Week 7 State of charge estimation
Aim: Simulate the 3 test cases from harness dashboard and write a detailed report on the results and What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation.
1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results:
>Now we need to simulate the 3 test cases from the harness dashboard, for this we need to select the harness dashboard from the project file which we have to download by the provided below given matlab link.
>After downloading the file we have to extract the zip file to a folder and then select the battery_system_R202a to extract the file again.
>Then after we need to get the access to the closed loop BMS harness dashboard by the below given data
Test<system
>After opening the file in matlab it shows like the below
>Now here we have to select to open the project and model and here after the whole project will be loaded in the matlab current folder and workspace
>Here we have to select the Test
>Now we have to Test the Sequences of 3 different conditions for this we have to adjust the above model into various conditions
Test Sequence Variants:
- Manual Variant (selection)
- BMS_StaeRequest subsystem which provides the state request commands
>The indicating lamps are here to shown any fault state high temp overvoltage charger voltage sensor overcurrent low teemp under voltage inverter state of a battery
>The green light indicates us that the all states are okay and battery is good to charge and discharge and red indicares the fault state.
>The rotating switch for manual variant to change the position during simulaation run time.
Procedure for Test 1:
>Here in the Test sequence variant select the state variant as 1.
>Here we can observe that the testsequence in BMS_Stae sequence > BMS_test sequence and there also we can see that te test case .
>Here After go to the BMS_StateRequest block and select the test sequence as 1.
>Here after go through the BMS_Testsequnce and then after it will look like this and select the sequence as 1 model,whcih shows below
>Now we can see that the test conditions we have double click on the test sequnce and the sequence will shows like this,
- Here fro the above fig we observes that the test sequence for driving is done for first 3000 sec
- Then after driving balancing of the cell goes for the next 1000 sec
- so after the balancing charging and balancing goes for the next 5000 sec
- But the post charging balancing occurs after the 9000 sec till to the 20000 sec.
Test Result-1;
- Here all the lights are indicates green.
- so we can conculde that there are no errors
>By observing the above plots we can say that the vehicle is initially in a driving state and charging was done at 90%
>So after charging reaches stand by mode which shows in the BMS state plot.Battery temp increases in driving .The battery voltage was increased by 4.2 V while charging
>The current plot shows the value of current supplied to the vehicle while driving,the SOC decreased up to the 50%bin driving condition and which increase while charging.
Test Result-2:
>Select the test sequence as 2 in the test sequence subsystem.
>The after in the BMS_State Request select the sequence test as 2 which shows in the below fig.
- The driving condition gos after the 10000 sec
>here all the details of the test will be performed in the simulation.
- Here all the lights are indicates green.
- so we can conculde that there are no errors
>The driving stage is from 0 to 5000 sec and then after the charging starts.
>Here in the driving cycle mode tje 0-10000 sec of the cellvoltage varies from 3.9 to 3.05 v which is an cutoff voltage of a cell and the entire cell is drained upto 8692 sec.the cell temp changes from 288k to 322k.
>The Soc decreased from 805 to 0%,same as the charging mode which is 10000 sec to 20000 swc the gets drained earlier before it gets recharges.
Test Results-3;
>Select the test sequence as 3 in the test sequence subsystem.
>here the test sequence had only one conditiond i.e the charging phase for 20000 sec completely.
>The after in the BMS_State Request select the sequence test as 3 which shows in the below fig.
- Here all the lights are indicates green.
- so we can conculde that there are no errors
>here the test sequence had only one conditiond i.e the charging phase for 20000 sec completely.
>By observing the above plots we can conclude that the SOC had reaches upto 100% while in charging state and remains smae for the rest of the time
>the temp of the battery pack is alco reduced in the stanging mode.
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 SOC, which is estimated from the discharging current, I batt, and previously estimated SOC values, SOC.
>SoC Estimation by Coulomb Counting is based on the measurement of the current and integration of that current over time. The State of Charge (SoC) of a battery cell is required to maintain it’s safe operation and lifetime during charge, discharge and storage.
>Coulomb counting gives a relative change in SoC and not an absolute SoC. If you measure the current over a given time step you have a measure of the number of Ah that have left or been received by the battery.
where:
- SoC(t) = estimated State of Charge at time, t
- SoC(t-1) = previous State of Charge at time t-1
- I(t) = charging or discharging current at time, t
- Qn = battery cell capacity
- Δt = time step between t-1 and t
Modified coluomb 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:
Ic(t) = K2I(t)^2 + K1I(t) + K0
where K2,K1 and K0 are 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.
An BMS System:
>BMS algoritham model protects reports the measurement from battery pack.
SOC estimation model-ECU block;
>By clicking the above ECU model we get the desired subsystwm.
>Here the subsystem consists of current power limit calculator ,state machine,SOC estimation,Balancing ,Battery management system.which all are working at their own desired function.
>Now by going throuh SOC estimation we get the desired subsystem which shown below,
>Here we find the Coulomb counting,UKF_EKF_1TC,State transition func,and measurement function.Now we going to discussed about the coulomb counting subsystem detaaily.
>Here it is an estimation of coulomb counting equation which is mensitionde above.
>The advantage of coulomb counting method is its simplicity and low computational cost.The temp and current from the battery is given as inputs.
>current signal is given to a gain block and temo is given to a capacity since it varies according to temp,these inputs are given for integration where current will be intgrated with respect to time.
>The output is given to another block where it s divided by the capacity,hence the SOC is estimated.