Variable-Inverter-Rectifier-Transformer: A Hybrid Electronic and Magnetic Structure Enabling Adjustable High Step-Down Conversion Ratios

This paper proposes a hybrid electronic and magnetic structure named a variable-inverter-rectifier-transformer (VIRT) that enables a transformer with fractional and reconfigurable effective turns ratios (e.g., 12: 0.5, 12: 2/3, 12: 1, and 12: 2). This functionality is valuable in converters with wide operating voltage ranges and high step-up/down, as it offers a means to reduce the turns count and copper loss within the transformer while also facilitating voltage doubling and quadrupling. These properties are especially beneficial for miniaturizing the transformer stage in many power electronics applications, such as universal serial bus wall chargers. We introduce the principle of operation of the structure and present models for its magnetic and electrical behavior. The instance of VIRT described in this paper comprises four half-bridge switching cells distributed around a planar magnetic core and connected to two "half-turns" wound through that core. By controlling the operating modes of the half-bridge cells, we gain control over the flux paths and current paths used in the transformer, and this hybridization enables fractional and reconfigurable effective turns ratios. An experimental prototype integrates the VIRT with a stacked-bridge LLC converter to accommodate a widely varying input (120-380 V-dc) and output (5-20 V-dc), and VIRT is shown to be highly beneficial in keeping efficiency high over this wide output voltage range.