Non-linear modelling and stability analysis of resonant DC–DC converters

Resonant dc-dc converters have found increasing application in industry in recent times. Yet, the methods of dynamical analysis and parameter design for this kind of system are not well developed. The averaging method cannot be used in such converters as the small-ripple assumption does not hold. The sampled-data model, which seeks to obtain a closed form expression of the state at a clock instant in terms of that at the previous clock instant, also becomes unwieldy for converters with many topological modes - a condition prevailing in all resonant converters. In this study the authors show that the Filippov method can be effectively applied for accurate s-domain small signal analysis as well as time domain stability analysis by locating the stability boundaries in the paramater space for such systems. The authors apply this method to three classes of resonant converters - the switch resonant converter, the resonant transition converter and the load resonant converter - and present the mechanisms by which these converters may lose stability as the parameters are varied. The theoretical results corresponding to the resonant transition converter are validated experimentally.