Project 2 Thermal modeling of battery pack

AIM

The objective of the project is to create 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.

Matlab model

Simulink block

Battery - 10.

Bus selector - 1.

Scope - 4.

Go to - 3.

Display - 2.

Ideal switch - 2.

Mosfet - 2.

Chart - 1.

Constant - 3.

Relational operator - 2.

Volatge measurement - 1.

Product - 2.

DC volatge source - 1.

Clock - 2.

Power gui - 1.

Assumptions

Battery nominal volatage - 7.2 V.

Battery capacity - 5.4 Ah.

Region of operation - 40 - 80 % of SOC.

Rated load - 100 W resistive load.

Time - 0 to 1500 seconds

Battery 

Implements a generic battery model for most popular battery types. Temperature and aging (due to cycling) effects can be specified for Lithium-Ion battery type.

Bus selector

This block accepts a bus as input which can be created from a Bus Creator, Bus Selector or a block that defines its output using a bus object. The left listbox shows the signals in the input bus. Use the Select button to select the output signals. The right listbox shows the selections. Use the Up, Down, or Remove button to reorder the selections. Check 'Output as virtual bus' to output a single bus signal.

Goto

Send signals to From blocks that have the specified tag. If tag visibility is 'scoped', then a Goto Tag Visibility block must be used to define the visibility of the tag. The block icon displays the selected tag name (local tags are enclosed in brackets, [], and scoped tag names are enclosed in braces, {}).

Volatge measurement

Ideal voltage measurement. The Output signal parameter is disabled when the block is not used in a phasor simulation. The phasor simulation is activated by a Powergui block placed in the model.

Display

Display input values. If the incoming signal is of type string, the 'Numeric display format' parameter selection does not affect the display of the string.

Mosfet

MOSFET and internal diode in parallel with a series RC snubber circuit. When a gate signal is applied the MOSFET conducts and acts as a resistance (Ron) in both directions. If the gate signal falls to zero when current is negative, current is transferred to the antiparallel diode.

Relational operator

It is used to select the region for the discharge of the battery happens. The operator is used between a clock & a constant block where the greater than & less than operator is used to define the region of operation. 

Product

This block acts similar to that of the and gate which provides the optput when the both the state are true & since we have set the operating range of discharge from zero to 1500 seconds. The discharge happens only in this region.

Ideal switch

Switch controlled by a gate signal in parallel with a series RC snubber circuit.

In on-state the Switch model has an internal resistance (Ron). In off-state this internal resistance is infinite. The internal resistance must be greater than zero. The switch model is on-state when the gate signal (g) is set to 1. It gets two inputs one from the pulse which runs on the condition set depending on the SOC of the battery & the volatge source.

Chart

The region of the battery operating region is set by the chart & since the lithium ion battery for better operation need not to be fully discharged or charged which will affect the life of the battery so for safer limits the region is set to 40 - 80% of the SOC.

Voltage source

The DC voltage source is connect to first & tenth battery & the total voltage must be higher than the cummulative sum of the all the series battery.

Results

Current

i) @ 40 deg C

The initial SOC is set to 35% the current is positive when the battery is charging & during the discharge current is constant & the charging the current is constant & it becomes zero the charging.

ii) @ 60 deg C 

iii) @ 80 deg C

SOC

i) @ 40 deg C

The SOC increases from the 35 to 80% & the during the discharge the SOC reduces to 40%. The current is high during the initial state & then the SOC is constant curve & after reaching the 80% the SOC is constant since the discharge is set during the 0 to 1500 seconds. The battery discharge doesnt occurs since the 80% occurs after 2000 seconds so the discharge doesnt occur.

ii) @ 60 deg C 

The SOC increases from the 35 to 80% & the during the discharge the SOC reduces to 40%. The current almost becomes zero so the charging occurs very slow as the temperature increases. 

iii) @ 80 deg C

The SOC increases from the 35 to 80% & the during the discharge the SOC reduces to 40%. The current almost becomes zero so the charging doesnt occur during the higher temperature due to the low current.

Cell temperature

i) @ 40 deg C

The temperature keeps on increasing during the charging & the as the SOC reaches the 80% value. The temperature value reaches to around 50 deg C.

ii) @ 60 deg C 

The temperature keeps on increasing during the charging & the as the SOC keeps on increaing. The temperature value reaches to around 70 deg C & since the SOC doesnt reaches to the highest value the temperature keeps on decreasing.

iii) @ 80 deg C

The temperature keeps on increasing during the charging & the as the SOC reaches the 80% value. The temperature value is constant at 80 deg C & SOC doesnt raises has the current value is high.