High Frequency Resonance Analysis And Resonance Suppression Of A Grid-tied Inverter Coupled With A Long Transmission Line

In a new energy distributed grid-connected system,when the inverter is connected to the grid via a long-distance transmission line,the wide-frequency domain and high-frequency multi-resonance phenomenon will appear in the inverter output current due to the non-negligible distributed capacitance of the transmission line.This will deteriorate the current waveform and reduce the power quality of the system.At the same time,the background harmonic voltage on the grid side will oscillate and amplify on the transmission line,further aggravating the system instability.Therefore,this paper studies the generation mechanism and suppression method of the above two types of high-frequency harmonic resonance phenomena in distributed power generation systems.In this paper,the grid-connected inverter and transmission line are modeled,and the Norton equivalent model of the inverter and the Thevenin equivalent model of the grid transmission line are obtained.When the amplitude of the inverter output impedance is equal to the amplitude of the transmission line impedance,and the phase angle difference is 180~°,the inverter output current will have a multi-resonance phenomenon.At the same time,the background harmonic voltage propagation equation is established based on the transmission line theory,and the influence of the harmonic output impedance of the inverter on the oscillation of the harmonic voltage along the line is investigated.According to the transmission characteristics of the wave,when the length of the transmission line tends to be infinitely,it can be considered that the reflection coefficient n of the specific harmonic wave tends to 0,that is,only the incident wave in the system has no reflected wave,so as to suppress the high-frequency resonance in the system.Based on this theory,this paper proposes a high-frequency harmonic resonance suppression strategy for grid-connected inverters considering a long-distance transmission line.With the original fundamental wave control strategy unchanged,the harmonic voltage and harmonic current of the inverter grid-tied point are extracted and multiplied by the corresponding virtual harmonic infinite coefficient to construct a given harmonic signal,and for multiple harmonics near the resonance frequency,multiple PR controller current loops are superimposed to control.With this method,the inverter can take into account the harmonic resonance suppression while outputting the fundamental wave current.The proposed strategy is verified on MATLAB/Simulink simulation software.Finally,a?-shaped transmission line model is established,and the correctness of the transmission line model is verified by FRA5097 frequency spectrum analysis and transmission line no-load test.An inverter platform based on DSPTMS28335 control was built to verify the correctness and effectiveness of the improved frequency resonance suppression strategy.