A Bidirectional Transformerless Voltage Regulator for Single/Three Phase Applications Based on Direct AC-AC Converter

In this paper, a novel AC-AC voltage regulator topology is proposed for single-phase and three-phase applications. The proposed structure provides a common ground between the input and output, eliminating the need for a transformer in series compensators. This results in significant reductions in size, weight, cost, and electrical complexity typically associated with transformers. The topology supports bidirectional power flow, enabling both power injection and absorption. Depending on the selected switching pattern, the converter can operate in buck, boost, or buck-boost modes, either in phase or out of phase with the input voltage, allowing flexible control of the output voltage relative to the input. The proposed structure offers continuous input and output currents, requires a low number of passive and active components, and operates without commutation issues or the need for snubber circuits. A comprehensive analysis of the converter's operation, switching patterns, interval-based behavior, gain and stress characteristics, and its extension to three-phase systems is presented. The simulation and experimental results of a prototype up to 2 kW validate the theoretical analysis.