Project 1

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.

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)

Nomial 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 33 cells in series

Number of cells in parallel

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

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.

2. Build a 3S2P battery pack configuration with generic battery block using Matlab/Simulink.