Fuzzy-expert system for voltage stability monitoring and control

Bodapatti, Nageswararao (1998) Fuzzy-expert system for voltage stability monitoring and control. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (12MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

In recent years, electric power utilities are forced to transmit maximum possible power through existing networks due to environmental, economic and regulatory changes. Due to these constraints, voltage instability has emerged as one of the most important areas of concern to modern power utilities. Voltage instability has been responsible for several system collapses in North America, Europe and Asia. -- This thesis presents fundamental concepts of voltage stability. It describes three traditional voltage stability indices namely singular value decomposition, L index and QV curves. A simple five bus system is used to highlight the limitations of these traditional methods. A more widely accepted technique like modal analysis along with continuation power flow is studied and simulations are carried out on the IEEE 30 bus system and the New England 39 bus system. The test results clearly indicate areas prone to voltage instability and also identify groups of buses and critical bus that participate in the instability and thereby eliminate the problems associated with traditional methods. Hence, modal analysis technique is not only used as a benchmark tool for the development of the proposed fuzzy-expert system, but also as an important tool for validating its accuracy. -- To understand this new approach, fundamental concepts of fuzzy logic based on the theory of approximate reasoning is dealt in detail. To get further insight into this alternate approach, a simple method using fuzzy sets for the voltage-reactive power control to improve the system voltage level is presented. A modified IEEE 30 bus system is used as an example to illustrate this method. Simulation results of this simple problem is encouraging and has been a useful starting point for the proposed fuzzy-expert system for voltage stability evaluation. -- The proposed fuzzy-expert system consists of two main components. The knowledge-base and the inference engine. Here, the key system variables like load bus voltage, generator MVAR reserve and generator terminal voltage which are used to monitor the voltage stability are stored in the database. Changes in the system operating conditions are reflected in the database. The above key variables are fuzzified using the theory of uncertainty. The rulebase comprises a set of production rules which form the basis for logical reasoning conducted by the inference engine. The production rules are expressed in the form of IF-THEN type, that relates key system variables to stability. The New England 39 bus system is taken as a case study to illustrate the proposed procedure. The expert system output is compared with the simulation results of a commercially available software ( VSTAB 4.1 ) output through modal analysis. The proposed system is fast and more efficient than conventional voltage stability methods.

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