This digest presents a closed-form time-domain model and Pontryagin's Minimum Principle (PMP)–based optimal control for a dual-active-bridge converter with stacked-secondary phasing (DAB-SSP), targeting isolated 48 V to 800 V DC-DC links in AI data centers and electric vehicle systems. DAB-SSP halves high-voltage device stress, enabling the use of enhancement-mode GaN devices on both bridges for reduced switching loss, extending ZVS range from 5% to 100% of full load, and higher power density. The proposed piecewise formulation captures the complete inductor-current trajectory, enabling explicit calculation of output power, RMS current, and ZVS boundaries. From this model, a PMP-based control law is derived that minimizes transformer RMS current using only algebraic computation, allowing direct and noniterative DSP-based real-time implementation. A scaled 20 V–400 V, 400 W GaN device-based prototype demonstrates 98.6 % peak efficiency and reduced RMS current versus single-phase-shift control, validating the method's potential for compact, high-efficiency, bidirectional conversion.
