Project 1
OBJECTIVES
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.
ANSWERS
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.
Aim of the Project: -
The Main Of this project is Design the battery pack configuration ,Draw the BMS topology for this battery pack using given data and also build 3s2p battery pack configuration by using the MATLAB/SIMULINK tool.
Theory: -
Battery Management System:-
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 of battery pack.
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.
BATTERY MANAGEMENT SYSTEM (BMS)
Solution: -
Given Data
Rated Voltage rating:120v
maximum voltage rating:120v
minimum voltage rating: 100v
Rated power rating:150Kw
continuous current requirement: Pmax = 1max* Vmax
Imax = Pmax/Vmax
Imax = 150*1000/120 =1250A
Peak current requirement: I/0.637=1250/0.637= 1962A
Peak current duration: 12min
Cell Comparison
Cell A (Cylindrical) Cell B (prismatic)
Nominal capacity:3.5Ah Nominal capacity: 4.5Ah
Max Current: 5A Max Current : 6A
Cell nominal voltage: 3.6V Cell Nominal Voltage : 3.6V
Max cell Voltage: 4.2V max cell Voltage : 4.2V
|
Cell A |
Cell B |
|
|
Maximum Discharge Current |
5A |
6A |
|
Temp (deg c) |
44 |
43 |
|
Time (min) |
15 |
15 |
Number of cells in series
Number of cells in series = Rated motor voltage / Nominal cell voltage
= 120/3.6 = 33.33
Rounding off the number of cells in series
Rounding off the number of cells depends on the maximum voltage and minimum voltage
case 1
Rounding off 33.33 to 33
Nominal battery voltage = Cell nominal voltage *33
= 3.6*33=118.8
Maximum battery voltage = cell maximum voltage *33
= 4.2* 33 =138.6V
Mini battery voltage = Cell minimum voltage *33
= 2.7*33 = 89.1V
case 2
Rounding off 33.33 to 34
Nominal battery voltage = Cell nominal voltage *34
= 3.6*34=122.4V
Maximum battery voltage = cell maximum voltage *34
= 4.2* 34 =142.8V
Mini battery voltage = Cell minimum voltage *34
= 2.7*34 = 91.8V
|
Battery voltage |
Case 1 |
Case 2 |
Targeted Voltage |
Values |
|
|
Battery Nominal voltage |
118.8 |
122.4 |
Nominal Voltage |
120V |
ok |
|
Battery Max Voltage |
138.6 |
142.8 |
Max Voltage |
120V |
|
|
Battery Min Voltage |
89.1 |
91.8 |
Min Voltage |
100V |
It's always better to have an EV Voltage
So, we can pick case 1 which is 34 cells in series
Number of cells in parallel 358
Cell A = 3.5Ah
Number of cells in parallel = continuous current/cell nominal capacity
= 1250/3.5 = 357.14
Cell B = 4.5Ah
Number of cells in parallel = iPhone continuous current/cell nominal capacity
= 1250/4.5 = 277.77
Rounding of the number of cells in parallel
Cell A = 3.5Ah
Number of the cells in parallel = 357.14
case 1
Battery capacity = 357*3.5 = 1249.5Ah
case 2
Battery capacity = 358*3.5 =1253Ah
Cell B = 4.5Ah
Number of the cells in parallel = 277.77
case 1
Battery capacity = 277*4.5 = 1246.5Ah
case 2
Battery capacity = 278*4.5 =1251Ah
it's always recommended to discharge the battery for continuous current in 1c.
