An Investigation of Direct and Indirect Powers of DC-DC Conversion Systems

The theory describing the fundamental limits on DC-DC conversion systems as first proposed by Wolaver is gaining popularity as it is applied in many situations to reduce loss in DC-DC converters. However there are some inconsistencies in the theory's predictions. This study applies Wolaver's theory to both a conventional boost converter and a full bridge in a partial power processing DC-DC conversion architecture. These two converters are shown to have the same predicted direct and indirect powers as they are topologically equivalent. However when simple loss models are incorporated into the analysis, the two converters show different behaviors in the direct and indirect path efficiencies. The partial power processor matches well with the theory but the conventional boost converter does not. The main reason for the breakdown in the theory is the difference between the operational and averaged waveforms of the converters. This leads to the conclusion that while the theory of the fundamental limits is sound, it's application needs careful consideration.