A Novel Topology for Fast Charging of Lithium Ion Batteries in a Battery Swapping Station

Abstract

The electrification of the transportation sector, particularly through the use of electric vehicles (EVs), is gaining importance due to its numerous benefits such as reduced emissions, increased energy efficiency, and improved air quality. However, the practicality of EVs is still hindered by challenges such as long charging times and limited charging infrastructure. In this context, battery swapping has emerged as a potential solution to address these challenges. Battery swapping allows for quick and convenient replacement of depleted EV batteries with fully charged ones, enabling nearly uninterrupted long-range driving. While battery swapping technology shows promise, there are still challenges to overcome, particularly in the design and operation of battery swapping stations (BSS). One critical factor is the charging time required to fully recharge the swapped batteries. Longer charging times result in larger stock requirements and higher costs for BSS stations. Therefore, developing a fast-charging strategy tailored for BSS stations is crucial to optimize their size, cost, and efficiency. This thesis proposes a novel topology for fast charging of lithium-ion batteries in a battery swapping station. The solution combines the advantages of an interleaved structure with the convenience and flexibility of battery swap and go (BSG) technology. The control design focuses on optimal utilization of idle chargers to minimize the charging time. A three-charger network is implemented and demonstrated to showcase the effectiveness of the proposed hybrid system. To estimate the state of charge (SOC) of the batteries accurately, a hybrid technique of open circuit voltage (OCV) lookup method and coulomb counting method is employed. A custom constant current-constant voltage (CC-CV) charging profiler shapes the power flow, offering versatility through mode switching. Simulations are presented for various load configurations and switching scenarios. The system exhibits robust transient handling, adaptiveness, and efficient load sharing without relying on complex computations. Results obtained from testing a small-scale battery demonstrate the effectiveness of the proposed solution. Charging times of batteries from 1% to 99.99% SOC are near ideal, highlighting the efficiency and speed of the fast-charging topology. The modular design of the system allows for scalability, accommodating different network sizes and battery specifications. This research work provides a cost-effective and efficient solution for minimizing the charging time of batteries in a battery swapping station, thereby reducing the minimum stock requirement and overall size of the station. These advancements contribute to infrastructure development and facilitate the adoption of electric vehicles, paving the way for a sustainable and clean transportation future.