Final Project: Design of an Electric Vehicle

AIM: Develop a MATLAB model of Electric Vehicle with suitable Blocks and analyse the results.

OBJECTIVES:

• Give proper system level configuration settings.
• Provide suitable model parameters according to the blocks.
• Comment out the results.
• Final Conclusion.

Why to choose Electric Vehicle:

There are many reasons why people are moving to Electric Vehicles (EV) to get them to the places they need to be. These include:

• Fast depletion of fossil fuel.
• Usage of EV will result in significant reduction in air pollution (CO2 emission) as transportation accounts for one third of all energy usage.
• With rapid urbanization around the globe electric vehicle is the need of the hour to serve everyone.
• Energy is not consumed while the electric vehicle is stationary, unlike internal combustion engines which consume fuel while idling thereby making it energy efficient.
• EVs are fun to drive because they are fast and smooth.
• Many studies show that the emissions from burning fossil fuels such as gasoline produce harmful greenhouse gases. EV’s produce no smelly fumes or harmful greenhouse gases.
• EVs are innovative and cool.
• EVs are a smart and convenient choice.

Comparing EV, ICE, PHEV and HEV:

Companies of BEV, PHEV and HEV:

BEV	PHEV	HEV
Tesla Model S	BMW i3 REX PHEV	Audi Q5
Nissan Leaf BEV	BMW i8 PHEV	Acura ILX Hybrid
Mitsubishi iMiEV BEV	Cadillac ELR PHEV	Cadillac Escalade Hybrid
BMW i3 BEV	GM Chevy Volt PHEV	BMW Active Hybrid
Smart EV BEV	Porsche Panamera S E PHEV	BMW Active Hybrid 5
Ford Focus EV BEV	Ford Fusion Energi PHEV	BMW Active Hybrid 7
-	Ford Cmax Energi PHEV	Honda Civic Hybrid
-	Toyota Prius Plugin PHEV	Honda CR-Z Hybrid
-	-	Hyundai Sonata Hybrid
-	-	Infiniti Q50 Hybrid
-	-	Infiniti Q70 Hybrid
-	-	Infiniti QX60 Hybrid
-	-	Infiniti M Hybrid
-	-	Kia Optima Hybrid
-	-	Lexus CT 200h
-	-	Lexus RX 450h
-	-	Lexus ES 300h
-	-	Lexus GS 450h
-	-	Lexus LS 600h L
-	-	Lincoln MKZ
-	-	Toyota Highlander Hybrid
-	-	Toyota Camry Hybrid
-	-	Toyota Prius
-	-	Toyota Prius C
-	-	Toyota Prius V
-	-	VW Jetta Turbo Hybrid

What is Electric Vehicle:

An electric vehicle (EV) is one that operates on an electric motor, instead of an internal-combustion engine that generates power by burning a mix of fuel and gases. Therefore, such as vehicle is seen as a possible replacement for current-generation automobile, in order to address the issue of rising pollution, global warming, depleting natural resources, etc. Though the concept of electric vehicles has been around for a long time, it has drawn a considerable amount of interest in the past decade amid a rising carbon footprint and other environmental impacts of fuel-based vehicles.

An Electric Vehicle (EV) is a vehicle that uses one or more electric motors or traction motors for propulsion. An electric vehicle may be powered through a collector system by electricity from off-vehicle sources, or may be self-contained with a battery, solar panels, fuel cells or an electric generator to convert fuel to electricity. EVs include, but are not limited to, road and rail vehicles, surface and underwater vessels, electric aircraft and electric spacecraft.

Flow process to Model the Electric Vehicle:

System-Level Configuration and Parameters

Input circuit:

Here the user defines the driver cycle and defines the behaviour of the vehicle movement for a particular time. In this, we have used 4 different types of inputs to run the simulation of our EV model. A Multiport switch is used to activate the which drive cycle input has to be run for simulation by changing the value of the constant.

• Drive Cycle Source:

It can generate a standard or user-specified longitudinal drive cycle. The block output is the vehicle longitudinal speed. There are different types of predefined drive cycles or can add in MATLAB workspace variables, including arrays and time series objects or spreadsheets.

• Slider Gain:

This block acts a slider when we can create our own driver cycle while the simulation is running by changing the position of the slider. The Maximum speed is set as 120 kmph with 1 kmph increment.

• Signal Builder:

This block is used to create and generate interchangeable groups of signals whose waveforms are piecewise linear.

This is defined drive cycle for 100 secs with gradual increase in acceleration still 30 seconds from 0 to 30 kmph and being constant still 50 seconds and increasing the speed gradually to 35 kmph still 77 seconds after attending top speed of 35 kmph, vehicle starts deceleration up to the speed of 0 kmph.

