Optimization And Coordination Of Emergency Control And Correction Control

The advancement of interconnected power grids and electricity markets provides strong supports for economic construction and development of our country. Meanwhile, it also brings new challenges to security, stability and reliability of power systems. Because security and stability of power systems are closely related to construction and stability of our country, it is imperative to develop new strategies to defend power systems blackouts, ensure security, stability and economical operation of power grids.Closed-loop discrete control is the main means of maintaining operational reliability of power systems after large disturbance, including generator tripping, load shedding, splitting, and so on. These measures can be divided into fault-driven emergency control and trajectory-driven correction control. Current researches focus on how to minimize control quantity or control cost of meeting stability constraints. Control schemes rely on system simulations and engineering experiences, and the decision-making is carried on with deterministic operation conditions, models, parameters, and fault scenarios.The decision-making factors of closed-loop discrete control include models and parameters, operation conditions, assumed faults, objective functions, constraints, control variables and execution time. Control strategies can not be optimized without reliable and efficient security and stability quantitative analysis algorithms. Extended Equal Area Criterion proposes the swing stability concept of high dimensional disturbed trajectories and the methods of assessing stability margin of every swing. It profoundly reveals transient stability mechanism and law of non-autonomous and nonlinear multi-machine power systems. Considering security and economy of power systems, the dissertation optimizes EC and CC, and coordinates them by using FASTEST software package. EC is a feed-forward control driven by faults. Its lag time is very small and cost-performance ratio is large. But its decision tables are made according to typical scenarios. The scenario errors maybe lead to serious over-control or deficient-control. CC is a feed-back control driven by trajectories. It is executed after insecure phenomena occur, so its cost-performance ratio is small. But its feed-back law can avoid over-control and deficient-control. The dissertation compares the criterion, execution time, cost and precision of EC and CC, as well as their generator tripping, load shedding and network splitting actions. Their optimized strategies with deterministic operation conditions and faults are also discussed.Power systems are random. Diverse stochastic factors are divided according to operation conditions and faults. Faults with different locations and types impact on stability of power systems differently. The control costs of same type faults are different when they occur at different grid topologies, unit commitment, injection power and system reserve. It is not economical and maybe brings about negative control effects to make control strategies by deterministic simulation with typical conditions and faults according to conservative principles. With consideration of non-determinism of tie-line power, clearing time, load level and load models, the influence of stochastic factors on power angle stability, frequency security and voltage security is analyzed by simulations on a Chinese power systems.If an emergency control is used to cope with uncertain factors occurring in small probability and high risk, it will most likely lead to over-controlled results in most of operational scenarios. If correction control is used in this case to cope with the factors that have a large probability to occur, the cost would be high. It is emphasized that the coordination of these two control modes with complementary characteristics physically as well as economically should be based on risk analysis. EC can reduce control strength of CC; CC can alleviate conservatism of EC and avoid power systems blackouts under unpredicted serious faults. Their coordination can improve adaptability and economy of defend systems. Considering the non-determinism of clearing time and load model, simulation studies undertaken on a power system show that the risk cost of optimized generator tripping scheme is reduced obviously.Load shedding can be driven by either faults (emergency load shedding) or trajectories (corrective load shedding). To deal with many non-deterministic factors, it is important to coordinate them. According to a decoupling-optimization and global-coordination framework, power system stability and security are analyzed with FASTEST software package considering the non-deterministic factors, and then fault-driven load shedding and trajectory-driven load shedding are optimized respectively and interactively. During the course of optimizing one of them, the newest results of another are taken as constrained scenarios. Iteration is conducted until the total risk of all assumed faults is not reduced obviously. With consideration of the non-deterministic factors of the assumed faults, load model and load level, simulation studies undertaken on a power system show that the optimal coordinative load shedding scheme reduces the risk cost obviously with a premise of maintaining stability and security of the power system.Splitting can be driven by either faults (fault-driven splitting performed at the second defense line), or trajectories (out-of-step splitting performed at the third defense line). Under absolutely deterministic conditions, only fault-driven splitting is needed to reduce impact on power systems. However, there are many of non-deterministic factors which weaken the necessity of fault-driven splitting but emphasize out-of-step splitting and the importance of coordinating them. Multiplying the control cost of all isolated sub-systems with the splitting probability is newly defined as the risk cost of splitting control proposed as an index in this paper, and the coordination is also based on this index. Then "on-line pre-decision and real-time match" is used to improve the adaptability of faults-driven splitting. The paper also proposes an adaptive out-of-step system that consists of a control center, local splitting stations and splitting devices. The control center would detect the location of an oscillation center automatically, and coordinate fault-driven splitting and out-of-step splitting according to the splitting risk. Local splitting stations would be responsible for on-line selecting the cutting sets of the power grid. Simulation studies undertaken on power systems show that this optimal and coordinative splitting scheme is effective and practical.This project is jointly supported by National Science Foundation of China (No. 50595413) and State Grid Corporation of China (No. SGKJ[2007]98&187&2009). Except for theoretical value, it is also expect to provide practical decision-making tools for interconnection and marketization of china power grids by improving in engineering earlier.