Available transfer capability evaluation study in system operation under electricity market and its enhancement by facts devices

Abstract

In this thesis, innovative studies are made on the Available Transfer Capability (ATC) evaluation methods in power systems with both dynamic and static constraints. The role of ATC as a market signal in addition to being a technical index in the power market environment and the interaction between the two roles are investigated. In addition, the ATC enhancement measures by Flexible AC Transmission Systems (FACTS) devices are also studied. With the development of deregulated power markets, higher power transfer between interconnected systems and reduced reactive power reserves together with intensified competition, push the network authorities to determine ATC in short time with satisfactory accuracy. Thus system operation with both desirable economical benefit and sufficient security can be performed timely. Due to the increased transaction level associated with open access, the transmission systems are operating under more stressed conditions near the stability boundary. An optimized operation point of power system obtained with conventional static security constraints is possibly either transiently unstable or voltage unstable under certain credible contingencies. The calculation difficulties imposed by dynamic security considerations other than static limits lie in how to treat with the multi-dimensional Differential-Algebraic-Equations (DAEs) associated with them. In this research, ATC evaluation methods with two different types of dynamic constraints are investigated. Firstly a variant Primal-Dual Predictor-Corector Interior Point Method (PDPCIPM) is proposed to solve ATC calculation with transient angle stability constraints. It has the advantages of fast convergence and reasonable accuracy as well as that its iteration speed is insensitive to the system scale and number of control variables. A Quasi-Steady-State (QSS) approximation method is then proposed to evaluate dynamic voltage constrained ATC with acceptable accuracy while the calculation speed is accelerated considerably. Under the new power market environment, economic factors should be considered on the condition of stability operation. Hence ATC calculation with consideration on both stability and price bidding is investigated by a variant PDPCIPM method and their interactions are analyzed. Through an innovative risk-based optimal method, ATC determination with different contingences associated with the system transient instability risk is also developed. In this proposed method, both probabilities and costs of transient instability events are considered and the optimal ATC is compromised between economics and security. Besides the studies on algorithms of ATC evaluation with a variety of constraints as well multiple objectives, the participants of power market also pay attention on how to increase the ATC between areas. The application of various FACTS devices to enhance ATC is also studied in this research. Case studies and analysis results are presented to show the efficiency and validity of the above methods for ATC calculation and their improvement issues.