A novel envelope response technique for large signal dynamic analysis of resonant converters

In this paper, a novel technique using orthogonal functions to analyze the large signal transitions in resonant converters is proposed. For a given resonant converter, another circuit is constructed with its response orthogonal with that of the original circuit. By combining two circuits into one complex circuit, Laplace transformation and its properties can be applied to derive the envelope response. When there are initial conditions in the resonant converters, orthogonal counterparts of these initial conditions are also investigated and derived. With the above method, large signal dynamic response of resonant converters excited by any external sources and initial conditions can be derived. As examples, series resonant DC/AC converters are investigated by the proposed method under some typical large signal transitions such as startup process with or without initial conditions, transitions when switching frequency, or DC supply voltage source, or load has a step change. General solutions of the envelope response of resonant inductor current are given in detail. The dynamic response as well as the steady state values are therefore obtained. The results are verified by PSPICE simulation. The proposed technique will also be applied to other resonant converters such as parallel resonant DC/AC converters, series resonant DC/DC converters and parallel resonant DC/DC converters.