Project 1
Project 1 - Battery Pack Design
Q 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.
Q 2) Build a 3S2P battery pack configuration with generic battery block using Matlab/Simulink.
Aim = The Main Of this project is to 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 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.
Solution-
Given data-
Required power = 150 Kw
Required Voltage = 120 V.
Battery details :-
Battery cell capacity = 3500 mAh= 3.5 Ah
Cell Nominal Voltage =3.6V
1.a) Design the battery pack configuration
for designing the Battery pack Configuration, firstly we have to find the two parameters as follows: -
i) Number of cells connected in Series
ii) Number of cells connected in Parallel.
i) Number of cells connected in Series -
total number of cells connected in Series = Required voltage / Nominal cell voltage
= 120 / 3.6
= 33.33 cells
this digits values are taken as rounding of calculation as followes-
case 1- considering lower round off series cells value (33)
therefore, nominal battery voltage = cell nominal voltage * number of cells in series
= 3.6 * 33
= 118.8 V
Case 2 - considering higher round off series cells value (34)
therefore, nominal battery voltage = cell nominal voltage * number of cells in series
= 3.6 * 34
= 122.4 V
So for rounding off the number of cells in series its always better to have more voltage than required voltage (120 V).
So, we can pick case 2 which is 34 cells in series.
ii) Number of cells connected in Parallel.
we know that
power = current * voltage
therefore, current = power / voltage
= (150*1000)/120
Continuous current = 1250 A
Number of cells in parallel = continuous current / cell nominal capacity
= 1250 A / 3.5 Ah
= 357.143
For rounding off number of cells in parallel
Case number 1- Considering lower round off parallel cells value (357)
Cell nominal capacity = 3.5 Ah
therefore, Rated capacity of the battery pack = lower value of number of cells in parallel * cell nominal capacity.
= 357 * 3.5 Ah
= 1249.5 Ah
Case number 2 - Considering higher round off parallel cells value (358)
therefore, Rated capacity of the battery pack = lower value of number of cells in parallel * cell nominal capacity.
= 358 * 3.5 Ah
= 1253 Ah.
for rounding off number of cells in parallel -
- its always recommended to discharge the battery for continuous current 1 C.
- Continuous current requirement = 1250 A.
- So we will consider case no 2 that is Considering number parallel cells value= 358.
From values (i) and (ii)
Number Of Cells Connected in Series = 34S
Number of cells Connected in parallel =358 P
We can conclude that,
The Battery pack Configaration = 34S358P
1.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 and used in 2 wheeler,3 wheeler or small energy storage battery pack system.
2)Master and Slave topology: -
This Topology is used for pack of greater than 18 cells in a series and used in High Energy storage purpose.
3)Modular Topology: -
This Topology is used for pack of 18 cells or greater than 18 cells in a series and it is used in very large energy storage battery pack system i.e. above 1 MW (Megawatt) battery pack system and battery capacity is 1 Mwh.
4)Distributed Topology: -
this is used in smaller battery packs where individual cells consist of a PCB voltage sensor separately.
Solution:-
From the Architecture of BMS we can said that the “AFE" 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 these cells connected in series and Architecture of BMS we Choose the Master and Slave topology of BMS for this EV battery pack Topology design.
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 AFE units with each AFE units slave Consists 17 numbers Of Cells connected in series.
Q 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
Procedure=
the objective of this is to connect batteries in 3S2P configuration in MATLAB /simulink.that is 3 cells should be connected in series and 2 cells should be connected in parallel.
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) in Simulink .
fig 1- Arrangement of 6 cells
Step@2)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.
figure 2- Battery connected in parallel connection
Step@3) Series and parallel connection: -
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.
Figure 3- Battery connected in series and parallel combination.
Step@4) 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 * 5.4 Ah
= 10.8 Ah
The model is for an 21.6 V with 10.8Ah battery capacity
Overall voltage of the battery pack = maximum voltage of the battery * no. of cells in series
= 8.38 V * 3
Overall voltage = 25 V.
Total Battery pack model: -
Figure 4 - 3S2P Battery pack simulink model
Output Scope results: -
Voltage scope: -
Overall voltage of the battery pack = maximum voltage of the battery * no. of cells in series
= 8.38 V * 3 = 25 V
fig 5 - Overall output voltage of the battery pack
from the above plot ,we can observe that the total battery pack voltage is reduced .
Battery pack details: -
Fig 6 - Single battery output for SOC,voltage and current.
plot 1 - the SOC (state of charge ) is started to reduce from 100% to 99.86% correspomding to the load given.
plot 2 - the current signal is determined by the load and the decrease in current is due to regenerative braking.
plot 3- the voltage is around 8.38 V. the increasing and decreasing voltage is with respect to the regenerative braking.
Conclusion=
We can studied Battery Pack Design and concluded as follows.
1.a) The battery Pack configuration is 34S358P
1.b) Battery BMS Topology is "Master and Slave " Topology is designed and explained theory regarding BMS topology.
2) The battery pack configuration(3S2P) with generic battery block using Matlab/Simulink is designed.