distortion,effectively improve grid-connected current quality due to full consideration of zero-current clamping phenomena.In order to suppress current harmonics caused by power grid voltage distortion,instruction current signals error,DC injection,a improved multi resonance QPR control strategy was proposed on the basis of analyzing the frequency domain of the closed-loop transfer function of grid voltage and instruction current signal.In comparison with multi resonance QPR control strategy,the proposedmethod can suppress DC injection by introducing PI controller.Finally,using matlab/simulink to implement simulation studied,simulation results verify the feasibility and effectiveness of the proposed method.