Condition-dependent characterization of the internal resistance of a Vanadium Redox-Flow-Battery

An equivalent circuit model of a 21 kW / 120 kWh vanadium flow battery is developed based on measurements of real-life operational data. The internal resistance of the battery is identified at different states of the battery system, without prior knowledge of the internal parameters of the battery. A validation of the equivalent circuit is performed while using different permutations of system states to determine the internal resistance of the VFB. The validation shows a decrease of up to 5 % in SOC simulation error when the change in internal resistance is considered, with SOC having the biggest impact on model precision. The greatest effect of the variable resistance is found during edge cases of battery operation.