Week 7 State of charge estimation

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

Closed Loop Harness Dashboard model by mathworks is as shown below.

To select one out of 3 test conditions , it can be selected via the test sequence Variant block which allows you to select which test needs to be simulated.The first one which can be seen below.

1st variant:

As we look at the test variant as shown below, it states that at the begining of the simulation the model will be in the driving condition,thereafter , 3000 sec it will be in balancing mode, after 1000 sec it will be in charging and balancing mode and after 5000 sec it will be having post charge balancing mode.

After simulating the model for 20000 sec as given as default.

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

It can be observed from the plot that the vehicle in the beginning, driving state and charging was done till 90%.After the charging mode it will reaches to the standby mode which can be seen from the BMS state plots. From the cell temperatures plot it is considered that the battery temperature increases in driving and charging. The battery voltage was rises to 4.2v 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 will increased while charging.

2nd variant:

The second variant simulates the below shown conditions.

Initially ,it is the driving condition and after 10000 sec there we can observe charging condition.

It was observed from the plot that the battery discharges completely in 8692sec and the vehicle does not go forword and the charging state was not acheived at 10000sec.Hence after this the vehicle comes to standby condition and simulation stops midway.

3rd variant condition:

Looking at the condition below for third variant of the simulation.It is just the condition charging condition from the start till the end of 20000 sec of simulation.

Looking at the plot we can seen that the battery starts charging and the SOC starts increasing from starting to around 2000 sec and stays stable at 100% continuously from 2000 sec untill 20000 sec.The peak current plot drops from 0 to 2000 sec and stays constant as the charge is not used there.

From the above simulated 3 variants of the simulation carried out it was observed that,

In the first simulation all the 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 stanby state of the vehicle.

In the second simulation it was just the dischrge as the SOC dropped to 0% in the driving state within 8600 sec and the charging state was not achieved at 10000sec.

In the third simulation, only charging was observed for the first 2000sec and the SOC remained at 100% constant for the next 18000 sec..

Part 2:

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

It measures,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 previous estimated SOC values,SOC(t-1).SOC is calculated by the following equation:

But there are several factors that affect the accuracy of Coulomb counting method includes temperature and battery history,discharge current and cycle life.

From the given model by Mathworks as shown below of BMS Closed loop model,when we seen inside the BMS ECU,

This is inside the SOC estimation block

This system carries out the estimation by coulomb counting equation 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 andCurrent 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.

Conclusion:

Hence BMS implements coulomb counting for SOC estimation is done