Optimal Architectures for Electric Vehicle Fast Charging and Impacts on Grid and Battery Life
With the growing adoption of electric vehicles (EVs), the demand for public charging infrastructure is increasing to support more widespread, out-of-home recharging options. At the same time, charging power levels are rising to reduce recharging times, making them comparable to the refueling durations of internal combustion vehicles (ICVs) and minimizing wait times at EV fast-charging stations (EVFS). However, the widespread deployment of high-power fast chargers introduces several challenges, particularly concerning power quality disturbances on the grid and accelerated degradation of EV battery life. Therefore, a optimally structured approach is required to achieve scalable megawatt-scale future EVFS. This thesis proposes optimal EVFS architecture that addresses both grid and battery related challenges posed by high-power fast charging while also meeting key design criteria such as cost optimization, power density, service reliability, and fault isolation. Two optimized DC-DC converter topologies are introduced for EV charging applications. The first is an isolated ultra-wide voltage DC-DC converter to accommodate both 400 V and 800 V EV platforms. The second is a power-dense partial power converter (PPC) topology suitable for both EV charging and integration with battery energy storage systems (BESS). Its bidirectional, non-isolated configuration makes it a cost-effective and efficient solution for coupling BESS with EVFS infrastructure. Incorporating these converter designs into the proposed EVFS architecture led to improved system efficiency, reduced total power converter ratings, and enhanced power density. A multi-zonal EVFS structure is introduced to reduce fault impacts and improve charging service reliability. Additionally, operational strategies are proposed to mitigate grid-side impacts, including demand fluctuations, total harmonic distortion (THD), and supraharmonic emissions. To address battery degradation, several fast-charging protocols are reviewed, and an unbiased evaluation procedure is proposed to accurately assess their impact on lithium-ion (Li-ion) cell lifetime. The thesis includes a detailed design and operational analysis of the proposed converters, supported by simulation and experimental results. A 156-stall, 55 MW case study of the multi-zonal EVFS architecture is presented to demonstrate its scalability, performance, and grid compatibility. Finally, experimental results from cyclic testing of Li-ion cells using the proposed evaluation methodology are provided to examine the effects of fast-charging protocols on battery lifetime.
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