Research On Resonance Suppression Method Of String Photovoltaic Inverter Under Weak Grid

In photovoltaic power generation systems,grid-connected inverters are crucial.With the continuous expansion of the scale of the photovoltaic industry,the number of grid-connected inverters is also increasing,and the problem of inverter resonance has become increasingly obvious.In addition,most of the distributed power generation systems are located in remote areas,and when integrated into the public grid,long transmission lines often bring non-negligible grid impedance to the system,resulting in poor effectiveness of traditional resonance suppression methods and reduced system stability.Therefore,in order to eliminate resonance,this thesis uses string photovoltaic inverter as the research object to carry out resonance suppression research under weak grid.The specific content is as follows:First,the background and significance of the research in this article are explained,the classification of string photovoltaic grid-connected systems and inverter resonance problems are analyzed,and the current research status of inverter resonance mechanism and suppression methods are summarized.Secondly,aiming at the problem of large changes in grid impedance under weak grids,a design method of LCL filter parameters under weak grids is proposed.The characteristics of the filter are analyzed,the mathematical model of the LCL filter is established,and the conditions for the selection of filter parameters are obtained.The grid-connected system controlled by Proportional Integral(PI)is verified by Matlab.The simulation results show that the proposed method can complete the parameter design of the LCL filter under different power grid conditions.Then,aiming at the inverter’s own resonance,a method for suppressing the resonance of the string photovoltaic inverter based on negative virtual capacitance is proposed.The negative virtual capacitance is added to eliminate the influence on the actual capacitance,and an estimator is introduced for parameter estimation to ensure the accuracy of compensation.The simulation model built by Matlab proves that the resonance is effectively suppressed after adding the proposed method.Finally,for inverter series resonance,a resonance suppression method for string photovoltaic inverters based on adaptive notch is proposed.By adopting the quasi-passive measurement method to measure the grid impedance in real time,update the improved notch filter and Quasi-Proportional Resonance(QPR)controller parameters,obtain the control structure block diagram of the system and analyze its stability through the bode diagram.The simulation of the proposed resonance suppression method by Matlab software shows that the proposed method has a significant improvement in static and dynamic performance,which verifies the correctness and effectiveness of the resonance suppression method.