Project 2

Using MATLAB/simulink and the drive cycle from the attached excel sheet, find-

1. The max heat generation of the battery
2. The SOC of the battery at 2 *104second of the battery operation

Battery resistance

2 milli ohm

Consider the battery resistance is 0.5 mOhm, delta time is 0.1 and entropic factor is 2

1. The max heat generation of the battery:-

Heat Generation calculation

There are two heat sources for the battery heat generation

1. Joule heat
2. Entropy heat

The heat generated = joule heat + entropy heat

Joule heat

From ohm's law, V = IR

When a current is flowing through a resistance, there is heat dissipated in the resistor. This heat dissipation is called joule heating. Joule heating is also known as ohmic heating.

Power,

p= V*I = IR*I = I^2*R

Heat

H = intP.dt = int I*I Rt= I^2Rt

Joule heat

H = I^2*RT

Where, p= power

v = voltage

I= Current

R = Resistance

H = Heat

T = Time

The heat produced in a resistor is

• Directly proportional to the square of the current flowing through it.
• Directly proportional to resistance.
• Directly proportional to the time for which current flows through it.

Entropy heat

The heat generation due to entropy change inside a battery occurs when electrochemical reactions are performed. The entropy heat is reversible heat resulting from changes in open circuit voltage with respect to temperature at two electrodes

As entropic heat is twice the joule heat, the formula is

Average heat generated = Average joule heat +2(average joule heat)

Maximum heat generated = Maximum joule heat + 2(Maximum joule heat)

Average heat is calculated by taking the average value of current and time

average of time =1929/26=74.19sec

Average value of current =-24.7184/26=-0.9507

Therefore joule heat generated=I^2Rt=(-0.9507^2)*2*74.19=0.134Watt

Total Average heat generated=Joule heat+Entropy heat=0.134W+2(0.134W)=0.402 Watt

Maximum Heat Generation of the battery

The maximum current in the drive cycle is I = -0.896 at time t = 2 minutes(120 seconds)

Battery resistance = 2 milliohm

maximum heat generated =I^2Rt=(-0.896^2)*2*120= 0.192 Watt

The total heat generated =Joule heat+Entropic heat

= 0.192 W+2(0.192W)

=0.576Watt

The maximum Heat Generation of the battery is 0.576watt

2) The SOC of the battery at 2 *104 seconds of the battery operation.

The SOC refers to the State of Charge of the battery, which is the capacity percent left in the battery which can be used. It is a very important thing which teles about the battery status which helps in using the battery in a proper manner.

The SOC can be measured in different ways. Some of them are listed below

• Voltage Translation Method (VT)
• Coulomb counting method (CC)
• Combination of VT and CC

The VT and CC have their own advantages ad disadvantages so to get the accurate value we have to use the Combination of VT and CC.

Voltage Translation Method (VT):

It is measured by the Open circuit Voltage of the battery and compared it with the Datasheet of the battery and SoC is estimated. It cannot be used while the battery is in operation.

Coulomb counting method (CC):

It is calculated by the formula

SOC = total charge input / Max capacity of the battery

Total charge input = charge current * time (H)

Or

Z(t) = Z(0) - 1/Cn ∫ Ni*i(t) dt with the limits of 0 to t

where, Cn = Battery Nominal Capacity

Z(t) = State of charge

i(t) = Instantansous cell current

t = time

Ni = coulomb efficiency

Z(0) = initial state of charge

+ for discharging

- for charging

Due to Faid in the battery capacity over time it shows an error

Combination of VT and CC:

To avoid the calculation of SOC both the Voltage Translation Method (VT) and Coulomb counting method (CC) are used combinedly.

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

blocks used :

1) Battery :

Here we used the default values of the Li-ion battery.

2. Drive_cycle

3. Controlled voltage source

4. Resistance

5. Battery

6. Bus selector

7. Powergui

8. Scope

• The Drive_cycle is given as the input to the model.
• Here the drive_cycle stop time is 2*104 i.e 208sec, but given data is 156Sec
• so the simulation run time is 156sec
• Here the output of the drive_cycle is given to the current controlled source which is connected to the battery as a load
• so here the battery is discharged according to this signal given by the data.
• Here the powergui block is required for any simulation of the Simulink model.
• It is mainly used to store the equivalent Simulink circuit which represents the state space model.
• The output of a battery is given to the scope through the bus selector

Output results:

The above graph gives the results of SOC voltage and current

Here we operated the SOC of the battery at 156Sec

And we can also see how the SOC of the battery changes it mainly decreases from 100 to 94.5 and voltage also decreases

Result and Conclusion:

1. The max heat generation of the battery

The Max heat generated in which the current flows in and out i.e., charge and discharge due to internal resistance and chemical reaction during charging and discharging of the battery the heat is generated of 0.576 Watt

2. The SOC of the battery at 2 *104second of the battery operation: but given data is 156 Sec