Improved modulation strategy for a LLC-type resonant converter in a solar application

Inhalt:
This paper presents the implementation of an improved modulation strategy for a LLC-type resonant converter in a solar application. The modulation is neither the frequency modulation nor the phase-shift modulation, but a new hybrid modulation technique also depending on a current zero-crossing in the resonant tank. Using only one control parameter, a significantly increased input-to-output voltage ratio can be controlled without losing soft switching. A complex state machine is presented including safety features. Experimental results demonstrate the functionality.