A comparison of different design methods for the multiresonant LLC converter with capacitive output filter

Faced with ever shorter product cycles, SMPS designers require fast and reliable modeling tools. In case of resonant converters the derivation of the exact solution is complex and time-consuming. Thus, simplified calculation methods are attractive. However, the reduced accuracy of these approximation methods has to be taken into account carefully. In this paper, the concepts of the First Harmonic Approximation (FHA) and the extended First Harmonic Approximation (eFHA) of the multiresonant LLC converter with capacitive output filter are discussed. Furthermore, the accuracy of both approximation methods is evaluated in detail with respect to the results of the exact solution in the time domain.