Week 7 State of charge estimation
Week 7
State of charge estimation
Abhishek Anil Patil | Introduction to battery technology | 26/04/2022
Objective
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?
Study 1
Simulate the 3 test cases from harness dashboard and write a detailed report on the results
The test harness dashboard is shown below
The test sequence variant block has three cases of which the first case is selected
The BMS sequence chart is as follows
The chart signifies that the vehicle starts in the driving condition. After 3000 seconds, it goes in balancing mode for 1000 secs. For the next 5000 secs it goes in charging and rebalancing mode.
Results
In the driving state, the battery is charged till 90%
Battery temperature increases in the charging state
SOC decreases in the driving state and then increases in the charging state\
Case 2
Vehicle is in driving state for 10000sec. then it goes into charging.
Results
There is a fault condition
The fault occurs during the charging state.
The fault occurs because of high temperature.
Case 3
There is only one state, charging, for 20000 sec.
Results
SOC goes from 80 to 100 in 1500 secs.
The voltage attains a steady state
The current drops to zero
The remaining charging occurs through constant voltage
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 [20]. 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:
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.
The corrected current is the function of discharging current. There is a quadratic relationship between the corrected current and discharging current of battery. By practice of experimental data, corrected current is calculated by the following form:
where k2,k1,k0 , and are constant values obtained from the practice experimental data.
In modified Coulomb counting method, SOC is calculated by the following equation:
The experimental results show that the accuracy of the modified Coulomb counting method is superior to the conventional Coulomb counting method.
SOC estimation block
Coulomb counting block
This block does the coulomb counting using the equations shown above
Temperature and current are taken as inputs
The current is integrated and then divided by the capacity to get the SOC