The Regulation Characteristics of Bridge Modular Switched-Capacitor Ac-Ac Converter

The switched-capacitor (SC) converter has become a hot candidate to replace power electronics transformer (PET) in commercial and residential applications, especially in micro-grids. However, its poor regulation blocks it wide application. This paper presents an improved phase-shift control strategy for a resonant bridge modular switched-capacitor (RBMSC) ac-ac converter. On the basis of maintaining existing merits of the reported BMSC-based ac-ac converter, its output voltage can be adjusted continuously with a relatively wide margin, breaking through inherent difficulty in step-less regulation. Meanwhile, the bidirectional operation, including step-down and step-up modes, could be realized conveniently by changing the of range phase-shift angle. In addition, the partial switches are turned on under zero voltage switching (ZVS) and all switches realize ZVS turn-off, resulting in reduction of switching loss. Due to one switch in each bidirectional switch always works under synchronous rectification state instead of diode conduction, conduction loss will be reduced compared with other SC ac-ac converters. Most importantly, the safe-commutation issue in the introduced resonant branch is well solved and the voltage spike across switches is alleviated significantly. Finally, the experimental results are provided to demonstrate the validity of the theoretical principle of the converter.