On-the-Fly Topology-Morphing Control—Efficiency Optimization Method for LLC Resonant Converters Operating in Wide Input- and/or Output-Voltage Range

This paper presents a control method for efficiency improvement of the LLC resonant converter operating with a wide input-voltage and/or output-voltage range by means of topology morphing, i.e., changing of power converter's topology to that which is the most optimal for given input-voltage and/or output-voltage conditions. The proposed on-the-fly topology-morphing control maintains a tight regulation of the output during the topology transitions so that topology transitions are made without noticeable output-voltage transients. The performance of the proposed topology morphing method is verified experimentally on an 800-W LLC dc/dc converter prototype designed for a 100-V to 400-V input-voltage range.

I. Introduction

In many applications, power conversion circuits are required to operate with a wide input-voltage and/or output-voltage range. For example, a majority of single-phase ac/dc power supplies used in today's computer and telecom power systems must operate in the universal ac-line range from 90 to 264 V_RMS and provide constant- or variable-voltage regulated output(s). Typically, telecom ac/dc power supplies provide a regulated output between 42 and 58 V, whereas power supplies for desktop, networking, and server applications deliver a constant voltage with single or multiple output(s). However, to further improve the energy efficiency, single-output server power supplies with two-level selectable output voltage have been recently introduced. Specifically, these power supplies with dynamically adjustable output voltage deliver a 12-V output at full- and mid-range loads, whereas at light loads, their output voltage is reduced to 6 V to improve the light-load efficiency.