Design and implementation of an unregulated DC-DC transformer module using LLC resonant converter

Alemdar, Öztürk Şahin
A traditional high-power front-end DC-DC converter can be replaced with an array of paralleled standardized converter modules when modular design is applied. Modular front-end DC-DC converters represent many desirable properties such as expandability of output power capacity, redundancy implementation, simplified thermal management, and reduced design cost. However, in order to benefit from modular design, load current sharing must be accomplished among the paralleled modules. In this thesis, an LLC resonant converter is proposed as an unregulated DC-DC transformer (DCX) module for modular front-end DC-DC converter applications. In order to achieve current sharing capability, the droop current sharing method is employed in the LLC DCX module. To implement the droop method, both voltage feedback loop of the converter and inherent gain characteristic of the LLC resonant converter topology are utilized. To select the circuit components of the proposed module, a methodical design process is presented. Practical design considerations including planar transformer implementation, secondary-side rectifier selection, primary-side MOSFET selection and control loop implementation are investigated. A 500kHz 200W LLC DCX module converting 360-400VDC input to 12.5-11.75VDC output is built and its performance characteristics are demonstrated. The dimension of the module is 106mm × 61mm × 13mm and it achieves 89.9% efficiency at full load. A two-module array 400W front-end DC-DC converter and a three-module 400W front-end DC-DC converter having 2+1 redundancy configuration are implemented to demonstrate both steady-state and transient current sharing performance of the proposed module. 
Citation Formats
Ö. Ş. Alemdar, “Design and implementation of an unregulated DC-DC transformer module using LLC resonant converter,” M.S. - Master of Science, Middle East Technical University, 2016.