Week 7 State of charge estimation
Simulation of the 3 test cases from harness dashboard.
harness dashboard project file can be downloaded with the reference link
The battery model harness dash board is represented below.
Go to test sequence block
Select the 1 st case
When simulation will start, the model will be in driving condition. After 3000 seconds it will be in standby mode and after 1000 seconds it will be in charging mode. Now run the simulation
Here all the indicators are green. So we can see no errors and we check the plot for this model and is shown below
From the plot we can see the vehicle is initially in driving state and charging was done till 90%.
After charging it reaches to standby mode.
It can be seen in BMS state plot. Battery temperature increases in driving and charging.
2) Now change the test sequence variant in case two.
Go to the BMS state request block
From the above graph, a fault condition occurred in second case.
3) Now by changing the test Sequence Value to 3
This condition has only one phase and that is charging. Thus 0 to 20000 seconds simulation runs.
- Here we can see that the soc reached 100% in charging and remained in stand by mode. Cell temperature also decreased when standby mode was achieved.
From the 3 cases we observer that only charging takes place thus SOC was 80% at first , then SOC increases to 100% in 2000 seconds then SOC remains constant at 100%.
What is coulomb counting?
coulomb counting:-
The Coulomb counting method measures the discharging current of a battery and integrates the discharging current over time in order to estimate SOC . Coulomb counting method is done to estimate the discharging current, , and previously estimated SOC values, . SOC is calculated by the following equation:
Modified Coulomb Counting Method
To improve the Coulomb counting method, a new technique called modified Coulomb counting method is proposed. The modified Coulomb counting method uses the corrected current to improve the accuracy of estimation.
The corrected current is the function of discharging current. There is a quadratic relationship between the corrected current and discharging current of battery. By practice of experimental data, corrected current is calculated by the following form:
SOC is calculated by the following equation:
A BMS system in the file is represented below.
Bms algorithm block is opened
A subsystem opens when we click on the Coulomb Counting
- This system does the estimation by coulomb counting equation mentioned above.
- Advantage of coulomb counting method is its simplicity and low computational cost.
- Temperature and current from the battery is given as inputs.
- Current signal is given to a gain block and temperature is given to capacity since it varies according to temperature.