A Hybrid Design Approach for an LLC Resonant DC‐DC Converter Based on Time‐Frequency Domain Analysis for Electric Vehicle Application

ABSTRACT This paper presents a novel design approach for an LLC resonant DC‐DC converter tailored for electric vehicle battery chargers. The design methodology considers the non‐linear load, ensuring a narrow switching frequency range and zero‐voltage‐switching (ZVS) conditions for optimal soft‐switching. A hybrid design procedure is proposed with a strong emphasis on high efficiency and power density. The resonance frequency and an accurate range for the magnetising inductor are calculated by time‐domain analysis using the efficiency formula. The resonant capacitor, magnetising inductor and resonant inductor are then calculated by frequency‐domain analysis, considering ZVS conditions and the non‐linear load's profile. In the time‐domain analysis, a 3D surface map of efficiency versus resonance frequency and magnetising inductor provides an accurate resonance frequency and the range for the magnetising inductor. Furthermore, by drawing a surface map of load considerations versus the calculated resonance frequency and the defined magnetising inductance range, based on the load's profile and ZVS conditions, the optimal design parameters are identified by applying the maximum switching frequency and inductance ratio. Finally, the step‐by‐step design methodology is validated through experiments on a prototype converting 400 V from the input to an output voltage range of 320 to 420 V at 3.3 kW with a peak efficiency of 97.9%.