Project 1

1. ANSWER

Aim:
To design the battery pack with the capacity 150Kw 120V by using 3500mAh 3.6V with BMS topology for the battry pack.

In order to design the battery pack we need cells configuration which are connected in series and parallel to meet the requirment.

Given:
Required Rating Capacity = 150Kw
Required Rating Voltage = 120 V
Nominal cell capacity = 3500 mAh=3.5 Ah
Nominal cell voltage = 3.6V

First convert the battery capacity 150Kw to Ah

Capacity (in Ah) = Power (in kW) / Voltage (in V)
So, the capacity required for the battery pack would be:
Capacity = 150,000 / 120 = 1250 Ah.
And Voltage are 120 V.

Series:
Number of cells in series = (Required voltage or Rating 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

Total volatge = nominal votage of cell * number of cells in series

The condition to choose the number of cells are-

1. Nomial voltage of battery should not excide the Load volatge
2. Max Volatge of battery should be less than the Load Max Volatge
3. 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
There fore Number of cells in series = 33
Output total volatge will be 118.8V
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 or Rated Capacity)/ cell capacity
Number of cells in parallel = 1,250 / 3.5= 357.14
We have to round off to lower value and higher value
The output capacity = cell capacity * number of cells in parallel

We can round off to higher value = 358
The output capacity = each cell capacity * number of cells in parallel = 358*3.5 = 1,253Ah
The number of cells in Parallel = 358
The Output Capacity will be 1,253 Ah
The Current can be limitted to requied value bu using current limitters.

Now the battery pack is made of 33S358P pack so that it can meet the required output of 120v,1250Ah or 120V 5Kw.
As the number of cells in series and parallel are very high which makes manufacturing difficult. So, we need to divide it into sub battery packs and remake the connections to get the requried output.

As the BMS Supports the max 18 cells in series so we need to divide the 33 sereis cells to 18 cells series sub battery pack which leads to 2 series es sub connections one with 18 and another with 15.

For each sub pack, 51 parallel cells must be created in order to create a compact parallel connection.

Total result in 2 sub battery packs in sereis one with 18 cells in series and another with 15 cells in series and 7 sub battery pack in parallel each with 51 cells in parallel and any one with 52 to meet the requirment 33S358P.



Block diagram:
• The series connection is indicated by the back line.
• The parallel connection is indicated by a blue line.
• 33S51P is created by series-connecting each 18S51P pack with each 15S51P pack.
• When all seven 33S51P (18S51+15S51) are joined in parallel, 33S358P is produced.
• In order to meet the need for 33S358P, one parallel connection is increased in the last pack's sub-pack, which contains an 18S52P series with a 15S52P pack.

(B) Battery Management Sytem (BMS):
BMS Topology used in this battery pack is Master and Slave BMS Topology. 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 14 and a Master controller which can handel 14 slaves.


The BMS blocks built with three 18-cell slave controllers that are AFE, and they transform the analogue output from the battery's voltage sensor into a digital signal. As depicted, there are two slaves connected in series. Slave-1 will collect data from module-1 and pass it to slave-2, who will then collect data from module-2. Slave-2 then combines the data from slaves-1 and 2 and sends it all to the master controller, which is an MCU. It manages the battery pack in accordance with the protocols that the MCU is provided.
We can also use the combination of 7 Master and slave BMS i.e., 2 slaves 18S358P and 15S358P and a master controller of 7 numbers. All master control will have one single controller or all 7 master controllers can be directly connected to the MCU. But it's a costly and complicated process.

Conclusion:
The battery pack was made to design as 33S358P divided into sub battery packs which is combination of 18S51P series with 15S51P, this combination is paralled with 7 copies as shown above toatl results in 33S358P with capacity of 150Kw with 120V.
To charge and discharge the Total battery pack Master and Slave BMS topology is used which is efficient in all ways like cost, design,control and instalation.