State of charge estimation of battery using Coulombs counting Method

AIM:

To understand what coulomb counting is and how BMS implements the same for SoC estimation.

EXPLANATION:

The state of charge of a battery can be defined as the ratio of the current capacity to that of the rated capacity of the cell

SoC=Q_c(t)/Q_r(t)

In coulomb counting method the state of charge is estimated by integrating the discharge current over a period of time. The previous values of SoC are also needed for this calculation. The estimation is not very accurate since it is affected by parameters like temperature and history of usage.The equation for the estimation is as follows

SoC(t)=Soc(t-1)+(I_c(t)*`Delta`t)/Q_r(t)

The simulink model associated with the coulomb counting method of SoC estimation is as follows

The battery is connected to a current sensor from the value of current is obtained. It is given as input to a gain block which has gain set at 1/3600. The value of charge is obtained as the output of the gain block.The charge is then integrated over a particular time and then subtracted from 1 to get the state of charge of the battery.

Here the method is applied to a simple battery but the same can be done for a battery of bigger capacities as well.

RESULT:

The method of coulomb counting for SoC estimation and the way the BMS applies it for SoC calculation is understood