Studies on optimal charging conditions for vanadium redox flow batteries

A model based non-linear optimisation approach is proposed to obtain the optimal charging current and electrolyte flow rate trajectories (as functions of time) for a vanadium redox flow battery. The optimisation objective is formulated to minimise the total energy consumption of the battery and pumping system. Three operational constraints are addressed by the proposed optimisation: firstly, the input current and electrolyte flow rate are maintained to be within the limits of the power and hydraulic systems, respectively; secondly, charging of battery to a predefined SOC target within a given time frame is achieved; finally, the flow rate is properly constrained to avoid oxygen and hydrogen evolution. Two case studies were conducted under different time limit constraints. The optimisation results are compared with the existing approaches. It has been found that the proposed approach successfully regulated battery SOC to reach target with increased overall system efficiency.