An investigation of the natural balancing mechanisms of modular input-series-output-series DC-DC converters

Modular converters have many advantages, however the need to balance voltages and currents equally among the different cells requires careful consideration. Natural balancing occurs when all cells receive the same switching information and the inherent circuit operation balances the different voltages and currents. Natural balancing had been proposed for other modular topologies but it was stated that this method is not applicable to the input-series-output-series, ISOS, converter as it does not have any natural balancing abilities. In this study it is shown that the ISOS have a weak natural balancing ability similar in operation to that of the flying-capacitor converter. When the voltage dependent losses are included in the analysis an additional strong balancing mechanism is also identified.