Influence Mechanism Of Temporal And Spatial Distribution Characteristics For Frequency Dynamic In Large-scale Power Grids

One prominent feature of a large-scale power grid is spatial and temporal distribution of frequency dynamic,when the power grid operates as an interconnected grid.At present,the analysis mehod about frequency dynamic is to build the detail models of power system components,and to solve the basic differential-algebraic equations in the time-domain by simulation method.But the traditional methods cannot analyze and explain the spatial and temporal distribution characteristic in theoretical layer.Hence,it is necessary to build a new frequency dynamic analysis theory to explore the formation mechanism and influence rule.It is of great significance in theory and practice for the safe operation and stable control of large-scale interconnected grids.This paper is devoted to study the science questions about spatial and temporal distribution of frequency dynamic and electromechanical disturbance propagation.The mathematical model considering spatial information of frequency dynamic analysis is built,and the dispersion phenomenon is utilized to explain the absorption mechanism of electromechanical disturbance.Next,the physical essence of the propagation of frequency dynamic is explorted from the view of the reflection and transmission phenomena.Based on the wide-area measurement data including the real time dynamic information of power grid,a novel method used to extract the spatial and temporal distribution information of frequency dynamic is proposed.The dissertation contains 5 aspects as follows:(1)The temporal and spatial evolution model of frequency dynamics is built based on the models of synchronous generator,electric transmission line and governor in the chain power system.The generalized wave equation is derived for the discrete model and the frequency wave concept is proposed to discribe the spatial and temporal distribution characteristic of frequency dynamic.The frequency dynamics of 2 models,a standard test system and China southern power grid,are analyzed to verify the theoretical results.The qualitative and quantitive conclusions are obtained.(2)Based on classical wave theory,the dispersion relationships of frequency dynamic with different detailed degree are devied and the physical significance of dispersion relationship is analyzed.The influence of internal reactance of generator upon dispersion is discussed.The attenuation characteristic of frequency wave is also analyzed,and the attenuation coefficient is obtained.(3)The transmission and reflection phenomena of frequency wave are analyzed based on the disceret model of power grids.The transmission and reflection coefficients in the discrete model are obtained and compared with them in the continuum model.The result indicates that the transmission and reflection of frequency wave are influnced by the oscillating frequency.(4)The statistic model of frequency dynamic is built based on the empirical orthogonal function analysis.This model can decompose the wide area measurement data into spatial and temporal functions,and extract traveling-and standing-wave components of frequency dynamic.Some quantitative indexes are defined to measure traveling-and standing-wave components.The propagation speed of frequency wave is also obtained by the information extracted from the wide area measurement data.(5)The spatial-temporal characteristics of frequency dynamic in power grids are verified by actual power grids and wind power system from the view of simulation.The traditional operation forms of wind power generation cannot effectively provide inertial support for the integrated power grid,so lead to the drop of inertial level of the whole power grid.Naturally,the propagation characteristics of frequency wave are affected.Moreover,the network structures of actual power grid are rather complex,and the parameters of electrical components are not uniform,these factors result in many propagation paths of frequency wave and the propagation form also intricate and complex.