Single-Stage Isolated AC-DC Converter Based on LCL Resonant DAB Converters With Single-Loop Control

This article presents a single-stage ac-dc converter composed of a synchronous rectifier and a dual active bridge (DAB) converter with an LCL resonant tank. The optimum dual-phase-shift (DPS) control for the LCL-DAB converter is analyzed to make a tradeoff between the zero voltage switching (ZVS) and conduction loss. Based on the DPS control, the analytical expression of the input current of the single-stage ac-dc converter is revealed. It indicates that the input current is only associated with the phase-shift angle and the output voltage rather than the input voltage. Therefore, the control strategy of the LCL-DAB single-stage ac-dc converter is proposed to achieve the output voltage and input current regulation with the single-loop control. Without the inner current loop, the converter can still achieve unit power factor and high-quality input current regulation, which eases the implementation and controller design in the digital control. By designing the turns ratio of the transformer and resonant inductor based on the 3-D loss surface, the efficiency is further improved. A 1-kW prototype demonstrates the effectiveness and good performance of the control strategy and the design consideration.