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.

 

Aim:

To design the battery pack with the capacity 150Kw 120V by using 3500mAh 3.6V. And BMS topology for the battery pack

 

Calculation:

To design the battery pack we need cells which are connected in series and parallel to meet the requirment.

Let us concider the cells with

Nominal voltage = 3.6V

Capacity = 3500mAh = 3.5Ah

 

Number of cells in series:

 To find the number of cells in series we need battery nominal voltage of the car.i.e 120V

 

`Numb er\ of\ cells\ i n\ series=(Rated\ bat ter y\ vol ta g e\ of\ the\ car)/ (n o mi nal\ cell\ vo l t a g e`

 

`Numb er\ of\ cells\ i n\ series=120/3.6`

 

 `Numb er\ of\ cells\ i n\ series=33.33`

 

We have to round off to lower value and higher value 

Case-1) Number of cells in series = 33

Case-2) Number of cells in series = 34

 

Total volatge = nominal votage of cell * number of cells in series

	Number of cells in series	Total voltage of         the cells(V)	Battery voltage of the car(V)
Case - 1	33	33*3.6 = 118.8	120
Case - 2	34	34*3.6 = 122.4	120

 

By seeing above table we can conclude that we need to satisfy the battery nominal voltage 120V

It's always better to have more voltage.

So I will choose 34cells in series.

 

Number of cells in Parallel:

To find number of cells in parallel we need continous current requirement or Battery capacity of battery

 

`Num b er\ of\ cells\ i n\ parall el=(Cont i nous\ current\ required)/(cell\ no m i n al\ ca p acity`

 

`Cont i nous\ current\ required=(Total\ power)/(bat tery\ vol t a g e`

 

`Cont i nous\ current\ required=(150**10^3W)/(120V`

 

`Cont i nous\ current\ required=125A`

So,

`Num b er\ of\ cells\ i n\ parall el=(125A)/(3.5Ah`

 

`Num b er\ of\ cells\ i n\ parall el=35.71`

 

We have to round off to lower value and higher value 

Case-1) Round off to lower value, Number of cells in parallel=35

Case-2) Round off to higher value Number of cells in parallel=36

Battery capacity = cell nominal capacity * number of cells in parallel

 

	Number of cells in Parallel	Battery          Capacity(Ah)	Requred     capacity(Ah)
Case - 1	35	35*3.5=122.5	125
Case - 2	36	36*3.5=126	125

 

It's always recommended to discharge the battery for continous current in 1C rate

case 1 not satisfies the 1C discharge of the battery but case 2 satisfies the 1C discharge

So,I choose 36cells in parallel

Now the battery pack is made of 34S36P so that it can meet the required output of 120V,150kW.

As the number of cells in series and parallel are very high which makes manufacturing difficult. So, we need to divide it into sub battery packs and remake the connections to get the requried output

 

To select the Topology we need no.of cells in series

EV's battery consists 34 cells in series.

For more than 18 cells we have to choose master slave BMS or modular BMS.

So,I choose Master slave BMS topology.2 slaves required to monitor the 34 cells

The BMS Slaves provide the balancing in each cell of the battery module and BMS Master provides the balancing of each module in the battery pack. For BMS Slaves, the balancing cell (target) has two different modes: one (over–discharged) is being charged while the other (overcharged) is discharging.

and it is cheaper compared to modular BMS and less complicated compared to modular BMS and controlling and manufacturing will be easy.

Master slave BMS topology: 

 This architecture comprises of the Master and Slave BMS units. The slave unit monitors, balances and controls a group of battery cells within the battery module. It communicates with the master unit through a communication interface. The Master unit is responsible for state estimation, control of Power Distribution Unit (PDU) and external communication. A master-slave BMS is similar to a modular system, in the sense that it uses multiple identical modules (the slaves), each measuring the voltage of a few cells.

However, the master is different from the slaves and does not measure voltages. It only handles computation and communications.

 

BMS architecture for the above topology :

 

Above architecture shows the complete MAster &  slave BMS topology consists 34cells in series and 36 cells parallel.

each slave consists 17cells and total 2 slaves are connected.both slaves are not connected to MCU directly.slave1 is connected to slave 2 and slave 2 is connected to MCU It communicates with the master unit through a communication interface.The each slave unit monitors, balances and controls a group of battery cells within the battery module and The Master unit is responsible for state estimation, control of Power Distribution Unit (PDU) and external communication

 It consisting of input sensors of volatge,current and temperature. The voltage sensor analog signal is converted to digital signal by AFE, the current sennsor analog signal is converted to digital signal by the MCU or we can connect the ADC converter between the Current sensor and MCU, the temperature sensor analog signal is converted to digital signal by the MCU or we can connect the ADC converter between the Temperature sensor and MCU. The switch brake the circuit by the command given be the MCU. The CAN and RS485 are Communication protocalls to the Outside world.

 

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

Aim:Simulation of the battery pack using 3S2P configyration

 

 

Above simulation is designed for 3S2P configuration of battery pack.

This contains 3 cells in series and 2cells in parallel.series connection is done by connecting cells +ve to the -ve of another cell and parallel connection is done by connecting same terminal of the battery to Same terminal of another battery.

If anyone want to use battery means he should connect the load to the respective terminals to which is shown as +ve and -ve

 

Conclusion:

The battery pack was designed as 34S36P and it is furthe divided into sub battery packs which is combination of 17S36P series with 17S36P.Total results in 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 instalation.

Simulation of battery which is having 3 cells in series and 2 cells in parallel is designed.