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Switching Transition Analysis and Optimization for Bi-directional CLLC Resonant DC Transformer (CLLC-DCX)

Topology circuit
Fig. 1. CLLC-DCX topology.
  In this nugget, a comprehensive switching transient analysis for open-loop CLLC-DCX with DAS modulation is presented as shown in Fig. 1. Among seven ZVS transition types, one desir-able “Sync-ZVS” transition is identified with merits of minimum deadtime, load-independent volt-age-gain, and no deadtime conduction loss as shown in Fig. 2. In order to achieve this “Sync-ZVS” transition in the full load range, ACS method was proposed based on currents decomposi-tion. Following this method, an overall design procedure for open-loop CLLC-DCX with DAS modulation was proposed to achieve high efficiency.

  Finally, the proposed “Sync-ZVS” transition and “ACS” method are both verified by three 18 kW CLLC-DCX prototypes with DAS modulation, which all operate around 500 kHz and have 98.8% peak efficiency as shown in Fig. 3. The proposed method has great potential to improve the performance of DCX used in EV charging system and solid- state transformer.
Modulation diagram
Fig. 2. “Sync-ZVS” transition.
Experimental waveform
Fig. 3. Simulation and experimental results of CLLC-DCX with “Sync-ZVS” transition.(a) Voltage waveforms. (b)
Current wave-forms. (c) Zoomed-in voltage waveforms (d) Zoomed-in current waveforms. The CLLC-DCX
operates at 18 kW with fs,opt as 455 kHz.

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