This paper presents a comprehensive examination of the challenges associated with achieving high-bandwidth control in dc-dc converters used in unfolding-based ac-dc systems. High bandwidth control is essential for maintaining grid-side power factor correction and improving output power regulation, but can be challenging to implement without affecting the converter stability. This paper identifies the main issue as an undesirable resonance between the grid inductance and dc-link capacitors and investigates the resonance phenomenon using the extra element theorem. A control-based technique is proposed to address the issue by emulating current sources/sinks that provide active damping of the resonance and facilitate high-bandwidth control. The results, obtained through simulation-based analysis and hardware validation of a 21 kW prototype, demonstrate a tenfold increase in achievable bandwidth with the proposed control technique compared to operating the system without damping.
