Design and Analysis of an Integrated DC-DC Boost Charger for Electric Vehicle Applications Based on Wound Rotor Synchronous Machines

The automotive industry is increasingly adopting integrated onboard chargers (IOBCs) to improve efficiency, reduce system volume, and enable high-voltage fast charging using existing traction components. In parallel, the limited availability and cost volatility of rare-earth materials are motivating the adoption of magnet-less traction machines such as the wound rotor synchronous motor (WRSM), which offers enhanced operational flexibility through controllable rotor excitation. This article presents a WRSM-based integrated charger capable of boosting conventional charging voltages for high-voltage battery electric vehicles while utilizing the machine windings during charging operation. To improve charging efficiency, a Joule-loss minimization strategy is proposed to determine the optimal charging current references while ensuring zero average charging torque over the entire charging interval. Furthermore, a residual torque sensitivity analysis is conducted under machine parameter deviations to evaluate the robustness of the proposed optimization strategy. In addition, an interleaved pulse-width modulation (PWM) scheme is introduced to reduce charging current ripple and torque pulsations, achieving approximately 35-40% ripple reduction depending on the rotor electrical position. The influence of rotor position and carrier phase shift on charging current ripple and residual torque is also comprehensively analyzed. Simulation and experimental results validate the effectiveness of the proposed integrated charging system.