A Simple Optimal Trajectory and Thermal Balance Control Strategy for Full-Bridge LLC Resonant Converter With Wide Voltage Range Application

Full-bridge (FB) LLC resonant converter is a promising candidate for wide voltage range applications with multiple operation modes. By simply adjusting the gate driving signals, the FB LLC converter can be reconfigured as half-bridge (HB) LLC converter to extend the converter operation range. However, in the HB mode, the operating status of the four switches is different. One switch of the phase leg is turned on permanently and another one is turned off, while the other two switches of another phase leg are operating in high switching frequency mode. It is obvious that the thermal performances for these four switches are different, which will lead to a reliability issue from long-term perspective. In this article, the thermal balance control strategy in HB mode is proposed by interchanging all four possible circuit states to make sure the thermal stresses for all four switches are same. On the other hand, to avoid the transients during transitions of different circuit states in HB mode, a simple optimal trajectory control strategy is proposed. The analysis demonstrated that to ensure smooth and fast transition, only a constant time is required to be inserted during the transition, which requires no sensors and complicate calculation. Experimental and simulation results have been presented to demonstrate the effectiveness of the proposed strategy.