Large-Signal Modeling for Full-Bridge LLC Resonant Converter Using Extended Hyperbolic Tangent Function

The accuracy of continuous model is important for characteristic analysis and real-time simulation of power electronic converters. Due to unique resonant tank structure, LLC resonant converter operates in continuous current mode and discontinuous current mode respectively in different operating frequency regions. It is difficult to realize unified description of its various operating modes by continuous model. To deal with this problem, this paper proposes a large-signal modeling method for full-bridge LLC resonant converter using extended hyperbolic tangent function. Firstly, characteristics of full-bridge LLC converter in each operating frequency region are analyzed. Based on this, a large-signal discontinuous model is established, which can realize unified description of various operating modes of the LLC converter. Then, an extended hyperbolic tangent function with steepness factor/impulse coefficient is constructed, and the large-signal continuous model of full-bridge LLC converter is established by using this function. Based on this model, continuous system approach can be directly applied for real-time simulation and controller design. Compared with the existing large-signal continuous model, the proposed model has lower order and higher accuracy. In addition, it can provide high-accuracy switching information of secondary-side power devices in time domain, which can be used as a reference for synchronous rectification design. Finally, simulation and experimental results verify the accuracy and effectiveness of the proposed model.