Implementation and Study of Constant-Frequency LLC Resonant Converter
This chapter presents an LLC resonant converter with constant frequency. Since LLC resonant converters possess the advantages of high efficiency and low electromagnetic interference, they are widely used in many applications. However, the EMI filter desig
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Abstract This chapter presents an LLC resonant converter with constant frequency. Since LLC resonant converters possess the advantages of high efficiency and low electromagnetic interference, they are widely used in many applications. However, the EMI filter design becomes more complex because of the variable-frequency operation of LLC resonant converter. Therefore, in this chapter, a circuit configuration of a buck converter cascade an LLC resonant converter, buck-fed LLC resonant converter, is proposed to complete constant-frequency operation and simplify the EMI filter design. The buck converter is applied in the proposed converter as the input source for the LLC resonant converter. In addition, by adjusting the output voltage of the buck converter, the output regulation and constant-frequency operation of the proposed converter can be achieved. Finally, a prototype of the buck-fed LLC resonant converter with input voltage 380–400 V and output 24 V/10 A is implemented. The experimental results demonstrate the feasibility of the proposed converter. Keywords Constant frequency • EMI filter • LLC resonant converter • Cascade • Buck-fed LLC resonant converter
S.-Y. Lin • Y.-N. Chung (*) Department of Electrical Engineering, National Changhua University of Education, Changhua 50007, Taiwan e-mail: [email protected] S.-K. Changchien Department of Automation Engineering and Institute of Mechatronoptic Systems, Chienkuo Technology University, Changhua 50007, Taiwan C.-M. Hong Department of Electrical Engineering, Chienkuo Technology University, Changhua 50007, Taiwan J. Juang and Y.-C. Huang (eds.), Intelligent Technologies and Engineering Systems, Lecture Notes in Electrical Engineering 234, DOI 10.1007/978-1-4614-6747-2_75, # Springer Science+Business Media New York 2013
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1 Introduction DC-DC converters are commonly applied in many applications with constantfrequency operation. However, the greater switching loss and series electromagnetic interference (EMI) are the main drawbacks. Because of high efficiency, soft-switching, and sinusoidal voltage and current of the power paths, LLC resonant converters are widely used in many power conversion applications, such as PC power, LCD TV power, and LED backlight [1–4]. Generally, LLC resonant converters are operated with variable switching frequency to meet the output requirements [5]. However, base on variable-frequency operation, the EMI filters are relatively difficult designed for suppressing the harmonic and the electromagnetic interference noise of LLC resonant converters. As operation frequency range with load change and the operation frequency is lower in full load that LLC resonant converters make bigger in volume. Moreover, the higher switching frequency is necessary to LLC resonant converters for output requirements under no load or light load that the output voltage cannot be effectively regulated. Several researchers proposed to discuss DC-DC resonant converters with constant frequency [6–8]. Agrawal proposed LLC series resonan
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