Week 7 State of charge estimation

1. Simulate the 3 test cases from harness dashboard and write a detailed report on the results

MODE 1

1. First 3000sec - Driving
2. After 1000sec - Balancing
3. Next 5000sec - Charging & Balancing
4. After that    - Post charge balancing

• Cell voltage continuously varies while driving (high discharge & low charging) & increase on charging
• Current decreases at as charge increase on charging period 0.4 - 0.9. CC chargint to CV
• SOC remains steady after full charge
• Cell temperature increase up to full charge and gradually reduce
• BMS state shifts to driving, charging accordingly & standby after full charge
• Balancing command starts on charging

MODE 2

1. Driving for 10000sec
2. Then charging

• Voltage reduces to 3v
• Vehicle stops at 8692sec
• Temperature reaches to 320 from 290
• SOC reduces from 0.8 to 0.4
• BMS state remains only in driving mode
• Balancing command not executed since the vehicle can't reach target of 10000sec

MODE 3

1. Charging only

• Full charge in 2000sec
• Current decreases gradually as charge increase
• Temperature increases up to full charge & remains steady
• Same as SOC
• BMS state remains only in charging mode
• Balancing command executed whole time

2. What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ? Coulomb Counting Method

Coulomb Counting Method

• Integration of current over the time period
• measures the discharging current of a battery
• integrates the discharging current over time in order to estimate SOC
• estimated from the discharging current, , and previously estimated SOC values
• SOC is calculated by

• Temperature, battery history, discharge current, and cycle life affects accuracy of Coulomb counting method

Modified Coulomb Counting Method

• Uses the corrected current to improve the accuracy of estimation
• Quadratic relationship between the corrected current and discharging current of battery
• The corrected current is the function of discharging current
• where , k2, k1 and k0 are constant values obtained from the practice experimental data

• Works in three different formats
• First block is coulomb counting
• Integration is done by discrete time integrator
• Implemented in z domain
• Current is integrated over the time
• Give simple idea about SOC