Project 1

Aim:

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

Calculations:

To design the battery pack we need cells which are connected in series and parallel to meet the requirment. The required condition - 120v and 150kW

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: In series connection the voltage multiplies. Hence to get the no of cells in series with nominal cell value of 3.6 v to meet 120v, we must do the following

Number of cells in series = required voltage / Nominal voltage of the cell

Number of cells in series = 120/3.6 = 33.33

We need 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 nominal 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

Nominal voltage of battery should not exceed the Load voltage (120v)

Max Voltage of battery should be less than the Load Max Voltage

Min Voltage 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

Therefore Number of cells in series = 33

Output total voltage 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 / cell capacity

Number of cells in parallel = 1,250Ah / 3.5Ah = 357.14

We have to round off to lower value and higher value

Case-1) Round off to lower value = Number of cells in parallel = 357

Case-2) Round off to higher value Number of cells in parallel = 358

The output capacity = cell capacity * number of cells in parallel

	Number of cells in Parallel	total Capacity(Ah)	Required current
Case - 1	357	357*3.5 = 1,249.5	1250
Case - 2	358	358*3.5 = 1,253	1250

We can round off to higher value = 358

The output capacity = each cell capacity * number of cells in parallel = 358*3.5 = 1,253 Ah

The number of cells in Parallel = 357

The Output Capacity will be 1,253Ah

The Current can be limitted to requied value by using current limiters.

BMS topology:

Topology Adaption:

1. Since 18 cells are in connected in series

2. Large energy storage: 150kW but less than 1Mega Watt

considering above scenario, we adopt Master slave topology with following configuration

1. cell pack 1= 17 cells in series

2. cell pack 2= 17 cells in series