Design of a Grid-Friendly DC Fast Charge Station with Second Life Batteries

DC-fast charge (DCFC) may be amenable for widespread EV adoption. However, there are potential challenges associated with implementation and operation of the DCFC infrastructures. The integration of energy storage systems can limit the scale of grid installation required for DCFC and enable more efficient grid energy usage. In addition, second-life batteries (SLBs) can find application in DCFC, significantly reducing installation cost when compared to solutions based on new battery packs. However, both system architecture and control strategy require optimization to ensure an optimal use of SLBs, including degradation and thermal aspects. This study proposes an application of automotive SLBs for DCFC stations where high power grid connection is not available or feasible. Several SLBs are connected to the grid by means of low power chargers (e.g. L2 charging station), and a DC/DC converter controls the power to the EV power dispenser. The architecture of the DC bus, the size and state of health of the battery system determine efficiency, cost, and reliability of the station. A technical and economic comparison is proposed, evaluating solutions with different battery pack sizes and control strategies. An accurate numerical model is used to evaluate the performance of the different architectures. A realistic usage profile of the charging station is defined and real-world scenarios are considered for the SLB parameters.