Project 1
Q1). Design a battery pack for a car roughly 150 Kw with 120 V. Use 3500 mAh 3.6V nominal NMC chemistry cell.
- Design the battery pack configuration.
- Draw the BMS topology for this battery pack.
Solution: (a)
Requirement of 120v and 150kw we need to find the number of cells connected in series and parallel.
First convert the battery pack capacity 150kw to Ah total battery pack
P = 150 Kw
V = 120 v
I = P / V = 150 kw / 120 v
= 150*1000 / 120
= 1250 ampere (A) h
Series
Number of cells in series = required voltage / Nominal voltage of the cell
= 120 / 3.6 = 33.33
We have to take round of cells to lower value and higher value
Number of cells in series = 33
Number of cells in series = 34
Total voltage = nominal voltage of cell * number of cells in series
33 => 33 x 3.6 = 118.8
34=> 34 x 3.6 = 122.4
Individual battery cell
3500 mAh= 3500 / 1000 =3.5 Amp h.
v = 3.6v
To make total battery pack voltage for in this case 34 total number of cell is required.
Parallel
No. of parallel cells = total battery current / single cell capacity = 1250 / 3.5 = 358
Total no. of cells = No. of series cells x No. of cells parallel = 34 x 358 = 12,172 .
Here, we Designed a battery pack for a car roughly 150 Kw with 120 V, 1250Ah for that 12,172 total no. of cells are required.
(b) Answer:
Master and Slave Topology is Used in battery packs which consist of more than 18 number of cells in series.
Here we have two AFE, each AFE consists of 17 no. of cells in series., so 17*2 = 34
Total no cell is 34.
Generally,
it is used in four wheelers and large energy storage battery pack system.
Q2). Build a 3S2P battery pack configuration with generic battery block using Matlab /Simulink.
3S2P battery pack 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.
We have to place total number of cells in battery pack (6 cells) in Simulink,
The figure shows the battery connected in series and parallel combination. Batteries are connected from terminal to terminal in a way that the positive (+) 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.
Model Explanation:
The figure shows the 3S2P battery Simulink model. The voltage measurement block is connected across the battery pack measure the battery pack voltage. The scope output for the battery pack consists of SOC (State of Charge), Current and Voltage. The controlled current signal is given as 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,
Sr.no Battery parameters value
1 Nominal voltage of a cell 3.6 V
2 Rated capacity of a cell 3.5 Ah
3 Maximum voltage of a cell 4.0 V
Nominal voltage of the battery pack = no. of cell of series * nominal voltage of a cell
= 3 * 3.6 = 10.8 V
Rated capacity of the battery pack = no. of the cell in parallel * rated capacity of a cell
= 2 * 3.5 = 7 Ah
The Model is for an 10.8V, 7 Ah Battery.
Scope output result below single battery:
The figure shows the single battery output for SOC, voltage and current.
Frist plot – The SOC (state of charge) is started to reduce from 100 % to 98% corresponding to the load given.
Second plot – The voltage is around 4.2V. The decreasing voltage is with respect to the regenerative braking.
Third plot – The current signal is determined by the load and the decrease in current is due to regenerative braking.
Scope output result below voltage measurement:
The figure shows above the overall output voltage. The calculation for the overall output of the voltage pack is given below:
Overall voltage of the battery pack = maximum voltage of the battery * no. of cells in series
= 4.2 * 3 = 12.6