State Of Charge Estimation Based On Sliding Mode Observer For Vanadium Redox Flow Battery

State of charge (SOC) of the batteries is a key indicator for battery monitoring and control. Long-time operation of vanadium redox flow batteries (VRBs) may cause ion diffusions across the membrane and the depletion of active materials, which will lead to capacity fading and internal resistance increasing. A selection of proper SOC method considering capacity fading factor is critical. In previous studies, capacity fading factor is not considered when SOC observer has been designed. In addition, the traditional method - extended kalman filter - is not appropriate to estimate SOC when the battery capacity is decaying. In this paper, an adaptive method, sliding mode observer (SMO), capable of dynamic estimation is proposed based on a model considering capacity fading. The simulation result shows that a capacity loss of 13.9% is estimated based on the diffusion model. The mean error between the observed and the modelled capacities is 0.14 Ah.