Research On Some Key Problems Of On-Line Pre-Decision System For Large Scale Interconnected Power System

Dynamic security assessment (DSA), covering transient angle stability, voltage security and frequency security, has been historically conducted in an off-line operation-planning environment, in which the stability of the near-term forecasted system conditions are exhaustively determined. The results (stability limits and controls) are loaded into look-up tables and are accessed by the operators. The limits for the nearest matching condition in the study set are then used as the actual operation limits.However, actual operating conditions usually do not match the predetermined ones used for off-line calculations, especially in power market environment that can easily lead to unpredictable operating conditions. The uncertainty of future operating conditions points to the need for on-line DSA to meet the requirements of the development of power network interconnection and power market.In ideal on-line DSA , the system stability for the current operating condition is computed as it occurs, and with sufficient speed to allow time for the operator to react if a contingency analyzed is shown to be potentially insecure. Even with advances in computer technology and detailed time-domain simulation of large and complicated power system models, the questions as to how to access the stability margin and sensitivity information, simplify external system, and calculate in real time remain unsolved and are challenging research topics.Due to the framework of "on-line pre-decision, real-time match" (proposed by Prof. Xue.Y in 1993), this thesis sets forth the importance of on-line pre-decision system (OPS) for interconnected power system control. It is emphasized that not only angle stability, but also voltage and frequency security should be embraced in the control system, and preventive control and emergency control should be studied under the coordinated framework. The question as to how to deal with the state data from multi EMS and multi stability control systems is discussed in this thesis. The cluster of workstations is utilized to realize the distributed computation.Coherency is a theoretic rationale for power system dynamic equivalents. Only if each sub-system to be reduced keeps coherent inside respectively, dynamic characteristics of original system can then be rigorously preserved. The researches and applications of dynamic equivalents are assessed in this thesis, by aspects of coherent definitions and several key ideas, coherency identifications, equivalent models and parameters. The principle of dynamic equivalents should correspond with the essence of power system, and coherency of generators is influenced deeply not only by parameters and topological structures, but also by disturbance scenarios. Only if stability information is excavated out directly from the whole disturbed trajectories, coherency can be identified from non-autonomous and nonlinear system. The predominant modes of trajectories reflect the inner mechanism of system dynamic behavior and show to be well applicable in the future.Based on coherency characteristics of rotor angles as well as bus voltages, placement of phasor measurement units (PMU) is optimized in this paper. All potentially critical-modes for transient angle stability are identified by Extended Equal Area Criterion (EEAC), and then a PMU is assigned to one of the power plants in each critical cluster. All potentially critical bus-clusters for transient voltage stability are identified via assessing transient voltage stability and transient voltage-dip acceptability, and then a PMU is assigned to one bus in each critical bus-cluster. Moreover, the optimal sequence for placingthe PMUs is proposed. The effectiveness of the proposed algorithm is verified with numerical simulation on a real power system, and the resultant scheme is being implemented.The harmonious unity of security and economy is the external theme for power grid corporations to be faced with. The technologies of security analysis and control have been fully realized to be the key of sustained development of power system, and OPS seems to be the only way to prevent continuous contingencies and deal with system cascade outages. The State Grid Dispatch Center, Southern Grid Dispatch Center and other province dispatch centers all set about to plan and build on-line transient security and control systems, and this thesis can be the reference.