Abstract: To obtain the unified optimal control of dual-active-bridge（DAB） converters for full range operations, a three-phase-shift（TPS） optimal control strategy was studied by making full use of the freedom degrees of DAB control for minimum current stress. The switching modes under mismatch conditions of primary and secondary dc voltages were analyzed. The key electrical parameters and their local optimum solutions of optimal switching modes were deduced, and a unified global optimization strategy was obtained. A hysteresis mode was proposed to achieve a smooth transition among the modes near the voltage matching point. The experimental results show that the achieved TPS strategy has the characteristics of small calculation and unified continuous express compared with the conventional single-phase shift and double-phase shift control. Also, the TPS strategy can effectively reduce the current stress and improve the conversion efficiency which has a good engineering implication.