New Phase Current Balancing Control for a Cryogenic Ultra-Low-Loss Bidirectional Multi-Phase Full-Bridge DC-DC Step-Down Converter

This paper proposes a new phase current balancing control method for multi-phase full-bridge step-down dc-dc converters with bipolar output voltage, targeting cryogenic ultra-low- loss power supplies for high-temperature-superconducting (HTS) magnet systems of future particle accelerators. Achieving ultralow losses requires balanced average phase currents but prohibits the use of dedicated phase current sensors or shunts. Therefore, the proposed method reconstructs the phase current imbalance information by indirectly sensing the dc input capacitor current via the dv/dt and processing it in the frequency domain with low computational complexity. Compared to similar existing methods that only target half-bridge dc-dc step-down converters, the proposed method supports full-bridge topologies and high phase counts, as confirmed by detailed circuit simulations with 12 full-bridge phase modules. Finally, the balancing can be improved by phase inductance estimates based on indirectly sensing the output capacitor current, and carrier-to-phase reassignment utilizing the balancing controller information ensures optimum ripple cancellation at the output.