Analysis of a series resonant converter

Abstract

The authors develop a method for creating a linearized dynamic model for a series resonant converter operating with a small-amplitude modulating signal and a modulation factor much lower than one. The model was worked out by studying the evolution of the average values of the state variables. With suitable operating conditions, this method has led to the control-to-output transfer function of the converter under study. Comparison of the theoretical results with experimental data from a low-power prototype confirms that the proposed model is well-suited to describing the physical system under the operating conditions which are of practical interest. Additionally, the experimental results have shown that the linearized model is also valid for modulation factor values close to one. A problem of theoretical rather than application interest in this continuing investigation of resonant converters regards the shift of the dominant pole when fs/fo tends towards one. This shift, which has been detected experimentally, is caused by a reduction in equivalent impedance at the rectifier output.<>