Morphing control strategy of wide input voltage DR-LLC converter for vehicle power supply

Abstract

Electric vehicles have experienced substantial global growth. However, significant fluctuations in the output voltage of power batteries and abrupt changes in the input voltage of DC–DC converters pose major challenges to their safety and reliability, thereby impeding sustainable development. This paper proposes a frequency-prediction-based topology morphing control strategy (FPTMC) for a dual resonant cavity LLC (DR-LLC) converter. The strategy aims to accommodate a wide range of input voltages while enhancing the reliability of the vehicle's power supply. Firstly, the topology of the DR-LLC converter is introduced, utilizing a fundamental wave analysis method for modelling purposes. This analysis results in three distinct voltage gain models corresponding to various topology modes, thereby enabling the converter to manage a wide spectrum of input voltages. Then, a geometrically simplified state plane analysis is employed to derive switching frequency models for the three topology modes, facilitating real-time prediction of the necessary switching frequency during topology transitions. The proposed control strategy, which relies on frequency prediction, effectively mitigates the problem of voltage spikes during these transitions. Finally, both simulation and experimental results validate the accuracy and feasibility of the proposed wide input voltage control strategy for DR-LLC converters in vehicle power supply systems.