近年來，模組串接型轉換器(MMC)因優異的擴充彈性而逐漸成為中壓等級的工業應用主流。伴隨著與日俱增的重視，各種架構的模組串接型轉換器也陸續被提出。其中，模組串接型中性點鉗位橋式轉換器結合了兩種常見的多階層轉換器之結構，故能有效率地提高輸出電壓之階層數。因此，此優勢讓該多階層技術在高功率的應用上更具潛力與發展性。
儘管模組串接型中性點鉗位橋式轉換器在輸出階層上有著明顯的優勢，但中性點鉗位架構將無法避免地受制於中性點電位浮動。因此，本論文基於筆者實驗室所提出的平均功率平衡控制法(APB)，提出追加一中性點電壓平衡控制來穩定每個串接模組中的中性點電位。故本論文中的控制法不僅能平衡各模組間的電壓，亦能平衡模組內的上下電容電壓。本論文亦架設實驗室的模組串接型中性點鉗位橋式轉換器平台之靜態虛功補償器，並以測試結果驗證本論文所提出的控制法之正確性。

Modular multilevel converter (MMC) has emerged as the mainstream of industrial mediumvoltage
applications recently for its flexibility in extension. A variety of MMC topologies have
been proposed for years. Among them, the NPC-based MMC is a combination of two conventional
multilevel topology which raises the output levels efficiently. Therefore, the NPC-based
MMC technique is more promising for high-power applications where the static var compensator
is chosen for verification in this thesis. Despite the advantage of NPC-based MMC is obvious, the NPC structure suffers from the neutral point voltage fluctuation inevitably. Accordingly, this thesis presents a control method to address the NPC-based MMC which is adapted from the average power balancing (APB) technique proposed by author’s laboratory. Compared with original APB, an additional neutral point
voltage balancing control is embedded. Consequently, the adapted method balances not only the
DC voltage of each cell, but also the voltage of upper and lower capacitor within every cell. To
verify the proposed method, a test bench of STATCOM implemented with NPC-based MMC has
been constructed and laboratory test results are presented to validate the performance of proposed method.

Abstract i
Acknowledgment ii
List of tables v
List of figures vi
1 Introduction 1
1.1 Background 1
1.2 Circuit topology 3
1.3 Thesis organization 4
2 Literature review 5
2.1 Introduction 5
2.2 Modulation technique 6
2.3 Average power balancing with zero-sequence voltage injection 9
2.4 Offset injection for 5-level NPC-bridge 26
3 Operation Principle 38
3.1 Introduction 38
3.2 Vector plane of single-phase NPC-bridge 40
3.3 Unipolar PWM technique on vector plane 42
3.4 Control block diagram 61
4 Laboratory Test Results 64
4.1 Introduction 64
4.2 Function validation of STATCOM realized with NPC-based MMC 67
4.3 Experimental test results of neutral point voltage balancing control 71
5 Conclusion and Future Work 118
5.1 Conclusion 118
5.2 Future work 119
Reference 120

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