• From Spreadsheet:

This block is called out the self-created drive cycle made in Excel sheets and use as an input.

• Multiport switch:

It passed through the input signals corresponding to the truncated value of the first input. The inputs are numbered top to bottom, where the first input port is the control port and the other input ports are data ports.

Driver Controller:

The input from the drive cycle is attached to VelRef port, the feedback is gained from the vehicle body which acts as feedback signal is connected to VelFdbk. The AccelCmd & DecelCmd are the output signal given for accelerating and braking to the vehicle. A terminator block is connected to Info port as we are not using any bus signals for this model. A constant block is attached to the Grade port as road grade angle is 0 in our case, i.e. the vehicle is running at a straight road.

• Longitudinal driver block:

It is a parametric longitudinal speed tracking controller for generating normalized acceleration and braking commands based on reference and feedback velocities. They use the external actions to input signals that can disable, hold, or override the closed-loop commands determined by the block.

Ports Name Description

VelRef Input port for the reference velocity signal

VelFdbk Input port for the feedback velocity signal

Grade Input port for the gradeability to the vehicle (road grade angle)

Info Bus signal for Gear, clutch, acceleration, etc.

AccelCmd Output port for the acceleration signal command

DecelCmd Output port for the deceleration or braking signal command

Parameters

Battery, Power Converter and DC Motor:

This is the main circuit where the input signals are processed and are sent at the output. Here the important blocks are Controlled PWM Voltage and H-bridge. The H-bridge is connected to the DC motor and Battery. The electrical power from the battery source is converted into the mechanical output of the DC motor. There are 3 stages.

Motor Controller

Stage-1: PWM controlled voltage

Stage-2: H-bridge motor drive

Stage-3: Simple DC motor

At stage-1: Two controlled voltage sources are used; one takes the input signals for acceleration from the longitudinal drivers as output signal and another is used for deceleration or braking.

At stage-2: The circuit consists of a controller and an H-Bridge. The controlled PWM voltage block receives the input signal from the Acceleration's Controlled voltages source and generated modulated width pulses output for the H-Bridge and which is connected to the positive terminal of the block. The PWM signals are received by the H-Bridge connected to the PWM port of it. The other controlled voltage source is connected to the braking port of an H-Bridge. The reverse port is connected to the ground along with the Reference port. Here we have selected as Average control mode as the simulation mode to reduce the time for the overall operation.

At stage-3: DC motor receives the input signal from the H-Bridge through the current sensor. The rotational motion signal is sent as an output of the motor shaft. A mechanical rotation reference is connected at the constant port.

A battery is attached separately, which is not directly connected to the DC motor but is used for visualization of the SOC of the battery. The signal from the current sensor goes into the controlled current source block. Thus, generating current whenever the vehicle goes into regenerative mode. A subsystem is attached to display the SOC of the battery which is in series with the output signal of the current sensor. Electrical reference acts as a ground and is connected whenever a ground source is required.

• H-Bridge:

This block represents an H-bridge motor drive. The block can be driven by the Controlled PWM Voltage block in PWM or Averaged mode. In PWM mode, the motor is powered if the PWM port voltage is above the Enable threshold voltage. In Averaged mode, the PWM port voltage divided by the PWM signal amplitude parameter defines the ratio of the on-time to the PWM period. Using this ratio and assumptions about the load, the block applies an average voltage to the load that achieves the correct average load current. The Simulation mode parameter value must be the same for the Controlled PWM Voltage and H-Bridge blocks.

If the REV port voltage is greater than the Reverse threshold voltage, then the output voltage polarity is reversed. If the BRK port voltage is greater than the Braking threshold voltage, then the output terminals are short circuited via one bridge arm in series with the parallel combination of a second bridge arm and a freewheeling diode. Voltages at ports PWM, REV and BRK are defined relative to the REF port. If exposing the power supply connections, the block only supports PWM mode.

PWM - pulse width modulation is the method of reducing average power delivered by an electrical system by effectively chopping it up into discrete parts.

Port Name Description

PWM Input port for PWM voltage

REF Input port for reference PWM voltage

REV Input port for reverse signal

BRK Input port for brake signal

Parameters:

Here the power supply is kept at internal and simulation mode as Average (for less run time). Regenerative braking is enabled for always.

The input thresholds are kept unchanged and in the bridge parameters

The output voltage amplitude is set to 300 V.

• Controlled PWM Voltage:

This block creates a Pulse-Width Modulation (PWM) voltage across the PWM and REF ports. The output voltage is zero when the pulse is low, and is equal to the Output voltage amplitude parameter when high. Duty cycle is set by the input value.

The Simulation mode can be set to PWM or Averaged. In PWM mode, the output is a PWM signal. In Averaged mode, the output is constant with value equal to the averaged PWM signal.

