Lu Rengui

Comparison and Evaluation of Charge Equalization Technique for Series Connected Batteries

Charging and discharging of series connected batteries as a whole is associated with charge imbalance problems, which will result in damage to battery cells and reduction of battery life. Various circuits for charge/discharge equalization have been proposed. But so far there is no criterion for comparison and evaluation. In this paper, all the circuits are divided into four groups according to the structure, and each of them is qualitative analyzed and marked with 5-degree marking system. The results are helpful for people to select suitable charge/discharge equalization method. Furthermore, based on experimental results a novel evaluation method with two parameters is proposed, which is very convenient for estimating the equalization effects in static and dynamic equalization. All the results can be used for further study on charging equalization technique.

State of charge Estimation for NiMH Battery based on electromotive force method

State of charge (SOC) estimation of NiMH battery is a key technology in electric vehicle/hybrid electric vehicle (EV/HEV). In this study, a relationship between SOC and electromotive force (EMF) is obtained based on the study of discharge experiments at different SOC. In addition, equivalent circuit model is used to estimate the SOC of NiMH battery. The analysis of experiment data shows a relation between EMF and SOC. Then, according to the analysis of the equivalent circuit, an equation between EMF and terminal voltage is built. Therefore, SOC can be estimated by terminal voltage. Two different tests that include constant discharge and variable current discharge are undertaken to verify precision of the SOC estimation method. The result of two tests show the method is suitable for NiMH battery SOC forecast in static or steady state.