3-Bridge LLC resonant converter for achieving wide output voltage control range based on topology morphing

Abstract

In this paper, a control method for a 3-bridge LLC resonant converter operating with a wide output voltage control range is described. Duty changes that stem from switching devices cause topology transitions that allow the converter to shift sequentially across four operating modes, where the primary resonant tank circuits and the secondary terminals can be connected in parallel or in series making it possible to achieve a wide controllable output voltage (7.5–120 VDC). During topology mode transitions, morphing control within narrow hysteresis bands, which is achieved by varying the switching frequency and duty of the switching devices, maintains a tight regulation without noticeable output voltage transients. To verify the performance of the proposed converter, a 5-kW 700 VDC input prototype with an output voltage ranging from 7.5 to 120 VDC is built and tested.