Project 1
- Design a battery pack for a car roughly 150 Kw with 120 V. Use 3500 mAh 3.6V nominal NMC chemistry cell.a
Let us concider the cells with
Nominal voltage = 3.6v
Capacity = 3500mAh = 3.5Ah
To meet the requirment of 120v and 150Kw, we need to find the number of cells connected in series and parallel.
First convert the battery capacity 150Kw to Ah
Amper hour = Watt hour / Voltage
Amper hour = 150*1000 / 120 = 1,250 Ah
SERIES
Number of cells in series = required voltage / Nominal voltage of the cell
Number of cells in series = 120/3.6 = 33.33
We have to round off to lower value and higher value
Case-1) Number of cells in series = 33
Case-2) Number of cells in series = 34
Total volatge = nominal votage of cell * number of cells in series
|
Number of cells in series |
total voltage |
Requred voltage |
|
|
Case – 1 |
33 |
33*3.6 = 118.8 |
120 |
|
Case – 2 |
34 |
34*3.6 = 122.4 |
120 |
The condition to choose the number of cells are
- Nomial voltage of battery should not excide the Load volatge
- Max Volatge of battery should be less than the Load Max Volatge
- Min Volatge of battery should be greater than the Load min Voltage
We have to round off to lower value so that it will not excide the required value
NO.OF. CELL IN SERIES = 33
OUTPUT TATOL VOLTAGE = 118
The output voltage can be adjusted to 120v by a Buckboost converter to meet the requirment of 120v
Parallel
Number of cells in parallel = required capacity / cell capacity
Number of cells in parallel = 1,250 / 3.6 = 347.22
We have to round off to lower value and higher value
Case-1) Round off to lower value = Number of cells in series = 347
Case-2) Round off to higher value Number of cells in series = 348
The output capacity = cell capacity * number of cells in parallel
|
Number of cells in Parallel |
total Capacity(Ah) |
Requred voltage |
|
|
Case – 1 |
347 |
347*3.6 = 1,249 |
1250 |
|
Case – 2 |
348 |
348*3.6 = 1,251 |
1250 |
We can round off to higher value = 348
The output capacity = each cell capacity * number of cells in parallel = 348*3.6 = 1,251Ah
THE NUMBER OF CELLS IN PARALLEL = 347
THE OUTPUT CAPACITY WILL BE 1251Ah
The Current can be limitted to requied value bu using current limitters.
BMS Topologi used in this battery pack is Master and Slave BMS Topologi. Because the total battery pack is made of sub battery packs so controlling and manufacturing will be easy.
Master and Slave BMS which has number of slave controllers are 16 and a Master controller which can handel 16 slaves. 
It consisting of input sensors of volatge,current and temperature. The voltage sensor analog signal is converted to digital signal by AFE, the current sennsor analog signal is converted to digital signal by the MCU or we can connect the ADC converter between the Current sensor and MCU, the temperature sensor analog signal is converted to digital signal by the MCU or we can connect the ADC converter between the Temperature sensor and MCU. The Realy module control the Realy which make or brack the circuit by the command given be the MCU. The CAN and RS485 are Communication protocalls to the Outside world.
The Blocks inside the red line are the BMS blocks. It isdesigned with the three 18 cell Slave controller which is AFE, it converts the anolog signal from voltage sensor in the battery to Digital signal. The 3 Slaves are connectes in seres as shown, the salve-1 will collect the data feom module-1 and send to slave-2, slave -2 will collect the data from module-2 , now the salve -2 consisting the data of slave-1 and 2 and it sends the both the data to slave-3, the save-3 will collect the data from module-3, now the slave-3 consisting the data of slave-1,2 and 3, like continues for all 16 slaves and at last all the data is send to Master controller which is MCU. It control the battery pack according to the protocals which is given to MCU.
Note that all the slave have a capacity of 18 cell series connection even though half of the sub battery packs have only 15 series cell besuse if we want to upgrade the capacity we can do by increasing Ah of battery pack i.e., by incresing the number of series cells. It makes easy to upgrade the battery pack but in a limitted way.
We can also use the combination of 8 Master and slave BMS i.e., 2 slaves 18S52Pa and 15S52P and a master controller of 8 numbers. For all master control will have one single controller or all the 8 master controllers can directly connected to the MCU. But its costly and complicated process.
- Build a 3S2P battery pack configuration with generic battery block using Matlab/Simulink.
- 3S means 3 cell should be connected in series
- 2S means 2 cell should be connected in parallel
3*2 = 6 cells
STEP-1
PARALLEL CONNECTION:
- Batteries are connected from connected to same terminals of the other batteries that is positive terminals (+) of the one battery connected with positive (+) and negative terminals connected with other battery negative terminals(-).
SERIES CONNECTION
- One battery positive terminals(+) with another battery negative terminals(_-)
MODEL DIAGRAM
This parameters are inside the battery block diagarams
- Nominal cell voltage = 7.2 V
2 .Rated capacity of the cell = 5.4 Ah
- Maximum voltage of the cell = 8.3 V
Nominal voltage of the battery pack = no. cell in series* nominal voltage of the cell
=3*7.2= 21.6 v
Rated capacity of the battery pack = no. cell in parallel* rated capacity of the cell
=2*5.2Ah=10.4Ah
This model is 21.6v and 10.4Ah
SOC
- The state of charge (SOC) is started to reduce from 100% corresponding to load
CURRENT
The current signal is determined by load and decrease in current is due to regenerative braking
VOLTAGE
The voltage is around 8.3 v . the increasing and decreasing voltage is respect to regenerative braking
