A Novel Capacitor Voltage Self-Balancing Modulation Method for Three-Level DAB Converters

The capacitor voltage balancing is crucial for the reliable operation of three-level dual-active-bridge (DAB) converters. In contrast to previous balancing control methods, this letter proposes a capacitor voltage self-balancing modulation method by introducing an improved switching sequence (ISS) for the neutral-point-clamped (NPC) full bridge. In proposed ISS, only one capacitor participates in the energy transfer when the output voltage polarity of the NPC full bridge remains unchanged. Capacitor voltage imbalance will induce a DC bias in the transformer current, thereby facilitating capacitor voltage balancing. Finally, experimental results are provided to validate the effectiveness of the proposed balancing method.