A Novel Ultrawide Output Range DC–DC Converter for EV Fast Charging
Authors: Sai Bhargava Althurthi; Kaushik Rajashekara; Tutan Debnath
Extended Abstract:
The rapid growth of electric vehicles (EVs) has increased the demand for high-power fast chargers capable of supporting both 400 V and 800 V battery systems within a single platform. However, existing reconfigurable DC–DC converter solutions face challenges in achieving an ultra-wide output range while maintaining optimal performance and compactness. Conventional multi-module designs, which use series or parallel connections of identical modules at the output side, compromise design simplicity and achievable multi-mode optimization. To overcome these challenges, this paper proposes a novel ultrawide output voltage reconfigurable LLC resonant DC–DC converter designed to meet the diverse voltage requirements of future EV fast-charging systems.
Unlike existing reconfigurable multi-mode DC–DC converters, the proposed topology employs a three-winding high-frequency transformer (HFT) with optimally designed unequal secondary windings connected to two voltage-doubler rectifier bridges, which are dynamically reconfigured through additional MOSFET–diode switching pairs. By combining half-bridge (HB) and full-bridge (FB) operations on the primary side with three distinct secondary configurations, the converter achieves six operating modes i.e., two more than conventional designs with equal secondary windings. The increased number of operating modes minimizes the output voltage span assigned to each mode, thereby reducing the operating frequency range (OFR) and improving magnetizing-to-resonant inductance ratio (MRR) optimization to limit reactive power circulation.
A detailed design procedure for the LLC tank is presented to enable continuous output voltage regulation from 100 V to 1100 V with constant current (CC) charging. The proposed converter’s closed-loop performance is validated through PLECS simulation model delivering a 30 A CC output, demonstrating inter-mode transitions and voltage regulation. Furthermore, a 700 W laboratory prototype is experimentally tested under open-loop conditions to verify all six operating modes and their respective gain characteristics.
