Small Signal Audiosusceptibility Model for Series Resonant Converter

TL;DR

This paper develops a novel small signal model for Series Resonant Converters to predict output voltage ripple caused by input ripple, analyzing audiosusceptibility resonance and providing design guidelines validated by experiments.

Contribution

It introduces a new discrete state space and small signal model for SRC, including an analysis of audiosusceptibility resonance and design region determination.

Findings

Resonance peak identified in AS transfer function.

A design region exists where AS gain remains below unity.

Model predictions closely match experimental results.

Abstract

Models that accurately predict the output voltage ripple magnitude are essential for applications with stringent performance target for it. Impact of dc input ripple on the output ripple for a Series Resonant Converter (SRC) using discrete domain exact discretization modelling method is analysed in this paper. A novel discrete state space model along with a small signal model for SRC considering 3 state variables is presented. The audiosusceptibility (AS) transfer function which relates the input to output ripple is derived from the small signal model. Analysis of the AS transfer function indicates a resonance peak and an expression is derived connecting the AS resonance frequency for input ripple with different SRC component values. Further analysis is done to show that a set of values for SRC parameter exists, which forms a design region, for which the normalized gain offered by the SRC for input ripple is less than unity at any input ripple frequency. A test setup to introduce the variable frequency ripple at the input of SRC for the experimental evaluation of AS transfer function is also proposed. Influence of stray parameters on AS gain, AS resonance frequency and on SRC tank resonance frequency is addressed. An SRC is designed at a power level of 10kW. The analysis using the derived model, simulations, and experimental results are found to be closely matching.