Research On Propagation And Control Of Electromechanical Disturbance In Power Systems

Disturbance is the direct inducement of threatening the safe and stable operation of power system.The traditional method based on mathematical model simulation can not effectively explain the inherent mechanism of the electromechanical dynamic process in power system.The electromechanical wave theory analyses the propagation process of electromechanical disturbances from the new perspective of wave mechanics,which provides a new idea for studying the evolution mechanism of electromechanical dynamic space-time propagation in power system.However,there are still many problems in the application of electromechanical wave theory to the stability analysis and disturbance propagation control of large power grids,which need to be studied in depth.In this paper,theoretical derivation,numerical calculation and simulation analysis are used to study the conditions for continuous processing of discrete power system,the disturbance propagation in actual power grid and the control of disturbance propagation in interconnected power grid based on superconducting magnetic energy storage device.In this paper,the theory of electromechanical disturbance propagation is briefly introduced.Based on the propagation of rope wave,the principle of disturbance propagation and the similarity between electromechanical wave and mechanical wave are expounded.Based on the one-dimensional chain power network,the disturbance propagation equations and expressions in the continuum model and the discrete model of power system are derived respectively.The waveforms of disturbance propagation in the two models are plotted,and the propagation laws of disturbance are analyzed.The process of disturbance propagation is visually displayed.The foundation of studying the electromechanical disturbance propagation in power system is the establishment of continuum model,but the results obtained when the continuum model is used instead of the actual discrete system to study the electromechanical dynamics of power system are inevitably some different.In this paper,the relative deviation between discrete model and continuum model of power system are quantitatively analyzed.The relative deviation and mode shapes are studied by modal analysis method in structural mechanics.It is concluded that when the generator density is large or the wavelength of the disturbance wave is much larger than the interval between adjacent generators,the continuum model can be used to replace the actual discrete model to study the dynamic process of the power system.The propagation of electromechanical disturbance in China Southern power grid is studied.Firstly,the temporal and spatial distribution characteristics of frequency variation in power grid are analyzed,and the estimation formula of disturbance propagation velocity is given.Subsequently,the propagation velocity of frequency wave is studied by setting generator tripping at different locations in power system.It can be known that the system inertia,the direction of the disturbance propagation and the magnitude of unbalanced power will affect the disturbance propagation velocity.Finally,for the pure HVDC connected asynchronous interconnected power grid,the frequency dynamic characteristics of power system under HVDC blocking fault and mechanism of disturbance propagation in HVDC system are studied.The disturbance control of interconnected power grids is studied.Firstly,based on the reflection and transmission characteristics of disturbance propagation,the zero-transmission control strategy of two-area interconnected power grid is deduced,and the influences of the control strategy on the power system stability are analyzed from the point of view of energy flow.Then,on the basis of zero-transmission control,the disturbance quenching control strategy is designed by using the transient energy function analysis method.Finally,the effectiveness of the control strategies is verified by PSCAD/EMTDC simulation.