An accurate analysis method for an LLC resonant converter and a time-domain analysis (TDA)-based voltage gain curve derivation algorithm are proposed in this paper. When applied to an LLC resonant converter, the TDA method can obtain high-accuracy current and voltage waveforms by solving nonlinear equations for circuit parameters through operation-mode analysis. An LLC resonant converter operating mode classification algorithm was proposed based on the results of this analysis. The circuit voltage and current values in the steady state were quickly and precisely derived using this algorithm. An accurate power-loss analysis is required to design a high-efficiency converter. Therefore, TDA is a powerful tool for designing an LLC resonant network. The proposed TDA-based LLC resonant converter analysis and voltage gain curve derivation algorithm provides high-accuracy voltage, current value estimation and voltage gain curves for all switching-frequency ranges. The effectiveness of the proposed algorithm is verified using a 500 W LLC resonant converter prototype experiment.

SiC MOSFETs are used in many power conversion applications because of their superior characteristics, such as fast switching speed, low on-resistance, and high operating temperature. In certain high-power systems, SiC MOSFETs are connected in parallel to enhance their current capacity and power efficiency. However, compared with Si-based devices, the current imbalance caused by the parasitic inductance difference becomes more severe when driving SiC MOSFETs in parallel, owing to the fast switching speed. Furthermore, the power loop inductance imbalance that occurs when constructing a half-bridge with parallel SiC MOSFETs has rarely been addressed in previous studies. In this study, a half-bridge switching power module based on parallel-connected SiC MOSFETs is proposed to solve the current imbalance through a symmetric structure of the gate and power loops. The effects of the magnitude and imbalance of the gate and power loop inductances in the half-bridge structure based on parallel-connected devices are also explained. A detailed printed circuit board layout of the proposed switching power module is provided, and the inductance symmetry is verified through simulations. A double-pulse test is conducted to verify the current-balancing capability of the proposed switching power module. In addition, an LLC resonant converter is designed using the proposed switching power module, and the power loss between parallel SiC MOSFETs is compared. The experimental results indicate the total power loss error between the parallel-connected SiC MOSFETs of the proposed power module is only 1.94%.