Continuous current requirement = 1250A
So, we will Choose case 2 From both cellA and cell B
Cell peak Current
Individual cell peak current = Load peak current / Number of cells in parallel
Cell A = 3.5Ah
Number of cells in parallel 358
Individual cell peak current = 1962/358 = 5.48 A
Cell B = 4.5Ah
Number of cells in parallel 278
Individual cell peak current = 1962/278 = 7.05 A
|
Cell A |
Cell B |
|
|
Individual cell peak current requirement |
5.48A |
7.05A |
|
Maximum Discharge Current |
5A |
6A |
|
Temp (deg c) |
44 |
43 |
|
Time (min) |
15 |
15 |
So, cell A will be finalized and the number of cells in parallel will be 358
Battery pack configuration
33S358P is our battery pack configuration
Now the battery pack is made of 33S358P pack so that it can meet the required output of 120v,1250A or 120V, 150Kw
As the number of cells in series and parallel is very high it makes manufacturing difficult. So, we need to divide it into sub-battery packs and remake the connections to get the required output
As the BMS Supports a max of 18 cells in series so we need to divide the 33 series cells into 18 cells series sub-battery pack which leads to 2 series sub connections one with 18 and another with 15
To make it compact parallel connections we need to make 51 cells in parallel for each sub pack which leads to 6 parallel connections and one 52 Cells in parallel connection
The total result is 2 sub-battery packs in series one with 18 cells in series and another with 15 cells in series and 6 sub-battery packs in parallel each with 51 cells in parallel and one with 52 to meet the requirement 33S358P.
One sub-battery pack configuration is 18S51P and another sub-battery pack configuration is 15S51P which results in a 33S52P pack with 7 copies. these 33S52P are connected in parallel (One of the packs with 33S52P) to make 33S358P.
Basic connections block diagram:
The back line indicates the series connection
Blue Line indicates the Parallel connection
Each 18S51P pack is connected in series with each 15S51P pack resulting in 33S51P
All 7 33S51P(18S51P+15S51P) are connected in parallel results in 33S358P
Note that the last pack in parallel connection contains a 18S52P series with a 15S52P pack, one parallel connection is increased in that sub-pack to meet the Requirement of 33S358P
e can conclude that
The Battery pack Configuration = 34S358P
Battery pack Configuration image:-
Battery Pack Configuration (34S358P)
b. Draw the BMS topology for this battery pack:-
BMS Topology:-
Fig :-BMS TOPOLOGY BLCOK DIAGRAM
Basically BMS topology is classified into following four(4) types:-
1)Centralised Topology;-
This Topology is used for only pack of 18 cells or less than 18 cells in a series only.
2)Master and Slave topology:-
This Topology is used for pack of 18 cells or greater than 18 cells in a series .
High Energy storage purpose
3)Modular Topology :-
This Topology is used for pack of 18 cells or greater than 18 cells in a series.
Large Energy storage purpose
4)Distributed Topology:-
This Topology is used for pack of 18 cells or greater than 18 cells in a series.
Very large Energy storage purpose
Solution:-
From the Architecture of BMS we can said that the "AFU" Allows only 18 cells connected in series per one unit of module.
Hence ,
we required series cells is 34 cells
Therefore we are dividing these 34 cells as 2 slave sets with 1 number of MCU master unit as follows
Slave 1= 17 cells
Slave 2= 17 cells
Based on this cells connected in series and Architecture of BMS we Choose the Master and Slave topology of BMS for this Ev battery pack Topology design.
Battery Management System (BMS):
BMS Topology used in this battery pack is Master and Slave BMS Topology. Because the total battery pack is made of sub-battery packs so controlling and manufacturing will be easy.
Master and Slave BMS have a number of slaves are 2 and a Master controller can handle 2 slaves.
It consists of input sensors of voltage, current, and temperature. The voltage sensor analog signal is converted to a digital signal by AFE, the current sensor analog signal is converted to a digital signal by the MCU or we can connect the ADC converter between the Current sensor and MCU, and the temperature sensor analog signal is converted to a digital signal by the MCU or we can connect the ADC converter between the Temperature sensor and MCU. The Realy module controls the Realy which makes or brack the circuit by the command given by the MCU. The CAN and RS485 are Communication protocols to the Outside world.
The Blocks inside the red line are the BMS blocks. It is designed with the three 18 cell Slave controller which is AFE, it converts the analog signal from the voltage sensor in the battery to a Digital signal. The 2 Slaves are connected in series as shown, the salve-1 will collect the data from module-1 and send it to slave-2, slave -2 will collect the data from module-2, now the salve -2 consisting of the data of slave-1 and 2 and sends all the data to Master controller which is MCU. It controls the battery pack according to the protocols which are given to MCU.
