Hybrid Electric Vehicle: Design of an Electric Vehicle

PROJECT:

Create a MATLAB model of electric car which uses a battery and a DC motor. Choose suitable blocks from Powertrain block set. Prepare a report about your model including following:

OBJECTIVE:

1. System level configurations

2. Model parameters

3. Results

4. Conclusion

THESIS:

Introduction:

• An electric vehicle (EV) is defined as a vehicle that uses an electric motor for propulsion instead of an internal combustion (IC) engine used by conventional vehicles.
  
  
• The power needed for the operation of an EV can come from a variety of sources such as batteries, generators, or through a collector system.
  
  Batteries fitted in to the body of an EV are of high energy densities to meet the power demands and range requirements.
  
  Generators generate electrical energy from an input of mechanical work and are a part of the electric motor, and they operate during braking to produce the regenerative braking.
  
  Collector are off-vehicle systems that allows for the charging of an EV from homes or public charging stations.
  
  
• EVs are increasing due to the need of the hour to reduce the emissions, that are damaging to the environment.
  
  
• EVs can meet the same performance standards of conventional vehicles and even surpass that of theirs and this has been seen with the automotive companies, i.e. Tesla.
  
  
• EV’s offer several advantages over conventional vehicles besides the lack of pollution and lack of need to rely on fossil fuels.
  - One is that, EVs are more efficient meaning that they offer more MPGe (miles per gallon gasoline equivalent).
  - Regenerative braking in EVs adds to their efficiency as the unused energy in braking gets reused purposefully.
  - Another benefit is that EVs have lesser maintenance costs than you would have with IC engine vehicles e.g. changing oil, transmission fluid.
  
  
• EVs are still a relatively new technology and only account for 2-3% of the worldwide market. This is because they cost considerable more than conventional vehicles due to the high cost of batteries and electric components.
  
  
• Another disadvantage is that the components in EVs operate at high voltages and currents and this can be a hazard if the components explode or don't work as they should.
  
  
• A compromise between IC engine vehicles and EVs exists as Hybrid Electric Vehicles (HEVs). HEVs combine an IC engine with an electric propulsion system to produce a 'hybrid' between the two different classes of vehicles. The purpose of this is to use the power available from the electric powertrain to improve the fuel economy of the vehicle so that it does not rely on the petrol/diesel all alone. This in turn will also improve the overall performance of the HEV.
  
  
• In this report, I will be modelling an electric vehicle with a DC motor and battery system using the SIMULINK software. The components I will need for my model exist as blocks in the SIMULINK block library. I will be modelling this EV for a drive cycle and measure the velocity characteristics and the current and SOC characteristics of its battery system.

Components:

The main components of an EV are:
- Batteries: They store the electrical energy needed to power the EV in all of its systems and needs. They are categorised into two types,
1. Traction battery
2. Auxillary battery
- Power converters: They convert the power coming from the battery to a usable form for the motor.
- Motor controllers: They are the electronics which control the amount of power delivered to the motor via the control signals.
- Motor/generator: Motor is used for propulsion in order to move the vehicle in forward or reverse motoring. The generator is a part of the motor and just works in the opposite method to the motor
- Transmission system: It is needed for the vehicle to change speeds as it accelerates/decelerates.
- Wheels/tires: They are needed for traction on the roads.
- Thermal system (cooling): This is needed for maintaining a proper operating temperature range of the electric motor, power electronics, and other components.
- Onboard charger: This takes the incoming AC electricity supplied via the charge port and converts it to DC power for charging the traction battery. - Charge port: This port allows the vehicle to connect to an external power supply in order to charge the traction battery pack.

