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 ?
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1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results
To select one of the 3 test conditions, it can be selected via the Test Sequence Variant block which allows you to select which test needs to be simulated. The first variant was selected initially for the simulation which can be seen below.
Test Case 1
Here we can see all the lights have turned green as there is no fault or errors in the model.
As we look at the test variant as shown below, it states that at the start of the simulation the model will be in the driving condition, thereafter, after 3000 seconds it will be in balancing mode, after 1000 seconds it will be in charging and balancing mode and after 5000 seconds it will be in post charge balancing mode.
After simulating the model for 20000 seconds as given default.
It can be observed from the plot that the vehicle is initially in the driving state and charging was done till 90%. After the charging mode it reaches to the standby mode which can be seen from the BMS state plot. From the Cell temperatures plot it is observed that the battery temperature rises in driving and charging. The battery voltage was increased to 4.2 V while charging. The current plot shows the current value supplied to the vehicle while driving. The SOC was observed to be decreased around 50% in driving condition, which increased while charging.
Test Case 2
Coming to the second variant condition to simulate.
It was observed from the plot that the battery discharges completely in 8692 seconds and the vehicle does not go forward and the charging state was not achieved at 10000 seconds. Hence the vehicle comes to standby condition and simulation stops midway.
Test Case 3
Coming to the third condition.
Looking at the condition below for third variant of the simulation. It is just the continuous charging condition from the start till the end of 20000 seconds of simulation.
Looking at the plot it can be seen that the battery starts charging and the SOC starts increasing from beginning to around 2000 seconds and stays stable at 100% continuously from 2000 seconds until 20000 seconds. The peak current plot drops from 0 to 2000 seconds and stays constant as the charge is not used anywhere as the driving is not present.
From the above simulated 3 variants of the simulation carried out it was observed that,
- In the first simulation all three conditions were simulated such as driving charging and the stable state hence the charging and discharging were observed and in the end the constant 100% SOC was observed because of the standby state of the vehicle.
- In the second simulation it was just the discharging as the SOC dropped to 0% in the driving state within 8600 seconds and the charging state was not achieved at 10000 seconds.
- In the third simulation, only charging was observed for the first 2000 seconds and the SOC remained at 100% constant for the next 18000 seconds.
2.What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ?
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(t), which is estimated from the discharging current, I(t), and previously estimated SOC values, SOC(t-1). 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 counting method is proposed. The modified Coulomb counting method uses the corrected current to improve the accuracy of estimation.
