A New Modeling Method for Burst Mode with Three-pulse Trajectory Control of CLLC Resonant Converter

The CLLC resonant converter is a promising candidate for their superiority in soft switching, wide output range, and symmetrically bidirectional operation. However, CLLC converter still faces the problems of the low efficiency under light-load conditions due to core loss in magnetic components and smooth voltage regulation characteristic at high frequency. In order to solve the problems above, in this article a new modeling method based on the state space equations is presented which can decouple the equations into two completely independent small equations. And then the analyses are carried out in two state plane coordinate systems, finally map the results back to the original coordinate system. Based on the modeling method mentioned above, a novel burst-mode control for the CLLC resonant converter is proposed in this article. The burst-on time is fixed and a three-pulse pattern is used. In contrast, the burst-off time is modulated while the load changes. In order to achieve the highest efficiency steady state in the shortest time, it is only necessary to adjust the length of the first pulse. Then the next two pluses will settle the converter under the steady state mentioned above. As a result, the low frequency ripple of the output voltage of the converter can be kept constant minimally without additional filters.