A Dual-Active-Bridge with stacked-secondary phases (DAB-SSP) enables high voltage gain, bidirectional operation, and wide ZVS range for AI rack converters. Conventional single-phase-shift (SPS) suffers from circulating current and conduction loss under wide ratios. This work develops a closed-form time-domain model for dual-phase-shift (DPS) control of the DAB-SSP, deriving analytical expressions for inductor current, RMS stress, and power transfer. Optimal operating points are identified using a constrained optimization framework, showing reduced current stress compared to SPS. A GaN-based prototype validates the model, achieving 98.6% efficiency, wide-range ZVS, and robust step-load response. Results confirm DPS as an optimal modulation strategy that improves efficiency and power density for next-generation HVDC data-center converters.
