An Accurate Dynamic Time-Domain Model for LLC Resonant Converter by Considering Nonideal Components, Various Modulation Strategies, and Dynamic Process

In order to improve the performance of LLC resonant converters in wide voltage range applications, many novel modulation strategies other than traditional pulse-frequency modulation (PFM) have been proposed, such as pulse-width modulation (PWM) and phase-shift modulation (PSM). However, the existing modeling method cannot be extended to other modulation methods easily. In most cases, the existing models are developed based on the assumption of ideal components, which neglect parasitic components and dead time effect. Practically, these non-ideal factors have a significant influence on the steady state operation and the soft switching performance. Besides, due to the complexity and nonlinearity of the operation process, it is difficult to conduct the small signal analysis. In this article, an accurate dynamic time domain model is developed based on stages iteration, considering common parasitic components, the dead time effect, and various modulation methods. It can reflect the implementation of zero voltage switching (ZVS) and the high frequency oscillation under the light load. Based on the improved dynamic model, a convenient and accurate small signal analysis method is proposed. Simulation and experimental results are presented to verify the accuracy of the model. Compared to the traditional model, the relative error of the voltage gain can be reduced from 14.2% to 5.0%.