Modeling and Analysis of Coupled Inductors in Power Converters

Abstract

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 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -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 performance is readily predicted by the proposed model. It is found that in an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -phase coupled inductor converter, the voltage waveforms driving the leakage inductors are no longer the phase node voltages but are the modified voltages with a frequency <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> times the original switching frequency. In addition, their magnitudes also vary with the coupling coefficient among the coupled windings. Through coupling, a converter is capable of responding faster to load transient depending on the coupling coefficient and control mechanism, and that dependency is analytically revealed in the paper. Finally, a two-phase buck regulator is experimentally tested to verify the proposed model.