Integrated DC Boost Charger in Post-800V Architecture with Open-End Winding Machine – Magnetic-Domain Modelling and Torque Analysis

Next-generation powertrain architectures proposed within EU Horizon projects adopt operating voltages above 800 V, providing improvements in efficiency as well as reductions in copper usage and system weight. However, post-800 V vehicles must remain backward compatible with existing 400 V and 800 V charging infrastructure, which requires the installation of an additional onboard DC boost charging unit on the vehicle. This paper proposes an integrated DC boost charging solution that reutilizes the open-end winding electric machine and the traction inverter of the electric powertrain, enabling backward compatibility while further reducing system cost and weight. In charging mode, the electric machine is repurposed as a passive inductive component, imposing a strict requirement of stationary operation with zero torque generation, which fundamentally differs from the driving mode characterized by rotor rotation and electromagnetic torque production. Consequently, conventional electric machine modeling approaches based on the rotor-oriented reference frame are not applicable to charging operation due to the unsymmetrical and unbalanced three-phase currents in the machine windings. To evaluate the machine behavior and develop charging control strategy, this paper introduces a magnetic-domain model based on physical model using phase self- and mutual-inductance parameters, from which the electromagnetic torque is directly derived based on the interaction between magnetic flux and phase currents. The simulations compare the charging current ripple and electromagnetic torque generation of a stationary open-end winding machine under two charging configurations: open-winding charging and neutral-point charging. The results show that the open-winding charging configuration exhibits lower current ripple than the neutral-point charging configuration due to higher inductance utilization. However, a non-zero charging torque is generated in the open-winding charging configuration and is strongly dependent on rotor position. The specific rotor positions corresponding to zero torque are identified and used to optimize the charging process.