Dynamic Modeling of LLC Resonant Converter Using Extracted Two-Harmonic Approximation and Comparative Analysis With Other Approaches

Resonant converters are widely used in various applications due to their wide input voltage range, high efficiency, and high power density. The mathematical modeling of these converters has great importance because they have both AC and DC states, simultaneously, which poses challenges for controller design. In this paper, a dynamic mathematical model of the LLC resonant converter is extracted by developing the common first harmonic approximation (FHA) model to a two-harmonic approximation (THA) model, and its accuracy is compared with other conventional models, including the FHA, the dynamic pharos (DP), non-linear mathematical models. As a reference model, circuit experimental model has been used for comparison. The comparison metric is the sum of squared errors in transient and steady-state modes, expressed as a percentage of the steady-state peak value. Furthermore, the output of the mathematical models and simulations is evaluated against practical results from a prototype.