The effect of higher low-voltage DC levels on the efficiency of high-power charging systems

Abstract

The increasing demand for high-power charging has accelerated the transition from conventional 400 V architectures toward higher DC voltage systems such as 800 V, 1200 V and 1500 V. While higher DC voltage reduces charging current and associated conduction losses, it also introduces increased switching losses and higher semiconductor voltage stress. Therefore, the influence of higher DC voltage on overall charging-system efficiency requires systematic evaluation.

This thesis investigates the effect of higher DC voltage levels on the efficiency of high-power charging systems operating under equal-power conditions. A simplified system-level analytical model of a high-power DC fast charging system with an isolated Dual Active Bridge (DAB) converter was developed in MATLAB/Simulink. The model employs an averaged loss approach to evaluate current magnitude, conduction losses, switching losses and overall system efficiency across voltage levels ranging from 400 V to 1500 V at a fixed charging power of 300 kW.

The results demonstrate that increasing the DC voltage level significantly reduces output current and associated thermal stress, with the current decreasing from 750 A at 400 V to 200 A at 1500 V. Overall efficiency improved from approximately 97.5% to 99%; however, the improvement became progressively smaller at very high voltage levels due to increasing switching-related losses. The analysis identified the most favourable operating region near 1200 V, where the reduction in conduction losses was most effectively balanced against voltage-dependent switching losses.

The findings indicate that higher-voltage architectures can improve power density and reduce current stress in ultra-fast charging systems, while also increasing voltage-related design complexity. The study provides a structured analytical framework for voltage-level selection in future high-power charging infrastructure.