“…A number of methods are used to estimate the battery SOC, such as ampere-hour integral method [5], open circuit voltage method [6,7], the internal impedance method [8], neural network [9,10], Kalman filter algorithm [11,12], unscented Kalman filter [14][15][16][17], particle filter [2,3,18,19] and other nonlinear observers [1,20]. Compared with the Ah integral method or open circuit voltage method, a closed-loop SOC estimation method based filter is attracting more attentions; Neural network method is required to be used within the scope of training data, when the application scope is beyond training experimental data, the accuracy will be decreased [9,10]; Kalman filtering algorithm can be used for various state estimation of the battery [11,12].…”