State of Power and State of Charge Estimation of Vanadium Redox Flow Battery Based on An Online Equivalent Circuit Model

Accurate power estimation can ensure safe and reliable operation of vanadium redox flow energy storage system (VRB-ESS) so that the battery does not violates the safe operating limits. The parameter variation of equivalent circuit model (ECM) of VRB affects the accurate estimation of state of power (SoP), especially when considering the aging effects of the battery. In this paper, state of charge (SoC) and state of power (SoP) are estimated respectively. Firstly, the recursive least square (RLS) method is applied for online identification of the equivalent circuit parameters of VRB, then unscented Kalman filtering (UKF) is used to predict SoC of VRB, and lastly, the charged or discharged power can be predicted according to the accurate battery terminal voltage under limiting conditions. The results show that the UKF is capable for both the SoC and SoP estimation accurately.