Boundary Control Based Capacitor Voltage Balancing for Two/Three-Level Neutral-Point-Clamped Dual-Active-Bridge Converters

In a three-level DC-DC converter, capacitor voltage imbalance increases voltageor current stress and affects converter stability. In this paper, a capacitor balancing method based on fast transient boundary control for two/three-level neutral-point-clamped dual-active-bridge converters is proposed. In this method, elliptic and circular boundaries will be used to regulate the dynamic trajectory of the converter in the geometrical domain. Switching the elliptic trajectory can change the capacitor charging and discharging without affecting the output waveform compared to the conventional method. In addition, boundary control can improve the dynamic performance of the converter. The effectiveness of the proposed control is verified by simulation.