本研究提出以分切合整數位控制法(D-Σ digital control)實現多階層模組化雙向轉換器。多階層模組化轉換器廣泛應用於靜態同步補償器、高壓直流輸電、背對背系統、馬達驅動、及電池儲能系統等。
分切合整數位控制法的主要特點是能把隨著電流大小而不同的電感值納入考量，如此一來，跟傳統的控制法相比，在相同的電感下，分切合整數位控制法能夠得到較小的電感體積。藉由使用此控制法，每一相的控制器可以精準的算出相應的責任比率，再經由交錯式脈波寬度調變，以達到電流漣波縮小的效果。本研究也建立了另一部多階層模組化轉換器，用來實現循環功能測試。主轉換器執行整流模式，穩定直流鏈電壓，而副轉換器執行併網模式，將能量饋入市電端。此外，模組電容穩壓是在分切合整數位控制法所計算出來的責任比率中加入一個微幅的微調量，來進行模組電容穩壓。
本研究的主要貢獻包含以下幾點，第一點為採用分切合整數位控制法，此方法除了可以考慮電感值變化，也可利用此控制法得出模組電容電壓表示式，對調整模組穩壓速度及降低漣波電壓也有很大的幫助。第二點為採用中央控制器處理均流問題，把上臂與下臂直流鏈電壓感測進中央控制器裡，經由直流鏈電容穩壓公式的計算，可以得出相應的電流命令，再利用串列通訊協定，傳送給每相控制器，以達到均流效果。第三點為採用多階層架構，可以實現高壓直流傳輸。利用模組串接，可以有效地提高直流鏈電壓，如此一來，在遠距離直流微電網傳輸過程中，可以選擇較細傳輸導線。最後，本研究實作一組主、副多階層模組化雙向轉換器系統，並經由實測結果驗證本論文所提出的控制法則。

This research proposes how to use division-summation (D-Σ) digital control to realize modular multilevel converters. Modular multilevel converters (MMCs) are widely used in STATCOM, HVDC, back-to-back power transfer systems, motor driving and battery storage systems.
The main characteristic of D-Σ digital control is that it can take inductance variation into consideration when inductor current changes. Compared with conventional control laws, D-Σ digital control can reduce core volume under the same inductance. Each controller in a phase can precisely determine control law for current tracking, and through interleaving PWM, current ripple can be reduced. In this research, we also implement another modular multilevel converter to realize power recycling test. One converter works in rectification mode to regulate dc-bus voltage, the other works in grid-connection mode to inject power into the grid. Besides, D-Σ digital control introduces a small duty ratio modulation to achieve cell-capacitor voltage regulation.
There are several major contributions in this research. The first one is to adopt D-Σ digital control. The advantages of using this control law are that we can not only take the inductance variation into consideration, but can obtain a cell voltage expression, which helps a lot in regulating cell voltage and reducing voltage ripple. Secondly, we adopt a central controller to deal with current sharing. By sensing the upper and lower dc-bus voltages into the central controller, current commands can be determined correspondingly. Then, the command is transfered to each-phase controller through a serial communication interface to realize equal current sharing. Thirdly, we adopt the MMC to realize two HVDCs and to effectively improve the dc-bus voltage regulation. It is useful in reducing diameter of transmission line for a long-distance dc microgrid.
Finally, two bi-directional modular multilevel converters have been implemented, and measured results have verified the current tracking control law and voltage regulation schemes.

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