Wide Area Security Assessment And Control For Bulk Power System With WAMS Data

With the constant expansion of AC/DC paralleling transmission network in China, growing power demand and the high penetration of renewable energy, the power system is operating to its limitation, and the security and stability of power system is facing grievous challenge, which attracts remarkable attention from industrial and academic research. In order to boost the stable and secure performance of grid’s operation, and to boost the margin to surmount categories of cascaded faults, the real-time security and coordinated control on grid’s status quo via wide-area measurement system(WAMS) is becoming an essential trend of power industry advancements. However, the information from WAMS is evidently the so-called “big data”, thus it will be vital for operators in power system to filter key dynamic features from data deluge so as to carry out the appropriate power operation and control. Therefore, this dissertation performs the research work on power system analysis on security and stability and coordinated control, the main discussion is put forward as follow:(1) The methodology is presented to construct wide-area thermal security region via WAMS measurement. To start with, the topological characteristics of security region boundary is explored, thereby determining the approximation of security region boundary. Then, the algorithms are proposed and validated to rapidly approximate security region boundary with multiple constraints. On the basis of this, the concepts of “cut-set admittance” and “cut-set phase difference” are defined, and these definitions are generalized for the construction of large-scale interconnected power grid’s thermal security region. Via the proposed approximated algorithm and the signals from WAMS, the wide-area power system thermal security region can be constructed in cut-set phase difference space. Lastly, these methods are applied to China Southern power Grid(CSG), and the WAMS in CSG is utilized to build up the thermal security region for CSG with “N-1” constraint.(2) A voltage stability monitoring algorithm is put forward on the basis of WAMS data. Initially, the relative gain matrix is adopted to the partition for voltage stability control, and the partition method treats voltage stability critical buses as the regional voltage pilot buses. Subsequently, grid’s voltage stability critical buses are identified via WAMS, and the voltage coupling level between power injection buses and voltage stability critical buses are quantitatively appraised via the relative gain, then the voltage stability critical injection zones can be dynamically divided. On the basis of divided voltage stability critical injection zones and further analysis on WAMS signals, the prediction and control strategy is proposed on the basis of widearea voltage stability sensitivity, thereby monitoring and enhancing voltage stability effectively. Finally, the proposed methods are demonstrated in the Polish power system.(3) As a matter of fact, the ringdown data and ambient data indeed exist in the field-measurement data. On the basis of stochastic subspace theory, the general algorithm is put forward to identify grid’s dominant oscillation modes with above two kinds of signals, thereby realizing the online monitoring of power system dynamical stability. To begin with, two stochastic subspace ordering strategies which are respectively based on singular value cumulative contribution rate and mean value are put forward to tackle the problems that the order of stochastic subspace is intricate to determine. To resolve the flaws that stochastic subspace identification may introduce noise modes and calculation modes, the spectrum features of power system lowfrequency oscillation are utilized to build up the multiple-stage filtering strategy for dominant oscillation mode in power system. Further, in order to correctly and effectively filter and identify the dominant oscillation modes, the identification algorithms including mode match, cluster analysis and hierarchical clustering are proposed on the basis of stochastic subspace identification. Eventually, the proposed methods are applied in CSG’s dynamical online stability monitoring.(4) A general approach for coherency detection in bulk power systems is developed using the Projection Pursuit(PP) theory. Supported by the concept of Center of Inertia(COI) in power systems, the PP theory is employed to model the wide-area coherency detection as an optimization problem. In the proposed method, the optimal projection direction in high dimensional orthogonal space is explored in order to detect the coherency groups via the data from synchronous Phasor Measurement Units(PMUs). Two quantitative indices constructed with Projection assessment Index(PI), the objective of the optimization model, are then defined in order to determine the critical coherent group and the dominant coherent groups. The coherency detection criterion and the implementation framework for the proposed approach are also presented. Simulation data from the 16-machine 68-bus test system and China Southern power Grid(CSG), along with actual field-measurement data retrieved from WAMS database in the CSG, are employed to demonstrate the effectiveness and applicability of the proposed algorithm under different disturbances. It is shown that the proposed methodology successfully detects the dominant coherent groups of generators and buses in bulk power system via the wide-area fieldmeasurement data.(5) The influences of WAMS delay on power system stability are also studied. Using the periodical characteristics of the critical eigenvalues of the critical points, a critical function is formulated by space mapping, and then solved in a finite interval by bisection method. By this way, the critical eigenvalues of the critical points and their corresponding information can be derived and used to compute the critical time delay by the inverse mapping. The small disturbance based methods also proposed to determine the small signal stability region. Then the proposed methods are applied to time delay space in larger scale to carry out the research on topological features of delay stability boundary. And it is found in further analysis of the results that the introduction of time delay can only beget Hopf bifurcation rather than saddle node bifurcation for a given stable system.