Week 7 State of charge estimation
Question 1) Simulate the 3 test cases from harness dashboard and write a detailed report on the results
Ans:
Report:
1. In test case 1 all the conditions of the battery are healthy.
2. In test case 2, a fault state has arised due to high temperature in cell no2
3. In test case 3 all the conditions of the battery are healthy.
4. Test Case 1 scope output:
l Cell Temperature: They reached maximum of 317K at 500 secs and then graduallly decreasing with minimal slope
l Cell Voltages: Cell voltages observed a transient condition at start and remained constant at 4.2V after 500 secs
l SOC: It started from 80% and reduced to 45% at 400 secs and then gradually increased to 100% (SOC-1) and other 92%.
l BMS State: For first 300 secs it was in driving state. For few 100 secs it came to standby and then again for around 500 secs battery was charging. After which it was in standby mode.
l Pack Current: The pack current observed transient wave at start with current going negative. After, it raised to a peak of 30A at 400 secs. Then, gradually decreased and settled at zero.
l BalCmd: Except one cell all other cells were having value 0 and observed a slight step up at the last moment. While, one cell observed the step at 300 secs and remained constant throughout.
l All the other states were healthy.
5. Test Case 2 Scope Output:
l Cell Temperature: It started from 280K and reached maximum of 323K at 600 secs and then graduallly decreasing with minimal slope
l Cell Voltages: Cell voltages observed a transient condition at start and remained constant at 3.9V after 600 secs
l SOC: It started from 80% and reduced to 30% at 500 secs and then gradually increased to 70-78%.
l BMS State: For first 500 secs it was in driving state. For few 100 secs it was charging and after that it observed a battery fault at 600 secs throughout the drive cycle.
l Pack Current: The pack current observed transient wave at start with current going negative. After, it raised to a peak of 30A at 500 secs. Then, gradually decreased and settled at zero.
l BalCmd: Except one cell all other cells were having value 0. While, one cell observed the step at 500 secs and remained constant throughout.
l It was observed that the battery had a fault state of high temperature.
6. Test Case 3 Scope Output:
l Cell Temperature: It started from 288K and reached maximum of 292.5K at 200 secs and then graduallly decreasing with minimal slope.
l Cell Voltages: Cell voltages observed a no transient condition at start remained constant at 4.1-4.2 V after 200 secs
l SOC: It started from 80% and then gradually increased to 92-100%.
l BMS State: Charging state was observed from the start till end.
l Pack Current: The pack current observed 30A of starting current at almost 0 secs and then gradually decreased to zero at 200secs and remained constant.
l BalCmd: Except one cell all other cells were having value 0 till 1600 secs. While, one cell observed the step at 0 secs and remained constant throughout.
l All the other states were healthy.
Question 2) What is coulomb counting?
Ans:
l Coulomb counting is a method for estimating the state of charge (SOC) of a battery by tracking the amount of current that has been added or removed from the battery. It is a relatively simple and inexpensive method, but it is not as accurate as other methods, such as open circuit voltage (OCV) and electrochemical impedance spectroscopy (EIS).
l Coulomb counting works by integrating the current flowing into and out of the battery over time. The SOC of the battery is then calculated by dividing the integrated current by the battery's capacity.
l The following equation shows how to calculate the SOC of a battery using coulomb counting:
SOC = (SOC_0 - ∫ I dt) / C
where:
SOC is the state of charge of the battery
SOC_0 is the initial state of charge of the battery
I is the current flowing into or out of the battery
t is the time
C is the capacity of the battery
· Coulomb counting is a widely used method for estimating the SOC of batteries in electric vehicles, hybrid electric vehicles, and other battery-powered devices.
· Here are some of the advantages and disadvantages of coulomb counting:
Advantages:
Simple and inexpensive
Can be implemented in hardware or software
Relatively accurate for short periods of time
Disadvantages:
Not as accurate as other methods, such as OCV and EIS
Can be affected by battery temperature and aging
Requires accurate knowledge of the battery's capacity
Overall, coulomb counting is a versatile and useful method for estimating the SOC of batteries. It is particularly well-suited for applications where accuracy is not critical and cost is a major factor.