A Fuzzy Logic Voltage Collapse Alarm System for Dynamic Loads. Zhang Xi. Master of Science in Electrical and Electronics Engineering

Transcription

1 A Fuzzy Logic Voltage Collapse Alarm System for Dynamic Loads by Zhang Xi Master of Science in Electrical and Electronics Engineering 2012 Faculty of Science and Technology University of Macau

2 A Fuzzy Logic Voltage Collapse Alarm System for Dynamic Loads by Zhang Xi A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical and Electronics Engineering Faculty of Science and Technology University of Macau 2012 Approved by Supervisor Date

3 2 In presenting this thesis in partial fulfillment of the requirements for a Master's degree at the University of Macau, I agree that the Library and the Faculty of Science and Technology shall make its copies freely available for inspection. However, reproduction of this thesis for any purposes or by any means shall not be allowed without my written permission. Authorization is sought by contacting the author at Address: Faculty of Science and Technology, University of Macau Telephone: Fax: N/A xxbb212@gmail.com Signature Date

4 3 University of Macau Abstract A Fuzzy Logic Voltage Collapse Alarm System for Dynamic Loads by Zhang Xi Thesis Supervisor: Professor Wong Chi-Kong Electrical and Electronics Engineering The voltage collapse due to the failure of dynamic load restoration can suddenly occur before its static limitation, the estimation of this kind of voltage stability is still at the exploratory stage. In this thesis, fuzzy based voltage collapse alarm systems are proposed by considering both of static limitation and dynamic load restoration. The proposed alarm systems provide different degrees of alarm for the current operating state of power system and indicate that voltage collapse may occur, which is helpful for operators to take actions in advance. A lot of different voltage stability indices (VSIs) are studied, finally Line Stability Factor (LQP) is found to be an effective index to indicate the system transfer limitation when dynamic load is considered and it is selected as one of the inputs of the alarm systems. In order to represent the dynamic load characteristic, dq/dt and dp/dt are proposed to be the other inputs of the alarm systems. In the previous alarm system, all buses of the power system are monitored. However, voltage collapse often starts at weak area, then proliferates to the overall system and makes the whole system breakdown. As a result, in this thesis, not all the buses but only critical areas that contains the proposed reactive power valley (RPV bus), weak lines and VCA-connection lines between different voltage control areas (VCAs) are monitored. After the theoretical analysis is finished, verifications are done through Matlab simulation. The feasibility and efficiency of the alarm system is verified on IEEE 39-Bus New England System with induction motor as dynamic load.

5 4 Key words: Voltage Collapse, Alarm System, Power Transfer Limit, Voltage Stability Index, Load Dynamics, Power Restoration, Weak Area, Voltage Control Area (VCA), Reactive Power Valley (RPV), Weak Line

6 5 TABLE OF CONTENTS LIST OF FIGURES...7 LIST OF TABLES...10 LIST OF ABBREVIATIONS...11 ACKNOWLEDGMENTS...13 CHAPTER 1 Introduction Project Study Background Overview of Voltage Stability Definition of voltage stability Static analysis of voltage stability Dynamic analysis of voltage stability Literature Review of Voltage Collapse Assessment Novel methods to assess voltage collapse Voltage collapse assessment using AI technology Voltage collapse assessment using fuzzy logic Research Goals and Challenges Thesis Organization...58 CHAPTER 2 Monitoring Targets Voltage Control Areas (VCA) Weak Buses Weak Lines Voltage Stability Weak Area Case Study for Weak Area, Bus, Line Case 1 (Motor stalls before limitation) Case 2 (Motor stalls after limitation) Chapter Summary...79 CHAPTER 3 Effective Indicators...81

