Thermal Balance Modulation of Switching Devices for Hybrid-Clamped Three-Level Full-Bridge LLC Resonant Converter

The hybrid-clamped three-level full-bridge LLC resonant converter is widely employed in subway power systems and ship-integrated power systems due to its notable attributes of soft switching and low input voltage requirements for the switching devices. Nonetheless, the existing wide voltage range modulation modes suffer from thermal imbalances in switching devices, posing limitations on their application in high-power scenarios. In order to address these issues, the three modulation modes optimized for thermal balance are proposed by analyzing the conditions for achieving soft-switching and thermal equalization. When integrated with the original modulation modes, these optimized modes effectively balance the conduction loss in the switching devices and achieve a wide range of voltage gain. Moreover, the proposed modulation transition method facilitates swift and efficient transitions between modulation modes, while minimizing the impact on voltage and current caused by the transition process. The experimental prototype with 1.5kW power level and 125V-1kV input voltage range is built to verify thermal balance effect of switching devices under the proposed modulation mode and performance of the proposed modulation transition method.