Research On Mechanism And Prevention Measures Of Low Frequency Oscillation Caused By Unit

Low frequency oscillation is always an important threat to the safe operation of power grid,and recently many low frequency oscillation events caused by generator causes occur in China Southern Power Grid.However,the oscillation mechanism of these events is not clear,so the mechanism and suppression measures of low frequency oscillation caused by the unit need to be further studied.The main contents of this paper include the study of mechanism and the prevention measures of the low frequency oscillation.In this paper,a mechanism identification method for low frequency oscillation caused by a speed control system was proposed.Through the extraction of oscillation characteristics based on WAMS and the initial modal analysis of the system,the criterion of the mechanism of low frequency oscillation was formed,which is used to judge whether the mechanism of low frequency oscillation is negatively damped or forced.When judging the mechanism of oscillation is forced oscillation,a method to judge the mechanism of low frequency oscillation caused by speed regulation system was formed,through the correlation analysis of low frequency oscillation and speed regulation system.According to the theory of electromechanical wave,the propagation characteristics of low frequency oscillation in power grid were presented.The power phase angle of the generator which the oscillation source locates in is the most advanced and the farther away the electrical distance from the oscillation source,the larger phase lags.On this basis,using measured data of wide area measurement system(WAMS),the phase relationship of electromagnetic power fluctuation can be analyzed to locate the low frequency oscillation source fast and accurately.The time-domain simulation results and the measured data from WAMS verified the validity of the low frequency oscillation propagation characteristics analysis and the feasibility of the location method of the oscillation source.A method of the coordinated optimization of multi-control system for steam turbine generator unit was proposed in this paper.The primary frequency modulation performance and dynamic stability of the power system were taken into account in the method.The multi-control system to be optimized includes the excitation regulation system,the power system stabilizer(PSS),the speed control system and the boiler-turbine coordinated control system(CCS).The taboo search(TS)algorithm was introduced as a means to obtain the optimal values of the system control parameters.The simulation result shows that the method can coordinate the primary frequency modulation performance and the dynamic stability of the system,and can effectively prevent the low frequency oscillation caused by the improper multi-control system parameters setting.