Project 1

Design a battery pack for a car roughly 150 Kw with 120 V. Use 3500 mAh 3.6V nominal NMC chemistry cell.

1. Design the battery pack configuration.
2. Draw the BMS topology for this battery pack.

Ans:

Given;

Power = 150 kW

Voltage = 120 V

Capacity = 3500 mAh = 3.5 Ah

Nominal/single cell voltage = 3.6 V

Then, the no. of cells in series = Total voltage/single cell voltage = 120/3.6 = 33.34 = 34 cells.

Power = V*I

I = Power/Voltage = 150000/120 = 1250 A

No. of cells in parallel = Current/Capacity = 1250/3.5 = 358 cells

So, there are 34 cells in series and 358 cells in parallel

ie, the battery pack configuration is 34S 350P.

BMS topology :

As there are about 34 cells in series in the battery pack, we have to use Master-Slave topology as the BMS topology in which Master/slave is a model of communication for hardware devices where one device has a unidirectional control over one or more devices. This is often used in the electronic hardware space where one device acts as the controller, whereas the other devices are the ones being controlled.

Here, a master controller is connected to 2 slave controllers with their respective AFEs , where the first slave controller is having 18 cells (maximum cells that can be connected to an AFE) and the second controller is having 16 cells.