Dual-edge modulated four-switch Buck-Boost converter

Abstract

Four-switch Buck-Boost (FSBB) converter is a simplified cascaded Buck and Boost, it has two active power switches and two synchronous rectifiers (SRs). Compared to the traditional Buck-Boost converter, FSBB converter has some advantages such as positive output and lower voltage stress across the power devices. The two active power switches can be controlled independently, thus two freedoms, i.e. the duty cycles of the switches, are available to regulate the output voltage, leading to various control strategies. In order to reduce the inductor current ripple, a dual-edge modulation (DEM) is proposed, which lets the two switches be modulated with leading edge and trailing edge respectively. Based on the DEM, 2-mode DEM is derived to reduce the root-mean-square (RMS) inductor current, as a result, the conduction loss in the power switches and the inductor is reduced. In the 2-mode DEM, the input voltage range is divided into two regions with the value of the output voltage as the boundary, FSBB works in Boost mode and Buck mode in the lower voltage region and higher voltage region respectively. In the two modes, only one pair switches, i.e., the active power switch and its corresponding SR, are high-frequency switched, the other one are fully on or off, so the total switching loss is reduced. In order to avoid the wigwag between the two modes, one more region is introduced between the afore-mentioned two regions, which is located around the value of the output voltage, Within the introduced region, FSBB works in Buck-Boost mode with all the four switches operating at high frequency. In order to the switching loss, the switching frequency is reduced in Buck-Boost mode. Thus a 3-mode dual-frequency DEM is proposed. A 48 V (36-75 V) input, 48 V@6.25 A output prototype is fabricated in the lab, and the measured efficiency is higher than 96.5% over the entire input voltage range and the efficiency at the nominal input voltage is 97.8%.