Stability Analysis And Control Strategy Research On LCL Grid-connected Inverter Under Weak Power Grid

Facing the world energy crisis and increasingly severe environmental pollution problems,distributed generation systems based on new energy provide an important way to solve the problem.As an important interface between the distributed power generation unit and the power grid,the stable operation of the grid-connected inverter plays a vital role in the safe and stable operation of the distributed power generation system and high-quality grid-connected current.As the penetration of distributed power generation continues to increase,the grid environment also changes.At this time,the grid can no longer be directly equivalent to an ideal voltage source.The characteristics of its weak grid put forward a higher stability for grid-connected inverters.Claim.This paper takes the LCL grid-connected inverter system as the research object,and proposes a grid-connected current control strategy that is more adaptable to the weak grid according to the influence of the weak grid characteristics on the stability of the grid-connected inverter,which ensures the grid-connected system’s Stability and high-quality grid-connected current.This paper first establishes the mathematical model of the grid-connected inverter system under ideal grid conditions and weak grid conditions.Through modeling,the influence of the grid equivalent impedance under weak grid conditions on the stability of the grid-connected system and the suppression of the grid are analyzed.The influence of background harmonic suppression ability is pointed out that the inductive component of grid impedance reduces the bandwidth and phase angle margin of the grid-connected system,thereby reducing the stability of the grid-connected system and the ability to suppress the background harmonics of the grid.At the same time,the modeling and analysis of the multi-machine parallel resonance characteristics under weak power grid conditions are pointed out.It is pointed out that the multi-machine parallel coupling characteristics under weak power grid conditions are more complicated.The equivalent impedance of the power grid leads to the coupling between grid-connected inverters.The quality of the grid current deteriorated further.In order to reduce the system phase margin under weak grid conditions,this paper proposes an adaptive control strategy for grid-connected current based on grid impedance detection technology.The first is to detect the grid impedance,and adjust the grid-connected current controller parameters and capacitor current feedback coefficients in real time to the detected grid impedance.Through this adaptive control strategy,the grid-connected system can maintain a higher bandwidth and phase margin.To adapt to a wide range of grid impedance changes.Finally,through simulation and experimental prototypes,the correctness and effectiveness of the proposed grid equivalent impedance detection scheme and adaptive control strategy are verified respectively.