Week 7 State of charge estimation
Aims:
- Simulate the 3 test cases from the harness dashboard and write a detailed report on the results.
- What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation?
Theory:
here given in the question
Matlab model to simulate the 3 test conditions from harness dashboard and to explain how BMS implements coulomb counting is as given below:
Part 1: Simulate the 3 test cases from the harness dashboard and write a detailed report on the results.
The Closed Loop Harness Dashboard model by Mathworks is shown below.
To select one of the 3 test conditions 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, states the 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, a 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 the vehicle while driving. SOC decreased 50% in driving conditions, 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 a charging condition.
the battery discharges completely in 8692 seconds vehicle does not go forward the charging state was not achieved in 10000 seconds. the vehicle comes to standby condition and the simulation stops midway.
Coming to the third condition.
at the condition third variant simulation. Its continuous charging condition starts at 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 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 was observed that,
- first simulation all three conditions were simulated driving charging and stable state hence charging and discharging in end constant 100% SOC standby state of the vehicle.
- second simulation discharging SOC dropped 0% in driving state 8600 seconds charging state not achieved at 10000 seconds.
- third simulation, only charging observed for first 2000 seconds SOC remained 100% constant, next 18000 seconds.
Part 2: What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation?
The Coulomb counting method measures discharging the current battery and integrates discharging current over time in order SOC. Coulomb counting SOC(t), which is estimated discharging current, I(t), estimated SOC values, SOC(t-1). SOC is calculated by the following equation:
several factors affect the accuracy Coulomb counting method including temperature, battery history, discharge current, and cycle life.
Modified Coulomb Counting Method
Coulomb counting method a new technique called the modified Coulomb counting method is proposed. current to improve the accuracy of estimation.
corrected current is discharging current. The quadratic relationship between the corrected current and discharging current of the battery.
where k2, k1, and k0 are constant values
In the modified Coulomb counting method, SOC is calculated
The results show accuracy modified Coulomb counting method is superior to the conventional Coulomb counting method.
BMS Closed Loop model, seen inside the BMS ECU,
And then inside the SOC estimation block
where the Coulomb counting was carried out. The model for the same can be seen below.
This system carries the coulomb counting equation main advantage of coulomb counting of its simplicity and low computational cost. Temperature and current as input from battery current rent signal are given to gain b ck temperature is given capacity it varies according to temperature. in ts given integration current integrated wrt time. output is to another block is divided capacity SOC is estimated.
Conclusion:
The 3 test cases the from harness dashboard were simulated and discussed successfully along with the coulomb counting done by BMS for SOC estimation.