中文摘要
由於太陽再生能源發電對島嶼獨立電網運轉之安全性與經濟性極為重要，本文探討聖多美島電力系統併接大型太陽能發電系統之經濟效益衝擊分析與系統穩定度分析。本文收集聖多美島與普林斯比之電力系統架構，並對本研究之相關背景知識做回顧，然後建立兩島之電力系統與相關假設事例，並建構電力潮流分析模型與動態模擬模型。經由併接太陽能發電系統之穩態與暫態模擬可知24%的光伏滲透率所造成之電壓變動，並不會超過系統運轉之電壓限制。然而，當系統太陽能滲透率大於總發電量供給之12%時，當系統故障發生時所造成之頻率擾動，將違反其頻率限制，而導致使太陽能發電系統解聯，因此建議系統之PV滲透率必須小於12%。在所建議之12%太陽能滲透率條件下，當系統發生故障如:發電機解聯、太陽能發電系統解聯、傳輸線解聯等系統擾動下，系統之頻率、電壓將可回復至穩定。所有故障事例中，以匯流排故障最為嚴重，其模擬結果建議系統之臨界故障清除時間為0.35秒。在確定了系統最佳太陽滲透率，本研究亦對PV系統建置之經濟效益影響進行探討，若考慮太陽能發電計畫之生命週期為25年，則可知其投資回收年限為5年。最後，本論文提出未來研究方向，以強化聖多美電力系統之穩定度、可靠度及提升再生能源滲透率。

ABSTRACT
Considering the observed importance surrounding PV generation systems in today’s world of electric power generation schemes, this thesis investigates the stability and economic impact of interconnecting a utility-scale PV system to the power system of Sao Tome Island (Sao Tome PS). Thus, general information of Sao Tome and Principe as nation is first provided; followed by a brief description of its electric power system. Next, some background literature supporting the investigation are reviewed. Original system and case scenario assumptions are established, proceeded by the modeling of both systems for power flow and dynamic studies. Simulation results obtained during steady-state and dynamic analyses following the integration of PV system show that PV penetration level of 24% does not cause sufficient voltage fluctuation to undermine the voltage constraint imposed on the system operation. Nevertheless, due to the probability of the system facing frequency instability providing a contingency which can lead to frequency constraint violation, and consequent trip of the PV system when the system experiences a penetration level larger than 12% of total generation supply; a utility-scale PV generation optimal penetration level not greater than 12% is advised. Constrained by the aforesaid contingency-dependent frequency violation, transient stability results when the system is experiencing 12% penetration suggests that, following a disturbance – machine trip, PV trip, line trip, bus fault, or line fault – the system is able to recover its frequency stability, voltage stability, and synchronous stability; providing the fault is cleared, in the latter case, within the system CCT. When subjected to the worst kind of disturbance – the bus-fault – the simulation results indicate for a system CCT of 0.35 seconds. Having determined the PV generation optimal penetration level for the system, the economic impact was investigated; financial analysis suggests that the present PV penetration yields a PBY of 5 years with an estimated avoided diesel-oil generation cost worth 7.15 million US dollars if a PV project with 25-year life cycle is considered. Finally, due to several vulnerabilities Sao Tome PS is presently facing, urgent studies to improve the island’s power system stability, reliability, quality, and the level of renewable generation penetration become extremely important and necessary; therefore recommended.

THESIS VERIFICATION LETTER i
ACKNOWLEDGMENTS iii
ABSTRACT iv
TABLE OF CONTENTS vi
LIST OF FIGURES viii
LIST OF TABLES xii
ACRONYMS AND ABBREVIATIONS xiii
CHAPTER 1: INTRODUCTION 1
1.1. Objective of The Thesis 2
1.2. Content of The Thesis 2
CHAPTER 2: DESCRIPTION OF SAO TOME ISLAND POWER SYSTEM 3
2.1. Generation System 3
2.2. Transmission and Distribution System 6
CHAPTER 3: BACKGROUND LITERATURE REVIEW 9
3.1. Power Flow Analysis 9
3.1.1. Power Flow Problem Definition 9
3.1.2. Network Model and Power Flow Problem Formulation 9
3.1.3. Power Flow Solution Methods 15
3.1.4. Power Flow Solution Applied in this Study – The N-R Method 16
3.2. Power System Stability 20
3.2.1. Synchronous Stability 20
3.2.2. Voltage Stability 23
3.2.3. Frequency Stability 24
3.2.4. Dynamic of a Synchronous Machine 24
3.2.5. The Swing Equation 25
3.2.6. Two Machine System and Coherent Swinging 27
3.2.7. Equal Area Criterion and Fault Clearing Effect 28
3.3. Renewable Power Generations 32
3.3.1. PV Generation System 35
3.3.2. PV Resource – Solar Irradiation 36
3.3.3. PV Power Generation Mathematical Model 37
CHAPTER 4: STABILITY IMPACT OF A UTILITY-SCALE PV SYSTEM ON SAO TOME PS 41
4.1. Adopted Methodology for the System Study 41
4.1.1. Base Case Assumptions – Original System 41
4.1.2. Original System Power Flow Modeling 45
4.1.3. Original System Dynamic Modeling 47
4.1.4. Case Scenario Assumptions – PV System Integration 49
4.1.5. PV System Power Flow Modeling 49
4.1.6. PV System Dynamic Modeling 53
4.2. Original System 54
4.2.1. Steady-state Analysis 54
4.2.2. Transient Stability Analysis 57
4.3. Case Scenario – PV System Integration 67
4.3.1. PV Generation Optimal Penetration 67
4.3.2. Steady-state Analysis 74
4.3.3. Transient Stability Analysis 77
CHAPTER 5: ECONOMIC IMPACT OF PV PENETRATION ON SAO TOME ISLAND POWER SUPPLY 90
5.1. PV System Financial Analysis 90
5.1.1. Net Present Value 90
5.1.2. Pay Back Year and Avoided Diesel-oil Generation Cost 92
CHAPTER 6: CONCLUSIONS - CONTRIBUTIONS – AND FUTURE WORKS 94
6.1. Conclusions 94
6.2. Contributions 95
6.3. Future Works 95
REFERENCES 97
APPENDICES 99

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