A reduced-order observer is developed in this paper. The target is for sensorless current control of Dual Active Bridge (DAB) converters. Inherent from some relevance researches, this research also uses the Fundamental Harmonic Approximation analysis to establish the observer model. The observer uses the Terminal 2 voltage as the only feedback signal. No current sensors are required. Experimental results show that the load current can be estimated with high accuracy. The load angle which represent the reactive power can also be estimated with the error less than ±5 degrees. The observer can be used for current mode control or voltage mode plus current feedforward control of DAB converters.