A Combined Power Factor Correcting and Active Voltage Balancing Control Technique for Buck-Type AC/DC Grid-Tied Flying Capacitor Multilevel Converters

Single-stage Power Factor Correction (PFC) ac-dc rectifiers open a pathway to achieve high power density and efficiency in grid-connected rectifier applications where the target dc voltage is lower than the peak ac voltage (e.g. data center power delivery, LED drivers). Typically in data center and similar applications, a two-stage solution employing a step-up ac-dc stage followed by a step-down dc-dc stage is employed to achieve grid to 48 V conversion. This approach suffers from the efficiency penalty of a cascade of power converters and typically lower power density due to the design of two separate power conversion stages. A single-stage, buck-type PFC rectifier where the output dc voltage is lower than the peak ac voltage circumvents these issues. This work analyzes and develops a single-stage buck-type PFC rectifier utilizing a six-level flying capacitor multilevel (FCML) converter with active flying capacitor voltage balancing and current control to achieve high power density rectification in a single-stage solution. This work is the first to achieve active balancing of capacitors combined with PFC operation in a step-down FCML rectifier.