Week 7 State of charge estimation

Aims:

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?

Theory:

here given in question

Matlab model to simulate the 3 test conditions from harness dashboard and to explain how BMS implements coulomb counting is as given below:

https://in.mathrks.com/matlabcentral/fileexchange/72865-design-and-test-lithium-ion-battery-management-algorithms

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

The Closed Loop Harness Dashboard model by Mathworks is as shown below.

To select one of the 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 variant was selected initially for the simulation which can be seen below.

the test variant as shown below, it states start of the simulation model in the driving condition, after 3000 seconds it will be in balancing mode, after 1000 seconds in charging and balancing mode and after 5000 seconds it will be in post charge balancing mode.

After simulating the model for 20000 seconds as given default.

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

plot the vehicle is initially driving state charging 90%. to the standby mode from the BMS state plot. From the Cell temperatures plot is observed in battery temperature rises in driving charging. The battery voltage was increased to 4.2 V while charging. The current value supplied to vehicle while driving. SOC decreased 50% in driving condition, which increased while charging.

Coming to the second variant condition to simulate.

The second variant simulates the below shown conditions.

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

the battery discharges completely in 8692 seconds vehicle does not go forward the charging state was not achieved 10000 seconds. the vehicle comes to standby condition and simulation stops midway.

Coming to the third condition.

at the condition third variant simulation. It continuous charging condition start till end of 20000 seconds of simulation.

the battery starts charging SOC starts increasing beginning to around 2000 seconds stable at 100% continuously from 2000 seconds until 20000 seconds. The peak current drops 0 to 2000 seconds and stays constant as the charge is not used anywhere as the driving is not present.

• From the above-mentioned three simulation variations, it was observed that, in the initial simulation, all three conditions were simulated—the driving, stable, and constant 100% SOC standby states of the vehicle.
  Second simulation: in the driving state at 8600 seconds, the SOC discharged at 0%, and the charging state was not achieved at 10,000 seconds.
  Third simulation: SOC remained 100 percent constant for the next 18000 seconds, with charging occurring only for the first 2000 seconds.

Part 2:How does coulomb counting work?Use the aforementioned model to explain how BMS uses coulomb counting to estimate SOC.
The Coulomb counting method incorporates the discharging current over time in order SOC and measures the battery's discharging current.SOC(t), which represents the estimated discharge current, I(t), and SOC(t-1) are the estimated SOC values.The following equation can be used to determine SOC:
The accuracy of the Coulomb counting method is influenced by a number of factors, including temperature, battery history, discharge current, and cycle life.

Modified Coulomb Counting Method The modified Coulomb Counting Method is a brand-new method that is proposed.current to increase estimation precision.
discharged current is corrected current.The quadratic relationship between the battery's discharging current and corrected current.
where k2, k1, and k0 are constants, the modified Coulomb counting method calculates SOC. The results demonstrate that the accuracy of the modified Coulomb counting method is superior to that of the conventional Coulomb counting method.

And then inside the SOC estimation block

where the Coulomb counting was carried out. The model for the same can be seen below.

The simplicity and low computational cost of this system are the main advantages of coulomb counting equation.Temperature and current from the battery as inputs.The gain block's temperature and capacity are determined by the current signal, which varies with temperature.integration of the given inputs at the present timecapacity SOC is estimated before output is divided into another block.