7 6 3.1 Comparison of Line Voltage Stability Indices (VSI) Indices formulation and their relations Case studies for line VSIs Comparison of Bus Voltage Stability Indices (VSI) Indices formulation and their relations Case study for bus VSIs Indicators on Load Dynamics Theoretical analysis Case study for indicators on load dynamics Chapter Summary CHAPTER 4 Voltage Collapse Alarm System Fuzzy Inference System (FIS) Fuzzy sets and membership functions Fuzzy rules Generic fuzzy system Voltage Collapse Alarm System (Structure 1) Voltage Collapse Alarm System (Structure 2) Case Study for Voltage Collapse Alarm System Case 1 (Before power transfer limit) Case 2 (After power transfer limit) Chapter Summary CHAPTER 5 Thesis Conclusion BIBLIOGRAPHY VITA...155

8 7 LIST OF FIGURES Number Page Fig. 1.1 Power system stability classifications...16 Fig. 1.2 Circuit representation...19 Fig. 1.3 P,V and I as a function of Rl, for a lossless system(r=0) and tanφ= Fig. 1.4 The V-P curves...21 Fig. 1.5 The V-Q curves...22 Fig. 1.6 Aggregate load response to a step-voltage change...26 Fig. 1.7 Slip-torque curves as V varies...31 Fig. 1.8 Motor fed through a line...31 Fig. 1.9 Network and motor QV curves...32 Fig Two-bus LTC system...32 Fig PV curve of two-bus system...33 Fig V-P Load restoration...34 Fig Radial system...37 Fig Thevenin equivalent of a power system seen from a load bus...37 Fig Simple line power system...38 Fig Bus Power System...39 Fig π equivalent branch Model for voltage stability research...40 Fig Load bus and rest of the system represented with a source and a line...48 Fig Major disadvantages of previous researches...57 Fig. 2.1 Reactive power valleys (RPV bus) ( + : power flow into the bus)...68 Fig. 2.2 Representation of weak lines...68 Fig. 2.3 Voltage control areas of IEEE 39-Bus System...71 Fig. 2.4 Weak buses in case Fig. 2.5 critical VCAs with weak buses and weak lines (case 1)...73 Fig. 2.6 Weak buses in case Fig. 2.7 critical VCAs with weak buses and weak lines (case 2)...77 Fig. 2.8 Flow chart of monitoring targets determination...80

9 8 Fig Two-bus power system model...82 Fig Bus New England Test System...89 Fig Line stability indices (line 2423) and motor slip...92 Fig Powe flow and voltage characteristic (case1)...93 Fig LVSI when θ-δ approaches Fig Line stability indices (line 2829) and motor slip...95 Fig Power flow and voltage characteristic (case2)...96 Fig. 3.8 Thevenin equivalent of a system...97 Fig A simple two-bus Thevenin equivalent system...99 Fig Bus indices and motor slip (bus 24) Fig A typical induction motor model Fig Active Power-Speed characteristic curve of induction motor Fig Reactive Power-Speed characteristic curve of induction motor Fig Admittance-voltage characteristics of induction motor Fig power-voltage characteristics of induction motor Fig Reactive power injected to a bus and dq/dt Fig Active power injected to a bus and dp/dt Fig Three effective indicators selected for the voltage collapse alarm system Fig. 4.1 Basic structure of voltage collapse alarm system Fig. 4.2 Representation of crisp and fuzzy subset of X Fig. 4.3 Four modules of a fuzzy system Fig. 4.4 Voltage collapse alarm system (structure 1) Fig. 4.5 Membership function for input variable LQP Fig. 4.6 Membership function for input variable dq/dt Fig. 4.7 Membership function for input variable dp/dt Fig. 4.8 Membership function for output variable DVSI Fig. 4.9 Fuzzy inference system in structure Fig Four degrees of alarm Fig Voltage collapse alarm system (structure 2) Fig Membership function for input variable dq/dt Fig Membership function for input variable dp/dt Fig Membership function for output variable DL...125

