To address the inability of conventional dual active bridge (DAB) converters to simultaneously achieve zero backflow power and global soft switching under wide input voltage variations, an improved triple-phase-shift (ITPS) modulation strategy for LCL-T resonant DAB converters is proposed. First, the power transfer characteristics and soft-switching behaviors of the LCL-T resonant DAB converter are analyzed, deriving the control variable expressions for achieving zero backflow power under different voltage conversion ratios. Subsequently, by leveraging the symmetry of the LCL resonant network and incorporating ZVS constraints considering switching device parasitic capacitances, unified ITPS modulation control expressions are derived that are continuous over the entire operating range, have a uniform form, and require low computational effort, with the modulation trajectories further optimized. Finally, a 1 kW experimental prototype validates the effectiveness of the proposed modulation strategy. Experimental results demonstrate that the ITPS modulation strategy achieves a wider input voltage range, zero backflow power, and global soft-switching capability, compared to conventional modulation strategies.