Design-oriented steady-state analysis of LLC resonant converters based on FHA

The aim of this paper is to present a comprehensive design methodology for an LLC resonant converter, based on a detailed quantitative analysis of the steady-state operation of the circuit. This analysis follows the first harmonic approximation (FHA) approach, which tremendously simplifies the system model, leading to a linear circuit, which can be dealt with through the classical complex AC-circuit analysis. Two of the major benefits of the LLC resonant topology are the ability of the power MOSFETs and secondary rectifiers to be soft-switched and the capability of operating down to zero load. The design-oriented steady-state analysis presented in this paper addresses these two constraints quantitatively, allowing the designer to derive the circuit parameters which not only fulfil input voltage and output power specification data but also soft-switching and no-load operation constraints