Abstract: In order to further enhance the efficiency of dual active bridge (DAB) DC converter over a wide voltage and full power range, a frequency-domain-based pigeon search algorithm with penalty factors was proposed to optimize the root mean square (RMS) value of the inductor current of the DAB DC converter. The harmonic order of the optimization target was determined using relative harmonic accuracy and relative difference. For the optimization variables in frequency domain, a modulation strategy combining the optimization variables in the frequency domain with the switching points in the time domain was further proposed. Finally, an experimental platform for a 1 kW DAB converter was established to validate the effectiveness of the proposed modulation strategy. The results show that the maximum experimental efficiency under the proposed strategy reaches up to 97.53%, which is 3% higher than that of traditional modulation strategies.