Multi-objective optimal charging current and flow management of Vanadium Redox Flow Batteries for fast charging and energy-efficient operation

Abstract

High charging current density results in faster charging and reduces the capacity fading in Vanadium Redox Flow Batteries (VRFB). On the other hand, it leads to the reduced energy efficiency of the battery. Also, the lower electrolyte flow rate in VRFBs results in less energy consumption by pumps leading to the higher energy efficiency of the VRFBs. However, higher electrolyte flow rates have the benefit of reducing voltage loss of VRFBs. To address these trade-offs, closed-loop charge control and flow management in VRFBs are necessary. In this paper, a multi-objective optimization is proposed to optimize the charging duration and flow management of the VRFB simultaneously during the battery charging. A new formulation is proposed for modeling the pumps’ consumption based on affinity laws valid for centrifugal pumps, and the formulation is resulted in a new electrolyte flow management for VRFBs. Further, three case studies are defined in charging mode for verification of the proposed formulations via a nine-cell VRFB unit laboratory prototype. To show the advantages of the proposed formulation, the formulation is compared with previously published papers on optimization of the electrolyte flow rate and charging current of VRFBs. The results show the consistency of the optimal formulations.