Instantaneous Current Control of a Three-Phase Dual-Active Bridge Converter for Smooth Mode Transition under a Hybrid Modulation Scheme

The three-phase dual-active bridge (DAB3) converter is widely utilized in high-power conversion systems due to its bidirectional power flow capability, inherent soft-switching characteristics, and reduced filter size. Traditional single-phase-shift (SPS) control realize soft-switching under heavy loads, while the asymmetrical duty cycle control (ADCC) can achieve soft-switching under light loads. By combining these two modulation methods, the soft-switching range can be extended, leading to higher overall efficiency. However, direct mode transition between these two methods can result in transformer current imbalance, also shown as current bias and overshoot. To enhance dynamic performance during the mode transition between SPS and ADCC, a hybrid-mode instantaneous current control method is proposed based on the space vector analysis. Optimal transient current trajectory is identified to eliminate DC-bias and overshoot, while maintaining the soft-switching operation in the transient state. The proposed approach is described by a unified mathematical model to facilitate the control implementation. The proposed control methods are validated through mathematical analysis and simulations.