A Novel Hybrid Converter with Wide Range of Soft-Switching and No Circulating Current for On-Board Chargers of Electric Vehicles

  • Tran, Van-Long (Dept. of Electrical Engineering, Soongsil University) ;
  • Tran, Dai-Duong (Dept. of Electrical Engineering, Soongsil University) ;
  • Doan, Van-Tuan (Dept. of Electrical Engineering, Soongsil University) ;
  • Kim, Ki-Young (Dept. of Electrical Engineering, Soongsil University) ;
  • Choi, Woojin (Dept. of Electrical Engineering, Soongsil University)
  • Received : 2016.12.01
  • Accepted : 2017.08.02
  • Published : 2018.01.01


In this paper, a novel hybrid configuration combining a phase-shift full-bridge (PSFB) and a half-bridge resonant LLC converter is proposed for the On-Board Charger of Electric Vehicles (EVs). In the proposed converter, the PSFB converter shares the lagging-leg switches with half-bridge resonant converter to achieve the wide ZVS range for the switches and to improve the efficiency. The output voltage is modulated by the effective-duty-cycle of the PSFB converter. The proposed converter employs an active reset circuit composed of an active switch and a diode for the transformer which makes it possible to achieve zero circulating current and the soft switching characteristic of the primary switches and rectifier diodes regardless of the load, thereby making the converter highly efficient and eliminating the reverse recovery problem of the diodes. In addition an optimal power sharing strategy is proposed to meet the specification of the charger and to optimize the efficiency of the converter. The operation principle the proposed converter and design considerations for high efficiency are presented. A 6.6 kW prototype converter is fabricated and tested to evaluate its performance at different conditions. The peak efficiency achieved with the proposed converter is 97.7%.

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Fig. 1. Proposed hybrid phase shift full bridge-half bridge LLC converter

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Fig. 2. Key waveforms of the proposed hybrid converter

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Fig. 3. Mode of operation of the proposed converter

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Fig. 4. Relationship between the PSFB transformer turnratio n1 and output voltage of the LLC converter

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Fig. 5. CC/CV charge characteristics of the battery and theZVS design point of the proposed on-board charger

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Fig. 6. Hardware prototype of the proposed hybrid on-board charger

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Fig. 7. Primary currents waveforms of the PSFB and LLCconverters (upper) and the input current waveforms(lower)

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Fig. 8. Voltage and current waveforms of the leading legswitches

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Fig. 9. Current and voltage waveforms of the lagging legswitches

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Fig. 10. Diode voltage and current waveforms at thesecondary side of the HB LLC converter

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Fig. 11. Diode current and voltage waveforms at thesecondary side of the PSFB converter

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Fig. 12. Output inductor current and freewheeling diodecurrent waveforms of the PSFB converter

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Fig. 13. Measured efficiency of the proposed on-boardcharger

Table 1. Specifications of the proposed on-board charger

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Table 2. Comparison of hybrid on-board chargers

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