Three-phase LLC resonant converters are attractive for high-power applications due to their reduced output current ripple, improved thermal distribution, and inherent scalability. However, component tolerances in resonant tanks often cause phase current imbalance, leading to asymmetric conduction losses among the converter phases, output ripple, and uneven thermal stress. This paper proposes a simple online balancing algorithm that dynamically adjusts input voltage phase shifts to equalize RMS phase currents in real-time. The presented approach is capable of achieving a low unbalance factor even under severe mismatch conditions. The algorithm was validated on an 11 kW LLC prototype, achieving operation with an unbalance factor less than 2% over the full operating frequency range. Results demonstrate improved electrical symmetry and reduced thermal stress, confirming the practicality of the proposed strategy for high-power three-phase LLC converters.
Frolov et al. (Sat,) studied this question.