MATLAB Modelling of the EV

Vehicle Technical Specification:

SL.	PARAMETERS	VALUE	SI UNIT
1.	Vehicle Weight	1200	Kg
2.	Wheels Per Axle	2	-
3.	Total Length	4127	mm
4.	Total Height	1487	mm
5.	Total Width	1746	mm

Using MATLAB SIMULINK System Block for Electric Vehicle design:

Blocks used in Electric Vehicle design are as the following:

• Drive Cycle Source: 1
• Constant: 3
• Longitudinal Drive: 1
• Controlled Voltage Source: 2
• Controlled PWM Voltage: 1
• Solver Configuration: 1
• Electrical Reference: 2
• H-Bridge: 1
• DC Motor: 1
• Mechanical Rotational Reference: 1
• Current Sensor: 1
• Battery:1
• Controlled current source: 1
• PS-Simulink/Simulink-PS Converter: 4
• Vehicle Body: 1
• Tire: 4
• Simple Gear: 1
• Side shaft: 1
• Go To: 2
• PS Constant: 2
• Gain: 2
• Zero Order Hold: 1
• Rate Transition: 1
• Discrete Time Integrator: 1
• Sum: 1
• Integrator: 1
• Divide: 1
• Display: 1
• Scope: 4

1. For System Level Configuration

To model an EV in SIMULINK, we will need to model the aforementioned components separately and then have them work together. All the main components are available in the library of SIMULINK blocks and we will be adding each component and configuring its parameters to fit the requirements of the model. First, the vehicle main body is considered.

1. Vehicle Body

The Vehicle Body block represents a two-axle vehicle body in longitudinal motion. The vehicle can have the same or a different number of wheels on each axle. For example, two wheels on the front axle and one wheel on the rear axle. The vehicle wheels are assumed identical in size. The vehicle can also have a centre of gravity (CG) that is at or below the plane of travel.

The block accounts for body mass, aerodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile. Optionally include pitch and suspension dynamics. The vehicle does not move vertically relative to the ground.

The block has an option to include an externally-defined mass and an externally-defined inertia. The mass, inertia, and centre of gravity of the vehicle body can vary over the course of simulation in response to system changes.

To model a vehicle's body, the vehicle body block is added and this is shown below:

• This block contains 6 ports that can be used to model the various aspects of the vehicle body.
• The ports are mentioned and elaborated below:
  - H : This stands for 'Hub' and is used to connect the hubs of the wheels to the main body of the vehicle.
  - V : This is a signal output port for 'Velocity' and is used to output the speed/velocity at which the vehicle is moving at.
  - W : This is a signal input port that works to model a 'headwind' acting on the vehicle by giving a speed for it.
  - NR : This is a signal output port to model the rear wheel normal forces.
  - NF : This is a signal output to model the front wheel normal forces.
  - Beta - This is a signal input port that works to model the vehicle on an inclination angle to create the effect of a hill climbing force.

• If we double click the vehicle body block, we can see and modify its parameters present in different tabs, i.e. Main, Drag, Pitch, Variables and this is shown in the image below:

As you can see, we are able to modify various parameters of the vehicle body present in the MAIN tab, considering they have been left with the default values assigned when the block was added to the workspace
- Mass
- Number of wheels per axle
- Distance of the centre of gravity to the front and rear axles

• The next comes the parameter, DRAG tab and this is shown below:

We can see that the parameters are as the following:
- Frontal area
- Drag coefficient
- Air density

Considering a sedan
- Value of drag coefficient was changed to 0.3 from the default value 0.4
- Meanwhile, air density and frontal area are left with the default values assigned when the block was added to the workspace

Now, giving the detailed inputs of the parameters of vehicle body used for the EV Modelling are as the following:

• Mass: 1200 Kg
• Number of wheels per axle: 2
• The horizontal distance from CG to front axle: 1.854 m
• The horizontal distance from CG to the rear axle: 2.2730 m
• CG height above ground: 0.5 m
• Externally-defined additional mass: OFF
• Gravitational acceleration: 9.81 m/s^2
• Negative normal force warning: OFF
• Frontal area: 2.21 m^2
• Drag coefficient: 0.30
• Air density: 1.18 kg/m^3
• Pitch dynamics: OFF
• Beginning Value of Velocity: 0 m/s

2. Tires:

The Tire (Magic Formula) block models a tire with longitudinal behavior given by the Magic Formula [1], an empirical equation based on four fitting coefficients. The block can model tire dynamics under constant or variable pavement conditions.

