Week 7 State of charge estimation

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

Block of Model:-

• Test sequence Variant (it has 3 different test conditions)
• Manual Variant (selection)
• BMS_StateRequest subsystem to provide the state request commands.
• Indicating lamps are there to show any fault state, High Temp, Overvoltage, Charger, Voltage Sensor, Overcurrent, Low temp, Under Voltage, or Inverter state of a battery. The green light tells us that all states are Ok and the battery is good to charge and discharge and the red indication will indicate the fault state.
• Rotating switch for the manual variant to change the position during simulation run time
• BMS_Closed Loop:- this subsystem contains BMS ECU and Plant as two main subsystems let us see this block in detail:-

BMS ECU:- The BMS ECU gets to have two inputs which are BMS_Input which is feedback from the Plant model and The state Request is coming from the state machine. This is generating output as BMS Output and Info which have current power limit calculation in State Machine, SOC estimation, and Cell balancing logic as shown below:-

Plant:- This subsystem contains a Battery pack, precharge circuit, and charger/loads.

In the battery pack, there are two configurations which are 1 module (6 cells) and 16 modules (96 cells).

Here we have selected 1 module for simple calculation and less simulation time.

• In the scope SOC of the module, Cell voltages, Pack Current, Cell Temperature, BMS state, and cell balancing command are seen as output.

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

For simulating the three test cases we have to go to the Test sequence Vaeiant and select their Test Case one by one.

a) Test Case 1:-

The test case 1 is selected as shown below in the dialog box and click OK to implement it.

We can see the Test sequence in BMS_StateRequest>BMS_TestSequenece and there we can see that the test case we have selected is as shown below:-

Now to see what are the test condition we have to double click on the Test Sequence and the test sequence will be shown as follows:-

The editor figure tells us about the test sequence and it is as follows:-

• Driving is done for the first 3000 sec.
• Then after driving Balancing of cells occurs for the next 1000 sec duration.
• After the balancing Charging and balancing occur for next 5000sec
• Post Charge Balancing is occurring from 9000sec till 20000 sec (i.e. simulation end time.)

Results of Test Sequence 1:-

Simulation runs for 20000 sec and the result is as below:-

The Lamp indication was green for all states which means the model is fault free.

i) Driving (Discharging) mode (0-3000 sec):- All the cells for the first 3000 sec are in the driving mode so the discharge of all the cells occurs and it varies in the range of 3.1 to 3.9 V (min and max.).

Cell temperature increases from 288K to 302 K.

SOC also reduces from 80 % to 45% for the EKF technique.

ii) Balancing mode (3000-4000 sec):- After 3000 sec for 1000 sec, cell balancing occurs and the Modules are in standby mode and they are having constant voltage near about 3.7V.

Cell temperature reduces slowly as no current flow through the cells during balancing.

SOC is also constant during this period i.e. 45% for the EKF technique.

iii) Charging and Balancing (4000- 9000 sec):- After 4000 sec the charging occurs and the cell voltages increased from 3.7 to nearly about 4.2 V in Constant current mode with the current of nearly 30A and then the constant voltage charging starts and the current reduces from 30A to 2.6 A Charging and balancing of cells occur till 9000 sec.

Cell temperature also starts to increase exponentially up to the constant current region and reduces as current flow reduces in constant voltage mode.

SOC also increases from 45% to 94% in this mode for the EKF technique.

iv) Post charge Balancing (9000- 20000sec):- After 9000 sec the post cell balancing starts under standby mode.

Cell temperature reduces in this mode and tries to reach the ambient temperature.

SOC remains constant at 94%.

b) Test case -2:-

The test case 2 is selected as shown below in the dialog box and click OK to implement it.

We can see the Test sequence in BMS_StateRequest>BMS_TestSequenece and there we can see that the test case we have selected is as shown below:-

The editor figure tells us about the test sequence and it is as follows:-

• Driving is done for the first 10000 sec.
• Then Charging is done for the next 10000 sec.

Results of Test Sequence 2:-

Simulation runs for 20000 sec and the result is as below:-

The Lamp indication was green for all states which means the model is fault free.

i) Driving Mode (0-10000 sec):- The cell voltage varies from 3.9 V to 3.05 volt which is the cut-off voltage of the cell and the entire cell is drained up to 8692 sec.

Cell temperatures vary from 288K to 322.5K.

SOC reduces from 80% to 0% (cell got fully drained) in the drive mode under 8692 sec.

Cell balancing is not performed here.

ii) Charging Mode (10000- 20000 sec): The cell got drained earlier before reaching this mode.

c) Test case- 3

The test case 3 is selected as shown below in the dialog box and click OK to implement it.

We can see the Test sequence in BMS_StateRequest>BMS_TestSequenece and there we can see that the test case we have selected is as shown below:-

The editor figure tells us about the test sequence and it is as follows:-

• Charging is done for the entire simulation period i.e. 20000 sec.

Results of Test Sequence 3:-

The Lamp indication was green for all states which means the model is fault free.

i) Charging (0-20000 sec):- Cell Voltages increase from their initial values and after 2000 sec they got constant.

Pack current initially starts from 0 to 30A and then starts decreasing when the constant voltage mode is there to 2.5 A and got fully charged up to 2000 sec.

SOC was initially 80% and in 2000 sec it got fully charged which is 100%.

Cell temperature starts to increase initially and when the battery got fully charged then decreases down to the ambient temperature.

2)To explain coulomb counting for finding the SOC estimation in BMS.

Coulomb counting:

SOC(State Of Charge) is defined as the rate of available capacity to its maximum capacity when a battery is fully charged and describes the remaining percentage of the battery

capacity.

To find this SOC% we are using the coulomb counting method.

The coulomb counting method measures the discharging current of the battery and integrates the discharging current over time to estimate SOC.

Which can be estimated from discharrging current(I(t)),previously estimated SOC values(SOC(t-1)).The relation can be given as,

Modified Coulomd counting:

In this technique discharge current is corrected with a function, and the corrected current is found for accurate SOC estimation.

The function can be given as,

K0, K1, and K2 are constant values obtained from the practice experimental data.

The SOC relation can be given as,

SOC estimation in the BMS model:

To see the model of the Coulomb counting technique in the BMS model, click the subsystem of SOC_Estimation and click Coulomb counting.

It is developed as shown below,

Here the discharge current from the battery is given to gain with a value of 1/3600 to convert current to Ahr.

The value is divided by capacity due to temperature change and then integrated with a gain value of 1 with sample time -1 as we are using a discrete integrator.

The saturation limits are from 0 to 1.

We will get the SOC values from 0 to 1 multiplied by 100 to get in the percentage of SOC.