Study On Analytical Modeling And Suppression Strategy Of Interharmonic Currents In The Photovoltaic Power Generation System

The grid-connected generation of large-scale renewable energy,represented by solar energy,has already become an irresistible development trend in new power systems.However,with the increase of PV grid-connected capacity,the interharmonics has been more and more obvious,which threatens the steady operation of power systems.In addition,interharmonics will cause the low frequency oscillation of electromechanical system,and influence load capacity and insulation of electrical equipment.Interharmonics will also affect the normal operation of control equipment with the voltage over zero point as the synchronous signal.Therefore,research on the generation mechanism and propagation rule and suppression strategy of interharmonics in photovoltaic generation system has the theoretical necessity and engineering emergency for analyzing the power quality issues caused by photovoltaic generation.In this paper,the equivalent topological structure of PV generation system including photovoltaic array,MPPT control and grid-connected inverters is firstly analyzed.Based on the topological structure,the control model of inner and outer loops is built in dq rotating frame.Then the analytical model for interharmonic current caused by DC disturbance of photovoltaic inverter is established through derivation and coordinate conversion.Utilizing DC disturbance voltage,control parameters of grid-connected inverter and grid impedance parameters,the RMS value,frequency and phase angle of interharmonic current output by grid-connected inverter can be quantitatively calculated.In PSCAD platform,simulation examples verify the accuracy of the established model.Besides,the amplitude-and phase-frequency characteristics of interharmonic current caused by DC disturbance voltage are explored.The influence of two-loop control parameters and system impedance parameters on RMS value of interharmonic current is also further studied in-quantitative way.On the basis of the established interharmonic current analytical model of typical photovoltaic power station,the suppression strategy of intreharmonic current in PV generation system is also studied,using the virtual impedance control method with second order generalized integrator(SOGI)notch filter.By introducing virtual impedance on the side of the network-side inductance,the method effectively reduces the interharmonic current amplitude output by the photovoltaic system without increasing the system loss.Meanwhile,the application of SOGI notch filter can achieve the tracking accuracy of fundamental current while suppressing the interharmonic current.The system simulation verifies the feasibility and effectiveness of the suppression strategy.