Research On Chaos Characteristics And Suppression Of Low Frequency Oscillation In AC/DC Hybrid Transmission System

Large-scale grid interconnection and long-distance power transmission have become the development trend of contemporary power grids.With the development and application of HVDC transmission system,while it provides a better solution for the power system to achieve large-scale grid,high-voltage,and long-distance power transmission,a larger and more complex AC/DC hybrid transmission system has also been formed,which undoubtedly poses new challenges to the stability and reliability of the power system.Among them,the low-frequency oscillation of the power system is one of the common threats that cannot be ignored,and exploring its generation mechanism is an important cornerstone of its control.As a complex nonlinear system,the power system exhibits nonlinear electromechanical oscillation dynamic behavior which is one of the important factors causing low frequency oscillation.This paper analyzes the low-frequency oscillation of the AC/DC hybrid transmission system based on the nonlinear chaotic mechanism,and designs the low-frequency oscillation controller to ensure the safe and stable operation of the system.First of all,this paper introduces the low-frequency oscillation of the power system based on the nonlinear bifurcation mechanism and the chaotic mechanism,and combines the mathematical model of the typical four-dimensional power system to explain the chaotic characteristics and the chaotic criteria in detail.Secondly,considering the generator power angle and speed,the load node voltage amplitude and phase angle,and the DC current and rectifier firing angle in the HVDC system as the system state variables,this article establishes a twoparameter six-dimensional mathematical model of AC/DC hybrid transmission system with using the load reactive power and the DC reference current value,control system gain,and DC transmission line resistance value in the HVDC system as bifurcation parameters.In addition,the limit stable operating point of the system is analyzed by bifurcation theory,and then the existence of chaos is verified by the Largest Lyapunov exponent spectrum and power spectrum of the two-parameter system.What’s more,this paper analyzes the low-frequency oscillation characteristics of the system under chaos with the bifurcation diagram,timing diagram,attractor Phase diagrams,and explores the influence of the system’s lowfrequency oscillations with chaos mechanism by the parameters of the HVDC system.Finally,this paper designs an internal model controller based on the -order inverse system for the low-frequency chaotic oscillation of the AC/DC hybrid transmission system.The simulation results illustrate that the system can work stably at the target operating point under the action of the designed controller,and the robustness and stability of the controller are verified by changing the internal parameters of the system and applying external interference.