一般LLC串聯式諧振轉換器，透過變頻控制方式調節輸出電壓，然而操作頻率越高會受到二次側開關寄生電容的影響，導致增益無法調降，逕而限制增益之操作範圍，而電路只能提高最大增益點實現寬範圍應用，然而這將使操作頻率遠離諧振頻率，並且使操作頻率範圍增加，逕而導致效率降低。
本論文提出透過變頻模式控制並加入波谷切換模式控制和輕載策略突衝模式控制，其中所提之波谷切換控制操作於較低之增益區間，並於輕載以下透過突衝模式控制調節輸出電壓。本論文先推導半橋LLC串聯諧振轉換器之轉移函式，並敘述傳統串聯諧振轉換器的動作區間，接著對波谷切換控制與突衝模式控制動作時序進行分析，最後根據不同控制策略進行比較，之後根據不同控制分別使用模擬軟體分析品質因數Q、電感比值K對增益所造成的影響，並根據分析結果規劃一設計流程。
最後根據USBPD3.1之輸出規範，研製一台輸出電壓5 V~48 V、最大輸出功率240 W並搭配本論文控制策略之半橋LLC串聯諧振轉換器，並與一台相同輸出規格並使用一般變頻控制之半橋LLC串聯諧振轉換器做比較，根據實測結果證明，本論文所提之控制策略可操作於較低之增益區間，因此可降低操作之最大增益值，逕而使操作頻率接近諧振頻率，另外也有較寬之增益操作範圍，因此更適合於寬範圍之應用場合。

General LLC series resonant converter, through the fequency modulation control to adjust the output voltage, but the higher operating frequency will be affected by the secondary side switch parasitic capacitance, resulting in the gain can not to adjusted down, the diameter and limit the operating range of the gain, and the circuit just only increase the maximum gain point to achieve a wide range of applications, but this will make the operating frequency far to the resonant frequency, and the operating frequency range increases, and reduced efficiency.
In this thesis, it’s proposed that the Valley switching mode control and light load strategy burst mode control are added to frequency modulation control, in which the proposed valley switching control operates in the lower gain range, and the output voltage is adjusted by the burst mode control below light load. This thesis first to derives the transfer function of the half-bridge series resonant converter, and describes the operation interval of the traditional series resonant converter, after that analyzes the operation timing of the valley switching control and the burst mode control. Finally compare according to different control strategies, and uses simulation software to analyze the effect of quality factor Q and inductor ratio K on gain to different controls, and plans a design process according to the analysis results.
Finally, according to the specification of USBPD3.1, develop a half-bridge LLC series resonant converter with an output voltage of 5 V~48 V and a maximum output power of 240W, which is matched with the control strategy of this thesis. Compared with the half-bridge LLC series resonant converter, according to the actual measurement results, the control strategy proposed in this thesis can operate in a lower gain range, so the maximum gain value of the operation can be reduced, so that the operating frequency can be close to the resonant frequency, In addition, it has a wider gain operating range, so it is more suitable for a wide range of applications.

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