Final Project: Design of an Electric Vehicle

COMPONENTS:

The main components of the EV are:

• Wheels/tires
• Battery Motor/generator
• Motor controllers
• Power converters
• Transmission system

Main simulation diagram:

In the below picture, we have done the simulation of an electric vehicle using various drive cycles by using powertrain blockset available in simulink library.First, there is the inputs where we have connected two different drive cycles which provides the reference for the longitudinal driver which compares the two speed and gives accelerator and braking commands to the motor controller block. battery block and vehicle body blocks are further attached and scopes are used for displaying the working status.

System level configuration

Modelling the whole vehicle in SIMULINK we need to model the above mentioned components separately and make them work together. All the main components are available in the library of SIMULINK blocks. so We add components and configure the parameters to fit the working requirements of the model.

This block contain 6 ports which can be used to model various aspects of the vehicle body. The ports are mentioned below;

• H- This stands for hub and is used to connect the hubs of the wheels to the main body of the vehicle.
• V-Physical signal output port which stands for velocity' and is used the output the velocity of the vehicle.
• W- Physical signal input port and allows us to model a wind velocity that acts aginst the vehicle.
• NR- Physical signal output port to connect to connect the rear wheels
• NF- Physical signal output port to connect the front wheels of the vehicle.
• Beta- Physicall signall input port which allows the vehicle to undergo an inclination of hill climbing force.
• Model parameters to set up mass, frontal area and others.

The above blocks are forming a subsystem which serves as a part for the whole vehicle. Four tires are connected, where the right two tires are the rear wheels and the remaining two are the front wheels they are interconnected to the hub of the vehicle body block. and their respective axles are connected accordingly. We here have connected the rear axle with the gear as we want the model to be a rear wheel drive vehicle. Here the wind velocity port and hill-climbing angle ports are connected to physical constant blocks which are kept as zero.

Tire blocks parameters:

here we can change the geometry, dynamics, rolling resistances and other characteristics.

Simple gear

The follower to base teeth ratio has been set to 2 and the output shaft rotates in the same direction as the input shaft.

All these blocks are categorised into a single subsystem which we have names as vehicle body block, which takes the mechanical input from the motor and controller block into the gear and displays the velocity at which the vehicle body moves.

MOTOR AND CONTROLLER SUBSYSTEM:

Components

• DC motor
• H-bridge
• Controlled PWM voltage
• Controlled voltage source
• Current sensor

DC motor

For the EV model, I have selected to use DC motor block because DC motors are easy to model and have a very few parameters to run for a particular application. There are two sides of the block, the mechanical side is on the right and the electrical side is on the left mechanical side has tow ports C and R, C stands for casing and is the stable part and Rise the rotor which produces a torque. The electrical side has a positive and negative side for the voltages to be applied. If positive voltage is applied to the motor block from the positive to the negative terminal then a positive torque will act from C to R port. The direction of the torque can be changed by changing the sign of the back emf or the torque constant Here i have connected the c port to the mechanical rotational reference because it will be stationary. The R port is connected to the gear in the vehicle body block

The block by rated power, rates speed and no load speed. This lets us modify the parameters such as DC supply voltage, rated load.

H- bridge

This is a power converter which is needed to provide power of the correct form and magnitude from one component to other. In case of EV’s a power converter is needed to provide a DC voltage from the battery of the EV to the DC motor, so that it can function properly at the required parameters. Here i have used an H-bridge motor drive as my power converter. The left side is for controlling the voltage signals and the right side terminals to provide the controlled voltage to the DC motor the left side ports are:

• PWM- Pulse width modulation
• REF- Reference
• REV- Reverse
• BRL- Brake

The simulation is kept in average mode because PWM mode will take longer durations of simulation.

Controlled PWM voltage:

Next, I have used controlled PWM voltage to provide a controlled pulse width modulated voltage to the H-bridge block. The pulses of voltage created by this block are dependent on the duty cycle which is in that ratio of the time that the switch ON to the time taken for one cycle

Duty cycle formula :- Ton/Ton+Toff = Ton/Tcyc, where Ton = on time Tcyc = Time taken for one cycle.

Controlled voltage source

This block provides the necessary voltage that is powerful enough to maintain the voltage at the output regardless of the current that passes through it. In this subsystem @ control voltage blocks have been used. One block is used for acceleration and other to provide the voltage for deceleration.

Electrical reference block is used to create grounding effect for electrical circuits. In my model, we have used it in 2 parts. First to create an electrical ground between Controlled voltage source, controlled PWM voltage, H-bridge blocks. The second is for the battery system which will be modelled afterwards.

Solver configuration block is used to solve any necessary equations in a model. I Have used them in the connection to the REV port of the H-Bridge block.

Battery subsystem

Nominal voltage is sufficient for supplying the voltage to DC-motor and H-bridge blocks.

