以脈寬調變控制之定頻諧振轉換電路分析與評估

Analysis and Evaluation of Pulse-Width Modulated Resonant Converter with Fixed Switching Frequency

葉洪瑋(Hung-Wei Yea)

指導教授 ： 吳黎明

健行科技大學/電資學院/電機工程所/碩士(2013年)

https://doi.org/10.6824/UCH.2013.00020

摘要

傳統D類諧振轉換電路具有零電壓切換與頻率調變等特徵，重載時享有高效率，相關設計與應用技術已於電源供應器市場商品化。然因切換頻率變動，諧振電路的電磁干擾濾波器不易設計，此外，變頻控制晶片因功能需求較多，例如電壓控制振盪器與週邊電路等，價格較一般脈波寬度調變(PWM)控制晶片昂貴許多，使轉換器成本增加。另一方面，以相位偏移進行控制之相移諧振電路沒有變頻問題，但相移晶片成本更高。
為避免變頻調變的缺點，本論文提出以低成本的PWM調變方法取代變頻調變，進行D類半橋諧振電路的定頻控制。為達此目的，諧振電路首先以最糟情況設計，並以接近諧振頻率的固定切換頻率，在全負載範圍內定頻操作。接著以電壓迴授機制，以非互補方式調整半橋開關的PWM波寬，使之小於一半的周期，此外，由於開關導通時間變短與半橋休止時間變長，本論文檢視並分析電路的零電壓切換特性與開關寄生電容效應，評估電路的諧振行為與負載變化對轉換器可控性的影響，並對電路效率改善提出建議方案及示範。
為驗證所提控制方法的可行性並確定電路性能，本論文設計、模擬並製作一組規格為180W/380Vin/19Vout的原型LLC諧振電路，分別以類比與數位兩種PWM產生方式實現電路控制功能，其中類比控制採用PWM 晶片 TL494，數位控制使用數位訊號處理器TMS320F28035晶片。實驗結果顯示，所提PWM控制方法在諧振電路確具可行與可控性，所測電路波形幾與模擬預測一致，最大效率發生在60%負載的92.7%，轉換器於最糟情況下(320Vin)的全載效率為94.1%。

關鍵字

LLC諧振轉換電路 ； 零電壓切換 ； 脈寬調變 ； 頻率調變

並列摘要

Characterized by zero voltage switching and frequency modulation, the traditional Class-D resonant converter enjoys high performance in efficiency at heavy load. Technologies related to converter design and applications have been commercialized in the power supply industry. However, the electromagnetic interference filter coupled with the resonant converter is hard to design due to dynamic variation of the switching frequency. In addition, the chip used to generate driving signals is relatively expensive, compared to pulse-width modulation, as additional functions like voltage controlled oscillation and peripheral circuits are required in the chip. Another chip used in phase-shifted resonant converter needs no frequency modulation but costs more.
In this thesis a different control strategy is proposed in aim of avoiding disadvantages from frequency modulation. The innovated idea is to use pulse-width modulation (PWM) to control the resonant converter. To reach that end, first the resonant converter is designed under the worst case and operated at a frequency near the optimal operating point in a full load range. Non-complementary PWM waveform is designed and controlled via voltage feedback, resulting in pulse-width to lower than half of the switching period. Furthermore, owing to decrease in switch on-time and increase in dead band, the zero voltage switching and resonant effect caused by switch parasitic capacitances is examined and analyzed. Besides, the impact on controllability in terms of resonance behaviors and load conditions is evaluated. Renovated measure that helps improving converter efficiency under PWM control is suggested and demonstrated.
To verify feasibility and confirm performance, the thesis designs, simulates, and implements a prototype LLC resonant converter with specification rated at 180W/380Vin/19Vo. The PWM control strategy is realized by both analog and digital approaches, respectively, namely the TL494 is the analog IC and digital signal processor TMS320F28035 is the digital IC. The experimental results show that the proposed converter is feasible and controllable. The measured waveforms from prototypes confirm the predictions from simulation. The maximum efficiency occurs at 60% load and is 92.7%. When the converter is operated at the worst case (320Vin)，the full load efficiency is 94.1%.

並列關鍵字

Pulse-width modulation ； Frequency modulation ； Zero voltage switching ； LLC resonant converter

參考文獻

參考文獻

[1]吳財福，吳永駿，沈志隆，陳耀銘，陳建志，李坤彥，陳裕愷，吳毓恩，「電力電子學綜論」，全華圖書股份有限公司，民國97年。

[2]江炫樟，「電力電子學」，全華圖書股份有限公司，民國97年。

[3]林建志，「升壓型諧振電路及其太陽能照明應用研究」，清雲科技大學，碩士論文，民國96年。

[4]陳雅君，「LLC諧振轉換器之設計與研製」，國立成功大學，碩士論文，民國98年。