This paper proposes a nonlinear control system based on a nonlinear observer to manage the active and reactive power within a single-phase-frequency-modulated Dual-Active-Bridge DC/DC converter directly. It is accomplished by employing a nonlinear controller to regulate the direct and quadrature current, id(t) and iq (t), as they are directly proportional to two power components, respectively. A nonlinear observer is designed to detach two current components from the average absolute value irec,avg of the transferred current. Since irec,avg is a DC quantity, very high sampling frequency is not required allowing to use the popular DSP, such as TMS320F28335, for processing. Experiment results show that the performance of the observer is fine when the converter operates under soft-switching condition which is achieved by assigning a positive value for the quadrature current iq (t). Under such condition, the amplitude error is in the range of ±1% while the absolute load angle error is less than 2 degrees in the scale of 360 degrees for one switching cycle. In term of control stability, id (t) and iq (t) are well regulated by the nonlinear controller at any desired values.