Control Technology For Improving The Stability Of Distributed Photovoltaic Grid Connected Inverter

With the implementation of the national "Double carbon" plan,the comprehensive utilization of new energy is particularly important.In the transmission process of photovoltaic power generation,due to the long transmission line,there is a non-negligible line intpedance in the power grid,which makes the power grid exhibit weak grid characteristics.which has a greater stability for the operation of the grid-connected inverter.Therefore.this paper unalyzes the unstable conditions of photovoltaic grid-connected inverters under weak grid conditions and studies the control methods to improve the stability.The mathematicat models of photovoltaic cells and inverters are established.In order to select the ideal damping furm.different active damping filters are analyzed.and the output impedance model of the inverter is obtained according to the inverter model.The influence of the system parameters on the inverter is analyzed by applying the impedance ratio stabilty criterion.The analysis shows that the grid impedance affects the stability of the The inductive impedance component of the grid will reduce the phase angle margin of the system,which will reduce the ability of the inverter to suppress the harmonic components caused by the grid voltage,thereby reducing the stability of the system.In this paper,the series virtual impedance is used to correcct the output impedance or the inverter,but the phase angle margin is limited,and it is difficult to select appropriate virtual impedance parameters.Too high parameters will reduce the modulus value of the inverter output impedance in the low frequency band,affecting the The system’s ability to suppress grid-connected harmonics cannot cope with large-scale changes in grid impedance.In this regard,this paper proposes a phase angle compensation control based on virtual impedance,which increases the system phase angle margin by reducing the phase angle difference at the intersection frequency of the inverter output impedance and the grid impedance amplitude.Through the simulation of Matlab/Simulink platform,it is verified that the inverter can operate stably in a wide range of grid impedance changes after adding phase angle compensation control,which proves the effectiveness of the improvement.