Comparative evaluation of 12-switch single-stage bidirectional isolated ac-dc power converters

This paper investigates and compares two state-of-the-art concepts for single-stage bidirectional ac-dc power converters with high-frequency insulation based on a single high frequency transformer (HFT) and 12-switch structures, with power factor correction (PFC) capability. While the switch count of the systems is identical, there are crucial differences regarding the control and operating principles and supplementary components. The first considered system is a Y-type converter controlled using a simple square wave for the primary side and space vector modulation (SVM) for the secondary bridge. The second converter is based on the conventional B6 bridge topology on each side, controlled using well-known sinusoidal pulse width modulation (SPWM) with harmonic injection. The power flow is regulated by phase shift for both approaches, similar to a dual active bridge (DAB) converter. The comparative evaluation is founded on theoretical analysis and simulations of a case study for the converters interfacing conventional 400 V grid with a 800 V DC load with a rated power of 6.6 kW. The component parameters, stresses, and power loss estimation are considered, as well as the realization effort for the low voltage model and possible medium voltage extension for solid-state transformer (SST) systems.