Voltage Self-Balance Mechanism Based on Zero-Voltage Switching for Three-Level DC-DC Converter

Voltage balance of series capacitors is crucial for multilevel converters. In this article, a new voltage self-balance mechanism based on zero-voltage switching (ZVS) for a three-level dc-dc converter is proposed. First, the near-CRM (critical conduction mode) to realize ZVS and its resonance transition are analyzed in detail. Then, the resonance times at peak and valley currents are analytically expressed, and it is discovered that the additional duty cycles are induced by the ZVS resonant transitions between the switch parasitic capacitors and resonance inductor. Meanwhile, the unbalanced capacitor voltages alter the initial resonance conditions, so that the resulting additional duty cycles tend to counteract the unbalanced voltages. To further quantify the proposed voltage self-balance mechanism, not only the relationships between the effective duty cycle and the unbalanced voltages are formulated, but also the overall feedback mechanism of the passive voltage self-balance is modeled and illustrated. Finally, a three-level dc-dc converter prototype is constructed to experimentally verify the ZVS and voltage self-balance mechanism in the near-CRM mode.