SOC (state of charge) estimate subsystem:

To measure the state of charge of the battery, a sub-system was created of various blocks. The first block is integrator block used to handle data transfer and integrate the value of the current signal with respect to time and next is the Gain block is used in order to multiplier divide the signal coming from integrator block. This block will divide the current signal with the ampere rating of battery which is 140(Ah)*3600(sec in hour). Assuming the battery is always fully charged I have added the constant block with a value of 1 representing 100%.Next a sum block is used to perform addition and subtraction operations a these blocks are made into a subsystem called SOC estimate. A scope block is used at the junction of the PS-Simulink converter block to plot the output signal of the current from the battery.

Speed measurement:

In order to measure tyhe speed. I have modified the scope block to have two input ports where one port takes the output velocity signal from the vehicle sub-system block and other port takes the output signall from the drive cycle to the reference velocity port on the longitudinal driver block. This has been done to compare the two speeds and check weather they overlap and achieve the same speed.

Distance measurement:

a Mathematical blocks and scope block is used to measure the distance travelled by the vehicle. First we had to implement the integrator block to integrate the velocity signal that is output from the velocity sub-system. Dividend block along with constant block having a value of 3600 is used to divide the integrated speed. This will give us the distance travelled in kilometres.

Longitudinal driver and drive cycle:

The longitudinal driver block is used for giving normalized acceleration and deceleration commands to a controller based on two sets of data. The first data is the reference velocity and second data is the feedback velocity. The reference velocity data coming from drive cycle source and is compared to the feedback velocity data coming from the vehicle body. If the reference velocity is greater than the feedback velocity, an acceleration command will be given as an output to the controlled voltage source. If the reference velocity is lesser than the feedback velocity, a deceleration command is given as output to another control voltage source. For the output acceleration and deceleration commands i have used Simulink-PS converter block. In this case the input signal; is velocity data and this is logic data which have to be converted to a voltage signal The ports in this block are

• Velref- This stands for the reference velocity and it is the velocity data provided from a drive cycle source.
• Velfdbl- This stands for feedback velocity and it is coming from the vehicle's body velocity port
• Grade - This port provides a grade or inclination angle on which the vehicle is travelling in degrees. Info- This port is for the bus signals which consists of block calculations
• Accelcmd- This port provides the acceleration command to a controlled voltage source
• Deacclcmd- This port provides the deceleration command to another voltage source.

Drive cycle:

A drive cycle is a data set that contains velocity and time data for the purpose of modelling the motion of a vehicle. It is a plot of the vehicle velocity against the time and it is made to resemble typical driving conditions that a consumer may experience themselves in. For example here i have used one drive cycle data that is ‘FTP75’ : Drive cycles are used by various testing procedures such as mileage, pollution tests, and acceleration and top speed tests. There are three ways of implementing a drive cycle. One method is to create your own drive cycle with spreadsheet or excelsheet. Another method is use a signal builder and create signals according to the user and the method that we used is to implement industry standard drive cycles which are previously used to test parameters of the vehicle.

Results: I ran above drive cycle for my EV model and took the outputs from given speed, current and SOC. The distance travelled by the vehicle in the drive cycle is also measured using the display block. The run time is 1068 seconds.

Speed scope

The blue signal represents the vehicle body speed while the yellow signal referes to the FTP75 drive cycle data. The longitudinal driver doesn’t maintain the drive cycle data as there is a gap between real life driving and cycle created on computers.

Current scope:

Current variation throughout the cycle

SOC:

The SOC scope shows how the state of the battery varies over the drive cycle time, The battery was modelled to begin with an SOC pf 1 that is 100%. As the simulation starts the charge of the battery gets decreased and when the vehicle is in braking mode the uplift in the graph shows that regenerative braking is working to maintain the battery charge. Here we can see that after the whole simulation is over the State of charge percent lies at 94% after 1068 secs.

Distance travelled:

Results: I ran the above drive cycle for my EV model and took the outputs given from speed, current and SOC scopes. The distance travelled by the vehicle in the drive cycle is also measured using the display block. Before simulation the run time was updated according to the drive cycle time

1068secs.

Distance travelled is 3.853 km in 1068 seconds and charge remaining is 94%

Google link for model:

https://drive.google.com/file/d/1CgflIdJIQzs9gPB4yFfvM_JoIHyfH0R_/view?usp=sharing

Conclusion:

The EV model has been created with necessary block components using the SIMULINK software and the model have been simulated for an industrial drive cycle "FTP75" The simulation has produced the results of the velocity of the vehicle, current flowing from the battery and state of charge as well as the distance travelled in the simulation time. The EV model was able to follow the commands given by reference velocities from the drive cycle data. The distance travelled by my EV model was 3.853kms and seems to be appropriate value based on the FTP75 drive cycle. The SOC of the battery was discharged efficiently up to 75% from full charge. This model has also included some features like regenerative braking which was evident in the current scope and state of charge scope. My Ev model has been attached to this report as an .slx file.