Week 7 State of charge estimation
1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results
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First we have to simulate 3 test cases from harness dashboard.
The battery model harness dashboard is represented below.
1) Click on the Test sequence Varient Block and select test acse as 1
Now by clicking on the BMS Sequence block we get the chart
WWhen simulation will start the model will be in driving condition After 3000 Seconds it will be in standby mode and after 1000 seconds it will be in charging mode.Now by running the simulation
Results:
Here all the indicators are green So we can seen no errors and we check the plot for this model and is shown below.
From the plot we can see the vehicle is intially in driving state and charging was done till 90% After charging it reaches to standby mode. It can be seen in BMS state plot Bettery temp. increases in driving and charging Battery voltage was increased to 4.2V while charging. Current plot shows the value of current supplies to vehicle while driving SOC decreased up to 50% in driving conditionand it was increased while charging
2) Now change the test sequence Varient in case 2
Now by clicking on The BMS state request block
RESULT:
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
From the 3 cases we observed that only charging take place thus Soc was 80% at first then SOC increases to 100% in 2000 Seconds then SOC remains constant at 100%
2.What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ?
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Coulomb Counting:-
The coulomb counting method measure the discharging current of a battery and integrated the discharging current over time in order to estimate SOC Coulomb counting method is done to estimate the which is estimated from the discharging current. and prevoulsy, estimated SOC values SOC is calculated by the following equation
But there are several factors that affect the accuracy of Coulomb counting method including temperature battery history discharge current and cycle life.
Modified Coulomb Counting Method.
To improve the coulomb counting method a new technique called modified coulomb couting 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 currentof battery By practice of ecperimental data corrected current is calculated by the following form
Where K2, K1 and Ko are constant values obtained from the practice experimental data
In modified coulomb counting method SOC is calculated by the following equation
The experiment results show that the accuracy of the modified colulomb counting method is superior to the conventional coulomb counting method
But there are several factors that affect the accuracy of Coulomb counting method including temperature battery history, discharge current and cycke Life.
For example we can look into the project file we downloaded A BMS system in the files is represented below.
Bms algroithm models, protects report the measurement from battery pack.
By clicking On the BMS ECU we get the subsystem
By clicking on the SOC estimation block we get
From the above figure we observe the coulomb counting block
A Subsystem opens when we click on the coulomb counting
* This system does the estimation by coulomb counting eqauation mentioned above
* Advantage of coulmb counting method is its simplicity and low computational cost.
*Temperature and current from the battery is given as inputs
* CurrentSignal is given to a gain block and temperature is given to capacity since it varies according to temperature
* These inputs are given for integration where current will be integrated with respect to time
* This output is given to another block where it is divided by capacity
* Hence the SOC is estimated