Multimode Optimization of the Phase-Shifted LLC Series Resonant Converter

This paper presents a loss optimization method for phase-shifted LLC resonant converters operating with phase shift. The method features automatic detection of the preferred operational mode from the five possibilities for the topology. For a given power level and voltage transformation ratio it simultaneously determines the values of the resonant elements and transformer turns ratio. This work supplements and extends the available optimization tools for variable frequency operation and extends these to phase-shifted operation. The combined methods allow converters with much wider voltage regulation ranges to be designed. Numerical programming methods to determine the mode boundaries and to solve the steady-state solutions for the different modes of LLC converter are presented. A detailed loss model for a phase-shifted LLC is also discussed. A prototype of 30-403V, 295W is built to validate the optimization results. A comparison is made between an optimized and unoptimized converter. An extension to multipoint optimization, as required to optimize the European Weighted Efficiency is described.