Improving Damping in Power System Oscillations using Fuzzy Logic Stabilizer R.P. Sarath Chandrasena (PG/EE/21/99) A thesis submitted to the Faculty of Engineering, University of Moratuwa in partial fulfillment of the requirement for the degree of Master of Engineering In Electrical Engineering Under the supervision of Professor J.R.Lucas Faculty of Engineering University of Moratuwa Dr. N.K.Wickramarachchi Faculty of Engineering University of Moratuwa Dr. H.J.C. Peiris Faculty of Engineering University of Moratuwa January 2004 J h 3 5 Fuzzi Losic Power system Stabilizer Abstract In general, power system oscillations are damped out using power system stabilizer (PSS). Conventional power system stabilizers are based on linear control theory. Therefore, they provide optimal operation at the nominal operating point around which the system is linearised during their designing process. Power systems are in general non-linear and their operating point can vary over a wide range. Power System parameters also change with time because its configuration changes with time continuously. Therefore, a conventional power system stabilizer cannot provide better performance over the whole operating range since it cannot support the deviation of its parameters. Hence, a controlling method, which can tolerate the small deviation in system parameters, is highly welcome. Fuzzy Logic provides a simple way to arrive at a definite conclusion based upon vague, ambiguous, imprecise, noisy or missing input information. So, a controller based on Fuzzy Logic (Fuzzy Logic Controller) is one of the most promising solutions to the above problem. Since, it can tolerate the changes in the system parameters, it may provide a better performance over a wide operating range. Hence, in this research project, a power system stabilizer based on Fuzzy Logic (FLPSS) has been designed and various tests have been conducted on it in order to check its effectiveness. The performance of the designed FLPSS has been compared with the performance of a particular conventional power system stabilizer and the FLPSS has shown better performance at each occasions. 111 DECLARATION I hereby declare that this submission is my own work and that, to the best of my knowledge and behalf, it contains no material previously published or written by another person nor material, which to substal).tial extent, has been ;I accepted for the award of any other academic qualification of an university or institute of higher learning except where acknowledgement is made in text. ~~ R.P. S. Chandrasena January 2004 Q, Professor J.R. Lucas Project Supervisor January 2004 ... rJJ(r/0 Dr. N.~chchi Project Supervisor January 2004 11 Fuzzy Logic Power system Stabilizer Acknowledgement First and foremost I must offer my sincere thanks to my supervisors Prof. J .R.Lucas and Dr. N.K.Wickramarachchi for their encouragement and priceless personal guidance throughout the course of completing this work. Then my special thank and gratitude is deserved by my former supervisor, Dr. H.J.C.Peiris for providing me with the inspiration and support at the beginning of this research pr~ject. And I must also express my sincere thankfulness to the Head of the Department of Electrical and information Engineering, Faculty of Engineering, University of Ruhuna, Dr. W.L.S.Wickramaratne for providing me a peaceful environment to carry out this work until it became a success. I can never forget Dr. K.Gunawickrama, senior lecturer Department of Electrical and information Engineering, Faculty of Engineering, University of Ruhuna, from whom I always got advise throughout this project. Finally, my beloved wife, Shiromi, without your love and support, this thesis would not have been possible . ... .... lV Fuzzy Logic Power system Stabilizer Table of Contents Basic Acronyms................ . ................................................. 1v Chapter 1 Introduction 1 1.1 Power system oscillations............ .. ........ . .... .. ..... . .... 1 1.2 Rotor angle stability............................................. 4 1.2.1 Sma1l signal stability........................... . ........ 4 1.2.2 Transient stability........................................ 5 1.3 Damping Power System Oscillations......................... 6 Chapter 2 Conventional Power System Stabilizers 7 2.1 Introduction.............. . ............................ . ..... . .... 7 2.2 Problems with CPSS ............ . ..................... _I......... 9 Chapter 3 3.1 3.2 3.3 Chapter 4 4. 1 4.2 4.3 4.4 4.5 4.6 4.7 Designing a Fuzzy Logic Power System Stabilizer 11 Fuzzy Logic controller Structure...................... .. . . .... 11 Fuzzy Logic ToolBox in MATLAB............... . . . . ... . . .. . 13 FLPSS designing........ . .......... .. ...... . . .. .. . . .. ..... .. .... 14 3.3.1 Selection of control variables........................... 14 3.3.2 Fuzzify inputs......... . ................................... 14 3.3.3 Rule creation............................................. 16 3.3.4 Fuzzy inference.................................... . ..... 18 3.3.5 Defuzzification......................................... .. 20 ... FLPSS performance ..,. Test 01 ........................................................... . Test 02 ........................... . ............................... . Test 03 ................................ . .......................... . Test 04 ................................ . .......................... . Test 05 ..... .. ...................................... . ...... . ...... . Test 06 ....................................... . ..... . .. . . .. . . ..... . Test 07 ........................................................... . 22 23 28 29 30 32 34 35 Chapter 5 Conclusion 38 Appendix A Appendix B Appendix C Bibliography 40 ~ 43 46 52 v Fuzzy Logic Power system Stabilizer Basic Acronyms CPSS - Conventional Power System Stabilizer DspeedD - Derivative of the speed deviation FIS - Fuzzy Inference System FLC - Fuzzy Logic Controller FLPSS - Fuzzy Logic Power System Stabilizer l GUI -Graphical User Interface PSS - Power System Stabilizer speedD - Speed Deviation --.. Yl