A High Efficiency LLC Resonant Converter-based Li-ion Battery Charger with Adaptive Turn Ratio Variable Scheme

  • Received : 2017.02.16
  • Accepted : 2017.06.16
  • Published : 2018.01.01


This paper proposes an LLC resonant converter based battery charger which utilizes an adaptive turn ratio scheme to achieve a wide output voltage range and high efficiency. The high frequency transformer of the LLC converter of the proposed strategy has an adaptively changed turn ratio through the auxiliary control circuit. As a result, an optimized converter design with high magnetizing inductance is possible, while minimizing conduction and turn-off losses and providing a regulated voltage gain to properly charge the lithium ion battery. For a step-by-step explanation, operational principle and optimal design considerations of the proposed converter are illustrated in detail. Finally, the effectiveness of the proposed strategy is verified through various experimental results and efficiency analysis based on prototype 300W Li-ion battery charger and battery pack.

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Fig. 1. CC-CV charging profile

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Fig. 2. Proposed LLC resonant converter

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Fig. 3. Voltage gain curve of the conventional LLC resonantconverter

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Fig. 4. Voltage gain curve of the proposed LLC resonantconverter

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Fig. 5. Configuration of the proposed converter accordingto operational mode

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Fig. 6. The overshoot elimination algorithm: (a) theswitching frequency trajectory; (b) A flow chart

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Fig. 7. Optimal magnetizing inductance (Lm) selection.

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Fig. 8. Optimal number of turns of auxiliary windingselection

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Fig. 9. An integrated transformer of the resonant tank: (a)winding structures and (b) a manufactured prototype

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Fig. 10. Experimental setup of the prototype

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Fig. 11. Experimental result of the conventional LLCresonant converter: (a) at 10% load and (b) 80%load

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Fig. 12. Experimental result of the proposed LLC resonantconverter: (a) at 10% load and (b) 80% load

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Fig. 13. Efficiency comparison result between the conven-tional LLC resonant converter and the proposedone: (a) CC mode and (b) CV mode

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Fig. 14. Experiment waveforms during the CC-CV chargingprocess

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Fig. 15. Experiment waveforms under mode conversion:(a) without the overshoot-less algorithm and (b)with the overshoot-less algorithm

Table 1. Design parameters

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Supported by : Korea Institute of Energy Technology Evaluation and Planning (KETEP)


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