Week 7 State of charge estimation

Aim:-

1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results

2.What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ?

Study 1:-Simulate the 3 test cases from the harness dashboard and write a detailed report on the results.

The 3 test cases for the harness dashboard is simulated using the MATLAB file. The file needs to be downloaded from the given reference link. https://in.mathworks.com/matlabcentral/fileexchange/72865-design-and-test-lithium-ion-battery-management-algorithms . The battery model harness dash board is represented below.

1)Click on the Test Sequence Variant Block and select test case as 1

The test sequence has been set from the stated parameters. At the start of the simulation, 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.

From the plot, we observe the vehicle is initially in a driving state, and charging was done to 90%. After charging it reaches standby mode. It can be seen in the BMS state plot. Battery temperature increases in driving and charging. Battery voltage was increased to 4.2V while charging. The current plot shows the value of current supplied to the vehicle while driving. SOC decreased up to 50% in driving conditions and it was increased while charging.

2) Now change the test sequence variant in case two.

From the above graph, a fault condition occurs in the second case. So even after charging was started, the soc didnt increase. It continue to decrease.

3) Now by changing the test Sequence Value to 3

• Here we can see that the soc reached 100% in charging and remained in standby mode. Cell temperature also decreased when standby mode was achieved.

From the 3 cases we observe 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%.

Study 2:-What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation?

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 , which is estimated from the discharging current, , and previously estimated SOC values, . SOC is calculated by the following equation:s 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 , which is estimated from the discharging current, , and previously estimated SOC values, . SOC is calculated by the following equation:

Accuracy of the Coulomb counting method including temperature, battery history, discharge current, and cycle life are affected due to several factors.

Modified Coulomb Counting Method

To improve the Coulomb counting method, a new technique called the 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 the battery. By the practice of experimental data, the corrected current is calculated by the following form:

where k2,k1andk0k2,k1andk0are constant values obtained from the practice experimental data.

In the modified Coulomb counting method, SOC is calculated by the following equation:

The experimental results show that the accuracy of the modified Coulomb counting method is superior to the conventional Coulomb counting method.

But there are several factors that affect the accuracy of Coulomb counting method including temperature, battery history, discharge current, and cycle life .

For example we can look into the project file we downloaded.

A BMS system in the file is represented below.

BMS algorithm models, protects, reports the measurement from the battery pack.

• This system does the estimation by the coulomb counting equation mentioned above.
• The advantage of the 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.
• These inputs are given for integration where the current will be integrated with respect to time.
• This output is given to another block where it is divided by capacity.
• Hence the SOC is estimated.