Project 1

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

a. Design the battery pack configuration.

b. Draw the BMS topology for this battery pack.

ans:

Cell Specifications:

Nominal Voltage= 3.6V

Max. Voltage= 4.2V

Nominal cell capacity= 3500mAh = 3.5 Ah

Rated power=150kw

Rated voltage=120v

First finding the motor current= (rated power *1000)/rated voltage

= (150*1000)/120

=1250A

Number of cells in series = total voltage /cell nominal voltage

Assuming the max voltage as the total voltage

Number of cells in series = 120 /3.6

Number of cells in series = 33.33

Rounding off the number of cells in series depends on

• Maximum voltage
• Minimum voltage

Test-1

Rounding off 33.33 to 33

Nominal battery voltage = cell nominal voltage * 33

= 3.6 * 33 = 118.8V

Maximum battery voltage = cell max voltage * 1

= 4.2*33 = 138.6 v

Minimum battery voltage = cell minimum voltage * 1

= 2.7 *33 =89.1V

Test-2

Rounding off 33.33 to 34

Nominal battery voltage = cell nominal voltage * 34

= 3.6 * 34 = 122.4V

Maximum battery voltage = cell max voltage * 2

= 4.2*34 = 142.8v

Minimum battery voltage = cell minimum voltage * 2

= 2.7 *34=91.8V

Number of cells in parallel = Total current/cell nominal capacity

Number of cells in parallel = 1250/3.5

Number of cells in parallel = 357.14

The number of cells in series is taken as test-2 with 34 cells in series.

The number of cells in parallel is taken as 357 cells.

The nominal voltage of the battery pack = no. of cells in series * nominal voltage of a cell

= 34* 3.6

= 122.4 V

Rated capacity of the battery pack = no of cells in parallel * rated capacity of a cell

= 357 * 3.5

= 1249.5Ah

The overall voltage of the battery pack = maximum voltage of a cell * no of cells in series.

The overall voltage of the battery pack = 4.2 * 34 = 142.8V

The battery pack configuration is 34s357p

b.Draw the BMS topology for this battery pack.

For the above battery pack we have to draw the BMS topology based on number of cells connected in series so the number of cells is 34 cells so the cells are more than 18 then we use master & slave topology

In this topology we using daisy chain interface means it collects the all data of slave-1 is sent to slave-2 collects the 17 cells data and the slave-2 and slave-1 data sent to micro controller unit. The topology is shown below

2.Build a 3S2P battery pack configuration with generic battery block using Matlab/Simulink.

Total number of cells in battery pack = no.of cells in series * no.of cells in parallel

= 3*2

=6 cells

Series connection of a battery:

Batteries are connected from teminal to terminal in a way that the +ve terminal one battery is connected to -ve termnal of the other battery and -ve terminal of one battery is connected to +ve terminal of other battery.

Parallel connection of a batteery:

Batteries are connected from terminals to same terminals of the other batteries that is +ve terminal of one battery is connected to +ve terminal of other battery and -ve terminal of one battery is connected to -ve terminal of other battery.

The battery pack model is shown below

Model explanation:

The voltage is measured bu using voltage measurement and is connected across the battery pack and the scope is connected to bus selector and is connected to battery measurement port for measuring the SOC,voltage & current of the cell the constant block is connected to controlled current source and is given load to the battery pack.

Battery parameters are given below

Nominal voltage of cell = 3.6v

Rated capacity of cell =3.5Ah

Maximum voltage of cell =4.2v

Total number of cells in a battery pack = no.of cells in series * no.of cells in parallel

= 3*2 = 6 cells

Nominal voltage of the battery pack = no.of cells in series * nominal volatege of a cell

Nominal voltage of the battery pack = 3*3.6v = 10.8v

Rated capacity of battery pack = no.of cells in parallel * Rated capacity of a cell

= 2*3.5

Rated capacity of battery pack=7Ah

Overall voltage of the battery pack=maximum capacity of the cell*no.of cells in series

=4.2*3

Overall voltage of the battery pack =12.6v

Results :

After running the model the voltage like shown below

The voltage is dropped from 12.6v to 12.57v for this battery pack.

Cell SOC,Current & voltage are shown below

the three parameters are shown in this figure are all continuous and constant without any variation due to battery reliability.