Note that all the slaves have a capacity of 18 cell series connection even though half of the sub-battery packs have only 15 series cells because if we want to upgrade the capacity we can do by increasing the Ah of the battery pack i.e., by increasing the number of series cells. It makes it easy to upgrade the battery pack but in a limited way.
We can also use the combination of 7 Master and slave BMS i.e., 2 slaves 18S356P and 15S356P and a master controller of 7 numbers. All master control will have one single controller or all 7 master controllers can be directly connected to the MCU. But it's a costly and complicated process.
Conclusion:
The battery pack was made to design as 33S356P divided into sub-battery packs which is the combination of 18S356P series with 15S356P, this combination is parallel with 7 copies as shown above total results in 33S356P with a capacity of 150Kw with 120V.
To charge and discharge the Total battery pack Master and Slave BMS topology is used which is efficient in all ways like cost, design, control, and installation.
BMS Topology MODEL:-
Master and Slave Topology: -
>> Above Model is For BMS Topology of 34s358P battery pack Configuration model
>>This Topology consists 2 numbers of slave of AFU units with each AFU units slave Consists 17 numbers Of Cells connected in series.
Conclusion :-
We can conclude from above calculations
The battery Pack configuration is 34S358P
Battery BMS Topology is "Master and Slave " Topology is designed and explained theory regarding BMS topology.
2)Build a 3S2P battery pack configuration with generic battery block using Matlab/Simulink.
Aim)The main aim is design a given battery pack configuration by using the Matlab/Simulink Tool.
Given data :-
Battery pack configuration = 3S2P
Simulink model :-
For creating the Simulink model battery pack configuration we are used following blocks:-
Battery :-
scope:-
Procedure :-
Batteries in 3S2P configuration in Matlab/Simulink. That is 3 cells should be connected in series and 2 cells should be connected in parallel.
Therefore,
Total number of cells in battery pack = No. of cells in series * No. of cells in parallel
Then ,
Total number of cells in battery pack = No. of cells in series * No. of cells in parallel
= 3 * 2 = 6 cells
Step-1
Arrangement of 6 cells:-
The figure 1 shows the arrangement of 6 cells.
We have to place total number of cells in battery pack (6 cells)
Arrangement of 6 cells
Parallel connection: -
The figure 2 shows the batteries 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 of other battery and negative terminal (-) of one battery with negative terminal (-) of other battery
Battery connected in parallel connection
Series and parallel conn
The figure 3 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.
Battery connected in series and parallel combination
Model Explanation:-
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 block is 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 8.3V
Therefore ,
Nominal voltage of the battery pack = no.of cell in series * nominal voltage of a cell
= 3 * 7.2v
= 21.6 V
Rated capacity of the battery pack = no.of cell in parallel* rated capacity of a cell
= 2 * 5.4Ah
= 10.8Ah
The model is for an 21.6V 7 with 10.8Ah battery capacity
Overall voltage of the battery pack = maximum voltage of the battery * no. of cells in series
= 8.3V * 3
= 25 v
Overall voltage = 25 V
Total Battery pack model:-
https://drive.google.com/file/d/1SERXDl32v9rYXpQZLcRCt3SjWQanJTOC/view?usp=share_link
Output Scope results :-
Voltage scope :-
Overall voltage of the battery pack = maximum voltage of the battery * no. of cells in series
= 8.3V * 3 = 25 V
>>From the Above Plot is we can observe that the the total battery pack voltage is reduced bt 10% of the initial value.
Battery pack details:-
>> From the Above graph we can observe that the
Top Plot is (Voltage):-
>>The voltage is around 8.3V. The increasing and decreasing voltage is with respect to the regenerative braking
Middle Plot (Current):-
>> The current signal is determined by the load and the decrease in current is due to regenerative braking.
Bottom Plot(SOC%):-
>>The SOC (state of charge) is started to reduce from 100% to 99 % corresponding to the load given
Conclusion :-
The battery pack configuration(3S2P) with generic battery block using Matlab/Simulink is created.