臺灣博碩士論文加值系統

基波負載潮流分析是電力系統運轉與規劃最基本的工作。在理論分析上，我們往往將輸電系統視為平衡的三相系統。因此，輸電系統的負載潮流分析可以利用單相模式求解。然而配電系統因為先天上網路的非對稱關係，以及負載的不平衡，以致於傳統輸電系統的負載潮流分析方法，無法適用於配電系統中。此外，像牛頓拉佛森及高斯迭代等單相負載潮流分析法，也受限於配電系統的高電阻電抗比及輻射架構，而無法適用於配電系統負載潮流分析。因此，配電系統的負載潮流計算，必須尋求三相的求解分析方法才能完成。
本篇論文提出一套改良式的前進/後退三相配電系統負載潮流分析方法。在後退法中，我們利用克希和夫電流及電壓定律，求取系統每一線路電流及每一條線路上游匯流排或變壓器一次側的電壓。於前進法中，採用線性比例法則，求出變電所及具有分岐線之匯流排其指定電壓及計算電壓的實部及虛部比值。並利用匯流排指標，快速地決定出每一分支的末端匯流排位置。再將每一個分岐線匯流排或線路末端匯流排的計算電壓或初始電壓的實、虛部，乘以利用線性比例法則所求得的相對應實、虛部比值，以修正相對應匯流排的電壓值。整個迭代程序，直到變電所的計算電壓與指定電壓的差值，小於某一指定值才停止。
在所提出的三相配電系統負載潮流中，我們所考量的系統模型包括架空線路、地下電纜、不同接線型式的變壓器、集中式負載、均勻分佈式負載、電容器組以及汽電共生發電機模型等。我們利用美國電力電子工程師協會所提出的標準測試案例，依不同的系統負載、不同的系統它]及不同的線路電阻電抗比，進行模擬分析。藉由模擬結果，我們可以瞭解到，我們所提出的負載潮流分析方法，在計算速度上比前進/後退法及階梯法都來的快速，且並未因此而降低其精確性。

Load flow analysis is the most fundamental work for power system operation and planning. In transmission systems, the network is always treated as balanced. Then, the load flow problem for transmission system can be dealt by single-phase method. However, the distribution power system is unbalanced inherently because of unsymmetrical network and unbalanced loads. In such situation, the conventional load flow methods for transmission systems are not suitable for distribution systems. In addition, high R/X ratio and radial structure are also to restrict the use of single-phase load flow approaches. Therefore, the three-phase approaches are required for distribution system load flow studies.
The thesis proposes an improved forward/backward sweep algorithm for three-phase load flow analysis of radial distribution systems. In the backward sweep, the KCL and KVL are used to calculate each line current and the upstream bus voltage of each line or a transformer branch. Then, linear proportion principle for finding the real and imaginary ratios on each line section and bus index for fast mapping the terminal bus at each branch are exploited in the forward sweep to update the voltage at each junction or each terminal bus. The procedure stops after the mismatch of the calculated and the specified voltages at the substation is less than the predefined convergence tolerance. In the proposed method, the distribution component models including overhead lines, underground cables, different connecting type transformers, spot loads, distributed loads, capacitor banks and cogenerator are in consideration. The proposed solution algorithm has been described in details and tested by IEEE benchmark distribution systems with default system data, different system loadings, different power factors and different R/X ratios at different system loadings. Results show that the algorithm is accurate and computationally efficient in comparing with conventional forward/backward sweep method and ladder iteration method.

Table of Contents
Acknowledgment
Abstract I
Table of Contents V
List of Tables VIII
List of Figures XI
Chapter 1 Introduction 1
1.1 Motivations and Objectives 1
1.2 Contributions 2
1.3 Organization of Dissertation 4
Chapter 2 Component Models of Distribution System 6
2.1 Distribution Line Models 6
2.1.1 Overhead Lines 7
2.1.2 Underground Cables 11
2.1.2.1 Concentric Neutral Cable 12
2.1.2.2 Tape-Shielded Cable 15
2.2 Transformer Models 19
2.2.1 Delta–Grounded Wye Connection 20
2.2.2 Ungrounded Wye–Delta Step-Down Connection. 24
2.2.3 Grounded Wye–Grounded Wye Connection 25
2.2.4 Delta–Delta Connection 26
2.2.5 Open Wye–Open Delta 27
2.3 Load Models 27
2.3.1 Wye-Connected Loads 28
2.3.1.1 Constant PQ Loads 28
2.3.1.2 Constant Impedance Loads 29
2.3.1.3 Constant Current Loads 30
2.3.2 Delta-Connected Loads 30
2.3.2.1 Constant PQ Loads 31
2.3.2.2 Constant Impedance Loads 31
2.3.2.3 Constant Current Loads 32
2.4 Capacitor Models 32
2.4.1 Wye-Connected Capacitor 32
2.4.2 Delta-Connected Capacitor 33
2.5 Cogenerator Models 34
Chapter 3 Traditional Forward/Backward Methods 39
3.1 Forward/Backward Sweep Method 39
3.1.1 Backward Sweep 40
3.1.2 Forward Sweep. 41
3.1.3 Convergence Criterion 42
3.2 Ladder Iteration Method 44
3.2.1 Forward Sweep 44
3.2.2 Backward Sweep 45
3.2.3 Convergence Criterion 46
3.3 Comparisons of F/B Sweep and Ladder Iteration Method 47
Chapter 4 Modified Forward/Backward Sweep Method 49
4.1 Real and Imaginary Decompositions of Distribution Line and Transformer. 49
4.1.1 Voltage and Current Equations of Distribution Line 51
4.1.2 Voltage and Current Equations of Distribution Transformer 54
4.2 Linear Property of Decomposition Approach 58
4.3 Bus Indexing Scheme 60
4.4 Solution Algorithm 62
4.5 Convergence Behavior 65
Chapter 5 Case Studies 68
5.1 Benchmark Test Systems 68
5.2 Comparison for Default Systems 71
5.3 Effect of System Loading 79
5.4 Effect of System Power Factor 85
5.5 Effect of Different R/X Ratio at Different Loading Conditions 90
Chapter 6 Power System Education Software 101
6.1 GUI - Graphical User Interface 102
6.1.1 Control Panel 103
6.1.2 Property Editor 104
6.1.3 Alignment Tool 105
6.1.4 Callback Editor 106
6.1.5 Menu Editor 107
6.2 Architecture of Power System Education Software 108
6.3 Operation screen of PSES 110
Chapter 7 Conclusions and Future Work 123
References 126
Vita 131

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