Modeling and Analysis of Coupled Inductors in Power Converters

This paper describes a new approach to the analysis of switched mode power converters utilizing coupled inductors and presents a novel canonical circuit model for N-winding coupled inductors. Waveform and ripple of the winding current in a coupled inductor converter can be easily determined using the developed model similar to those obtained in an uncoupled inductor converter. Influence of coupling coefficient on converter steady state and transient performances is readily predicted by the proposed model and a comparison of coupled and uncoupled inductor converters is provided. It is found that coupling among windings effectively alters the phase node voltage waveforms driving the coupled inductors. Through coupling, a converter is capable of responding faster to load transient depending on the coupling coefficient and control mechanism, and this dependency is analytically revealed in the paper. Some design constraints regarding coupling coefficient are also discussed for two-winding and multi-winding coupled inductors in power converter applications. Finally, a two-phase buck regulator is experimentally tested to verify the proposed model.