The Sequential Algorithm for Combined State of Charge and State of Health Estimation of Lithium Ion Battery based on Active Current Injection.

When State of Charge (SoC), State of Health (SoH), and parameters of the Lithium-ion battery are estimated simultaneously, the estimation accuracy is hard to be ensured due to uncertainties in the estimation process. To improve the estimation performance a sequential algorithm, which uses the frequency-scale separation and estimates the parameters/states sequentially by injecting currents with different frequencies, is proposed in this paper. Specifically, by incorporating a high-pass filter, the ohmic resistance and the RC pair can be independently characterized by injecting high-frequency and medium-frequency currents, respectively. Using the above estimated parameters, the battery capacity and SoC can then be estimated concurrently. Experimental results show that the estimation accuracy of the proposed sequential algorithm is much better than the concurrent algorithm where all parameters/states are estimated simultaneously, and the computational cost can also be reduced. Finally, the experiments are conducted under different temperatures to verify the effectiveness of the proposed algorithm for various battery capacities.