Project 1

To design a battery pack for a car with a power output of 150 kW and a voltage of 120V, we need to determine the number of cells required.

First, we need to convert the power output from kW to W:

150 kW = 150,000 W

Next, we need to calculate the current required to produce 150,000 W at 120V:

I = P / V = 150,000 / 120 = 1250 A

Each cell has a nominal voltage of 3.6V and a capacity of 3500 mAh, which is equivalent to 3.5 Ah or 3500/1000 = 3.5 Ah.

To achieve the required voltage of 120V, we need to connect the cells in series.

Number of cells in series = 120V / 3.6V = 33.33 or approximately 34 cells in series.

To achieve the required current of 1250A, we need to connect the cells in parallel.

Number of cells in parallel = 1250A / 3.5A = 357.14 or approximately 357 cells in parallel.

Therefore, the battery pack configuration will be 34S357P.

The next step is to determine the physical layout of the battery pack. The cells will need to be arranged in a way that maximizes the use of space while also allowing for efficient cooling and heat dissipation. A common configuration is to stack the cells in a rectangular shape, with each row connected in parallel and each column connected in series. This configuration allows for a compact design while also providing a large surface area for cooling.

The battery pack will also need to be enclosed in a protective case to prevent damage from impact and moisture. The case should be made of a lightweight, durable material that can withstand the stresses of daily use.

b. Draw the BMS topology for this battery pack.

Master-slave BMS topology for the battery pack with a 34S357P configuration:

• The battery pack is divided into multiple modules, each containing a certain number of series and parallel cells. For example, each module could contain 14 series cells and 10 parallel cells, resulting in a nominal voltage of 50.4V and a capacity of 35Ah.
• Each module has its own local BMS circuit, which monitors the voltage and temperature of the cells in the module and controls the balancing of the cells if necessary. The local BMS circuit consists of a microcontroller, voltage and temperature sensors, and balancing circuitry. The microcontroller is responsible for reading the voltage and temperature of each cell in the module and determining whether any cells need to be balanced. If balancing is required, the microcontroller controls the balancing circuitry to equalize the charge between the cells.
• The local BMS circuits are connected to a master BMS circuit, which acts as the central controller for the entire battery pack. The master BMS circuit also consists of a microcontroller, which communicates with the local BMS circuits to receive data on the state of each module and to control the charging and discharging of the battery pack. The master BMS circuit also performs higher-level functions, such as state-of-charge estimation and fault detection.
• The communication between the local BMS circuits and the master BMS circuit is typically done using a serial communication protocol, such as CAN (Controller Area Network) or SPI (Serial Peripheral Interface). Each local BMS circuit has its own unique identifier, which allows the master BMS circuit to address each module individually.
• The master BMS circuit also communicates with other systems in the vehicle, such as the motor controller or power management system, to optimize performance and efficiency. For example, the master BMS circuit may provide information on the state of charge of the battery pack to the power management system, which can use this information to determine how much power to allocate to other vehicle systems.
• Fuses and relays are connected in series with the battery pack to protect it from overcurrent and short circuits. The fuses and relays are typically controlled by the master BMS circuit, which can open or close them as needed to protect the battery pack.

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

Total number of cells in battery pack = no.of cells in series * no.of cells in parallel

= 3*2

=6 cells

Series connection of a battery:

Batteries are connected from teminal to terminal in a way that the +ve terminal one battery is connected to -ve termnal of the other battery and -ve terminal of one battery is connected to +ve terminal of other battery.

Parallel connection of a batteery:

Batteries are connected from terminals to same terminals of the other batteries that is +ve terminal of one battery is connected to +ve terminal of other battery and -ve terminal of one battery is connected to -ve terminal of other battery.

The battery pack model is shown below

Model explanation:

The voltage is measured bu using voltage measurement and is connected across the battery pack and the scope is connected to bus selector and is connected to battery measurement port for measuring the SOC,voltage & current of the cell the constant block is connected to controlled current source and is given load to the battery pack.

Battery parameters are given below

Nominal voltage of cell = 3.6v

Rated capacity of cell =3.5Ah

Maximum voltage of cell =4.2v

Total number of cells in a battery pack = no.of cells in series * no.of cells in parallel

= 3*2 = 6 cells

Nominal voltage of the battery pack = no.of cells in series * nominal volatege of a cell

Nominal voltage of the battery pack = 3*3.6v = 10.8v

Rated capacity of battery pack = no.of cells in parallel * Rated capacity of a cell

= 2*3.5

Rated capacity of battery pack=7Ah

Overall voltage of the battery pack=maximum capacity of the cell*no.of cells in series

=4.2*3

Overall voltage of the battery pack =12.6v

Capacity: The capacity of a battery or cell is defined as the amount of energy that it can deliver in a single discharge. Battery capacity is normally specified in amp-hours (or milli-amp-hours) or as watt-hours.

Charge rate or C-rate : The definition of the charge rate or C-rate of a battery or cell is the charge or discharge current in Amperes as a proportion of the rated capacity in Ah. For example, in the case of a 500 mAh battery, a C/2 rate is 250 mA and a 2C rate would be1 A.

Constant-Current Charge: This refers to a charging process where the level of current is maintained at a constant level regardless of the voltage of the battery or cell.

Constant-Voltage Charge: This definition refers to a charging process in which the voltage applied to a battery is held at a constant value over the charge cycle regardless of the current drawn.

Cycle Life: The capacity of a rechargeable cell or battery changes over its life. The definition of the battery life or cycle life of a battery is number of cycles that a cell or battery can be charged and discharged under specific conditions, before the available capacity falls to a specific performance criteria - normally 80% of the rated capacity.

Cut-off voltage: As a battery or cell is discharged it has a voltage curve that it follows - the voltage generally falling over the discharge cycle. The definition for a cell or battery of the cut-off voltage cell or battery is the voltage at which the discharge is terminated by any battery management system. This point may also be referred to as the End-of-Discharge voltage.

Energy Density: The volumetric energy storage density of a battery, expressed in Watt-hours per litre (Wh/l).

Power Density: The volumetric power density of a battery, expressed in Watts per litre (W/l).

Rated Capacity: The capacity of a battery is expressed in Ampere-hours, Ah and it is the total charge that can be obtained from a fully charged battery under specified discharge conditions

Self-Discharge: It is found that batteries and cells will lose their charge over a period of time, and need re-charging. This self-discharge is normal, but various according to a number of variables including the technology used and the conditions. Self-discharge is defined as the recoverable loss of capacity of a cell or battery. The figure is normally expressed in a percentage of the rated capacity lost per month and at a given temperature. The self-discharge rate of a battery or cell is very dependent upon the temperature.

Specific Energy: The gravimetric energy storage density of a battery, expressed in Watt-hours per kilogram (Wh/kg).

Specific Power: The specific power for a battery is the gravimetric power density expressed in Watts per kilogram (W/kg).

Results :

After running the model the voltage like shown below

The voltage is dropped from 12.6v to 12.57v for this battery pack.

Cell SOC,Current & voltage are shown below

First plot shows SOC of the cell it is dropped from 100% to 99.86 %

Second plot shows Current of the cell it is nearly 1.8A

Third plot shows voltage of the cell it is dropped from 4.188v to 4.155volts