Small signal equivalent circuit modeling of resonant power converters

The small signal dynamic characteristics of switching converters with high frequency resonant elements are investigated using an equivalent circuit modeling approach. A systematic procedure is developed for analysis of resonant converters in the continuous conduction mode and applied to the series resonant converter, which is modeled by a lumped y parameter equivalent circuit. Each y parameter models the response of the switched tank elements to a disturbance at the input, output, or control terminals. Although the y parameters are discrete quantities, a low frequency continuous time approximation is possible, in which case each y parameter contains two zeros and two poles. The converter also has a low frequency pole owing to the output capacitor, the load, and the y parameter low frequency characteristics. Experimental verification of both discrete and continuous models is presented.;A proof by linear network theory is given which demonstrates that state space averaging can be applied to a wider class of converters than previously thought, including linear and nonlinear resonant switch (NRS) converters. State space averaging is used to develop equivalent circuit models of the NRS buck, boost and buck boost converters in both full and half wave operating modes. The resonant switching action introduces feedback of the filter states into the pulse width modulated circuit model. The canonical circuit model concept is extended to NRS converters, and parameters of an NRS canonical circuit model are derived. Experimental verification is presented of the NRS boost and buck converter models. Modeling and measurement techniques for magnetic components in the NRS buck prototype are discussed. Good agreement is obtained between experimental and theoretical results.