The longitudinal direction of the tire is the same as its direction of motion as it rolls on pavement. This block is a structural component based on the Tire-Road Interaction (Magic Formula) block.

To increase the fidelity of the tire model, you can specify properties such as tire compliance, inertia, and rolling resistance. However, these properties increase the complexity of the tire model and can slow down simulation. Consider ignoring tire compliance and inertia if simulating the model in real time or if preparing the model for hardware-in-the-loop (HIL) simulation.

The tires used in this EV model are the magic formula tires.

• There are several other tyre blocks that can be used for modelling a vehicle but the magic formula tires, well-fits in for the longitudinal behavior of vehicle tires on highways.
• They also allow us to model extra effects like:
  - Tire inertia
  - Stiffness
• The magic formula tire block is shown below:

• We can see that it has 4 ports:
  - N : This stands for Normal and it is the signal input port for the normal force acting on the tire.
  - S : This stands for Slip and it is the signal output port, that reports the slip acting on the tire.
  - A : This stands for Axle and it is the mechanical rotational conserving port for the wheel axle.
  - H : This stands for Hub and it is the mechanical translation port for the wheel hub.
• Double clicking the magic formula tire block, it takes us to its different parameter tabs,
  - MAIN
  - GEOMETRY
  - DYNAMICS
  - ROLLING RESISTANCE
  - ADVANCED

Parameter tab, MAIN

• Parametrize by, Load dependent Magic Formula coefficients is selected and the remaining parameters remain as default

Parameter tab, Geometry

• Here, only the rolling radius can be modified and has been set as 0.32m.

Parameter tab, Dynamics

• Here, we can model other additional effects that includes:
  - Tire inertia
  - The initial velocity

Parameter tab, Rolling Resistance

• Here, rolling resistance parameter on the tires is switched ON and a constant coefficient of rolling resistance of 0.015 along with avelocity threshold of 1e−3 is given as an input.

Parameter tab, Advanced

• Here, the velocity threshold is set to 0.1m/s. Less than the value of 0.1 m/s, the block will not model any of the aforementioned effects of motion on to the tire, hence called a 'threshold' velocity.

Now, giving the detailed inputs of the parameters of the magic tires used for the EV Modelling are as the following:

• Parameterize by: Load-dependent Magic Formula coefficients.
• Tire nominal vertical load – 4000 N.
• Magic formula C, D, E, BCD, H and V are default.
• Rolling radius: 0.32.
• Inertia: Specify inertia and initial velocity.
• Tire inertia: 0.5 kg*m^2.
• Initial velocity: 0 rpm.
• Rolling resistance: On.
• Resistance model: Constant Coefficient.
• Constant coefficient: 0.015
• Velocity threshold: 1e-3 m/s

3. Slip

• The 'S' port on the LR and LF tires are modelled with a certain degree of slip using a small subsystem.
• This subsystem uses a PS - Simulink converter which will be used again later on for other systems in this EV model.
• The slip subsystem used for the 'magic formula' tires is shown in the above image.

4. Gear

• Next, the transmission system of the EV is to be designed.
• Simple Gear block is chosen, so as to simplify the transmission system parameters.

This block models a gear system with a fixed gear ratio with no inertia effects, however we can modify the effects of the meshing of the gear teeth. A simple gear coupling has two inertias (shafts). The gear ratio between the follower (F) and base (B) is 2:1. Thus, the angular velocity of the follower shaft is half the angular velocity of the base shaft. The follower shaft torque is twice the base shaft torque.

• The simple gear block is shown :

• Double clicking the simple gear block takes us to its parameters tabs:
  - Main tab
  - Meshing losses tab
  - Viscous Losses
  - Faults

Parameter tab, Main

• Here, the main parameters of the simple gear are the follower to base teeth ratio and this has been set to 3.7 by default.
• The specification was updated, that the output shaft rotates in the same direction as the input shaft

Parameter tab, Meshing Losses

• The meshing losses, that has been selected follows a constant efficiency friction model with an efficiency of 0.86
• Follower power threshold was updated to a value of 0.001W.

