Week 7 State of charge estimation

AIM:

1. Simulate the 3 test cases from the 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. 

PROCEDURE:

1.

The above model is called the closed-loop harness model. It has three test cases which are executed below. The model holds the Test sequence variant to change the test cases and Lamps are connected to show the execution.

TEST CASE 1:

Here, test case 1 is been verified. The model has been run for 20000 seconds and the results are plotted.

The Test case is to execute the below criteria:-

• Driving for 3000 seconds
• Balancing for 1000 seconds
• Charging and balancing for 5000 seconds
• Post charge balancing for later.

 

The results plotted are for Cell voltages, cell temperature, SOC, Pack Current, and BMS state. The Plot shows that the vehicle is initially in a driving state. Then it was charged in Constant Current constant voltage mode. Afterwhich it was in standby mode. While driving, the battery reached the SOC of 45%, and then while charging, it reached 98%.

TEST CASE 2:  Driving for 10000 seconds.

the 

second case is to drive for 10000 seconds and later charged.

the graph shows that for 10000 seconds the system is in a driving state, the SOC of the system is continuously decreasing and the temperature is increasing simultaneously.

TEST CASE 3: The condition is to continuously charge.

the plot shows that system is continuously in charging mode, reaching 100% and moving to stand down. Temperature increases while charging and after reaching the standpoint, it decreases gradually.

2. 

Algorithms used for SOC and SOH Estimation are:

1. Coulomb counting, OCV
2. Kalman filter

Coulomb Counting:

The coulomb counting method, also known as ampere-hour counting and current integration, is the most common technique for calculating the SOC. This method employs battery current readings mathematically integrated over the usage period to calculate SOC values given by

where:

• SoC(t) = estimated State of Charge at time, t
• SoC(t-1) = previous State of Charge at time t-1
• I(t) = charging or discharging current at time, t
• Q_n = battery cell capacity
• Δt = time step between t-1 and t

 The coulomb counting method then calculates the remaining capacity simply by accumulating the charge transferred in or out of the battery. The accuracy of this method resorts primarily to a precise measurement of the battery current and an accurate estimation of the initial SOC.

The above model shows the charge estimation for the SOC.

The Current and Temperature is taken as input to the model. The Current multiplied with gain and the Temperature has wide range of capacity , so it is given to the capacity block. The temperature and the Current are given to the integrator block and integrated with respect to time. Thus the SOC is analysed from the block diagram.