Challenge

Week 7 State of charge estimation

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

ANSWER:-

By using the BMS model we take the closed loop harness dashboard model taken into account for our test cases.

for doing the test cases we select the test sequence variation block which allows us to select which test needs to be simulated.
The first variant was selected initially for the simulation which can be observed by below fig.

As we look at the test variant from the fig shown below , it states that at the start of the simulation of the model will be in the driving condition, thereafter after 3000 secs it will be in balancing mode, and after 5000 secs it will be in post charge balancing mode.

Here from scope results we can see all lights have turned green as there is no fault or errors in the model.

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.

Coming to the second variant condition to simulate. we select the test case 2:-

Initially it is the driving condition and after 10000 secs there is charging condition.

Here we can observe that from the pilot that the battery discharges completely in 8692 secs and the vehicle does not go forward and the charging state was not achieved at 10000 secs .
hence the vehicle comes to standby condiion and simulation stops midway.
After we move to test case 3 :-

By looking at the condition below for third test sequence of the simulation . it is just the continuous charging condition from the start till the end of 20000 secs 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 it stays stable at 100%continuously from 2000 seconds until 20000 seconds. The peak current plot drops from O 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 dr iving 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 dr iving 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 secs

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

ANSWER:-

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,l(t),and previously estimated soc values,soc (t-1).
soc is calculated by the following equation:

SOC (t) = SOC (t - 1) + (I (t) / Q(n)) *delta(t)

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.
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 and ko are constant values obtained from the practice experimental data.

In modified Coulomb counting method,SOC is calculated by the following equation:

SOC (t) = SOC ( t - 1) +( Ic(t) /Qn) (delt)*t

The experimental results show that the accuracy of the modifiedCoulomb counting method is superior to the conventional Coulomb counting method [l ].
From the given model by Mathworks as shown below of BMS Closed Loop model,when seen inside the BMS ECU.

And then the soc estimation block should open.

The coulomb counting block can be observed on the top of the model, where the coulomb counting was carried out. The model for the same can be seen below.

This system carries out the estimation by coulomb counting equat ion mentioned earlier. 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 wrt time. This output is given to anotherblock where it is divided by capacity and henceforth the SOC is estimated.

Conclusion:

The 3 test cases from harness dashboard were simulated and discussed successful ly along with the coulomb counting done by BMS for SOC estimation.

Ship work like this
in your own course.