10 9 Fig Fuzzy inference system in structure Fig dq/dt and dp/dt vs DL Fig IEEE 39-Bus New England Test System Fig Maximum of LQP for VCA Fig Maximum of dq/dt for VCA Fig Maximum of dp/dt for VCA Fig Three input indicators, VSL1 and voltage for critical VCAs (structure 1 in case 1) Fig Three input indicators, VSL2 and voltage for critical VCAs (structure 2 in case 1) Fig Comparison of VSL for two structures in case Fig Maximum of LQP for VCA Fig Maximum of dq/dt for VCA Fig Maximum of dp/dt for VCA Fig Three input indicators, VSL1 and voltage for critical VCAs (structure 1 in case 2) Fig Three input indicators, VSL2 and voltage for critical VCAs (structure 2 in case 2) Fig Comparison of VSL for two structures in case

11 10 LIST OF TABLES Number Page Table. 1.1 Recent voltage collapse...14 Table. 1.2 Dynamic load state and demand variables...29 Table.1.3 Comparison of ES, FS, NN and GA...45 Table. 1.4 Previous researches of voltage collapse prediction using FL...56 Table. 1.5 Advantages of this research compared with others...58 Table. 2.1 Weak area for voltage collapse...69 Table. 2.2 Voltage control area of IEEE 39-Bus System...70 Table. 2.3 Weak buses in case Table. 2.4 Weak area for voltage collapse (case 1)...72 Table. 2.5 RPV bus and weak lines for critical VCAs (case 1)...73 Table. 2.6 Weak buses stalled motors in critical VCAs with stalled time (case 1)...74 Table. 2.7 Weak buses in case Table. 2.8 Weak area for voltage collapse (case 2)...76 Table. 2.9 RPV bus and weak lines for critical VCAs (case 2)...77 Table Weak buses stalled motors in critical VCAs with stalled time (case 2)...78 Table. 3.1 comparison of FVSI, L mn, LVSI and LQP...87 Table. 3.2 Line index ranking...90 Table. 3.3 Variation of line indices with motor(24) slip increases...92 Table. 3.4 Variation of line indices with motor(28) slip increases...95 Table. 4.1 Fuzzy logic rules Table. 4.2 Four degrees of alarm Table. 4.3 Fuzzy logic rules for dynamic load...125

12 11 LIST OF ABBREVIATIONS VS: Voltage Stability CPF: Continuation Power Flow VSM: Voltage Stability Margin LTC: Load Tap Changers SNB: saddle-node bifurcation VSI: Voltage Stability Index RPR: reactive power reserves AI: Artificial Intelligent Technology ES: Expert System FL: Fuzzy Logic ANN: Artificial Neural Networks GA: Genetic Algorithm DT: Decision Tree AIS: Artificial Immune System FORL: Function Optimization by Reinforcement Learning ACO: Ant Colony Optimization PSO: Particle Swarm Optimization CVM: Core Vector Machines VCA: Voltage Control Areas RPV: Reactive Power Valley WAMS: Wide Area Measurement System FVSI: Fast Voltage Stability Index LVSI: On Line Stability Index

13 12 LQP: Line Stability Factor L mn : Line Stability Index VCPI: Voltage Collapse Proximity Index PTSI: Power Transfer Stability Index VSL: Voltage Stability Level FIS: Fuzzy Inference System MF: Membership Function DVSI: Dynamic Voltage Stability Index DL: Dynamic Load

14 13 ACKNOWLEDGMENTS First and foremost, I would like to express my sincere thanks and gratitude to my supervisor Prof. Wong Chi-Kong, for his inspiring guidance and constant encouragement during the course of completing the project and preparing this thesis. I would like to thankfully acknowledge the financial support of the Research Committee of University of Macau in completion of the research related to the thesis. I would like to thank my friends Liu Zhu-Lin and Liu Miao who had rendered their help in the completion of the project. I would also take this opportunity to thank my roommates Zhai Shu, Luo Mei and Dong Shan-Shan for their help during my Master studies. I wish to appreciate my friends in Power Electronics Lab for their direct and indirect help for me. Last but certainly not the least, I also wish to express my gratitude to my family members for their motivation and support.