本論文主旨在研製半橋串聯諧振轉換器操作於短路條件時的保護及定電流策略，其控制法結合變頻模式及脈波寬度調變模式控制，來達到有效的抑制輸出電流。為了找出電路操作於短路條件下，調整操作頻率對於諧振電壓及諧振電流的影響，本文透過數學分析找出操作頻率與輸出電流的關係，以提升操作頻率的手段來抑制輸出電流。但此方法的缺點是，操作頻率將會遠大於諧振頻率數倍。因此，顧慮到電路最大操作頻率，透過數學模型分析，找出在固定頻率下，縮小有效責任週期來達到限制諧振槽能量之效果。並且為了使開關皆具有零電壓切換之特性，當電路操作於短路條件下，將調整責任週期，使一次側上下橋臂開關操作於非對稱半橋模式。本論文實際完成一台240 W的串聯諧振電路，當電路操作於短路條件下，其輸出電流能被限制於22 A的條件下。

This thesis proposes a strategy of overcurrent protection and constant current for half-bridge series-resonant converter. The control algorithm combines pulse-width modulation (PWM) and pulse-frequency modulation (PFM) to effectively constrain the output current. The relationship between resonant voltage, resonant current and switching frequency are exploited base on the state plane analysis. It shows that increased switching frequency can limit the output current, however, at the cost of extremely high switching frequency which might be quite higher behind the resonant frequency. Under the limitation of a preset maximum switching frequency, decreased duty cycle is applied to limit the stored energy in the resonant tank. In order to achieve zero-voltage-switching (ZVS), the primary-side switches are gated with asymmetrical pulse widths. A 240 W series resonant converter was built. When the circuit operated in short-circuit condition, the output current is limited under 22 A.

[1] B. Yang, F. C. Lee, A. J. Zhang, and G. Huang, “LLC Resonant Converter for Front End DC/DC Conversion,” in Proc. IEEE Applied Power Electronics Conference and Exposition, 2002, pp. 1108-1112.
[2] B. Lu, W. Liu, Y. Liang, F. C. Lee and J. D. van Wyk, “Optimal Design Methodology for LLC Resonant Converter,” in Proc. IEEE Applied Power Electronics Conference and Exposition, 2006, pp. 1-6.
[3] R. Beiranvand, B. Rashidian, M. R. Zolghadri, and S. M. H. Alavi, “Optimizing the Normalized Dead-time and Maximum Switching Frequency of A Wide-adjustable-range LLC Resonant Converter,” IEEE Trans. Power Electron., vol. 26, no. 2, pp. 462–472, Feb. 2011.
[4] R. Beiranvand, B. Rashidian, M. R. Zolghadri, and S. M. H. Alavi, “A Design Procedure for Optimizing the LLC Resonant Converter as A Wide Output Range Voltage Source,” IEEE Trans. Power Electron., vol. 27, no. 8, pp. 3749–3763, Aug. 2012.
[5] R.Yu, G. K. Y. Ho,B. M. H. Pong, B. W.-K. Ling, and J. Lam, “Computer-Aided Design and Optimization of High-Efficiency LLC Series Resonant Converter,” IEEE Trans. Power Electron., vol. 27, no. 7, pp. 3243–3256, Jul. 2012.
[6] H. Hu, X. Fang, F. Chen, Z. J. Shen, and I. Batarseh, “A Modified High Efficiency LLC Converter with Two Transformers for Wide Input Voltage Range Applications,” IEEE Trans. Power Electron., vol. 28, no. 4, pp. 1946–1960, Apr. 2013.
[7] F. Musavi, M. Cracium, D.S. Gautam, and W. Eberle, “Control Strategies for Wide Output Voltage Range LLC Resonant DC–DC Converters in Battery Chargers,” IEEE Trans. Veh. Technol., vol. 63, no. 3, pp. 1117–1125, Mar. 2014.
[8] Z. Hu, Y. Qiu, Y. F. Liu, and P.C. Sen, “A Control Strategy and Design Method for Interleaved LLC Converters Operating at Variable Switching Frequency,” IEEE Trans. Power Electron., vol. 29, no. 8, pp. 4278–4287, Aug. 2014.
[9] B. Yang, F. C. Lee, “Over Current Protection Methods for LLC Resonant Converter,” in Proc. APEC, 2003, pp. 605–609.
[10] C. Zhao, X. Xie, X. Wu, J. Zhang, and Z. Qian, “The Design Consideration Comparisons of Two Clamping Modes Over Current Protection for LLC Converter,” in Proc. IEEE Telecommunications Energy Conf., 2006, pp. 1–5.
[11] X. Xie, J. Zhang, C. Zhao, Z. Zhao, and Z. Qian, “Analysis and Optimization of LLC Resonant Converter with A Novel Over-Current Protection Circuit,” IEEE Trans. Power Electron., vol. 22, no. 2, pp. 435–443, Mar. 2007.
[12] F. Duan, M. Xu, X. Yang and Y. Yao, "Canonical Model and Design Methodology for LLC DC/DC Converter With Constant Current Operation Capability Under Shorted Load," IEEE Trans. Power Electron, vol. 31, no. 10, pp. 6870-6883, Oct. 2016.
[13] H. Figge, T. Grote, N. Fröhleke, J. Böcker , F. Schafmeister ,“Over current Protection for the LLC Resonant Converter with Improved Hold-Up Time,” in Proc. APEC, 2011, pp. 13–20
[14] C. Tsang, M. Foster, D. Stone, and D. Gladwin, “Analysis and Design of LLC Resonant Converters with Capacitor-Diode Clamp Current-Limiting,” IEEE Trans. Power Electron., vol. 30, no. 3, pp. 1345–1355, Mar. 2015.
[15] P. K. Jain, A. St-Martin, and G. Edwards, “Asymmetrical Pulse-width-modulated Resonant DC/DC Converter Topologies,” IEEE Trans. Power Electron., vol. 11, no. 3, pp. 413–422, May 1996.
[16] G. Moschopoulos, and P. Jain, “A Series-Resonant DC/DC Converter with Asymmetrical PWM and Synchronous Rectification,” in Proc. IEEE Power Elec. Specialists Conf. (PESC), 2002, pp. 1522-1527.
[17] S. Mangat, M. Qiu, and P. Jain, “A modified Asymmetrical Pulse-width-modulated Resonant DC/DC Converter Topology,” IEEE Trans. Power Electron., vol. 19, no. 1, pp. 104–111, Jan. 2004.
[18] 黃卓文，「半橋串聯諧振轉換器輕載非對稱單側責任週期調變策略研究」，國立台灣科技大學電子工程系碩士論文，2008年。