Project 1
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.
Solution:
Rated Power (P rated) = 150kW
Rated Voltage (V rated) = 120V
Nominal Cell Capacity = 3500mAh
Nominal Cell Voltage = 3.6V
Rated Current (I rated) = Prated/V rated
= 150*103/120
Rated Current (I rated) = 1250A
Number of Cells in series = V rated/Nominal Cell Voltage (assuming maximum voltage = rated voltage)
= 120/3.6
Number of Cells in series = 33.33
Case 1: Considering Number of Cells in series as 33
Total Battery Voltage = Nominal Cell Voltage*Number of Cells in series = 3.6*33
Total Battery Voltage = 118.8V
Case 2: Considering Number of Cells in series as 34
Total Battery Voltage = Nominal Cell Voltage*Number of Cells in series = 3.6*34
Total Battery Voltage = 122.4V
As the Total battery voltage in case 2 is higher than the rated voltage, number of cells in series is taken as 34
Number of Cells in series = 34 cells
Number of cells in parallel = Rated capacity/Nominal cell capacity
= 1250/3.5
Number of cells in parallel = 357.14
Case 1: Considering Number of Cells in parallel as 357
Total Battery Capacity = Nominal cell capacity*number of cells in parallel = 3.5*357
Total Battery Capacity = 1249.5Ah
Case 2: Considering Number of Cells in parallel as 358
Total Battery Capacity = Nominal cell capacity*number of cells in parallel = 3.5*358
Total Battery Capacity = 1253Ah
Number of Cells in parallel = 357 cells
Therefore, the battery pack configuration is 34S357P
Master Slave BMS topology is used for this battery pack. In this architecture, there is typically one "master" module that oversees and controls the overall operation of the BMS, and multiple "slave" modules that monitor and control specific subsets of the battery pack. The master module communicates with the slave modules to gather information, make decisions, and ensure the proper functioning of the entire system.
The master-slave architecture allows for the scalability and modularization of the BMS, making it suitable for large battery packs with numerous cells. It also facilitates communication and coordination among different parts of the battery pack, ensuring safe and efficient operation.
Master Slave BMS Topology
Q.2. Build a 3S2P battery pack configuration with generic battery block using Matlab/Simulink.
Solution:
Aim: To build a 3S2P battery pack configuration with generic battery block using Matlab/Simulink.
Theoretical Calculation:
Nominal voltage of cell = 3.6V
Capacity of cell =3.5Ah
Maximum voltage of cell =4.2V
Number of cells in series = 3
Number of cells in parallel = 2
Nominal Voltage of battery pack = no. of cells in series * nominal voltage of a cell = 3*3.6
Nominal Voltage of battery pack = 10.8V
Capacity of battery pack = no. of cells in parallel * Capacity of a cell = 2*3.5
Capacity of battery pack = 7Ah
Maximum Voltage of battery pack = no. of cells in series * Maximum voltage of a cell = 3*4.2
Maximum Voltage of battery pack = 12.6V
Blocks used:
- Li ion battery (6)
- Bus Selector
- Powergui block
- Controlled current source
- Constant block
- Voltage measurement
- Scope block
- Display block
Simulink Model:
Cells are connected in 3S2P configuration (3 cells in series and 2 cells in parallel) as shown in the above figure. A Constant current source with the capacity of 3.5Ah (constant block) is connected to the battery pack acts as the load. The voltage measurement block is connected to measure the battery pack voltage. Scope is connected through the bus selector, which provides the voltage, current and SOC of the cell.
Result Screenshot:
The simulation is run for 1000sec.
Conclusion:
Simulink model for 3S2P battery pack configuration is built with generic battery block. The simulation is run for 1000sec. The SOC of the battery has reduced to 86.1% from 100% and the maximum voltage of the battery pack has dropped to 11.6V.