Discrete modeling of resonant converters — Steady state and small signal description

Discrete modeling seems to be a fast and accurate method for describing resonant switch mode power converters. This paper applies discrete modeling onto resonant converters and shows it exemplarily for the series resonant converter. It shows how to calculate a nonlinear large signal model from which the steady state can be derived, as well as small signal transfer functions as it is the control-to-output transfer function, the audio susceptibility, and the output impedance. Furthermore, different possibilities of how to obtain these three transfer functions are shown and discussed. An excellent agreement between the different calculation methods shows the accuracy of this modeling technique. A great emphasis of this paper is placed on the determination of small signal transfer functions of resonant converters since this has still been an open issue so far.