Project 2 Thermal modeling of battery pack
For a 10 cell series lithium ion battery model, simulate the thermal effects and compare life cycle performance at various temperatures, charge & discharge rates using MATLAB.
AIM:
For a 10 cell series lithium ion battery model is simulate the thermal effects and life cycle performance at various temperatures.
Theory:
This example shows how to simulate a battery pack consisting of multiple series-connected cells in an efficient manner. It also shows how a fault can be introduced into one of the cells to see the impact on battery performance and cell temperatures. For efficiency, identical series-connected cells are not just simply modeled by connecting cell models in series. Instead a single cell is used, and the terminal voltage scaled up by the number of cells. The fault is represented by changing the parameters for the Cell 10 Fault subsystem, reducing both capacity and open-circuit voltage, and increasing the resistance values.
It means that the battery is connected end to end. That is, the positive pole of the first battery is connected to the negative pole of the second battery, and the positive pole of the second battery is connected to the negative pole of the third battery, and so on.The series voltage is equal to the sum of the battery voltages, and the current is equal to the current flowing through each battery.A damage in one of the battery packs will cause the entire battery pack to be unusable or the voltage to drop. The series configuration is used where the voltage of a single cell is not sufficient. The series configuration is achieved by connecting the positive of a cell to the negative of another cell, as shown in the image below. The four lithium-ion cells of 3.6 V connected in series will give you 14.4 V, and this configuration is called 4S because four cells are connected in series.
Series connection can increase the total voltage.
SIMULINK MODEL:
Cell construction and working:
In this circuit we use lithium ion cell 1 to 10 Temperature sensor, ambient temperature block, convective block, state of charge, scope blocks of simulink.
Cell subsystem basically consists of a thermal model and liyhium cell 1RC block which calculate the temperature and thermal effect for cells and overall calculated for the battery. If one cell in series is faulty, cell matching is a challenge in an aging pack at the time of cell replacement. The new cell has a higher capacity than the others, which causes imbalance. That’s why battery packs are commonly replaced in units.
The block basically consists of capacitance value table which depends on an external physical signal inputs SOC and T. If it is assume that the capacitance value is slowly varying with time and hence the equation i = C*dv/dt holds.
Resistance value table which depends on an external physical signal output SOC and T.
BMS (Battery Management Systems) or its controller can determine the faulty battery by measuring the voltage at every point of the battery as shown below in the image. The one cell is faulty, which is giving 2.8 V instead of 3.6 V. Due to this, the battery voltage collapses, and the device will shut off sooner with a low-battery message. You can repair your battery pack by replacing this cell.
The 10 Cells is connected in series which is 1 to 4 is one batch and 5th cell is single and 6 to 10 is group of cells is connected.
The output one cell is connected with SOC estimation whereas other outputs is connected with AC current source for cyclic charge and discharge profile.
The below shown fig is AC current source in that peak amplitude is 50 Amps.
Convective Heat Transfer:
The Convective Heat Transfer block represents a heat transfer by convection between two bodies by means of fluid motion. The transfer is governed by the Newton law of cooling:
Q=k⋅A⋅(TA−TB),
onnections A and B are thermal conserving ports associated with the points between which the heat transfer by convection takes place. The block positive direction is from port A to port B. This means that the heat flow is positive if it flows from A to B.
Temperature Sensor:
The Temperature Sensor block represents an ideal temperature sensor, that is, a device that determines the temperature differential measured between two points without drawing any heat.
Connections A and B are thermal conserving ports that connect to the two points where temperature is being monitored. Port T is a physical signal port that outputs the temperature differential value.
The block positive direction is from port A to port B. The measured temperature is determined as T = TA – TB.
A Thermal conserving port associated with the sensor positive probe.
B Thermal conserving port associated with the sensor negative probe.
T Physical signal output port for temperature.State of Charge Estimation:
The above figure shows the Gain block parameter which is coloumb counting method measures the discharging current of battery and integrates the discharging current over time in order to esimate SOC.
The subsystem takes current as input and gives the battery SOC % as output A current sensor block is used and connected for SOC estimation.
Result:
The temperature is at 300 k that is 26.86 degrees c.
2. The temperatue is at 315 k 30.36 degrees c.
3. The Temperature is at 325 k 55 degrees c.
1. 1 to 4 cells are normal cells and 5th cell is faulty cell and 6 to 10 are normal cells as we are simulating the thermal effect on we give cyclic charge and discharge profile to circuit the waveform you can see in the above results all conditions is same but 5th cell was faulty the temperature is high than other cell. And life cycle of cell is reduced.
2. We give temperature of 300 k ie 26.85 degrees the 1 - 4 and 6-10 cell temperature is near to 316k.
3. In next condition the temperature is 315 k ie 30.36 degrees the 1-4 and 6-10 cells temperature is near 326k but the 5th cell temperature is goes to 345 k ie 66.3 degrees c and the drive cycle is shown which is cyclic charge/discharge drive cycle.
4. In other condition the temperature is 325 k that is 55 degrees c the 1-4 and 6-10 cell temperature is 330 k but the 5th cell temperature is at 80 degrees c and the drive cycle is shown which is cyclic charge/discharge drive cycle.
Conclusion:
We simulated the thermal effect and compared the life cycle performance various temperature, charge and discharge rates using MATLAB.