Now, giving the detailed inputs of the parameters of simple gear used for the EV Modelling are as the following:

• Follower (F) to base (B) teeth ratio (NF/NB): 2.
• Output shaft rotates: In the same direction as the input shaft.
• Friction model: Constant efficiency.
• Efficiency: 0.86.
• Follower power threshold: 0.001 W.

5. Side Shaft

• This block generally represents the mechanical rotational element.

Where,
T = Inertia torque
J = Inertia
Ω = Angular velocity
T = Time

• This has been added to the workspace to provide an ideal mechanical rotational inertia for the simple gear block.
• This block has only one mechanical rotational conserving port and the positive direction of the block is from the port to the reference point
• The inertia torque acts in the positive direction is the inertia is accelerated in the positive direction.
• The inertia block is shown below:

Parameter tab, Parameters

• The inertia block parameters only allow for us to modify the inertia and this parameter has been kept at the default value of 0.01

Now, giving the detailed inputs of the parameters of simple body used for the EV Modelling are as the following:

• Inertia: 0.01

6. Wind and Slope

• Here, the velocity block allows us to model the effects of wind resistance and road inclination through the 'W' and 'beta' ports respectively.
• In this model, 'PS - Constant' block has been used to model the parameters of wind and road inclination on the vehicle's motion.
• The block parameters of the wind and slope effects are shown in the images below:

Now, giving the detailed inputs of the parameters of Wind & Slope used for the EV Modelling are as the following:

• Wind effect: 2.22 m/s.
• Road incline: 0.

7. Velocity Subsystem

• The velocity port which outputs the velocity signal of the vehicle body block has been modified.
• The velocity signal that is output from the vehicle body block is measured in miles per hour.
• To change these units, a small subsystem from the output of the velocity port has been implemented.
• This subsystem uses the following blocks:
  - PS - Simulink converter - this block will convert the physical signal of velocity to a logic signal.
  - Gain - This block uses a multiplication factor of 1.6 to convert the miles per hour units to kilometres per hour.
  - Zero - Order Hold - This block is used implement a zero order hold sample period.
• The inside of the subsystem is shown below:

Now, giving the detailed inputs of the parameters of Wind & Slope used for the EV Modelling are as the following:

• Gain Block: 1.61
• Zero-order Hold: 0.01

Vehicle Body Subsystem

The system level configuration has been further simplified,

• As seen in the diagram above, the various blocks are connected to model the vehicle body.
• 4 magic formula tire blocks are used as the vehicle will have 4 tires, 2 on each axle.
  - The tires are LR, LF, RR and RF (left rear, left front, right rear, and right front).
• The normal ports of each tire are connected to the appropriate NR and NF ports on the vehicle body block.
• The hubs of each tire are connected together and an extra connection is made from them to the vehicle body block.
• The 'S' ports of the LR and LF tires have been modelled with a slip using a small subsystem.
• The simple gear and inertia blocks are connected to the axle port of the tires.
• The wind velocity and road incline are provided.
• The velocity port has been connected to the velocity subsystem and the connection from the subsystem is open to the 'v' port.
• The base port of the simple gear has been left open to the 'R' port to take in a rotational signal.
• If all these connections are made, all of these components can be selected and made in to a subsystem shown below:

• This subsystem is created so that less space is taken up in the workspace and now, we only need the open ended connections to be modified.

