Seamless Control of Full-Bridge and Half-Bridge Topology Morphing <i>LLC</i> Converter Based on State Plane Analysis

Abstract

The topology morphing (TPM) strategy, which involves switching between full-bridge and half-bridge modes, offers a promising solution to broaden the voltage gain range of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters without adding an extra device. However, due to the distinct voltage gain curves of these two modes, the existence of a stable operating point after TPM is not promised, resulting in system instability. To address this issue, this article proposes a design procedure based on peak gain trajectory, incorporating geometrically simplified steady-state state plane analysis. In this way, the predicted result shows a great agreement with the exact peak gain trajectory. In addition, a state plane–based topology morphing control (SPTMC) is introduced to mitigate significant output voltage transients caused by the abrupt TPM. With such a strategy, the desired switching frequency after TPM is forecasted and feedforward to the conventional linear control to ensure tight regulation of the output voltage during TPM. It is noted that neither a lookup table nor control scheme switching is required for the proposed control strategy. A prototype has been constructed to validate the feasibility of the proposed design procedure and the proposed SPTMC.