Robust digital control for an LLC current-resonant DC-DC converter

If a pulse frequency, a load resistance of an LLC current-resonant DC-DC converter are changed, the dynamic characteristics is varied greatly, that is, the LLC current-resonant DC-DC converter has non-linear characteristics. In many applications of DC-DC converters, loads cannot be specified in advance, and they will be changed suddenly from no loads to full loads. A DC-DC converter system used a conventional single controller cannot be adapted to change dynamics and it occurs large output voltage variation. In this paper, a robust digital controller for suppress the change of step response characteristics and variations of output voltages in the load sudden changes is proposed. Experimental studies using a micro-processor for the controller demonstrate that this type of digital controller is effective to suppress the variations.