本論文主旨為運用整合式變壓器於串聯諧振轉換器輕載效率改善之研究的探討與研製。對於串聯諧振式轉換器來說，由於功率開關元件達到零電壓切換，且因功率元件技術日益成熟之下，此功率元件所能降低的損失已達瓶頸，其餘電路的主要損失來自於磁性元件等部分。因此為了追求高效率與高功率密度，改善磁性元件即成為重要的課題。
整合式變壓器為多顆鐵心做整合後合成單顆鐵心，在多顆鐵心的架構之下能夠將輸入電壓分別跨至多顆鐵心上，使單顆鐵心上的磁通密度降低，進而減少鐵心損失，鐵心也較容易散熱，但因鐵心數量多且總體積大，因此利用磁通抵消的概念，使鐵心可整合成單顆鐵心，亦因整合式變壓器的有效磁路長度與磁阻的關係，使整合式變壓器在相同繞線柱截面積、相同鐵心體積與相同繞線圈數之下，可降低鐵心感值，進而提升諧振槽電流，使電路操作於輕載時更易於達到零電壓切換的條件，以提升輕載效率。最後實作出一台切換頻率為325 kHz、輸入為800 V轉輸出為800 V、而輸出最大功率為7.2 kW的串聯諧振轉換器。

The purpose of this thesis is to develop the research and implementation on the light-load efficiency improvement of series-resonant converters using integrated transformers. For a series-resonant converter, zero-voltage-switching on power switching devices is a common technique; besides, the power devices are increasingly improved on their operation losses. Therefore, further loss reduction on series-resonant converters has reached a bottleneck. In addition to the device losses, the major loss is resulted from the magnetic components. As a result, in order to pursue high efficiency and high power density on this kind of converters, it is an important issue to improve the magnetic components.
The integrated transformer integrates multiple magnetic cores to form a single one. By using an integrated core structure, the input voltage can be shared by the multiple cores to reduce the magnetic flux density on the individual cores, thereby reducing core loss. Furthermore, by elegantly arranging the core placement, the flux cancellation is achieved to reduce the effective magnetic circuit length of the integrated transformer and also the magnetic reluctance. Not only the core loss is further reduced, the integrated transformer can possess a lower magnetizing inductance without increasing the cross-sectional area of the transformer and turns number. This feature increases the magnetizing current, making it easier for the circuit to achieve zero-voltage switching under light-load conditions. Another advantageous feature to mention is that the distributively placed windings gain more space to dissipate the generated heat and lower the transformer temperature. A series-resonant converter with a switching frequency of 325 kHz, 800 V on both input and output, and maximum load of 7.2 kW is implemented.

[1] X. Li, and A. K. S. Bhat, “Analysis and Design of High-Frequency Isolated Dual-Bridge Series Resonant DC/DC Converter,” IEEE Transactions on Power Electronics, vol. 25, no. 4, pp. 850-862, April 2010.
[2] “Full Bridge LLC ZVS Resonant Converter Based on Gen2 SiC Power MOSFET,” Cree Power Application Engineering, CREE, 2014.
[3] “C2M0040120D,” Data Sheet, CREE, 2014.
[4] 蔡富斌，具同步整流之數位控制半橋串聯諧振轉換器之研製，國立台灣科技大學電子工程系碩士學位論文，2012年。
[5] G. C. Hsieh, C.Y. Tai, and S. H. Hsieh, “Design Considerations for LLC Series Resonant Converter in Two Resonant Region,” in Proc. IEEE PESC, 2007, pp. 731-736.
[6] D. Fu, F. C. Lee, and S. Wang, “Investigation on Transformer Design of High Frequency High Efficiency DC-DC Converters,” in Proc. Appl. Power Electronics, Conf. Expo., pp. 940-947, 2010.
[7] 林孟帆，高頻LLC串聯諧振轉換器之平板變壓器優化設計，國立台灣科技大學電子工程系碩士學位論文，2018年。
[8] M. Mu and F. C. Lee, “Design and Optimization of a 380-12V High-Frequency, High-Current LLC Converter with GaN Devices and Planar Matrix Transformers,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 4, no. 3, pp. 854-862, Sep. 2016.
[9] C. Fei, F. C. Lee, and Q. Li, “High-efficiency High-power-density 380V/12V DC/DC Converter with a Novel Matrix Transformer,” in Proc. IEEE APEC, pp. 2428-2435, 2017.
[10] D. Huang, S. Ji, and F. C. Lee, “LLC Resonant Converter With Matrix Transformer,” IEEE Transactions on Power Electronics, vol. 29, no. 8, pp. 4339-4347, August 2014.
[11] 陳冠瑋，具整合式矩陣變壓器之高頻LLC諧振轉換器，國立台灣科技大學電子工程系碩士學位論文，2017年。
[12] N. Mohan, T. M. Undeland, and W. P. Robbins, Power Electronics: Converters, Applications, and Design, 3rd Edition. New York: John Wiley & Sons, 2003, pp. 249-297.
[13] “LLC Resonant Half Bridge Converter,” H. Huang Applications Engineer, TEXAS INSTRUMENTS, August 2009.
[14] B. Yang, F. C. Lee, A. J. Zhang, and G. Huang, “LLC Resonant Converter for Front End DC/DC Conversion,” in Proc. IEEE APEC, pp. 1108-1112, 2002.
[15] B. Yang, R. Chen, and F. C. Lee, “Integrated Magnetic for LLC Resonant Converter,” in Proc. IEEE APEC, pp. 346-351, 2002.
[16] 吳義利，切換式電源轉換器，第二版，文笙書局，2005年。
[17] R. Redl, N. O. Sokal, and L. Balogh, “A Novel Soft Switching Full Bridge DC/DC Converter: Analysis, Design Considerations, and Experimental Results at 1.5 kW, 100 kHz,” in IEEE PESC Rec., vol. 6, no. 3, pp. 162-172, Jul. 1991.
[18] “1EDI20N12AF,” Data Sheet, Infineon, 2015.
[19] “R12P22005D,” Data Sheet, Recom, 2017.