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?

In fie exchange open the document of "design and test Li-ion Battery management alogrithm"

Downloaf the zip file and extract toa folder. The folder consists of these files as shown below.

After this BMS_closedLoop_harness_dashboard model file is opened and it is shoen below

Model of block :

1. Test sequence (it has 3 different test conditions)
2. manual variant (selection)
3. BMS_StateRequest subsystem to provide the state request commands.
4. indicating lamps are there to show anz fault ,high temperature,under low voltage, inverter state of a batter. green light tell us about the states are OK and battery is good to charge and discharge.
5. BMS_closed loop : this subsystem contain BMS ECU and plant as two main subsystems.

BMS ECU : The BMS have two input which are BMS__input which is feedback from the plant model and the state request is coming from the state machine this will generate the output as BMS output and info which have current power limit calculation in state machine, SOC estimation and celll balancing

PLant : this subsystem contain battery pacl percharge unit and charger/ loads

in the battery pack there are two configuration which are 1 module (6cells) and 16 modules(96 cells)

in the scope SOC module, cell voltages, pack current, cell temperature, BMS state and cell balancing command are seen as ouput.

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

for simulating the 3 test cases go to the test sequence varient and slecect test case one by one.

TEST CASE 1) :

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

The test sequence can be seen

BMS_StateRequest>BMS_testSequence and there we can see that the test case we have selected is shown

double clickkon the test sequence and the test sequence will be shown as :

the editor figure tell us about the test sequence and it as following :

1. Driving is done for first 3000 sec.
2. then after driving balancing of cell occurs for the next 1000sec duration
3. after the balancing charging and balancing occur for next 5000sec
4. post charge balancing is occurong after 9000sec till 200000sec

Result :

Simulaiton is done for 20000 sec and the result is shown as:

the lamp indication is green for all states which means the model is fault free

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

cell temperature increases from 288K to 302K

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

ii) Balancing mode (3000-4000 sec) : after 3000sec for 1000sec cell balancing occur and the modules are in standby and thez are constant voltage near about 3.7V

iii) Charging and Balancing (4000-9000 sec) : after 4000sec the charging occurs and the cel voltages increased from 3.7 to nearly 4.2V in constant current mode with current reduces from 30A to 2.6A charging and balancing of cells occur till 9000sec. Cell temperature also start to increase exponentially upto constant current region and reduces as current flow reduces in constant voltage mode.

iv) Post charging (9000-20000sec) after 9000sec the post cell balancing starts under standby mode.

SOC remains to 94%

b) Test case 2 :

the test case 2 is selected as shown in the dialog boz=x and click OK to implement it.

BMS_StateRequest>BMS_TestSequence and there we can see that the test case we have selected below :

the editor figure tell us about the test sequence and it has the following

i) Drvong is done for first 10000sec

ii) Then the charging is done for next 10000sec.

results of test sequence 2 :

simulation is done for 20000sec and the result is shown below

the lamp is grreen for all the states which means the model is fault free

i) Driving mode (0-10000sec) : the cell voltages varies form 3.9V to 3.05 v which is cut offf voltage of cell and the entire cell is drained upto 8692sec

cell temperature varies form 288K to 322.5k

SOC reduces from 80% to 0% in the drive mode under 8692sec.

ii) charging mode (10000-20000sec) the cell got drained earlier before reaching this mode

c) test case 3

the test care 3 is selected as shown

results of the sequence 3 :

the lamp indication were green for all states which means the model is fault free.

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

coulomb counting method :

The coulomb counting method measures the discharing current of a battery and integrates the discharging current over time in order to estimate SOC. coulomb counting methid is done to estimate the SOC(t) which is estimated from the discharging current and previously estimated SOC values (t-1)

soc is calculated by the following equation :

Modified coulomb 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 improce the accuracy of estimatio. there is a quadratic relationship between the corrected current. there is a quadratic relationship between the corrected current and discharging current of battery. By practive of experimental data corrected current is calculated by the following equation.

where k2, k1 and k0 are constant values obtained from the practice experimental data.

to observe the coulomb couting method we need to open the BMS_ClosedLoop > BMS ECU and then on SOC_estimation block

here we see that there are three method for calculations of SOC estimation and these are

1) coulomb counting

2) unscented kalman filter

3) Extended Laman filter

open Product adn discrete time integrator block

the discharfe current frim the battery given to a gain having a value of 1/3600 to convert A to Ah.

that current is divided by the capacity due to temperatute change and then integrated with the gain value of -1 and samle time -1 as discrete type integrator is used here

the saturation limits are given which are 1 to 0 so that we get the SOC value from 0 to 1 multiplied with 100% of SOC

This coulomb countig methods is simple amd require less computational comapred to other two methods.