Project 2
Aim :
Using MATLAB/simulink and the drive cycle from the attached excel sheet, find-
- The max heat generation of the battery
- The SOC of the battery at 2 *104second of the battery operation
| Time | Time Step | Battery Current |
| 00:00.4 | 0.1 | -0.9632 |
| 00:00.5 | 0.2 | -0.952 |
| 00:00.6 | 0.3 | -0.9072 |
| 00:00.7 | 0.4 | -0.9632 |
| 00:00.8 | 0.5 | -1.0304 |
| 00:00.9 | 0.6 | -0.9632 |
| 00:01.0 | 0.7 | -1.0304 |
| 00:01.1 | 0.8 | -1.008 |
| 00:01.2 | 0.9 | -0.9856 |
| 00:01.3 | 1 | -0.9632 |
| 00:01.4 | 1.1 | -0.9184 |
| 00:01.5 | 1.2 | -0.9296 |
| 00:01.6 | 1.3 | -0.9296 |
| 00:01.7 | 1.4 | -0.9296 |
| 00:01.8 | 1.5 | -0.9184 |
| 00:01.9 | 1.6 | -0.9408 |
| 00:02.0 | 1.7 | -0.896 |
| 00:02.1 | 1.8 | -0.9072 |
| 00:02.2 | 1.9 | -0.9072 |
| 00:02.3 | 2 | -0.9408 |
| 00:02.4 | 2.1 | -0.9296 |
| 00:02.5 | 2.2 | -0.9296 |
| 00:02.6 | 2.3 | -0.9968 |
| 00:02.7 | 2.4 | -0.9968 |
| 00:02.8 | 2.5 | -0.9408 |
| 00:02.9 | 2.6 | -0.9408 |
| Battery resistance | 2 milli ohm |
Consider the battery resistance is 0.5 mOhm, delta time is 0.1 and entropic factor is 2
1. Heat Genration calculation
There are two heat sources for battery heat genration
A. Joule heat
B. Entropy heat
Heat genrated = Joule heat + Entropy heat
Let,
Joule heat = I^2*R*t
Note : Entropy heat is double of Joule heat.
now,
Battery resistance is 2 mohm
Max. Current is 1.0304
Max.heat genrated = Max.joule heat + 2*( Max.joule heat )
= 1.0304^2*0.002*2.9 + 2*( 1.0302^2*0.002*2.9 )
= 0.0061 + 0.0122
= 0.0183 Joule
2. The SOC of the battery at 2 *104second of the battery operation using simulink.
State of Charge (SOC):
The SOC is the level of charge of an electric battery related to its capacity. The units of SOC are percentage points (0% = empty; 100% = full). It is also defined as the ratio of remaining capacity to the fully charged capacity.
Depth of Discharge:
A battery's depth of discharge (DoD) indicates the percentage of the battery that has been discharged relative to the overall capacity of the battery. Depth of Discharge is defined as the capacity that is discharged from a fully charged battery, divided by battery nominal capacity.
SOC Estimation Methods:
- Voltage translation method
- Coulomb counting method
Voltage Translation Method:
The battery voltage (open circuit voltage) is used to determine the state of charge of the battery pack.The voltage translation method is used in applications like consumer electronics (battery bank, trimmer, torch light) and small energy storage systems. The LCD and LED are used to determine the SOC. The errors in voltage translation methods are voltage fluctuation, noise in the system and cell chemistry. So, it is not used in electric vehicles.
Coulomb Counting Method:
The SOC is estimated based on in and out flow of current in the battery pack.
Case 1: Estimating SOC that before charging SOC is zero%
Let’s assume that the battery capacity is 100 Ah. If we charge the battery with 4A current for four hours, then the total charge will be 4A x 4h = 16Ah.
SOC % = Total charge input / max battery capacity x 100.
= 16 Ah / 100 Ah = 16 % SOC
Case 2: Estimating SOC that battery already has 50% charge
Where,
z(0) - Initial SOC
Cn - Battery nominal capacity
z(t) - State of charge
i(t) - Instantaneous cell current
t - time
ni - Coulomb efficiency
Simulink model :
Above figure shows the simulink model for the measurment of SOC for the battery. The contolled current source used as load. The input signal is given to the this block.
Battery parameters :
Nominal Voltage : 7.2 V
Rated capacity : 0.5 Ah
Initial SOC : 10 %
Input Signal :
Following image shows the input signal which is made from given data, and given to the controlled current source.
Note : The battery capacity is taken as 0.5 Ah while intial SOC is 10 %
Result :
As we seen above image the intial SOC of the battery is 10 %, then we charge it with given values of current w.r.t. time then SOC becomes 21 %