An Improved Sigmoid Function Based Large Signal Modeling for LLC Converter

In response to the demand for the analysis of dynamic characteristics and real-time simulation of LLC converters, a modeling method for a large-signal continuous model based on the improved Sigmoid function is proposed in this paper. To address the challenge of unifying the description of various operating modes of LLC converters under continuous and discontinuous current modes in different operating frequency regions, the switching process of the switch is approximated by the characteristics of the Sigmoid function. Herein, the step function and impulse function are serialized approximately, and the different working conditions of different models are thus linked to form a unified large signal model of the full bridge LLC converter. In comparison to existing large-signal models of LLC converters, the model proposed in this paper not only features a simplified equation form and increased accuracy but also provides accurate dynamic circuit characteristics. Finally, simulation and experimental results confirm the validity and precision of the model.