Research On Oscillation Analysis And Suppression Of Grid-connected Inverter Considering Frequency Coupling

With the development of new energy sources such as wind power and photovoltaics,a large number of power electronic devices have been used.In the case of weak power grids,the interaction between the inverter and the power grid,and the complex dynamic characteristics of the inverter have led to frequent oscillations in actual engineering.,Which has severely hindered the development of new energy,and the frequency coupling phenomenon of three-phase grid-connected inverters proposed in recent years will adversely affect the system.Therefore,this paper considers the impact of frequency coupling on the oscillation problem of grid-connected inverters.Research and put forward effective oscillation suppression methods.This paper first establishes the impedance model of grid-connected inverter considering frequency coupling.In the weak grid situation,the frequency coupling effect caused by the phase-locked loop(PLL)and the frequency coupling effect caused by the DC voltage loop are respectively modeled,and the impedance model of the grid-connected inverter in two cases is obtained.The accuracy of the impedance model when considering PLL and DC voltage loop is verified by Matlab / Simulink.Secondly,the factors affecting the oscillation characteristics of grid-connected inverters are analyzed.The influence of PLL,DC voltage loop,PLL and DC voltage loop work together and inverter output power on the oscillation characteristics of the system is analyzed.The influence of each phase on the oscillation of the grid-connected inverter when the PLL and the DC voltage loop work together is revealed.Quantify the degree of influence of different factors on the system oscillation,and point out that the frequency coupling brought by the PLL is the key factor affecting the oscillation of the grid-connected inverter.The results of analysis of each influencing factor are simulated and verified.Finally,a method for suppressing oscillation of grid-connected inverters considering the influence of frequency coupling is proposed.Starting from the duty cycle disturbance and current disturbance brought by the PLL,a method for suppressing the oscillation of the grid-connected inverter to reduce the influence of the PLL is proposed.The suppression effect of the proposed method on frequency coupling and the suppression effect of oscillation are analyzed.Finally,the effectiveness and dynamic performance of the proposed method are verified by experiments.