State of charge estimation model for Ni-Cd batteries considering capacity and efficiency

This paper proposes a new model for state of charge estimation in Ni-Cd batteries, considering the various definitions of capacities and efficiencies that take place in the charging and discharging of the battery. First, the main variables used to determine the capacity of an electrochemical battery are described. Second, coulombic efficiency in charging and in discharging processes is studied. Then, the different capacities defined and efficiencies considered are mathematically related and included in the estimation model. With the new proposed model, the effect of temperature and current rate on the capacity of the battery is analysed. These two parameters are considered to be the most influencing parameters. Finally, a characterization test is carried out on a single 11 Ah Ni-Cd cell and the results are used to verify the performance of the proposed model.