Envelope-Detection-Based Accurate Small-Signal Modeling of Series Resonant Converters

Abstract

Resonant converters have many desirable characteristics such as high efficiency, low component count and low electromagnetic interference production. The resonance phenomenon that enables this also makes their design and control a challenging process. Attempts have been made to determine the small signal control to output dynamics for resonant converters, however they either involve complex mathematics or numerical solutions which do not provide much insights and make it difficult to design controllers. This paper uses Fundamental Harmonic Approximation to model the different stages of Series Resonant Converter. Herein the small signal perturbations in control variable i.e. the switching frequency, result in perturbations in inductor current envelop that is analysed in the Laplace Domain. This current envelop is then used to analytically derive the control to output transfer function for the Series Resonant Converter. The modeling process is verified and validated by comparing the analytical frequency response with that obtained from Simulink simulation and experimental results. For wide output voltage application designs, the system performance and stability vary with the changing operating point. An example demonstrating the utility of the developed model in analysing such systems is also presented.