Open ended Connections:

1. Motor

• For the EV model, DC motor block has been selected as the motor.
• This is because DC motors are easier to model and have fewer parameters to modify for a particular application.
• The DC motor block is shown below:

• As we can see, there are 2 sides to the block:
  - The mechanical side on the right
  - The electrical side on the left.
• The mechanical side has 2 ports, C and R.
  - The C refers to the casing
  - The R for the rotation of the rotor which produces a torque.
• The electrical side has a positive and a negative terminal for the voltages to be applied. If a positive voltage is applied to the DC motor block from the positive to the negative terminal, a positive torque will act from the C port to the R port.
• The direction of the torque produced by the DC motor can be changed by changing the sign of the back emf or the torque constant.
  - The C port of the mechanical side needs to be connected to a mechanical rotational reference because it will be stationary.
  - The R port will be connected to the open connection of the simple gear from the vehicle body block.
• When the positive terminal on the electrical side is connected to the positive terminal of a power converter, our use case will result with a setup called H bridge.
• The mechanical rotational reference block is shown below:

• Double clicking the DC motor block takes us to its parameters.
• The electrical torque parameters are first considered and the necessary changes are made as shown in the image below:

• In the mechanical parameters, we can modify the rotor inertia, damping and initial rotor speed as shown in the image below:

• Once the DC motor block has been parameterized, the following connections are made:

2. Power Converter

• This is needed to provide power of the correct form and magnitude from one component to another.
• In the case of EVs, a power converter is needed to provide a DC voltage from the battery of the EV to the DC motor so that it can operate properly with the required parameters.
• Here, H-Bridge motor drive has been used as the power converter. Its block is shown below:
• The H Bridge has the followings:
  - The left side is for the controlling of the voltage signals (PWM)
  - The right side is for the terminals to provide the controlled voltage to the DC motor.
  - REF: This stands for Reference.
  - REV: This stands for Reverse.
  - BRK: This stands for Brake.
• Opening the H-Bridge block will take us to its parameters shown below:

Parameter tab, Simulation mode and load assumptions:

• H-Bridge is selected as to run on an internal power supply with an averaged simulation mode instead of the PWM mode.
  This is because using the PWM mode will result in significantly longer simulation times compared to using the averaged mode.
• The regenerative braking mode has been enabled.
• Load current characteristics has been updated to the smoothed.

Parameter tab, Input thresolds:

• Here, the various voltage limits of its 4 left hand side ports are left to their default settings.

Parameter tab, Bridge parameters :

• Only the first parameter of 'Output voltage amplitude' was modified. The connections for this block will be made later on.

3. Controlled PWM Voltage

• Next, Controlled PWM Voltage block has been used to provide a controlled pulse width modulated voltage to the H-Bridge block.
• The block will output the PWM voltage through its 'PWM' and 'REF' ports which will feed in to the same ports found on the H-Bridge block.
• The controlled PWM voltage block is shown below:

Parameter tab, PWM :

• Here, the parameters are maintained at their default values.
• 'Averaged' simulation mode has been selected so that the average value of the voltage pulses are generated and fed in to the H-Bridge.

NOTE:
The remaining parameters of Input Scaling and Output Voltage are unchanged.

4. Controlled Voltage Source :

• This block has been used because, it will provide the necessary voltage that is powerful enough to maintain the voltage at the output regardless of the current that passes through it.
• This controlled voltage source block is shown below:

• In this model, 2 controlled voltage sources have been used.
  - One block is to provide the voltage for the acceleration of the vehicle.
  - Another block is to provide the voltage for the deceleration of the vehicle.

5. Electrical Reference:

• The electrical reference block is used to create a grounding effect for electrical circuits.
• The electrical reference block is shown below:

• In the EV model, 2 of the blocks are being used:
  - The first is for to create an electrical ground between the controlled voltage source, controlled PWM voltage and the H-Bridge blocks. - The second is for the battery system

6. Solver Configuration

• The solver configuration block is used to solve any necessary equations in a model.
• Here, this has been used in the connection to the 'REV' port of the H-Bridge block.
• The solver configuration block is shown below:

Using the open-ended connection blocks that has been mentioned above so far, which includes motor, power converter, controlled PWM voltage, controlled voltage source, electrical reference and solver configuration:

• Connection that has been developed from them is shown below:

7. Longitudinal Driver:

• The longitudinal driver block is used for giving normalized acceleration and deceleration commands to a controller based on 2 sets of data:
  - The first data set is the reference velocity.
  - The second data set is the feedback velocity.
• The longitudinal driver block is shown below:

