Project 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.
Your Answers
1.Answer:
Given
Total power P =150Kw = 150,000 W
Total Voltage V =120V
cell capacity=3500mAh= 3.5Ah
cell nominal voltage=3.6V
a.Designing the Battery pack Configuration:
power= Total voltage* Total current
Total current = power/total voltage
= 150000w/120V
=1250 A
Therefore total curernt is 1.25 A
1.No of cells in series = Battery pack voltage/ cell nominal voltage
=120V/3.6V
=33.33= 34 (approx) cells
2. No of cells in Parallel= Battery capacity/cell nominal current
= 1250A/3.5A
= 358 (appox) cells
b.Draw the BMS topology for this battery pack:
We have 34 cells in series and 14 cells in parallel so by seeing the no of cells in series we can choose the sutaible BMS topology that can be Master Slave Topology.
In a Master-Slave Battery Management System (BMS) topology, the BMS is organized into a hierarchical structure where one central unit (the master) oversees and coordinates the operation of multiple subordinate units (the slaves). This architecture is commonly used in large-scale battery systems, such as those found in electric vehicles, data centers, and renewable energy installations. Here's how the master-slave BMS topology works:
1. Master Module:
The Master Module is the central control unit of the BMS hierarchy.
It is responsible for overseeing and coordinating the entire battery system.
The master module collects data from all the slave modules and makes high-level decisions regarding the battery's operation based on this data.
It communicates with external systems, such as the vehicle's control unit or charger, to manage charging and discharging processes.
2. Slave Modules:
Slave Modules are distributed throughout the battery pack or system.
Each slave module is responsible for monitoring a subset of cells or a portion of the battery.
They collect data on cell voltage, temperature, and other relevant parameters.
Slave modules communicate this data to the master module through a communication network.
Advantages of Master-Slave BMS Topology:
Centralized Control: The master-slave topology provides centralized control, allowing for efficient monitoring and decision-making for the entire battery system.
Data Coordination:The master module coordinates data from multiple sources (slave modules) to ensure that the BMS operates optimally and safely.
Redundancy: This topology often incorporates redundancy at the master level, ensuring system reliability even if one master module fails.
Simplified Communication:Communication within the BMS network is simplified, as the master is responsible for interacting with external systems and interfaces.
2.Answer:
AIM:
The objective of this article 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
Step1: 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 cell) in simulink,
Figure 1: Arrangement of 6 cells
Step2: 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 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
Model Explanation:
The figure 4 shows the 3S2P Battery pack 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 block is determined with battery capacity and it is given to the controlled current block.
Figure 4 : 3S2P Battery pack simulink model
The parameter given inside the battery is given below,
|
S.No |
Battery parameters |
Value |
|
1 |
Nominal voltage of a cell |
7.2V |
|
2 |
Rated capacity of a cell |
5.4Ah |
|
3 |
Maximum voltage of a cell |
8.38V |
Nominal voltage of the battery pack = no.of cell in series * nominal voltage of a cell
Rated capacity of the battery pack = no.of cell in parallel* rated capacity of a cell
The model is for an 21.6V 10.8Ah battery.
The figure 5 shows the single battery output for SOC, voltage and current.
- Plot 1: The SOC (state of charge) is started to reduce from 100% to 50% corresponding 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 V. The increasing and decreasing voltage is with respect to the regenerative braking.
Figure 5 : Single battery output for SOC, voltage and current
The figure 6 shows the overall output voltage of the battery pack. The calculation for the overall output voltage of the battery pack is given below.
Overall voltage of the battery pack = maximum discharge voltage of the battery * no. of cells in series
=25.14V