Hybrid Closed-Form Modulation Scheme for Three-Phase Dual-Active Bridge with Reduced RMS Current

Hybrid modulation schemes for three-phase dual-active bridges (DAB3) combine multiple modulation modes to improve the converter efficiency in a wide range of output power and voltage. This paper uses analytical expressions for the transformer current within the DAB3 as a metric for conduction losses in the closed-form hybrid modulation schemes asymmetric duty cycle control (ADCC) and minimum current stress operation (MCSO). Based on this analysis, a new boundary from ADCC trapezoidal modulation to single phase-shift modulation is proposed, which is placed at the line of equal current stress in both modes. Reduced losses in ADCC with the proposed boundary compared to the original boundary are found using a circuit simulation. Additionally, this paper shows that MCSO is advantageous regarding soft-switching area and losses in some operating points compared to ADCC, but results in a larger dc current ripple and lacks algorithms for fast operating point transitions.