Mode Transition for Increased Voltage Gain Range of a 4-Switch DC-DC Converter with Tri-State and Single Duty Cycle Control

The 4-switch bi-directional DC-DC converter operating with a tri-state logic can be used as a fast-acting power interface for energy storage devices in DC grids. By making the duration of one of the three states fixed, single duty cycle control for the injected current is possible. However, the range of voltage gains (V
o
/V
in
) in Boost and Buck-Boost modes is reduced, what precludes its use for interfacing supercapacitors (SCs), operating with half to rated voltages, to DC grids. This paper presents this issue and proposes a solution based on the dynamic transition between modes of operation as the input voltage varies. Simulation results for a supercapacitor connected to a DC grid through the 4-switch converter operating with the basic and the improved tri-state control logic are presented to demonstrate the benefits of the proposed technique.