A High-Frequency Isolated AC–AC Converter With Independently Controlled Bipolar Buck–Boost Dual Outputs

In this article, a new topology of a single-phase high-frequency isolated bipolar buck–boost ac–ac converter is proposed for application as a three-phase flexible ac-link (FACL) converter. The proposed converter comprises one input and two output ac ports, requiring only three discrete converters to implement a three-phase FACL converter with flexible magnitude and phase control. All three ports are electrically isolated through a three-winding high-frequency transformer, replacing the bulky and lossy power-frequency transformer used in existing FACL converters. Both output ac ports are decoupled in terms of voltage polarity and magnitude and can provide symmetric noninverting and inverting buck–boost outputs, improving voltage magnitude and phase control and reducing design complexity. Salient features of the proposed converter include the suppression of input and output harmonics through second-order harmonic filters and bidirectional operation with inductive load support. The topology is implemented with standard full-bridge inverter modules, simplifying the implementation and commutation process. A dedicated switching strategy is developed for various operational scenarios required in FACL applications. The proposed switching strategy allows current sharing among primary-side switches during high-current stress intervals, relieving current stress and conduction losses. Detailed analysis of the proposed topology is provided, including component stresses and ripples, comparisons, and simulation results. Finally, hardware results from a laboratory-scale converter are presented to verify the advantages of the proposed topology.