Week 7 State of charge estimation
Week 7 State of charge estimation
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 ?
Hint :(Download the file from the link and go to SOC estimation model-ECU block)
1 - Simulate the 3 test cases from the harness dashboard and write a detailed report on the results.
We need to select the harness dashboard from the project file which we download with the reference link
The battery model harness dashboard is represented below.
Select the Test sequence number from the subsystem block.
1. First test sequence module
It, Test case no1
When 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 see no errors and we check the plot for this model and is shown below.
From the plot,
- we can see the vehicle is initially in a driving state, and charging was done to 90%. After charging it reaches standby mode.
- It can be seen in the BMS state plot. Battery temperature increases in driving and charging. Battery voltage was increased to 4.2V while charging.
- The current plot shows the value of current supplied to the vehicle while driving. SOC decreased up to 50% in driving conditions and it was increased while charging.
2. Second test sequence module.
Now change the sequence number from the subsystem to 2
Here are the details of the test that will be performed in the simulation. The driving stage is from 0 to 5000 seconds and then charging.
RESULTS
As the system is having faults the red light is coming up. The fault of the state and the high temperature have occurred in the system.
From the above graph,
- a fault condition occurred in the second case. From the model, we can see what type of faults are occurred, in the graph, the system is not working since the faults arise.
- The SOC had stopped and the BMS state is showing a fault signal.
3. Third test sequence
This test sequence had only one phase that is the charging phase for complete 20000 seconds.
RESULTS
Here we can see that the SOC had reached 100% when in the charging phase and remain in the standby mode for the rest of the other time. The temperature of the battery pack also started reducing in the stand-by mode.
2 - 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, which is estimated from the discharging current, and previously estimated SOC values. SOC is calculated by the following equation:
- Where,
- SOC(t) = Actual SOC
- SOC_o = Initail SOC
- Cn = Capacity of Battery
- t = Instantanious time
- l(t) = Instantanious Current
But there are several factors that affect the accuracy of the Colomb 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 the 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 the battery. By the practice of experimental data, the corrected current is calculated by the following form:
Ic(t)=k2I(t)2+k1I(t)+k0">Ic(t)=k2I(t)2+k1I(t)+k0Ic(t)=k2I(t)2+k1I(t)+k0
where k2">k2k2, k1">k1k1, and k0">k0k0are constant values obtained from the practice experimental data.
In the modified Coulomb counting method, SOC is calculated by the following equation:
SOC(c)=SOC(t-1)+Ic(t)QnΔt">SOC(c)=SOC(t−1)+Ic(t)QnΔtSOC(c)=SOC(t-1)+Ic(t)QnΔt
The experimental results show that the accuracy of the modified Coulomb counting method is superior to the conventional Coulomb counting method.
But there are several factors that affect the accuracy of the Coulomb counting method including temperature, battery history, discharge current, and cycle life.
Now we can see it in the project file we downloaded. A BMS system is the file represented below.
BMS algorithm models, protects, reports the measurement from a battery pack.
Click on the BMS ECU & inside pf BMS ECU block we get SOC Estimation block
By clicking on the SOC estimation block we get the other subsystem. We get more block which helps to Run the program by other block in between this block we are getting Columb Counting block Which denotes that the
How Columb Counting helps in SIMULATION of BMS,
- On opening the coulomb control block we can see the calculation block.
- The advantage of the coulomb counting method is its simplicity and low computational cost.
- Temperature and current from the battery are given as inputs.
- The current signal 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 the 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.