對於三階中性點箝位轉換器存在著中性點電壓偏移的問題，本論文提出兩種中性電電壓平衡控制的方法，且皆可實現在三臂三線、三臂四線以及四臂四線架構。一種是零序電壓注入的技術，包含了五種方法去計算出電容電荷的量，以達成中性點電壓平衡。另外一種是雙極性調變模式，在此調變下，所有開關會在每個脈波寬度調變改變狀態，如此情況下相對中性點電壓就會有”正”、”零”及”負”電壓等級。在每個脈波寬度調變，藉由調整這三個區間就可以達成中性點電壓控制。此外，本論文採用新型的雙極性調變去消除中性點低頻電壓振盪。本論文將藉由理論及實作去驗證零序注入和雙極性兩種方法。

A significant problem with neutral-point-clamped (NPC) three-level converters is the fluctuation in the neutral-point (NP) voltage. In this thesis, there are two methods to realize neutral-point voltage balancing in the different structures including three-leg three-wire, three-leg four-wire, and four-leg four-wire system. One is zero-sequence- voltage injection voltage (ZSI) technique. The ZSI technique includes five methods which calculate capacitor charge to achieve NP voltage balancing control. The other is bipolar modulation technique. In bipolar modulation, the phase voltage with respect to NP point simultaneously has “p,” “0,” and “n” levels in every pulse-width-modulation (PWM) cycles. By adjusting the intervals among the three levels in a PWM cycle can achieve NP voltage balancing. Moreover, the thesis employs the novel bipolar modulation to eliminate low-frequency voltage oscillation in NP. In this thesis, both ZSI technique and bipolar modulation technique are verified by means of theory and experiments.

摘要 I
Abstract II
致謝 III
Table of Contents IV
List of Figures VI
List of Tables IX
CHAPTER 1 Introduction 1
1.1 Motivation 1
1.2 Contributions of the Thesis 2
1.3 Outline of the Contents 3
CHAPTER 2 Literature Review 4
2.1 Introduction 4
2.2 Phase Disposition PWM for Three-level NPC Converters 5
2.3 Neutral-point voltage balancing control 7
2.3.1 Zero-sequence injection technique 8
2.3.2 Space vector technique 12
2.4 The low-frequency voltage oscillation 18
CHAPTER 3 Operation Principal 21
3.1 Introduction 21
3.2 Zero-sequence injection technique for NP balancing control 22
3.2.1 Strategies for zero-sequence injection technique 28
3.3 Bipolar method for NP voltage balancing control 34
3.3.1 Unipolar modulation 34
3.3.2 Bipolar modulation 36
3.3.3 The bipolar Offset to balance NP voltage 37
3.3.4 Strategies for the bipolar offset 46
3.4 Low-frequency voltage oscillation elimination 50
3.5 Control block diagram 56
3.5.1 AC Voltage Controller in 3-leg system. 57
3.5.2 AC Voltage Controller in 4-leg system 61
CHAPTER 4 Implementation and Experimental Results 68
4.1 Introduction 68
4.2 Experiment results in three-leg three-wire system 73
4.2.1 Zero-sequence injection technique 73
4.2.2 Bipolar offset technique 81
4.3 Experiment results in three-leg four-wire system 85
4.3.1 Zero-sequence injection technique 85
4.3.2 Bipolar offset technique 86
4.4 Experiment results in four-leg four-wire system 87
4.4.1 Zero-sequence injection technique 87
4.4.2 Bipolar offset technique 90
4.5 Experiment results for the low-frequency voltage oscillation Elimination 93
CHAPTER 5 Conclusion and Future Work 95
5.1 Conclusion 95
5.2 Future Work 95
References 96

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