An observer-based control (OBC) strategy for dual-active-bridge converters is proposed in this paper. The target is not only to handle the active power transferring between two terminals, but also to regulate the phase difference between the primary voltage and current around specific minimum value. The value is chosen to reduce the conduction loss in the system. A reduced-order observer is developed to estimate the direct and quadrature components of the transmission current for use in a decoupled current control system. Since the DC terminal current is the only input of the observer, a low sampling frequency is enough to ensure an acceptable precision. Experiment results show that, the proposed OBC strategy can help improve the dynamic performance compared to that when using a single loop voltage mode system. Furthermore, at the high power range, the efficiency obtained when employing OBC method is improved by up-to 7.2%.
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