Parameters

The PWM frequency is set to 1000 Hz and the simulation mode is set to average because it also set as same in an H-bridge.

The input voltage for 100% duty cycle is keep at 5 V as default value.

The output voltage amplitude is set to 24 V for more accurate results.

• Controlled Voltage source:

The block represents an ideal voltage source that is powerful enough to maintain the specified voltage at its output regardless of the current passing through it. The output voltage is V = Vs, where Vs is the numerical value presented at the physical signal port.

The controlled voltage source block does not have any block parameters of its own. It receives input from the longitudinal driver block and gives output to H-bridge block.

• DC motor:

This block represents the electrical and torque characteristics of a DC motor. It assumes that no electromagnetic energy is lost, and hence the back-emf and torque constants have the same numerical value when in SI units. Motor parameters can either be specified directly, or derived from no-load speed and stall torque. If no information is available on armature inductance, this parameter can be set to some small non-zero value.

When a positive current flows from the electrical + to - ports, a positive torque acts from the mechanical C to R ports. Motor torque direction can be changed by altering the sign of the back-emf or torque constants.

Parameter

The model parameterization is set as by rated load and speed. The rated DC supply voltage is kept as 120 V. The speed values of the motor at no-load and rated speed is 5000 rpm and 3000 rpm simultaneously. The rated load is at 50 kW (it changes as per the drive cycle). The mechanical and Faults parameter are kept at default.

• Battery:

This block models a battery. If you select Infinite for the Battery charge capacity parameter, the block models the battery as a series internal resistance and a constant voltage source. If you select Finite for the Battery charge capacity parameter, the block models the battery as a series internal resistance plus a charge-dependent voltage source defined by:

V=Vnom * (SOC / 1−β⋅(1−SOC))

where, SOC is the state of charge

Vnom is the nominal voltage.

Coefficient β is calculated to satisfy a user-defined data points.

Parameters:

The nominal voltage is set above the DC motor's rated supply voltage and battery charge capacity is keep infinite as there will charging will regenerative braking. Rest other parameters are the default

• Controlled current source:

The block represents an ideal current source that is powerful enough to maintain the specified current through it regardless of the voltage across it. The output current is I = Is, where Is is the numerical value presented at the physical signal port.

• Current sensor:

The block represents an ideal current sensor, that is, a device that converts current measured in any electrical branch into a physical signal proportional to the current. Connections + and - are conserving electrical ports through which the sensor is inserted into the circuit. Connection I is a physical signal port that outputs current value.

• Mechanical rotational reference:

This block represents a mechanical rotational reference point, that is, a frame or a ground. Use it to connect mechanical rotational ports that are rigidly affixed to the frame (ground).

• Electrical reference:

Electrical reference port. A model must contain at least one electrical reference port (electrical ground).

• Solver configuration:

It defines the solver setting to use for simulation when there is connection between simscape blocks and Simulink blocks.

Vehicle body:

This subsystem represents the 4-wheeler vehicle body with the transmission.

A set of four tire block are used - two for the front axle and two for the rear axle and the required connections are made with the vehicle body block. The normal force signal from the vehicle body block is sent to the normal force input ports of the tires.

The A ports of the tire are the mechanical rotational conserving port and receive mechanical rotational input from the gearbox which receives its input from the DC motor.

The H port of the tire is the mechanical translational conserving port for the wheel hub and is connected to the H port of the vehicle body through which the trust developed by the tire is applied to the vehicle. Here we are not considering any slip, so a terminator block is connected to all the slip port of each tire. Also, grade angle and wind velocity are not considered.

The input is received from the DC motor to the simple gear block which is then transmitted to the wheel considering the inertia couple at the output shaft.

• Vehicle body:

The block represents a two-axle vehicle body in longitudinal motion. The block accounts for body mass, aerodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile. The vehicle can have the same or a different number of wheels on each axle. Optionally include pitch and suspension dynamics or additional variable mass and inertia. The vehicle does not move vertically relative to the ground.

Port Name Description

H It is the mechanical translation converting port associated with the horizontal motion of the vehicle body.

V Signal output port for vehicle velocity

W Signal output port for headwind speed

NR Signal output port for rear normal wheel forces

NF Signal output port for front normal wheel forces

Beta Signal output port for road inclination angle

Parameters

The weight of the vehicle is considered as 100 kg and rest of the parameters are same as default.

The vehicle Frontal area is set as 2 square meters and Drag Coefficient as 0.3.

• Tire (Magic formula):

The block represents the longitudinal behaviour of a highway tire characterized by the tire Magic Formula. The block is built from Tire-Road Interaction (Magic Formula) and Simscape Foundation Library Wheel and Axle blocks. Optionally, the effects of tire inertia, stiffness, and damping can be included.

