Research On Grid-Connected Current Control Of LCL Inverter In Non-Ideal Grid Environment

In complex grid environments,there are various problems in the operation of power systems.The existence of non-linear loads and short-circuit faults will cause the grid voltage to contain background harmonics and imbalances,and the presence of inductive components in the grid impedance will cause the grid voltage.There are a large number of low-order harmonics,which seriously affect the inverter output current quality.This paper aims to study the LCL-type inverter grid-connected current control method in complex grid environment to eliminate the influence of the network-side voltage disturbance and the inductive component of the grid impedance on the grid-connected current,thus improving the inverter's current output qualityFirstly,the mathematical model of the LCL type inverter is established under the abc three-phase coordinate system,the ?? two-phase stationary coordinate system and the dq synchronous rotating coordinate system.After analyzing its advantages and disadvantages,the model is selected in the dq coordinate system and decoupled,so that the inverter can be independently controlled on the dq axis,which lays a theoretical foundation for the following.Secondly,in the strong grid environment,some nonlinear loads and short-circuit faults in the grid cause harmonics and imbalance of grid-connected currents.A double-closed-loop current method based on grid voltage feedforward is proposed.Capacitance current feedback is added to the closed-loop current loop to increase the system damping to suppress the LCL filter resonance peak.The capacitor current can be obtained through the estimation process,avoiding the addition of unnecessary sensors,and introducing grid voltage feedforward control to eliminate the grid voltage.The effect of disturbance.The simulation results show that the inverter output current quality can be obtained better.Finally,for the weak grid environment,the inductive component of the grid impedance will reduce the stability of the inverter grid-connected system,and a modified weighted average current control strategy under weak grid is proposed.Based on the double closed-loop current control based on grid voltage feedforward,the grid impedance is added for analysis,and the new weighting coefficient is designed by the method of zero-pole cancellation.The obtained weighting coefficient is only related to the filter parameters,eliminating the inductive reactance of the grid.The influence of the grid-connected current reduces the system order.The simulation results verify that the grid-connected current still has good stability in the weak grid environment.