Electrical circuit model of a vanadium redox flow battery using extended Kalman filter

This paper presents an equivalent electrical circuit model for a unit cell all-vanadium redox flow battery (V-RFB). The developed V-RFB model consists of an open-circuit cell potential (Ecell(ORP)) which is in series with an ohmic internal resistance and parallel with an n-Resistor-Capacitor (n-RC) network. The Ecell(ORP) represents an intrinsic relationship of the V-RFB state-of-charge (SOC), while the n-RC networks represent the polarization characteristic and dynamic behaviour of the V-RFB. The Ecell(ORP) and ohmic resistance parameters are obtained through a direct measurement of an experimental setup of 25 cm2 unit cell laboratory unit V-RFB, whereas the two pairs of RC network parameters are identified through a recursive algorithm of extended Kalman filter (EKF). The accuracy of this model is verified with different pulse voltages at a few values of SOCs. Ultimately, the model is validated with an experimental charge-discharge characterisation of V-RFB system. Suggestion for system improvement is highlighted.