Week 7 State of charge estimation

Aim:-State of charge estimation

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 harness dashboard and write a detailed report on the results

Now, we have to simulate 3 test cases from harness dashboard. We need to, select the harness dashboard from project file which we downloaded with the 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 Varient Block and select test case as 1

Now by clicking on the BMS Sequence block we get the chart

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 by Running the simulation.

Results:-

Hence all are in the green plot. So we can see no fault and as shown in the graph

>The above plot consider the vehicle is initially driving state so that the charging was filled up to 90%

>After charging finish state its approach to below stand by mode

>It can be observed in the BMS status plot

>So that the battery temp increases when in its driving and charging so then it has increased up to voltage 4.2v during the charging

>We have seen that the current plot shows the value indicates of current supplied to the vehicle during in the driving

>Soc decreases as half of during driving state condition and it recovered increased at while charging

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

Now by clicking on the BMS state request block

Result:-

>As observed in the above graph, the occurs consider of fault conditions as in the second case

>so after charging was started the soc, not to increased so while duration it will decrease only

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.

Result:-

>As the above graph the state of charge reaches to 100%charging mood and remaining constantly only stand by mode

>where of cell temp also decreases when the stand by mode was reached up to that state

From all 3 cases we have observed that

>The only charging placing so that the soc was in the 80%at firstly state

>Then as second state case the soc increases 100% in a 2000seconds

>Third case the soc as remain the whole process constantly 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:

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

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:

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

In 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 battery pack.

By Clicking on the BMS ECU we get the Subsystem

By clicking on the SOC estimation block we get

From above figure we observe the Coulomb Counting block.

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.
• These inputs are given for integration where current will be integrated with respect to time.
• This outout is given to another block where it is divided by capacity.
• Hence the SOC is estimated.