Unified Control Strategy for Capacitor Voltage Balance and Transient DC Bias Suppression for Bilateral Three‐Level DAB Converter

This paper proposes a unified control strategy for bilateral three‐level neutral point clamped dual‐active‐bridge (3L‐NPC‐DAB) converters, addressing capacitor voltage imbalance and transient DC bias current. By analyzing the operational constraints of the 3L‐NPC bridge, the strategy decouples current polarity from midpoint voltage to prevent output waveform distortion. To maintain capacitor voltage balance, a complementary switching state method is employed, which regulates neutral point current by swapping the on‐times of specific switches without affecting the voltage waveform or causing power fluctuations. Simultaneously, to address the transient DC bias generated when phase‐shift values update, a suppression strategy based on carrier symmetry update is proposed. By adjusting the equivalent symmetrical midline of the five‐level output voltage and ensuring phase‐shift updates occur at the current zero‐crossing points, the transformer's volt‐second integrals are balanced instantaneously during dynamic transitions. This approach effectively reduces current overshoot and eliminates transient DC bias while avoiding interference with the voltage balancing control. The effectiveness of the proposed strategy is verified through simulation and experimental results, demonstrating rapid dynamic response and stable steady‐state performance.