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.

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

Q1)

AIM:

To Design a battery pack for a car with rating 150 Kw,120 V using a 3500 mAh 3.6V cell and Draw BMS topology.

Solution:

For Designing the battery pack configuration, we need to find no of cells in series and parallel so that it meet the requirement.

Given data

Power rating = 150Kw

Voltage rating = 120V

Cell nominal volage =3.6 V

Cell Nominal Capacity = 3500 mAh

So, Battery Ampere hour = 150Kw/120V = 1250 Ah

Now , we need to find the No of cells in series and parallel to meet requirement. The requirement condition is 120V, 1250 Ah

Cells in Series

Number of cell in series = Required Voltage/Cell Nominal Voltage

Number of cell in series = 120/3.6 = 33.33

Now we need to round off, We have two cases

Case 1- No of cells in series = 34

Case 2- No of cells in Parallel = 33

Case 1

Nominal battery voltage = cell nominal voltage * No of cells in series

= 3.6 * 34

= 122.4 V

Case 2

Nominal battery voltage = cell nominal voltage * No of cells in series

= 3.6 * 33

= 118.4 V

It is always better to prefer higher voltage. There fore no of cells in series is 34.

Cells In Parallel

No of cell in parallel = Rated Current / Cell Nominal Capacity

No of cell in parallel = 1250/3.5 = 357.14

Case 1- Roundoff to 357

Battery capacity = rated capacity of a cell * no of cells in parallel

= 3.5* 357= 1249.5 Ah

Case 2- Roundoff to 358

Battery capacity = rated capacity of a cell * no of cells in parallel

= 3.5* 358= 1253 Ah

So we are considering no of cells in parallel is 358

So our battery pack configuration is 34S348P

Now we need decide the BMS topology for our battery pack.

Since we have 34 no of cells in series we cannot use centralized topology and Distrubuted topology Since they only support a maximum 18 cells.

Modular topology usually use for large no of cells in series.So here we go for master slave topology .

As the BMS Supports the max 18 cells in series so we need to divide the 34 series cells to 18 cells series sub battery packs

So here sub battery pack is one with 18 cells in series and one with 16 cells in series.

So in our master slave topology there will 2 slave AFE in which one will collect the data of 18 cells in series and other will collect the data of 16 cells in series

The figure below shows master slave topology for our battery pack

Q2)

AIM:

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

Solution:

The battery pack configuration is 3S2P. Which means no of cells in series is 3 and No of cells in parallel is 2

The total No of cells = 3*2 = 6

The figure below shows the 3S2P battery pack configuration in simulink

Model Explanation

A resistor is connected to battery pack as a Load. The voltage measurement block along with scope and display is connected across the battery pack to measure battery pack voltage. With the help of bus selector a scope is connected to Cell, which gives SOC, Voltage and current of the cell. The simulation is done for 100 Sec and output is observed.

Cell Specifications:

Cell Nominal Voltage = 7.2 V

Rated capacity of cell = 5.4Ah

Nominal Voltage of battery Pack = Max voltage of cell * No of cell

= 7.2 V * 3 = 21.6 V

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

= 5.4 * 2 = 10.8 Ah

Overall Voltage of battery pack = Max voltage of cell * No of cell

= 8.3 * 3 = 24.9 V

We use a 1 ohm resistor as load and simulation for 100 sec

Result

The result below shows the SOC, voltage and Current of the single cell

We can observe that the SOC of battery is reduced to 94 % after running the simulation for 100 sec

The figure below shows the overall output voltage of cell

The total voltage of battery pack = Maximum voltage of cell* No of cells in series

The total voltage = 8.3*3 = 24.9 V

Conclusion:

• Designed a Battery pack configuration for the given specification and selected proper BMS topology
• Built a simulink model of 3S2P configuration and analysed the performance