Power System Wide-frequency Oscillation Analysis And Control Based On Nyquist Array Theory

In recent years,grid-integration of large-scale power electronic devices such as renewable power generation and direct current transmission has greatly changed the dynamic characteristics of the power system,making the power system exhibit complex dynamic behaviors and dynamic phenomena,and exacerbating the risk of wide-frequency dynamic stability.As a prominent problem to be solved urgently in power system stability analysis and control,the wide-frequency oscillation problem has seriously threatened the safe and stable operation of the power system.Therefore,it’s of important practical significance to in-depth research on it.At present,the traditional time domain and frequency domain analysis and control methods for power system wide-frequency oscillation have their own advantages and limitations.Among them,the time domain analysis method has limitations such as calculation difficulty,long simulation time,difficulty in analyzing and judging the influence of parameters on motion,complicated control structure design,and practical engineering application difficulties.However,the frequency domain analysis method is often used in univariate systems,which is difficult to judge and quantify the stability of actual power system connected to multiple power electronic devices.and traditional control methods generally address the dynamic stability of specific frequency bands.Therefore,this paper uses Nyquist array theory to systematically analyze the new problems of power system wide-frequency oscillation,and research the design method of power system wide-frequency oscillation control,making it more suitable for stability analysis and control of power system wide-frequency oscillation problems.In this paper,a systematic study of Nyquist array theory in multivariate frequency domain analysis theory has been carried out,which lays a solid theoretical foundation for the analysis and control of wide-frequency oscillation problems of power system.This paper takes doubly-fed wind power grid-connected system,AC-DC hybrid system and doubly-fed wind power via LCC-HVDC outgoing system as typical power system wide-frequency oscillation problems.First,the forward transfer function matrix and the feedback gain transfer function matrix in the power system wide-frequency oscillation analysis system model are derived,and the system is transformed into the general structure of the multivariable system.Then,based on the Nyquist array theory,the diagonal advantage characteristics of the system are judged.For diagonally d advantage systems,the Gershgorin band of the forward transfer function matrix can be drawn to intuitively analyze and understand the stability characteristics of the system;for non-diagonally dominant systems,additional damping controllers can be designed to control the system through the pseudo-diagonalization method,the system is transformed into a diagonal advantage system,and then stability analysis can be carried out.Finally,the effectiveness of the proposed method is verified by comparing with the eigenvalue calculation and time domain simulation results.In this paper,the research on power system wide-frequency oscillation has both theoretical value and engineering practical value.From the perspective of theoretical level,the application of Nyquist array theory recognizes and understands the wide-frequency oscillation problem of power systems from a new perspective of system diagonal advantages,and studies new behaviors and new phenomena in power systems,thereby enriching the analytical theory of power system stability and control system.From the perspective of engineering application,the application of Nyquist array theory,with its advantages of small calculation,fast simulation,intuitive analysis,and clear physical meaning,provides new guidelines for the stability analysis and control of power systems,so as to protect safe and stable operation of power system connected to multiple power electronic devices.