Research Of Harmonic Suppression For Multiple Inverter With LCL Filter

With the increasing scale of solar photovoltaic grid-connected power generation,the larger the number of grid-connected inverter in parallel,the more obvious the resonance problem of LCL-type grid-connected inverter,and the adverse impact on the power quality of the grid will increase.So the resonance problem in the photovoltaic grid system can not be ignored.Resolving the resonator problem of the inverter has become an important part in the photovoltaic grid-connected system,which is of great significance to the photovoltaic construction and the power quality of the grid.In this paper,the mathematical models of L-type,LC-type and LCL-type filters are analyzed,and L-type and LC-type filter are respectively compared with LCL-type filter.The Bode graphs of all three filters are obtained by using the simulation software Matlab.By comparing the Bode graphs,it is found that the LCL filter has the best effect on the filtering of the higher harmonics.LCL filter on the harmonic can be a good filter.Because the structure of the LCL filter itself has a resonance,the research of structure of the inverter,LCL filter parameters,damping method of resonance,and application of simulation are started.The corresponding Bode graphs are obtained by Matlab,and the corresponding damping of passive damping and double closed loop is simulated.The simulation results show that these methods have some suppression of resonance.But with the increase of parallel number and system power,there are some limitations.A method by introducing a conductivity feedback loop to the grid-connected inverter control algorithm is proposed.The capacitance in the LCL filter is connected in parallel with a conductance.The method is analyzed applied in from the photovoltaic grid-connected inverter to the PV grid-connected multi-inverter,and then the control algorithm is improved.Bode graphs of LCL filter in the multi-inverters by using the simulation software Matlab.By comparing the Bode diagram with and without the algorithm,it is found that the improved algorithm has obvious effect on the resonance suppression.