In order to solve the problems of difficult

high cost and poor accuracy of state-of-charge(SOC)estimation for vanadium redox flow batteries(VFB)

a joint SOC estimation method is proposed

based on forgetting factor recursive least squares(FFRLS) and multiple innovation unscented Kalman filter(MIUKF). The FFRLS algorithm is used to identify the equivalent circuit model parameters of vanadium redox flow batteries online

and the MIUKF algorithm is used for SOC estimation

so as to achieve the purpose of accurately estimating the SOC of vanadium redox flow batteries. Finally

a 5 kW/30 kW·h vanadium redox flow battery is taken as experimental platform to verify the method. The experimental results show that

compared with the RLS-UKF algorithm and FFRLS-UKF algorithm

the FFRLS-MIUKF algorithm has lower mean square error and root mean square error in the charging and discharging phases

which are 0.003 7

0.060 9 and 0.001 3

0.036 3.