Port Name Description

N Signal input port that applies the normal force acting on the tire

A It is the mechanical rotational conserving port for the wheel axle

S Signal output port that reports the tire slip

H It is the mechanical translational conserving port for the wheel hub

Parameters

The tire is parameterized by peak longitudinal force and corresponding slip and rest of the parameters are keep as same as default.

Rolling resistance is on with constant coefficient of 0.02.

• Simple gear:

Port Name Description

B Input signal for mechanical rotational conserving port from DC motor

F Output signal for mechanical rotational conversing port after gear reduction

Parameters

The gear ratio set as 3. The more the gear ratio the better the speed with more traction power. As torque is directly proportional to the speed. The gear ratio is high at the start of the vehicle as it requires more torque and as the speed increases, torques reduces and so as the gear ratio.

SOC (Stage of Charge):

This will determine the voltage level in the battery at each point of simulation. The output from the current block is received at the input signal of the block and display the characteristic of the battery voltage consumed for the particular drive cycle.

The sub-block of the SOC contains the Rate transition block, gain block and the discrete time integrator. The decrease & increase of the battery voltage is have multiple data point which is handle by the rate transistor. Then this converts these data points and calculate the SOC at each point of the drive cycle. The gain block will calculate the values and display on the scope.

• Rate Transition:

It handles data transfer between different rates and tasks.

Parameters

• Gain:

  The gain is given by

  K=1 / Vrated * Time

  where, time is in secs, i.e., 3600 and the multiplication is element-wise.

• Discrete-time Integrator:

It is the accumulation of the input signals.

Parameters

• Distance Calculation:

The output of the vehicle body is Velocity which is sent as feedback to the longitudinal driver block and is separately used to calculate the distance travelled by the vehicle through another subsystem - distance calculator.

The velocity signal is first integrated to calculate the distance and then divide by 3600 to convert the distance into km.

Electric Vehicle Model (FTP Drive Cycle):

RESULTS:

Case-1: FTP Drive Cycle

Comparing Vehicle input and Vehicle feedback

State of Charge (SOC in %)

Current and Voltage

Acceleration and Deceleration

Case-2: Signal Builder Drive Cycle

Model

Comparing Vehicle input and Vehicle feedback

State of Charge (SOC in %)

Current and Voltage

Acceleration and Deceleration

Case-3: From Spread Sheet Drive Cycle

Model

Comparing Vehicle input and Vehicle feedback

State of Charge (SOC in %)

Current and Voltage

Acceleration and Deceleration

Case-4: UDDS Drive Cycle

Model

Comparing Vehicle input and Vehicle feedback

State of Charge (SOC in %)

Current and Voltage

Acceleration and Deceleration

Comparing 4 case study Results:

Parameters	Case-1	Case-2	Case-3	Case-4
	FTP	Signal Builder	Spread Sheet	USSD
Vehicle weight (kg)	1000	800	1000	1200
Frontal Area (m^2)	2	3	3	3
Air drag	0.3	0.4	0.4	0.4
Rolling resistance	0.02	0.015	0.015	0.015
DC Motor load	50	70	60	60
DC Motor voltage supply	120	94	72	140
Nominal Battery voltage	240	240	150	200
H-Bridge output voltage	300	200	200	300
Top Speed (kmph)	25.2	35.2	70	25.2
Distance Travelled (km)	5.442	0.6575	1.495	3.729
SOC at the end of the drive (%)	73	95.6	74	79
Maximum speed reaches (YES/NO)	YES	NO	NO	YES

CONCLUSION:

We have observed the speed trace plots for all the drive cycles, the feedback speed plot and the reference speed plot overlap each other almost completely but there are regions where both the speeds are different. It is when the vehicle is decelerating.

The reference speed plot falls sharply but the feedback speed does not. This is due to the inertia of the vehicle body. As the inertia of the vehicle body is higher, it takes a longer duration for the vehicle to decelerate so, the overlapping is not 100%.

The battery's state of charge for each drive cycle can be visualized from the SOC plot. As long as the vehicle is accelerating the SOC is decreasing but as soon as the deceleration starts, the SOC plot goes slightly up. This is because the battery is being charged, due to regenerative braking during deceleration.

Plots of Current, Voltage, Acceleration and Deceleration have been shown for better understanding of the process.

Hence, we have Modelled the Electric Vehicle in MATLAB and the give objectives have been implemented.

REFERENCES:

• https://pluginbc.ca/wp/wp-content/uploads/2014/07/EV-Beginners-Guide_Final_Sept2_2014.pdf
• YouTube videos on Electric vehicle modelling-1 and 2