• The longitudinal driver block has the following ports:
  - VelRef : This stands for the reference velocity and it is the velocity data provided from a drive cycle source.
  - VelFdbk : This stands for the feedback velocity and it is the velocity data provided from the vehicle body's velocity port which outputs the velocity data.
  - Grade : This port provides a grade or inclination angle for the surface on which the vehicle is travelling in degrees.
  - Info - This port is for the bus signals which consist of block calculations e.g. acceleration/deceleration command,etc.
  - AccelCmd :- This port provides the acceleration command to a controlled voltage source.
  - DecelCmd : This port provides the deceleration command to another controlled voltage source.
• The working of the longitudinal driver block is simple:
  - The reference velocity data coming from a drive cycle source is compared to the feedback velocity data coming from the vehicle body block.
  - 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 the output to another controlled voltage source instead.
  - For the acceleration and deceleration commands to be given as output signals, PS converter block has been used.
• The longitudinal driver block parameters are shown in the image below:

• Here, PI controller has been used and the reference and feedback velocities to be in m/s units are set.
• Meanwhile, all the other parameters have been as it is.
• Grade port of the longitudinal driver block is connected to a constant block with a constant value of 0 since, no road inclination is modelled for the simulation. This can be seen in the image below:

8. PS converter block

• This block is needed whenever we wish to connect a Simulink input signal to a physical signal. In this case, the input signal is velocity data and this is logic data which we want to convert to a physical signal i.e.. voltages to the controlled voltage source.
• The Simulink - PS converter block is shown below:

9. 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. For instance, this can help to model highway driving situations, driving in urban areas, or driving with full power etc.
• Drive cycles are used by automotive companies for various testing procedures such as mileage, pollution tests, and acceleration and top speed tests. There are various different drive cycles that are industry standard e.g. Urban Dynamometer Driving Schedule (UDDS), FTP 75.

• In this EV modelling, industry standard 'WOT' drive cycle has been used. This drive cycle stands for 'Wide Open Throttle' and it models the situation where the vehicle is made to accelerate at full power and maintained at a particular speed and made to decelerate back to rest. The drive cycle block is shown below:

• By default, the drive cycle block is set to the FTP75 drive cycle. This can be modified by opening the block parameters shown below:

• When the 'WOT' drive cycle is chosen, some extra parameters are made available and has been updated for modification which are shown below:

Note: As we can see, with the 'WOT' drive cycle, we can modify the start time, time to start deceleration and the entire duration of the drive cycle.

• Once the drive cycle parameters have been set as shown above, the output port of the drive cycle can be connected to the reference speed port of the longitudinal driver block.
• Next, the connections is made as shown in the image below:

WOT PLOT
The plot below shows the custom WOT drive cycle that has been created with the following data,

• Start time: 5 seconds
• Nominal reference speed: 30m/s
• Deceleration to begin at t: 20 seconds
• The entire cycle duration: 30 seconds.
• The input and output velocity units: m/s.

10. Battery System

1. 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 the DC motor for it to operate. The battery block used is a simple one constituting of only the basic parameters. The battery block is shown below:

• The battery block parameters are shown below:

• Input data are as the following fed in the dialog boxes present above.
• The nominal voltage is selected, so that it is more than sufficient to supply the voltage to the DC motor and the H-Bridge blocks.

2. Controlled Current Source

• The controlled current source block is a part of the battery system used in the EV model.
• Similar to the controlled voltage source, this block will represent an ideal current source that is powerful enough to maintain the specified current regardless of the voltage across it.
• The controlled current source block is shown below:

3. Current Sensor

• The 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.
• This block is used to measure the current between the battery circuit (controlled current source) and the DC motor.
• The current sensor block is shown below:

• - The positive and negative terminals represent the terminals across which the current sensor is inserted in to the circuit.
  - The third port outputs the physical signal and in this model, it will send the signal to the controlled current source.
• From the image above, we can see that the current sensor is embedded in between the electrical side of the DC motor and the H-Bridge.
• The current sensor can be connected from its physical signal port to the remaining components in the battery system including an electrical reference block. This is shown in the image below:

