隨著經濟的發展與人們生活水準的提高，工廠的設立越來越多，維持良好的電力品質變成一個重要的議題。尤其是煉鋼廠中的電弧爐在運作時，會產生電壓降、電壓閃爍、電壓不平衡和諧波等問題。針對中高壓層級的應用，本篇論文選用了串接型的△接全橋轉換器。串接型的轉換器可以提升容量與額定電壓，然而串接型的電源轉換器有各個模組的直流電壓不平衡的缺點，必須發展一平衡控制方法來解決這個問題。本論文利用功率潮流的分析與推導，發展出以注入零序電流的方式來平衡各模組直流電壓的控制器，並針對上述電力品質問題發展補償策略。為了驗證串接型△接全橋轉換器對電弧爐補償的能力，本論文利用一三相三線的電源轉換器來作為可調整式的不平衡負載，以模擬電弧爐的動態並建立起實驗平台。

With the development of the economy and the improvement of the people’s living standard, there are more and more factories build in the power system. These factories may affect the power quality, especially the electric arc furnace (EAF). How to maintain the power quality has become an important issue. The power quality problems of EAF include voltage flicker, voltage drop, voltage unbalance and harmonics in power system. The modular multilevel cascaded converter with single-delta bridge cells (MMCC-SDBC) is chosen in this thesis for medium voltage applications. The structure of SDBC can increase power and voltage rating. However, one of the main disadvantages is the voltage unbalance between each cell. It needs to develop a balancing control method to solve the problem. The thesis uses power analysis method to design the DC voltage balancing controller by injecting zero sequence current and develops the compensation strategy to eliminate the power quality problems as mentioned above. In order to verify the compensation capability of SDBC, a three-phase three-wire converter based on digital controller is used to simulat the EAF performances.

摘要 I
Abstract II
Table of Contents III
List of Figures V
List of Tables VIII
CHAPTER 1 Introduction 1
1.1 Motivation 1
1.2 Outline of the Contents 3
CHAPTER 2 Literature Review 5
2.1 Introduction 5
2.2 Electric Arc Furnace 5
2.2.1 The Operation of the Electric Arc Furnace 6
2.2.2 Voltage Flicker 7
2.2.3 The Harmonics of the Electric Arc Furnace 11
2.3 EAF Compensation Based on MMCC-SDBC 13
2.4 DC bus Voltage Balancing Control Method 15
CHAPTER 3 Operation Principles 22
3.1 Introduction 22
3.2 Power Flow Analysis of MMCC-SDBC 23
3.2.1 Definition and Instantaneous Power Flow Concept 23
3.2.2 The Overall Power 26
3.2.3 The Cluster Power and Zero-Sequence Current Injection 27
3.3 The Controller of MMCC-SDBC 34
3.3.1 DC Capacitor Voltage Control 36
3.3.2 Unbalanced Load Compensation 39
3.3.3 The Control Block Diagram 41
3.4 The Operation of Unbalanced Load 43
CHAPTER 4 Test Benchs 44
4.1 Introduction 44
4.2 Delta-Connected Cascaded H-Bridge Converter 45
4.3 Unbalanced Load 48
CHAPTER 5 Simulation Results 51
5.1 Introduction 51
5.2 Simulated Unbalanced Load 51
5.3 EAF Compensation 54
5.4 Fault-Tolerant Operation 56
5.4.1 Raising DC Bus Voltage 58
5.4.2 Open Delta Connection 59
CHAPTER 6 Laboratory Test Results 64
6.1 Introduction 64
6.2 Simulated Unbalanced Load 64
6.3 EAF Compensation 66
CHAPTER 7 Conclusions and Future Work 71
7.1 Conclusion 71
7.2 Future Work 72
References 73

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