Simple unified analysis of dual inductor DC-DC converter topologies

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Kurt Beneder, Siemens
Timm Ostermann, Johannes Kepler Universität

Poster-Abstract

Discontinuous voltage nodes and branches with discontinuous currents are the primary contributors for EMC problems in DC-DC converters. To identify these nodes and branches one must analyze a DC-DC converter topology either per simulation or by circuit analysis. Traditionally this is done separately for each topology although unified analysis approaches are also well known. Our research presents a simple unified approach for related topologies. If the analysis is completed for one topology, the results are immediately applicable to a whole family of converters.

A dual inductor DC-DC converter like a Cuk converter function in an averaged modell as an ideal transformer with the transmission ratio as a function of the duty cycle. From this equivalent circuit, one can derive the voltage transfer ratio vs duty cycle for the Cuk, the SEPIC and Zetat converters trough a unified analysis. The wave forms of discontinuous voltage nodes are the same up to a dc offset due to different ground connections.

Also the waveforms in branches with discontinuous currents are also similar up to the sign, due to a different direction of power flow. Consequently, also the associated part stress due to these waveforms is the same. We validate our unified analysis results by comparing them with simulations. Further insight will be got, if one analyses not only switch 1 and switch 2 in opposite state, but also the states where both switches are on (short circuit), or both switches are off (high impedance) state. These conditions reveal further EMC-relevant behaviors which has to be considered.