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 battery management system (BMS) is said to be the brain of a battery pack. The BMS is a set of electronics that monitors and manages all of the battery’s performance. Most importantly, it keeps the battery from operating outside of its safety margins.

The battery management system is critical to the battery’s safe operation, overall performance, and longevity. Moreover, it protects whatever the lithium battery is installed in (boat, RV, etc.) and the people who are using it.

The primary function of the BMS is to protect the battery cells from damage caused by being overcharged or over-discharged. Additionally, the BMS calculates the remaining charge, monitors the battery’s temperature, monitors the battery’s health and safety by checking for loose connections and internal shorts. The BMS also balances the charge across the cells to keep each cell functioning at maximum capacity.

If it detects any unsafe conditions, the BMS shuts the battery down to protect the lithium-ion cells and the user.

Given Data:

Power = 150KW

Voltage = 120V

Cell Specifications:

Nominal Voltage = 3.6V

Capacity = 3500mAh = 3.5Ah

Cell Type = NMC

a. Design the battery pack configuration.

To Design a Battery Pack following two parameters need to be calculated:

1. Number of Cells in Series

2. Number of Cells in Parallel

1. Number of Cells in Series:

From given Data 

Nominal Voltage = 120V

Nominal Cell Voltage = 3.6V

Formula:

Number of Cells in Series = Rated Voltage/Nominal Cell Voltage

                                           = 120/3.6

                                          = 33.33

Number of Cells in Series = 33.33

Rounding of the Cells to highest or lowest Number

Nominal Voltage = Nominal Cell Voltage * Number of Cells in Series

Since it is NMC Cell so Max Voltage = 4.2V and Min Voltage = 2.7V

Max Voltage = 4.2V * Number of Cells in Series

Min Voltage = 2.7V * Number of Cells in Series

The condition to choose the number of cells are

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

Min Volatge of battery should be greater than the Load min Voltage

It is better to have Nominal Voltage Greater than Required Voltage  so selecting Case 2

So, Number of Cells in Series = 34

Output Voltage = 122.4V 

2. Number of Cells in Parallel

To Calculate Current Requirement

Power = Voltage * Current

Current  = Power/Voltage

Current = `(150*1000)/120`

Current = 1250A

Given Cell Capacity = 3.5Ah

Number of Cells in Parallel = Rated Current / Cell Nominal Capacity

                                            = 1250/3.5

                                            = 357.14

Number of Cells in Parallel = 357.14

Runding off to Higher Number 

So Number of Cells in Parallel = 358

The Battery Pack Configuration is selected as 34S358P with Total Number of Cells = 12172

b. Draw the BMS topology for this battery pack.

Now for selecting BMS there are 4 types of BMS Topology

a. Centralised Topology:

• This Topology is used in Battery Pack where BP consists of less than 18 cells in series.
• It is used in E2w, E3W and Small Energy Storage Systems.

b. Master and Slave topology:-

• This Topology is used in Battery Pack where BP consists 18 or more than 18 number of cells in series.
• It is used in Electric Cars and Large Energy Storage Systems.
• Here Every Slave has 1 Analog Front End(AFE).

c. Modular Topology :-   

• This Topology is used in Battery Pack where BP consists 18 or more than 18 number of cells in series.
• Used in 1MW Battery Pack Systems

d. Distributed Topology: 

• This Topology is used in Battery Pack where BP consists 18 or more than 18 number of cells in series.
• It is used in smaller battery packs whereb individual cell consist of  a PCB Voltage Sensor.

Since Cells in Series = 34

Cells in Parallel  = 358

Total No of Cells = Number of Cells in Series * Number of Cells in Parallel

                        = 34 * 358

Total No of Cells = 12172

Cells are divided such taht each Module will 17Cells in series and 179 Cells in Parallel so 1 m odule will consist of 3043 Cells. So 4 Such Modules will be required to form a Battery Pack with 122.4V 1251Ah

From above topologies selecting Master and Slave Topology

Master and Slave bms can handle more than 18 no of cells in series. So for above battery pack there will be 4 slaves and 1 Master MCU. Slaves wil collect data of its own module and give to other slave and that slave with its own module data with the previous module data will give to another Slave and the last slave will give all the data of 4 slaves to Master MCU. All the Slave will have 1 Analog Front End(AFE). Master and Slave have Scalability since more no of slaves can be added.

BMS ARCHITECTURE: MASTER AND SLAVE TOPOLOGY

https://app.diagrams.net/

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

The main aim is to design given battery pack configaration by using generic battery block in Matlab/Simulink Tool.

Data:

To Build 3S 2P Battery Pack Configuration

Number of Cells in Series = 3

Number of Cells in Parallel = 2

Total Number of cells in Battery Pack = No. of cells in series * No. of cells in parallel
                                                      = 3 * 2

                                                      = 6

Total Number of cells in Battery Pack = 6Cells

Step 1:

Arrangement of 6 cells. The Below figure shows 6 cells arranged to create a battery pack.

Step 2: Connecting Cells is Parallel 

The below figure shows the cells connected in parallel. For parallel connection, batteries are connected from terminals to same terminals of other batteries that is positive terminal (+) of one battery is connected with positive (+) terminal ofother battery and negative terminal (-) of one battery with negative terminal (-) of other battery.

Step 3: Connecting Cells in Series

The figure below shows the battery connected in series and parallel combination. Batteries are connected from terminal to
terminal in a way that the positive (+) terminal of one battery is connected with the negative (-) terminal of the other
battery and negative terminal (-) of one battery is connected with the positive terminal (+) of the other battery.

SIMULINK MODEL:

The voltage measurement block is connected across the battery pack to measure the battery pack voltage. The scope output used for the battery pack consists of SOC (State of Charge), Current and voltage. The controlled current signal is given as the load to the battery pack. The constant blockis determined with battery capacity and it is given to the controlled current block.

The parameter given inside the battery is given below:-

•  Nominal voltage of a cell 7.2V
•  Rated capacity of a cell 5.4Ah
•  Maximum voltage of a cell 8.3807V

Nominal Voltage of the Battery Pack = No.of cell in series * Nominal voltage of a cell
                                                    = 3 * 7.2

                                                    = 21.6V

Nominal Voltage of the Battery Pack = 21.6V                                                  

Rated Capacity of the Battery Pack = No.of cell in Parallel* Rated Capacity of a Cell
                                                     = 2 * 5.4

                                                     = 10.8Ah

Rated Capacity of the Battery Pack = 10.8Ah

The Battery Pack Rating is 21.6V, 10.8Ah ,233.28Wh

Maximum Voltage of Battery Pack = Maximum Voltage of Cell * No. of Cells in Series

                                                  = 8.3807 * 3 

                                                  = 25.14V

Maximum Voltage of Battery Pack = 25.14V     

RESULTS:

The above plot shows the battery pack total voltage. The Voltage has reduced from 25.2V to 25.13V.

The Simulation is run for 10seconds with discharge current of 5.4A

• The 1st plot shows SOC graph. The SOC has reduced from 100% to 99.85% n 10 seconds. The drop is linear since it is discharging and no charging is happening.
• The 2nd plot shows Cell Current graph. The current signal is determined by the load and the decrease in current is due to regenerative braking.
• The 3rd plot is Voltage graph. The voltage is around 8.38V at start of simulation and has reduced to 8.31V.

CONCLUSION:

The Battery Pack is designed for a car with 150KW 120V by using 3.6V 3.5Ah NMC Cell and BMS Topology is also selected for the Battery Pack. A 3S2P battery pack configuration with generic battery block using Matlab/Simulink is also created.