Week 7 State of charge estimation
1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results\
Ans:-1
i) First test case-
Select the test case and click apply
This selection consist of changes in masked BMS state request subsystem as
This consist of following operation as
a) Driving for first 3000 sec
b) After 3000 sec start balancing operation occur for next 1000 sec
c) Then charging occur for the next 5000 sec
Result:-
The lamp indication are showing green so there is no fault occurs during sequence.
Cell Voltage and current pack
For the first 3000 sec all 6 cells are in drive mode where discharge occurs majorly and in stand by mode for lesser duration at 1000 to 2000 sec.
The voltage varies from 3.1 V to 3.9 V in this range. After 4000 sec charging occurs, voltage raised from3.7 voltage to 4 V. At 4V to 4.2 V at constant current at 30A and after 4.2V as constant voltage, current reduces from 30 A to 2.6 A at the end of charging and cell balancing occurs upto 9000 secs. Ater 9000 sec post charge cell balancing starts. All cell voltages are balancing to a voltage with respect to cell 1 to 4.1 V.
Cell Temperature
For 3000 sec the temperature range of cells increase gradually from ambient temperature 288K to 302k. The temperature of cell 1 is lesser and cell 6 has higher temperature for all stages.
After 3000 sec to 4000 sec cells temperature are reduced slightly no current flows through cell in standby mode. After 4000 sec temperature start increases exponentially upto constant current region and start reduces as current flow reduces in constant voltage and cell balancing fregion upto 9000sec. After 9000 sec temperature still reduces and remains stable at reaching ambient temperature.
BMS state
For 3000 sec the battery module in drive mode. From 3000 to 4000 sec the battery module in balancing stand by mode and after 4000 sec upto 9000 sec the battery module in charging and balancing mode.
ii) Test case 2
Result
Result:-
Cell Voltage and pack current
The cell voltages varies from maximum 3.9V and reduces to 3.05 V at cutoff voltages upto 9000 sec. Entire capacity drained at 9000 Sec. The pack current discharges upto maximum 70A and slight charging occurs during over all drive.
Cell Temperature
Here cell 1 having lesser temperature variation from 288K to 302K. Cell 6 is having higher temperature variation from 288K to 32.5K. The cell Temperature are slightly reducing between the drive modes as these duration are in stand by mode.
Battery Module state
Small duration of stand by modes are not plotted in this plot as simulation upto 1000 secs command. But in actual practical situation stand by mode are not present as battery current drains by other similar EV's.
iii) Test case 3
Result
Cell Voltage and Current pack
Initially cell 2 voltage rises from 3.9v to 4.2 V and stabilises to 4.15V. Cell 1 rises from 3.85 V to 4.1 V and stabilises to 4.08 V The battery pack current raising from 0A to 30 A and starts to reduce to 2.5 A gradually at end of full charging upto 2000 secs. At 2000 sec the pack is fully charged to 100%.
Cell Temperature
The cell temperature continues to increase heat upto full charge and after that the temperature get started to reduce to ambient temperature.
Cell balancing
From 0 Sec the cell 6 and 2 start to balance with respect to cell 1 and all cell try to balancing at end of simulation.
SOC
The SOC gets fully charged at 2000 sec and remains at full charge for rest of sequence. The actual state of charge is around 93% as full charge bt UKF and EKF.
2.What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ?
Ans:- it is defined as as a rate of avaliable capacity to its maximum capacity when a battery is fully charged and describes the remaining percentage of the battery capacity.
The coulumb counting method measured discharging current of the battery and integratres the discharging current over the time in order to estimated SOC
The expression as
Modified Coloumb counting
In this technique discharge is corrected with the function and corrected current is find out for accurate soc estimate.
The SOC estimation in in BMS model
The discharge current is given to gain with 1/3600 to convert to AH. The value is divided by capacity due to temperature change. Then integrsted with a gain value of 1 with sample time as -1 as we are using discrete integrator. The saturation limit are from 0 to 1. SOC values from 0 to 1 multiplied with 100 to get percentage of SOC.