相移式全橋轉換器(PSFBCs)通常應用於隔離型的高直流電壓降壓及中、高功率的伺服器或通訊用電源上。相移式全橋轉換器被廣泛的應用是因為具有零電壓切換(ZVS)的特性，因此大幅降低硬切換所造成的切換損失。然而相移式全橋在固定盲時時間下輕載無法達到零電壓切換，因此文獻也提出變動盲時時間技術，其會隨著負載減少而將盲時時間增加，此方法雖有助於提升輕載效率，但會減少有效導通率。
本文提出數位控制多模式切換全橋轉換器(MMFBC)，所提出的控制器會根據負載大小切換不同的工作模式，本系統在空載時操作在突衝模式，輕載時為脈波寬度調變模式，重載時則為變動盲時時間相移模式，每個模式的轉換點是經由實驗結果所得到的。本文首先探討電路操作原理及設計準則，再透過數位訊號處理器dsPIC33FJ16GS502實現多模式切換、脈波寬度調變、相移量控制及變動盲時時間控制。本文實際製作輸出功率為 ( / )之直流/直流電源轉換器，以驗證所提出之電路分析與控制方法的正確性與可行性，根據實驗結果，本系統在不同負載下所有操作模式的平均效率比固定盲時高0.5%，其量測效率最高可達到92.9%，實驗結果還證明實現多模式控制技術可以顯著降低待機與輕載功率損失。

Phase shifted full bridge converters (PSFBCs) are commonly used to step down high DC bus voltages and/or provide isolation in medium to high power applications like server or telecom power supplies. PSFBC is adopted because this type of converter can achieve zero voltage switching (ZVS); therefore, considerably reduces the amount of switching losses associated with hard switching. However, ZVS may not be achieved under light-load condition and/or large input voltage if fixed dead time is utilized. Consequently, adaptive dead time techniques are sometimes utilized to increase the amount of dead time as the load decreases. However, this will decrease the effective duty cycle and consequently reduce the efficiency under light load.
In this thesis, a digitally-controlled multi-mode full-bridge converter (MMFBC) is developed. The presented system changes the operating mode of the full-bridge converter according to different load conditions. For very light load, burst mode control is adopted. Furthermore, pulsewidth-modulated (PWM) switching mode is used under light load condition and adaptive dead time phase shifted control is chosen for heavy load condition. The transition point between each operating mode is also investigated by experimental results. In this thesis, the operating principles, design guidelines are described first. A low cost digital signal controller dsPIC33FJ16GS502 is then adopted in this thesis to realize the multi-mode control, PWM control, phase shifted modulation and adaptive dead time control. To validate the correctness and the effectiveness of the proposed method, a 480 W, 48V to 10A prototyping circuit is implemented and tested. According to the experimental results, the measured efficiencies of all operating modes under different loads are all higher than 0.5% and the peak efficiency of the whole system can achieve 92.9%. Experimental results also demonstrated that the implemented multi-mode control technique can significantly reduce the losses under standby and light-load conditions.

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