4. SOC & Current

• SOC stands for state of charge and it is a measurement of the available charge in a battery.
• When a battery is fully charged, it is considered to have a 100% charge and conversely 0% charge if fully discharged.
• In this EV model, aim is to measure the current of battery,the SOC of the battery as the simulation runs. For this, scope block is being used which shows the output signal we wish to measure as a plot against time.
• 2 scopes have been used, one for the current and the other for the SOC. The scope block is shown below:

5. SOC Subsystem & SOC Estimate

• To measure the state of charge of the battery, a subsystem was created of various blocks.
• The first block is the Rate Transition block. It is used to handle data transfer between different rates and tasks.
• Next is the Gain block. It is used in order to multiply or divide the signal coming from the rate transition block.
• Here, the gain block will divide the current signal with the ampere rating of the battery which has been taken as 80Ah multiplied by 3600 (sec in an hour). This is shown in the gain block parameters below:

• Next, Discrete-Time Integrator block is used to perform a discrete integration of the current signal with respect to the time.
• A Constant block is used to represent the initial SOC of the battery. Assuming that the battery is always fully charged when performing a simulation.
• Next, Sum block is used to perform addition and subtraction operations.
• The signal from the discrete time integrator block will be subtracted from the constant block representing 100% charge.
• These components are connected as shown below:
• These blocks are then made in to a subsystem called SOC Estimate and linked with the battery circuit using the PS-Simulink converter block. 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. Another scope is used to plot the output signal of the SOC from the SOC subsystem. This is shown in the image below:

6. Speed Measurement:

In order to measure the speed of the EV model, scope is used with 2 input ports where:

• One port takes the output velocity signal from the vehicle subsystem block
• Other port takes the output signal from the drive cycle to the reference velocity port on the longitudinal driver block.

7. Distance Measurement

• The scope block and mathematical operator blocks are used to measure the distance travelled by the vehicle according to the drive cycle data.
• The area under a velocity time graph tells us the distance travelled by the EV. This means that the integral of the velocity with respect to time, gives us the distance travelled.
• Thus, the integrator block is assigned to integrate the velocity signal that is output from the vehicle subsystem.
• The integrator block is shown below:

• From the integrator block, Divide block along with a Constant block was used altogether, having a value of 3600 in order to convert the divided integrated speed signal which is in kilometres per hour by 3600. It gives the distance in kilometres.
• The constant block with a value of 3600 is shown below:

• The Divide block is shown below:

• Finally, a display block is used to show the distance travelled during runtime. The display block is shown below:

• If these blocks have been already added to the workspace, these all can be connected as shown in the image below:

• With the entire blocks and setup, EV model can be simulated.

ENTIRE BLOCKSET FOR THE EV MODEL:

Result

• WOT drive cycle was run for EV model and the outputs were noted from the given inputs of speed, current and SOC scopes.
• The distance travelled by the vehicle in the drive cycle was also measured using the display block.
• Before running, the Stop Time was declared to be 30 seconds.

Speed Scope

• From this scope, we can see 2 signals.
  - The blue signal represents the reference signal which originates from the drive cycle data
  - The yellow signal shows the actual velocity of the vehicle.
• The WOT drive cycle had been customized so that the vehicle begins acceleration under the WOT condition (i.e.. full power) at t = 5 seconds. This is supposed to be maintained till t = 20 seconds when the vehicle is supposed to begin deceleration. From t = 20 seconds to t = 30 seconds, the vehicle speed is back to 0m/s i.e.. rest.
• Observing the vehicle's actual velocity, as commanded, the vehicle begins at rest before accelerating under the WOT condition at t = 5 seconds. This acceleration is maintained till t = 20 seconds as the drive cycle commanded. At t= 20 seconds, the vehicle achieves a top speed of 26.8m/s. After t = 20 seconds, the vehicle begins to decelerate gradually till t = 30 seconds where the vehicle finishes with a velocity of approximately 7m/s. As mentioned earlier, the actual velocity could not match the drive cycle commands perfectly and this is due to several other factors.
• For example, In this model, road inclination has not been bused but there is a wind velocity of 5m/s. The effect was very insignificant, only affecting the top speed by 0.5m/s. However, the vehicle velocity has accelerated and decelerated as the drive cycle commanded. Obviously, the model is limited to the simulation time allotted. So if a longer simulation time is used, the vehicle may reach a higher top speed and may even decelerate back to rest.

