兩級式升降壓 LLC 諧振轉換器之數位控制與建模

Abstract

本文針對兩級式升降壓 LLC（Buck-Boost LLC, BBLLC）轉換器提出一種建 模與控制架構，以在寬輸入電壓範圍內實現優異的動態性能。本文建立了一套系統化的小訊號模型，用於分析升降壓（Buck-Boost）級對頻率響應之影響。此外，於補償網路中整合了陷波濾波器（Notch Filter），以精確抵消系統固有的無阻尼極點，有效抑制振盪並大幅提升相位裕度（Phase Margin）與整體穩定性。 為解決 vin 步階變化期間所導致之 vout 劇烈變動挑戰，本文導入輸入電壓前饋數位控制方法，顯著改善輸入電壓劇烈變動時的輸出電壓暫態調節能力。為實現可靠切換操作，本文推導精確之 Buck-Boost 電感電流 iLb 方程式，藉此進行死區時間 tdead 分析。此外，亦以解析方式建立零電壓切換（ZVS）與電壓增益邊界條件，為在所有操作模式下維持軟切換提供明確設計準則。最後，實作一台Pout = 200 W、Vin 為 70 V 至 400 V、Vout = 12 V 之原型機進行測試。實驗結果顯示，在 Vin 由 60 V 步階跳變至 90 V 之線電壓暫態測試下，輸出電壓過衝僅微幅變動 0.3 V。此外，所提方法不僅能在寬輸入電壓範圍內有效維持輸出穩壓，亦能於整個增益範圍內維持最佳化 ZVS 操作以實現高轉換效率，充分驗證本文理論模型、控制策略與設計準則之正確性與可行性。

This thesis proposes a modeling and control framework for a two-stage Buck-Boost LLC (BBLLC) converter to achieve superior dynamic performance across a wide input voltage range. A systematic small-signal model is developed to analyze the impact of the Buck-Boost stage on the frequency response. Furthermore, a notch filter is integrated into the compensation network to precisely counteract the undamped poles inherent in the system, effectively suppressing oscillations and significantly enhancing the phase margin and overall stability. To address the challenge of severe vout fluctuations during vin steps, a digital linetransient feedforward control is implemented, substantially improving the transient regulation capability. To achieve reliable switching operation, precise Buck-Boost inductor current iLb equations are derived to conduct a theoretical deadtime analysis with tdead. Additionally, the zero-voltage switching (ZVS) and voltage gain boundary conditions are analytically established, providing clear design guidelines for maintaining soft switching across all operating modes. Finally, a Pout = 200 W prototype regulating Vout = 12 V from Vin = 70 V to 400 V is implemented for testing. Experimental results show that during a line transient step from Vin = 60 V to 90 V, the output voltage overshoot is limited to only 0.3 V. Furthermore, the proposed methodology not only effectively maintains output voltage regulation over this wide input-voltage range but also achieves high conversion efficiency by maintaining optimized ZVS operation across the entire gain range. These results fully verify the correctness and feasibility of the proposed theoretical models, control strategies, and design guidelines.