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 48V (36-75V) input,
48V@6.25A 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%.