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Resonant CLLC converter

Bidirectional resonant CLLC as an alternative to the DAB: tank transfer function, simulation in both power directions, losses, transformer sizing and an optimiser for a CLLLC tank.

250 kWresonant800 V / 800 VSimscapeMATLAB
Resonant CLLC converter
Single-phase bidirectional CLLC: full bridges on both sides, resonant capacitors and inductances around the medium-frequency transformer.

What it is

The CLLC is a resonant, symmetric version of the isolated DC/DC stage: the series inductances and resonant capacitors on both sides of the transformer shape the current into a near-sinusoidal waveform, so the switches turn on at zero voltage and the turn-off current is small. Power flow and voltage gain are set by the switching frequency around resonance rather than by a phase shift.

Two studies are included: a Simscape bench of a 250 kW CLLC stage, and an analytic state-space model of a CLLLC tank (800 V / 800 V, 250 kW) with an optimiser for the resonant elements and the transformer.

What the bench does

  • Transfer function of the resonant tank and choice of the operating frequency range.
  • Simulation in both power directions with the same control code, device losses and spectrum.
  • First-cut sizing of the high-frequency transformer from the simulated volt-seconds and currents.

Figures

Simulation results in the forward direction: output current and voltage, device losses and the resonant-tank quantities.