Tristate Converters with Limited Duty Cycle

Abstract

Replacing the active switch of a DC/DC converter with a series connection of two active switches and a diode which is connected to the connection point of the two switches, changes the converter into a tristate one. The tristate concept changes the voltage transformation ratio of the original converter and influences the dynamics. Starting from a topology for limited duty cycles, four converters can be derived. There are two possibilities for the position of the second capacitor and so eight converter structures can be achieved. The position of the second capacitor influences the input current, the inrush, the stored energy, and the voltage stress of this component. When the input voltage has the other polarity, again eight converters can be designed. Changing all active electronic switches by current bidirectional ones (an electronic switch with an antiparallel diode) leads to bidirectional converters and increases the number of converters that are derived from the basic topology to thirty-two. The function of the four basic structures is explained, and the voltage transformation ratio calculated and graphically shown. The connections of the currents are explained. For one converter the large and the small signal models and two transfer functions are calculated, and simulation of the dynamics are shown.