Week 7 State of charge estimation
Test case -1)
Here in fig., we can see all the lights have turned green. as there is no fault or errors in the model.
As per the test variant as shown below, it shows 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 4000 seconds it will be in charge balancing mode.
It can be observed from the plot, the vehicle is initially in driving state and charging was done till 90%. After the charging mode it reaches to the standby mode which can 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 is increased while charging.
TEST CASE- 2)
The second test variant is shown below:
Here, 2 red lights blinks which shows that there are some faults in system.
It was observed from the plot that the battery discharges completely in 5000 seconds and the vehicle does not go forward and the charging state was not achieved at 7000 seconds. Hence the vehicle comes to standby condition and simulation stops midway.
TEST CASE-3)
As per below configuration in test case 3 variant, all lights are turned green after working.
hence it shows that there is no any fault in total system.
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.
As per the above plots 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 is observed that:
1) 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.
2) 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.
3) 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.
Ans 2)- 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 SOC(t), which is estimated from the discharging current, I(t), and previously estimated SOC values, SOC(t-1).
But there are several factors that affect the accuracy of Coulomb counting method including temperature, battery history, discharge current, and cycle life.
From the given model by mathworks, as shown below of BMS closed loop model, when seen inside-
BMS ECU Block
In Coulomb counting block-
This system carries out the estimation by coulomb counting equation. The main advantage of coulomb counting is that of its simplicity and low computational cost. Temperature and current are taken as input from the battery. Current signal is given to the gain block and the temperature is given to capacity as it varies according to the temperature. These inputs are given to integration where current will be integrated with respect to time. This output is given to another block where it is divided by capacity and henceforth the SOC is estimated.
Challenge Conclusion:
The 3 test cases from harness dashboard simulated successfully along with the coulomb counting done by BMS for SOC estimation.