Final Project: Design of an Electric Vehicle

SOLUTION:-

PROJECT: DESIGN OF AN ELECTRIC VEHICLE

Theory:

An electric vehicle(EV) is defined as a vehicle that uses an electric motor or a traction motor for propulsion instead of internal combustion used by conventional vehicles. Electric vehicle use electricity for power instead of fossil fuels like conventional vehicles . So, they do not produce any exhaust gases and pollution. The power needed in the EV come from batteries, generator or any collector system. Batteries fitted in the EV are of high energy densities in order meet the power requirements and range.

The power of a vehicle's electric motor, as in other vehicles, is measured in kilowatts (kW). 100 kW is roughly equal to 134 horsepower but electric motors can deliver their maximum torque over a wide RPM range. This means that the performance of a vehicle with a 100 kW electric motor exceeds that of a vehicle with a 100 kW internal combution engine which can only deliver its maximum torque within a limited range of engine speed. Energy is lost during the process of converting the electrical energy to mechanical energy. Approximately 90% of the energy from the battery is converted to mechanical energy, the losses being in the motor and drivetrain.Usually, (DC) electricity is fed into a DC/AC inverter where it is converted to (AC) electricity and this AC electricity is connected to a 3-phase AC motor. For electric trains, and some electric cars, DC motors are often used. In some cases, universal motors are used, and then AC or DC may be employed. In recent production vehicles, various motor types have been implemented; for instance, induction motor within Tesla Motor vehicles and permanent magnet machines in the Nissan Leaf and Chevrolet Bolt.

Most large electric transport systems are powered by stationary sources of electricity that are directly connected to the vehicles through wires. Electric traction allows the use of Regenerative braking, in which the motors are used as brakes and become generators that transform the motion of, usually, a train into electrical power that is then fed back into the lines. This system is particularly advantageous in mountainous operations, as descending vehicles can produce a large portion of the power required for those ascending. This regenerative system is only viable if the system is large enough to utilise the power generated by descending vehicles. In order for EV,s to dominate the automotive industries, Their needs to be more convinient ways for consumers to be able to charge their vehicles. There needs to be several charging stations on highways and this can be supported if most of the houses are solar powered. EV,s cost more than conventional vehicles because of the high cost of batteries and electric components.

HEV's combine an IC engine with an electric propulsion system to produce a hybrid between the two types of vehicles. The purpose of this is to use the power available from the electric power-train to improve the fuel economy of the vehicle so that it does not rely solely on the petrol/diesel for the fuel. This in turn will also improve the overall performance of the HEV. The IC engine can be used to power the electric motor to charge the battery oruse directly in the electric drive motor with acombination of motor and generator in one. HEV's also implement regenerative braking to recharge their batteries . EV's are still a relatively new technology and account for 2-3%of the world wide market. Whereas HEV's represent more of the market with 19% market share on all automobiles. The all time best selling HEV to date is the toyota prius.

In this report , I will be modelling an electric vehicle with a DC motor and battery system using the SIMULINK software. The model will run for a drive-cycle and measure the velocity characteristics, current, and state of charge characteristics of the battery system. The components i need to exist as blocks in the simulink block library.

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 emntioned 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 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 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 amd 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.

Tire block parameters:

Here we can also change the geometry , dynamics, rolling resistance other characteristics if we want

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 negetive side for the voltages to be applied. If positive voltage is applied to the motor block from the positive to the negetive terminal then a positive torque will act from C to R port. The directio of the torque can be cahnged 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 choosen to parameterize the block by rated power, rates speed and no-load speed. This lets us modify the parameterssuchas 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 fuction 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 signalsand 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 beacuse 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 powerfull enough to maintaion thr voltage at the output regardless of the current that passes through it.In this subsystem @ control voltage blocks ahve 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 andH-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 powerfull 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 negetive terminals across which thecurrent sensor is inserted in to the circuit. The third port outputs the physical signal , In my model it sends the signal to te 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 multiplyer divide the signal coming from integrator block. This block will divide the current signal with the ampere ratingof 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 substraction operations athese blocks aremade into a subsystem called SOC estimate. A scope block is used at the junction of the PS-simulink converter block to plot the output signall of the current from the battery.

Block parameters of the gain block:

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:

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. Dividen 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 kilometers.

Longitudional driver and drive cycle:

The longitudinal driver block is used for giving normalized acceleration and deacceleration commants 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 comand 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 anpother controll 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 resembl typicall driving conditions that a consumer may experience themselves in. For example here i have used two types of drive cycle data one is the 'newyork 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 spreedsheet or excelsheet. Another method isuse a signal builder and create siganls according to the user and the method that we used is to implement industry standard drive cycles which are previosly 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, surrent 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 eachother 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 bettery gets decreased and when the vehicle is in braking mode the uplift in the grapf 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, surrent 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%.