Project 2

Aim: To calculate the SoC% and maximum heat generated by the battery according to the given drive cycle and considering the given specifications using MATLAB/Simulink.

Theory:

Lithium Ion Batteries are new era of energy storage applications, Although it has its own flaws, due to its high energy density it is very popular now a days. Lithium Ion batteries have many chemistries, one of them is LiFePo4 which most commonly used.

The Li ion battery exhibits the heat whenever charging and discharging So, To calculate the heat generated in the battery we use the following formula

Formula:

Heat Generation = Joule Heat + Entropic Heat

Joule Heat = i^2 X r X t

Where, t = time (sec/hr)

i = battery current (A)

r = resistance (mohm)

these two types of heats are generated in the battery

The Joule heat is also known as ohmic heat because it is generated depend upon the current resistance of the battery with respect to time

Joule heat is given by

The entropic heat is commonly taken as entropic factor of 2

which means

By these two heats calculated we can calculate the heat generated in the battery

The Maximum Heat generated by the battery is given by

here Maximum Joule heat is given by

where

Hmax">Hmaxis maximum Joule heat

Imax">Imaxis maximum current

Rbattery">Rbatteryis internal resistance of the battery

t is the time were maximum current occurred

a) Calculating the maximum heat generated

Maximum current=-0.896

Maximum current time =120 sec

battery resistance=0.5mohms

Entropy factor=2

Maximum joules heat=

=(-0.896)^2*0.5*120)=48mj

Maximum heat generated=maximum joules heat+entropy factor=48+2=50mj

b) The SOC of the battery at 2 *104second of the battery operation

Now coming to State of charge of the battery which is so important in which state of charge is given by

SoC = Current capacity /Nominal capacity

but if we are having the current state of charge we have to use the Coulomb count method

The Coulomb Count Method is given by

were

Cn">Cnis battery nominal capacity

Z(t) is state of charge

i(t) is instantaneous current

t is time

ni">niis Coulomb efficiency

by this we can calculate the state of charge of the battery

Now let us design the battery model in Simulink to calculate the SoC% and current in the battery

Simulation Diagram:

SoC% Calculation for 208 seconds

The generic battery with 7.2V, 5.4Ah is connected to a Controlled current source with the current reference from the signal builder block in which the signal builder block is loaded with the currents with respect to time values from the given table. The simulation run time is set to 208 seconds.

Output of SOC%and Current

We can observe that the SOC% is discharging and charging in the above output by its simulink model connectivity .The positive symbol of the battery is connected controller current source negative and negative of the battery is connected to the positive of controlled current source and the controoled current source is connected to the signal builder to check the battery operation for 208 seconds

As we can see the both charging and discharging the SOC has been decreased only 1% of the battery as we can observed and also my drive cycle has been shown for the 208seconds as required.

Conclusion

A Battery model is designed in the Simulink with the given currents data and given specifications, Calculated SoC% for 208seconds of simulation run time, and also Calculated Maximum heat generated in the battery.

ariation also takes place, i.e. , For 1st drive cycle source SOC% = 91.8% and for 2nd drive cycle

source SOC% = 96.4%

Battery parameters:

Bus selector:

Resistance:

Drive cycle source:

Given drive cycle can be Import in MATLAB Workspace in a following manner,

1] First we to have prepare excel sheet with time and current values. Which is sown below,

2] Import this excel sheet in a MATLAB workspace.

3] Result in Command window will now look like as shown below.