Development of expert systems as on-line operational aids

Thesis (Ph. D.)--University of Washington, 1987In recent years, the interest in Expert Systems (ES) has grown rapidly. The application of expert systems to power system operations and on-line environments is a new area of research. In this thesis, the issues involved with on-line knowledge based systems for operations is investigated. To begin, the development and validation process involved in building two ES operational aids are discussed. One incorporated logical and heuristic rules for Customer Restoration And Fault Testing (CRAFT) of power lines with automatic switches. The other, referred to as VCES (Voltage Control Expert System), integrated numerical and heuristic techniques for reactive power/voltage control in a power system. Both expert systems are implemented as rule-based forward-chaining systems.Can expert systems such as CRAFT and VCES be applied in an on-line operation environment? The answer depends on the quality of the knowledge base and the computational efficiency. Besides validating the knowledge base, computation time is analyzed. Based on discrimination nets, used in many production system languages for pattern matching efficiency, a method is proposed to obtain the worst case computation time of a rule-based system. The method depends on bounding the individual computational components of the inference engine (pattern matching, conflict resolution, and actions) and partitioning rules into groups performing different tasks in the decision-making. The worst case time is obtained by combining the costs of each of these tasks. This research is a step toward insights into the application of knowledge based systems to power system operations and the efficient implementation of rule-based systems

Prediction of Critical Load Levels for AC Optimal Power Flow Dispatch Model

Critical Load Levels (CLLs) are load levels at which a new binding or non-binding constraint occurs. Successful prediction of CLLs is very useful for identifying congestion and price change patterns. This paper extends the existing work to completely solve the problem of predicting the Previous CLL and Next CLL around the present operating point for an AC Optimal Power Flow (ACOPF) framework. First, quadratic variation patterns of system statuses such as generator dispatches, line flows, and Lagrange multipliers associated with binding constraints with respect to load changes are revealed through a numerical study of polynomial curve-fitting. Second, in order to reduce the intensive computation with the quadratic curve-fitting approach in calculating the coefficients of the quadratic pattern, an algorithm based on three-point quadratic extrapolation is presented to get the coefficients. A heuristic algorithm is introduced to seek three load levels needed by the quadratic extrapolation approach. The proposed approach can predict not only the CLLs, but also the important changes in system statuses such as new congestion and congestion relief. The high efficiency and accuracy of the proposed approach is demonstrated on a PJM 5-bus system and the IEEE 118-bus system

Methods for Analysis and Quantification of Power System Resilience

This paper summarizes the report prepared by an IEEE PES Task Force. Resilience is a fairly new technical concept for power systems, and it is important to precisely delineate this concept for actual applications. As a critical infrastructure, power systems have to be prepared to survive rare but extreme incidents (natural catastrophes, extreme weather events, physical/cyber-attacks, equipment failure cascades, etc.) to guarantee power supply to the electricity-dependent economy and society. Thus, resilience needs to be integrated into planning and operational assessment to design and operate adequately resilient power systems. Quantification of resilience as a key performance indicator is important, together with costs and reliability. Quantification can analyze existing power systems and identify resilience improvements in future power systems. Given that a 100% resilient system is not economic (or even technically achievable), the degree of resilience should be transparent and comprehensible. Several gaps are identified to indicate further needs for research and development.ISSN:0885-8950ISSN:1558-067