Isolated Symmetric-Bipolar Bidirectional Buck-Boost AC-AC Converters With Reduced Components

This article introduces a new pair of symmetric-bipolar buck-boost ac-ac converters with bidirectional power flow capability. The proposed family includes two topologies with reduced active and passive components, particularly free of diodes-one with continuous input current and another with continuous output current. The converters are designed using a high-frequency tapped-winding transformer, leading to reduced winding requirements, unified magnetic elements, and better transformer utilization. This design also enhances the buck-boost gain, making the topologies suitable for a wide range of applications, especially for deep and shallow voltage sag and swell compensation in dynamic voltage restorers. The converters support bidirectional power flow and output voltage rectification, in addition to inverting and noninverting buck-boost operations, which expand their applications as solid-state transformers and single-phase rectifiers. Both circuits are free of commutation issues and ensure excellent performance with inductive and nonlinear loads. Comparisons with existing counterpart circuits show that the proposed topologies outperform in terms of maximum switch voltage, peak and average switching device powers, inductor and capacitor volume metrics, and efficiency. This article explains the operating principles of both topologies in detail, followed by an evaluation of their performance and key features using a hardware prototype, with the results summarized.