Analysis and Design for Current Balancing in Interleaved LLC Converters for Two-Stage DCX 48-to-1V Telecom Power Supply

Multi-phase interleaved LLC (MPILLC) converters are predominantly used as a fixed-gain high power density DC transformer (DCX) with high output current in the first stage of an intermediate bus architecture. This is particularly useful in 48-to-PoL (point of load) converters in data centers and telecom power supplies. By suitably designing the power stage, operating at the resonant frequency, and applying phase shift among individual phases, an MPILLC converter can achieve phase current balancing with reduced ripple voltage, which can also retain high efficiency over a wide load current range by utilizing the soft switching capability. However, this paper shows that small changes in tank parameters lead to significant phase current imbalance. Thereafter, an analytical framework is developed by considering the first harmonic approximation (FHA) technique to analyze the effect of parameter mismatches on individual phase currents. The framework is further extended to utilize the duty ratio as the control degree of freedom for balancing phase currents under a wide variation of power-stage parameters. Simulation results of a two-phase LLC converter are presented to demonstrate the accuracy of the analytical predictions as well as the usefulness of the proposed approach. The proposed technique can be extended to an increasing number of phase counts.