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

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 article uses fundamental harmonic approximation to model the different stages of a series resonant converter. Herein, the small-signal perturbations in control variable, i.e., switching frequency, result in perturbations in inductor current envelope that is analyzed in the Laplace domain. This current envelope 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 analyzing such systems is also presented.

Automated summary

Resonant converters are efficient and have low component count and electromagnetic interference. This article presents a modeling method using fundamental harmonic approximation to analyze the performance and stability of series resonant converters. The developed model is validated and verified using simulation and experimental results.