本篇論文於串聯型Δ接全橋轉換器中提出不平衡負載補償之應用，此補償包含正序虛功補償、負序電流補償以及低頻擾動補償。本論文之控制器可由功率潮流的分析與推導得知，藉由功率分析在負序電流補償的情況下注入零序電流以達成直流側電容電壓平衡控制。然而，注入零序電流將使轉換器相電流的峰值上升，導致開關元件有毀損的可能性。為了避免開關元件遭受破壞，本論文亦在Δ接全橋轉換器中提出一峰值電流限制策略以防止過電流的風險。此峰值電流限制策略及不平衡負載之補償將由實驗平台及模擬的測試結果進行驗證。

This thesis presents the application of a Delta-Connected Cascaded H-bridge Converter in unbalanced load compensation. The compensation includes positive-sequence reactive power compensation, negative-sequence current compensation, and low-frequency distortion compensation. The controller is designed by power flow analysis which achieves the dc capacitor voltage balancing by Zero-Sequence Current (ZSC) injection during negative-sequence current compensation. Nevertheless, the zero-sequence current injection raises the peak of phase current which may damage the switches of the converter. For avoiding the risk of over-current, this thesis also proposes a Peak Current Limit Control (PCLC) in delta-connected cascaded converter. Laboratory and simulation test results are provided to validate the proposed method.

Chapter 1 Introduction 1
1.1 Background 1
1.2 Organization of the thesis 3
Chapter 2 Literature Review 4
2.1 Introduction 4
2.2 Modulation Technique 4
2.3 DC buses Voltage Balancing Control Based on MMCC-SSBC & MMCC-SDBC 6
2.3.1 Dr. Akagi’s Zero-Sequence Current Method Based on 7-level MMCC-SDBC 6
2.3.2 Laboratory’s Zero-Sequence Voltage Method Based on 7-level MMCC-SSBC 14
Chapter 3 Operation Principle 24
3.1 Introduction 24
3.2 Power Flow Analysis 25
3.2.1 Definition and Instantaneous Power Flow Concept 25
3.2.2 The Overall Voltage Balancing Control 28
3.2.3 The Clustered Voltage Balancing Control Based on ZSC Injection 30
3.2.4 The Individual Voltage Balancing Control 38
3.3 Unbalanced Load Compensation and Proposed PCLC 39
3.4 The Current Controller 45
3.5 The Control Block Diagram 49
Chapter 4 Test Benches 51
4.1 Introduction 51
4.2 Star-Connected Cascaded H-Bridge Converter 52
4.3 Delta-Connected Cascaded H-Bridge Converter 55
4.4 Unbalanced Load 58
Chapter 5 Simulation Results 61
5.1 Introduction 61
5.2 Proposed Unbalanced Load Compensation 61
5.3 Laboratory’s ZSC Voltage Balancing Control Method 65
5.4 Summary 68
Chapter 6 Laboratory Test Results 68
6.1 Introduction 68
6.2 Proposed Peak Current Limit Control and Low-Frequency
Distortion Compensation 68
6.2.1 Laboratory’s ZSC Voltage Balancing Method 69
6.2.2 Low-Frequency Distortion Compensation 72
6.2.3 Proposed Peak Current Limit Control 75
6.3 Dr. Akagi’s ZSC Method Based on MMCC-SDBC 82
6.4 Laboratory’s ZSV method Based on MMCC-SSBC 84
6.5 Summary 88
Chapter 7 Conclusion and Future Work 89
7.1 Conclusion 89
7.2 Future Work 90
REFERENCE 91

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