Analysis of Feedback Control Loop for 1 MHz LLC Resonant Converter Using Digital Controller

Abstract

High switching frequency operation has been researched to produce small sized and high functional products. Moreover, high switching frequency and small output filter induce high crossover frequency which can achieve high system dynamics. However, significant drawback of digital controller is the limited control bandwidth due to time delay of computation process in control algorithm, zero-order-hold, and PWM generation. In this paper, the small signal analysis of 1 MHz LLC resonant converter are proposed to evaluate the closed-loop control stability against the time delay effect of the digital controller. The theoretical, simulation, and experimental approach will be presented to show the validity of the proposed analysis with the 1 MHz prototype converter.