Research On Ultra-Low Frequency Oscillation For Automatic Generation Control Of Power System

Ultra-low frequency oscillation occurs frequently in the actual power grid,which seriously threatens the safe and stable operation of power grid.It is found that ultra-low frequency oscillations belong to frequency oscillations,which are closely related to primary frequency regulation(PFR)mode and automatic generation control(AGC)mode.At present,the research on PFR mode has been relatively comprehensive for the calculation method,oscillation mechanism and corresponding inhibition measures of the oscillation mode,but there is still a lack of research on the difference between the two modes.Also,the induction mechanism,internal laws and key influencing factors of AGC mode are still lacking.In view of the above problems,this paper firstly introduces the frequency response model of power system,and expounds the behavior characteristics and stability criteria of state matrix in eigenvalue analysis theory,which provides model basis and theoretical basis for distinguishing the two modes and analyzing the mechanism of AGC mode.In this paper,the damping torque analysis theory suitable for frequency stability is studied.Three discrimination indexes of frequency loop correlation ratio,frequency observability and DTA sensitivity are established.The two types of oscillation modes and their performances are analyzed,and the performances and differences of the two frequency oscillation modes are clarified initially.Then,the dominant modes of AGC oscillations were identified based on homotopy function method,and the consistent relationship between eigenvalues and state variables was established.The correctness and reliability of the proposed method were verified by time domain simulation and Prony analysis.On this basis,the AGC model delay margin was solved by root locus analysis of the dominant mode and stability criterion of eigenvalue analysis theory.Furthermore,by introducing the time-delay into the DTA model,a DTA model with time delay is established to analyze the influence of time delay on AGC oscillation.Finally,the influence of PI controller on the system delay margin is studied,and parameters of PI controller are adjusted based on PSO algorithm,so that the system can obtain the maximum delay margin and ideal damping performance,improve the stability of small interference in the system frequency modulation process,and ensure the safe and stable operation of the power grid.