Electrochemistry-Driven Design of Multiwinding CLLC Resonant Converter

The voltage of the lithium-ion batteries is determined by its electrochemistry, which is critical for the optimum design of the connected converter. This, combined with the volume and weight limitations of electric vehicles (EVs), poses a few challenges in terms of increasing the power density and efficiency of the auxiliary power modules (APMs) The APM enables power transfer from the high-voltage traction battery to the low-voltage (LV) loads. Converter efficiency is generally highest at a selected input voltage, while the change in battery voltage is often disregarded when selecting that input voltage. This results in a reduced converter efficiency over the rest of the input voltage range, thereby reducing the potential range of the EV. Therefore, this article proposes a new design approach that considers the electrochemistry of the battery to weight the operation points of the converter and match the input voltage of highest efficiency to the voltage of highest differential capacity of the battery. Hence, the efficiency is better distributed over the entire operating range. Furthermore, a multiwinding CLLC converter with increased peak gain is proposed that distribute the current stress and improve thermal management on the LV side. Experiments verify the new design approach and the proposed converter and an efficiency of 96.6% and power density of 1.36 kW/L including cold plate, microcontroller and protection circuit are achieved.