Rational Symmetry-Guided Design of Resonant DC–DC Converters: Topology Screening, Feasible-Region Synthesis, and Tolerance-Aware LLC Assessment

Resonant DC–DC converter design requires family selection, feasible operating regions and component targets to be evaluated consistently. ResoSym-RD links topology-aware normalized screening to physical-unit synthesis based on the fundamental-harmonic approximation (FHA), rounded component targets and independently tested timing schedules. Series resonant (SRC), parallel-loaded resonant (PLRC), inductor–capacitor–capacitor (LCC) and inductor–inductor–capacitor (LLC) families retain their native reduced models. Nested search domains expose boundary-dependent coverage and trade-offs rather than a universal topology ranking. For a 360–420 V/48 V, 1 kW LLC case, the retained 20 µH/88 nF/106 µH targets have a minimum nominal normalized margin of 1.441. A prespecified rounded FHA comparator has a lower nominal margin and a higher ranking proxy, but a higher fixed-timing sampled pass fraction. With matched timing perturbations, an independent 20,000-realization test gives 99.925% charge-only feasibility for the locked schedule versus 98.860% for fixed 250 ns timing. A new common parasitic switched-circuit assessment compares both tanks over all nine corners. At equal 48 V output, the ResoSym-RD tank has 1.42% lower uniformly averaged modeled dissipation, but not at every corner. The uncorrected FHA schedule produces output errors up to 5.61%, and the ResoSym-RD peak-current error reaches 21.06%, establishing the need for time-domain closure. Executed commutation traces, step refinement and a separate numerical integrator support the declared generic circuit results. The study is an auditable pre-synthesis methodology, not a claim of measured efficiency, field reliability, electromagnetic interference (EMI) compliance or hardware qualification.