Modeling and design considerations of coupled inductor converters

In this part of the sequel on the modeling and analysis of coupled inductors and coupled inductor based multiphase switching converters, the recently developed symmetrical coupled inductor model is first extended to include the inductor winding dc resistance (DCR). The extended model is then used to analyze the influence of the coupling on the DCR based current sensing schemes popularly used in multi-phase switching regulators. It is found that the time-constant matching condition in coupled inductor converters needs to be modified to include the coupling coefficient. The proposed model is also used to derive the small-signal control-to-output transfer function of the converters incorporating coupled inductors, with which the effect of coupling on the dynamic behaviors of the converter power stage, such as resonant frequency and damping factor, can be easily evaluated.