2. Current Scope

• The current scope shows how the current flowing from the battery to the motor varies with the drive cycle time.
• Here, the current flowing through the circuit is 0A initially and this corresponds to the drive cycle commanding the vehicle to be at rest for this time period.
• At t = 5 seconds, when the vehicle is commanded to accelerate, the current instantaneously increases to a maximum current of 235.8A. This maximum current is achieved because at t = 5 seconds, the vehicle accelerates at maximum power under the WOT condition and so this will demand a high current from the battery.
• From t = 5 seconds to t = 17.5 seconds, the current decreases gradually to 134.3A. The highest current is always required when accelerating from rest due to the inertia of the vehicle. But once the vehicle is already in motion, it requires significantly lesser energy to continue accelerating.
• From t = 17.5 seconds to t = 20 seconds, the current flowing from the battery decreases more rapidly to 85.6A. This is because at this time, the acceleration of the vehicle began to level off meaning that the increase in speed in those 2.5 seconds was lesser than the increase from t = 5 seconds to t = 17.5 seconds.
• After t = 20 seconds, the vehicle decelerates, causing the current to drop instantaneously to the negative axis to a value of -107.4A. There is now a negative current flowing due to regenerative braking. When the vehicle decelerates, the throttle is no longer applied and so the kinetic energy from the motion is converted to electrical energy fed back to the battery of the EV. This reverse flow of current is what causes the negative current measurement.
• From t = 20 seconds, the deceleration continues, however the current flowing through the battery decreases in magnitude. This is because at t = 20 seconds, the vehicle had reached its top speed and hence its maximum kinetic energy. So, at that point there was more kinetic energy which could be converted to electrical energy for regenerative braking. The polarity of the current hence moves towards the positive direction because regenerative braking happens lesser and lesser until the vehicle comes to rest.
• At t = 30 seconds, the vehicle is still decelerating and finished with current measurement of -27.9A showing that regenerative braking is still occurring.

3. SOC Scope

• The SOC scope shows how the state of charge of the battery varies over the drive cycle time.
• The battery was modelled to begin with an SOC of 1 (100%) and so when the simulation begins, the SOC is at 1 until t = 5 seconds. This is because the drive cycle commands the vehicle to be at rest for that duration and so no discharge occurs from the battery.
• At t = 5 seconds, the vehicle is commanded to accelerate under the WOT condition and so the SOC of the battery decreases. Because the vehicle is accelerating at full power, the SOC falls from 1 but the rate of discharge decreases over the acceleration period eventually settling at a minimum SOC of 0.9914 at t = 20 seconds.
• At t= 20 seconds, the vehicle is commanded to decelerate and so the vehicle velocity decreases. This results in regenerative braking to occur which causes a negative flow of current back to the battery. Because this effect charges the battery, the SOC of the battery increases during the deceleration period.

Distance Measurement

• From the above picture, we can see that the display shows the distance travelled by the EV model for the customized WOT cycle to be 0.1106km.
• This measurement seems appropriate and correct since the WOT drive cycle is very short in duration and only requires an acceleration for half of the drive cycle's overall duration.

Conclusion

• The EV model has been created with the necessary block components using the SIMULINK software and the model has been simulated for a customized WOT drive cycle.
• The simulation has produced results for the following:
  - Velocity of the vehicle.
  - Current flowing from the battery.
  - SOC of the battery.
  - The distance travelled by the EV.
• The distance travelled by the EV model comes to be 0.1106km, based on the WOT drive cycle used.
• If the duration of the WOT drive cycle could have been tend to be made longer, this EV model could have exhibited as a true performance characteristics.