Project 2 Thermal modeling of battery pack

Objective:- 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.

Result:- 

Introduction:- 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.

We have taken the same model but decresed no of cells. Instead of no of cell which was 20 we have made it 10 cells. Also we have done some modifications in the model which will be discussed one by one.

Simulink model:- 

So here as we can see we have used 10 cells of lithium ion battery using matlab and simulink to find the thermal effect and life cycle performances related to temperature, charge and discharge and also conduction and convection blocks are used to show how the heat transfer takes place in battery packs. 

This model also shows how a fault can be introduced into one of the cells to the impact on battery performance and cell temperature. For faulty cells just we have increased the resistance value of the cell and increased the capacity and open circuit voltage. 

Connection:- 

10 lithium cells are connected in series with three segments. In first segment we have used 1-4 Cells. In the second segment we have used the faulty one which is 5th cell and the third segment we have used cell 6-10.

The heat transfer is observed between the cells by heat transfer blocks which is conduction and convection blocks.

Ambient temperature source is attached with temperature sensor to show the value also installed the display. 

The battery pack is connected to AC current source to observe the cyclic charge and discharge rate graph. Also we added a current sensor between the battery pack and the AC current source to calculate the SOC of the battery.

Also all three segments cells temprature is showing in the scope. 

Cell 1_4 Subsystem:- 

The cell subsystem basically consist of a thermal model and lithium cell 1RC block which calculate the temperature and thermal effect for cells and overall calculate the battery pack. 

We have used PS gain block which multiplies the input physical signal by a constant y=u*gain, Another block are voltage sensor and voltage source. 

The voltage sensor block represents an ideal voltage sensor. This is a device that converts voltage measured between any electric connection into a physical signal propotional to the voltages. 

The voltage source represents an ideal voltage source that is powerful enough to maintain the specified voltage at its output regardless of the current passing through it.The output voltage is V=Vs, Where Vs is the numeric value represents at its physical signal port.  

For this thermal model we have used some blocks which are Thermal reference, Controlled themrature source, Thermal mass, Themrature sensor etc.

• In the controlled temprature source we have three ports. Which is A, B and S. Where port A & B work as a source inlet and outlet. Port s is the physical signal port. 
• The thermal mass block represents a thermal mass which reflects the ability of a material or a combination of material to store internal energy. The property is charcterized by the mass of the matarial and its specific heat. the thermal mass is described with the following equation.  Q=c.m*dT/dt
• Themrature sensor block represents an ideal temprature sensor a device that determines the the temprature differential measured between two points without drawing any heat.  

Lithium Cell 1RC subsystem:- 

• In this subsystem basically capacitor value table which depends upon an external physical signal input SOC and T. It is assumed that capacitor value is varying with the time and hence the equation i=CdV/dt holds. 
• Resistance value R table depends an external physical signal inputs SOC and T.
• Voltage value EM implement the cell main branch voltage source determine value for capacity(C) and state of charge.The defining equation depends on cell temprature T.

For cell 1_4:- 

In this cell configuration we have used 4 nos in series. 

Initial temperature is 293.1K.

For Cell 5:- 

• For this segment we have only one cell which is cell no 5, Where we have declared it as a faulty cell. 
• Initial temperature is 293.1K.

In the electrical parameter we have changed some value to make it faulty cell.

• Capacity reduced by 0.95 factor.
• Open circuit voltage reduced by 0.9 factor.
• Terminal resistance increased by 5 factor.
• Cell resistance increased by 5 factor.
• Capacitance reduced by 0.95 factor. 

For cell 6_10:- 

• Here we have 5 nos cells are connected in series to make configuration of the setup.
• Initial temp is 293.1K.
• All parameters are same as Cell 1_4.

Temperature source:- 

This block represents an ideal source of thermal energy that is powerful enough to maintain a specified temperature at its outlet regardless of the heat flow consumed by the system. 

The source generates constant absolute temperature defined by temeprature parameter value. 

Here for the ambient temperature block used 293.1K. 

Conductive heat transfer:- 

The Conductive Heat Transfer block represents a heat transfer by conduction between two layers of the same material. The transfer is governed by the Fourier law and is described with the following equation:

where