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:

For 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.

Vehicle body:

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 against 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- Physical signal input port which allows the vehicle to undergo an inclination of hill climbing force.

Model parameters to set up mass, frontal area and others.

VEHICLE BODY SUBSYSTEM:

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 is kept as zero.

Simple gear block parameters:

This block models a gear system with fixed gear ratio with no-inertia effects. However, we can modify the messing of the gear teeth, Here 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 a 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 R is 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.

Here I have chosen to parameterize the block by rated power, rates speed and no-load speed. This lets us modify the parameters such as DC supply voltage, rated load. I have kept all values default except for the no-load speed, rated speed and 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. In the section of bridge parameters, the output voltage amplitude was modified to 400 volts according to the DC motor.

Controlled PWM voltage:

Next, I have used a '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 is ON to the time taken for one cycle. The duty cycle formula is given by:- Duty cycle= Ton/Ton +Toff= Ton /Tcyc. where Ton = On time, Tcyc=Time taken for one cycle.

Here all the parameters are set to their default values. I have chosen the averaged simulation mode so that it will feed voltage pulses within quicker simulation times to the H-bridge. The remaining parameters of input scaling and output scaling are unchanged.

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 deacceleration.

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:

Battery: The battery will be the energy store of the EV and will contain the electrical energy in DC form and provide this energy to operate.

Nominal voltage has been set to 600 volts, internal resistance has been set to 0.2 ohms and an infinite charging capacity

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

Controlled current source:

This block is a part in the battery sub-system. Similar to voltage source, this block produces an ideal current that is powerful enough to maintain the specified current regardless of the voltage across it.

Current source:

This current sensor block represents an ideal current sensor and is used to convert the current measured in an electrical circuit to a physical signal that is proportional to the current. It measures the current in the battery circuit and the DC motor. The positive and negative terminals across which the current sensor is inserted in to the circuit. The third port outputs the physical signal, In my model it sends the signal to the controlled current source.

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(secs 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 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.

Block parameters of the gain block:

Speed measurement :

In order to measure the 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:

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 siganal that is output from the velocity sub-system. Divided 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 deacceleration comments 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 deacceleration command is given as output to another control voltage source. For the output acceleration and deacceleration 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 deacceleration 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 two types of drive cycle data one is the 'New York bus cycle' and other is the 'Artemis motorway of 150kmph'. 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 excel sheet. Another method issue 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.

Block parameters:

Artemis Motorway 150kmph Drive cycle graph is given as input to the vehicle model-->

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.

Speed scope:

From this scope we can see two signals. The blue signal represents the vehicles body speed and the yellow signal is the Artemis drive cycle data . As we can see that the longitudinal driver successfully maintains the drive cycle data , process it and controls the vehicle's speed according to the reference speed. the graph overlaps each other effectively during acceleration and deacceleration.

Current scope:

This scope shows how current flowing from the battery to the motor varies with the drive cycle.

SOC scope:

The SOC scope shows how the state of the battery varies over the drive cycle time, The batter 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 75% 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.

From the above image the display block measured the distance as 8.306kms in 1068secs and charge remaining 75%.

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 "Artemis motorway 150kmph" 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 8.306kms and seems to be appropriate value based on the Artemis motorway 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.