Week 7 State of charge estimation

AIM:
To simulate the 3 test cases form harness dashboard and write a detailed report on the results and to refer to the given model and explain how BMS implements coulomb counting for SOC estimation.

GIVEN:
https://in.mathworks.com/matlabcentral/fileexchange/72865-design-and-test-lithium-ion-battery-management-algorithms

REQUIREMENTS:
Matlab Simulink

SIMULATION OF 3 TEST CASES FROM HARNESS DASHBOARD:

• initially we have to simulate 3 test cases form the harness dashboard.
• we can use the reference link provided https://in.mathworks.com/matlabcentral/fileexchange/72865-design-and-test-lithium-ion-battery-management-algorithms.

• click on the test sequence varient block and select test case 1

• now by clicking on the BMS sequence block we get the chart.
• on start of the simulation, the model will be in operating condition.

• after 3000 seconds it will be in standby mode and after 1000 seconds it will be in charging mode.

OUTPUT:

OBSERVATION:

• here all the indicators are gree. so we can see no errors shown below.
• from the plot we can see the vehicle is initially in driving state and charging was done till 90%.
• After charging it reaches to standby mode. It can be seen in BMS state plot. Battery temperature increases in driving and charging.
• Battery voltage was increased to 4.2V while charging.
• the value of current supplied to vehicle while driving is shown in current plot. SOC decreased up to 50% in driving condition and it was increased while charging.

2)Now lets change the test sequence varient to Case 2

• the driving stage is for 0 to 10000 seconds.
• after that charging stage occur.

OUTPUT:

OBSERVATION:

• from the above graph, it is observed that a fault condition is occured.
• the SOC has not increased even after charging was started, it continues to decrease.

3) Now lets change the test sequence varient to Case 3.

• this condition has only one phas and that is charging. thus 0 to 20000 seconds simulation runs.

OUTPUT:

OBSERVATION:

• here we can see that the soc reached 100% in charging and remained in stand by mode.
• Cell temperature also decreased when standby mode was achieved.

RESULT:

• From the above 3 cases we observe that only charging takes place so SOC was 80% initally, and then Gradually increased to 100% in 2000 seconds.
• then SOC remains Constant at 100%

COLUMB COUNTING:

• the coulomb counting method measures the discharging current of a battery and interfrates the discharging current over time in order to estimate SOC.
• it is done by estimating the current, which is estimated form the discharging current and previously estimated SOC values.

• but there are several factors that affect the accuract of coulomb counting method including temperature, battery,history,discharge current and cycle life
• 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.

• where k0,k1,k2 are constant values.
• SOc is calcualted by the following equation.

• the experimental results shows that the accuracy of the modified coulumb counting method is superior to the conventional coulomb counting method.

BMS IMPLEMENTATION WITH COULOMB COUNTING FOR SOC ESTIMATION:

• There are 2 main blocks in the cirucit one is the Battery management system electronic control unit and the other is Plant
• Plant is a battey source or power source while the BMS ECU is a software in a simulation environment.

(i) Battery Management system Electronic control unit:

• represents the software and controls part of the model, showing how cell balancing is done, Soc is estimated and response to different states.
• it also protects and reports the measurements from the battery pack.

• by clicking on the BMS ECU we get this sub circuit.

• by clicking on the SOC estimation block we get

• from above figure we observe the coulomb counting block.

• a subsytem opens when we click on the coulomb counting block

• the coulomb counting method is simplicity and low computational cost
• temperature and current from the battery is given as inputs.
• the temperature varies as the current signal is given to a gain block.
• hence the SOC is estimated.

(ii) Plant:

• the plant is the battery source or the power source
• it consists of battery pack, precharge circuit which is connected to charge and load
• they are connected in paralled connection, there is a charger connection and inverter connection
• the Drive load will discharge like a motor and inverter.
• Charge load, we have current source, changes battery in other direction, changes happens in current rate.

RESULT:

• Thus the simulation of the 3 test cases form harness dashboard is completed and the report on the results with reference to the given model is Explained.
• the BMS implements coulomb counting for SOC estimation is also completed successfully and output is verified.