An Extra-Element Small-Signal Model for a Current-Fed Resonant Dual-Active-Bridge Converter

This paper proposes a novel small-signal modeling method for the Current-Fed Resonant Dual-Active-Bridge (CF-RDAB) converter, which enables to strongly simplify the design of the regulators in the system. Such an approach divides the Small-Signal Model (SSM) of the CF-RDAB into the SSM of an Interleaved Boost (IB) converter and the SSM of a Resonant Dual-Active-Bridge (RDAB) converter, enabling to control them separately. Additionally, this article exposes a specific operating point in which the SSM of the CF-RDAB reduces to the SSM of the cascaded connection of the IB converter and the RDAB converter, as they were fully independent. In this operating condition, the stability of the whole CF-RDAB converter can be studied on the IB+RDAB cascaded connection with the Impedance-Based Stability Criterion (IBSC) and the Extra-Element Theorem (EET). Afterwards, this paper presents a control strategy that utilizes both the input duty-cycle and the phase-shift of the CF-RDAB to guarantee the stability of the system. The converter's model and control are experimentally verified on a 500W CF-RDAB prototype, displaying an excellent agreement between the theory and the measurements.