Project 2 Thermal modeling of battery pack

THERMAL MODELLING 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.
• This model will tell about how the temperature is spread among the battery cells when they are connected in series and how they perform at different ambient temperatures.
• The cells are connected in series and are placed in 3 packs. The first pack has 4 cells (1 to 4), the second pack has 2 cells (5 & 6), and the third pack has 4 cells (7 to 10).

ABOUT THE MODEL:

• By using MATLAB and Simulink the model is made to measure the temperature of the cells.
• The cells are connected in a series of three different packs by connecting them to a cyclic discharge profile.
• To measure the temperature of three different packs, three thermal sensors are connected to each of the packs.
• To measure the heat transfer rate block, an ambient temperature block, conduction heat transfer block are connected.

AC CURRENT SOURCE:

• The AC source represents a uniform current source that maintains a sinusoidal current source through it.

• It is independent of the voltage across its terminals.

SUBSYSTEM BLOCK:

• The subsystem block which contains a subset of blocks inside the model or a system.

• The subsystem block consists of a virtual subsystem or a non-virtual subsystem.
• It has two ports an input port and an output port.

CONDUCTIVE HEAT TRANSFER BLOCK:

• It is a thermal element located in the Simulink library.

• The block represents the conductive heat transfer between two layers of the same material.
• The conduction heat transfer is governed by the Fourier law.
• The port A and B are thermal conserving ports associated with two material layers.
• The port positive direction is from A to B.

CONVECTIVE HEAT TRANSFER BLOCK:

• It is a thermal element block which is located in the Simulink library.

• The block represents the convective heat transfer between two bodies by means of fluid motion.
• The motion of the heat transfer is governed by Newton laws of the cooling equation.
• The block positive direction is from port A to port B. The port A and B are conserving ports associated with the heat transfer taken by convection.

TEMPERATURE SOURCE:

• A constant source of thermal energy which is characterized by temperature.

• The Temperature Sourceblock represents an ideal source of thermal energy.
• This is enough to maintain a specified temperature at its outlet regardless of the heat flow consumed by the system.

SCOPE:

• A scope block is used to display the time domain signals which are related to simulation time.

• Scope blocks give multiple signals, multiple plots, simulation control, and modify parameters, auto-scaling of the axes.

RESULTS:

• The results are taken at five different ambient temperatures for 10 batteries.
• The corresponding max temperature of the batteries and the plots are specified in the following discussion.
• In the model, the ambient temperature is changed to see the relative rise in the pack temperatures of the batteries.
• The ambient temperatures are taken in the range of 10 and those are given as 293k, 303k, 313k, 323k, 333k.
• At different ambient temperatures, cells are plot. The individual maximum temperature for three different packs is given in the table:

Ambient temperature in (K)	Cells (1 – 4) in K	Cells (5&6) in K	Cells (7 – 10) in K
293	312	313	312
303	322	323	322
313	332	333	332
323	342	343	342
333	352	353	352

1. There is a slight increase in the temperature of the middle cells of the three packs because of the less area of the middle cells.
2. Due to less area, more amount of temperature is absorbed at the middle cells of the battery pack.
3. So, this is the reason why the middle battery pack is slightly higher than that of the surrounding temperature cells.
4. A clear picture is given in the Fig f where the middle cells are having slightly higher temperature when compared to the surrounding cells in the battery packs.
5. The orange line in the plot shows the maximum temperature that is attained by the middle cells of the battery pack.
6. Due to less area and the heat is transferred from the surrounding cells to the middle cells there is a slight increase in the middle cells of the battery pack.

fig a:	fig b:
fig c:	fig d:
fig e:	fig f:
Fig a: when the ambient temperature at 20oc. Fig b: when the ambient temperature at 30oc. Fig c: when the ambient temperature at 40oc. Fig d: when the ambient temperature at 50oc. Fig e: when the ambient temperature at 60oc. Fig f: maximum values obtained by the batteries at different ambient temperatures.