Final Project: Design of an Electric Vehicle

Electric Vehicle:

An electric vehicle runs on pure electricity without any consumption of conventional fuels. Any automobile that is propelled by an electric motor, using energy stored in the battery is called a pure electric vehicle. Battery electric vehicles store electricity on board with high-capacity battery packs. Their battery power is used to run the electric motor and all onboard electronics. These electric vehicles are hazardless and are charged from external electric supplies.

Why Electric vehicle?

A battery electric vehicle(BEV) has far fewer moving parts than a conventional gasoline-powered vehicle. There’s no need for liquid fuels or oil changes. There’s no transmission or timing belt to fail when you least expect it. In fact, most of the maintenance costs associated with an internal combustion engine are eliminated.

Even if your vehicle was to be fueled exclusively by electricity generated by coal, EVs have a better emissions profile than internal combustion vehicles. Not only is the overall emissions content lower, but the location and timing of the emissions are better. While a gasoline-powered vehicle emits pollution during peak driving hours in the middle of the city, the emissions from fueling an EV generally happen during off-peak driving hours at power plants in remote locations.

EVs are sophisticated and diversified, with many price and style options, but all with the reliability and power of traditional, gasoline-powered vehicles. A compact and quiet motor yields surprising acceleration: 100% torque at zero rpm, without the negative emissions associated with most cars on the road.

Electric vehicle block diagram:

system-level configuration:

The vehicle model mainly consists of,

• vehicle body
• motor and controller
• battery pack and power converter
• drive cycle source

The battery pack is the powerhouse of the Electric Vehicle model which supplies power to the motor and other equipment necessary for the efficient operation of the Vehicle. The power converter converts energy from battery to an optimum level as required by the motor. The converter is bi-directional which helps in taking regenerative energy back to battery thereby providing charging while deceleration of the vehicle. The vehicle body represents the body of the vehicle with wheels that are connected to the motor through a transmission system. Motor takes power from the battery as per load requirements with help of controller which reviews load requirements and produces proportional control signals with help of a feedback from the vehicle so as to obtain a smooth and efficient operation of the vehicle. Drive cycle source is a reference driving pattern taken for the simulation as per Drive cycle data.

Simulink model:

Detailed model study:

1.vehicle block:

Vehicle block consists of the vehicle body, tires, and transmission system.

• vehicle body:

This represents a two-axle vehicle body in motion. It accounts for body mass, aerodynamic drag, externally-defined mass, and center of gravity of the vehicle body.

Input ports:

W- wind velocity in m/s

beta - grade angle in radians

output ports:

V - velocity in m/s

NR - normal force on the rear axle(N)

NF - normal force on the front axle(N)

• Tires:

used to model a tire with longitudinal behavior given by equation based on four fitting coefficients. The block can model tire dynamics under constant or variable contact surface conditions.

Input Port:

N - Normal force acting on the tire, positive when force is acting downwards/towards the contact surface,

Output Port:

S -  Slip value relative to tire and surface of contact.

Conserving Ports:

H - represents a wheel hub that transmits thrust generated by the wheel to the body of the vehicle.

A - represents axle on which the tires are mounted.

• Gear:

A simple gear block is used to connect the motor to the rear axle of the vehicle. It represents the gearbox that connects the input shaft to the base gear and output from the foller gear.

Conserving Ports:

B - port associated with an input shaft (motor shaft)

F - port associated with the output shaft (axle/differential)

Gear ratio and output direction are modified. Meshing loss is kept constant and gear is having a constant efficiency throughout the simulation. Viscous losses and faults are kept at default conditions.

2.Motor and power converters:

The components and parameters present in these motor and power converters are,

• DC motor:

+ ---> ports receiving an electric signal associated with the motor positive terminal

-  ----> ports receiving an electric signal associated with the motor negative terminal

C ----> mechanical conserving port associated with the casing of the motor and is connected to a mechanical rational reference block

R ------>  mechanical conserving port associated with rotor shaft of the motor which products required input to the transmission system

It is parameterized to the rated load and speed condition.

Rated voltage, speed, and load values along with no-load speed is modified

• H-Bridge:

H-Bridge block is used to represent the H-bridge motor driver which controls the power input to the motor according to the load requirements. The output provided by the block is controlled voltage depending on the control signal

+  --->  Conserving port associated with positive load connection usually connected to the positive port of the motor.

-  ---->  Conserving port associated with negative load connection usually connected to the negative terminal of the motor.

PWM ----> Conserving port associated with PWM control signal (voltage pulses)

REF ---->Conserving port associated with a ZERO voltage reference.

REV ---->Conserving port associated with voltage controlling polarity change of Bridge output signal.

BRK -----> Conserving port associated with voltage when brakes are applied, thereby aiding the process of regenerative braking.

H-bridge is selected to have its own power source as internal.

the averaged summation is selected for faster simulation and regenerative braking is enabled.

Output voltage amplitude is set as equal to the rated voltage of the motor 

The acceleration(PWM) and deceleration(BRK) command signal from the driver is controlled by a Controlled Voltage Source before it is fed to the H-Bridge. Default parameters are maintained for the Controlled Voltage Source.

• Controlled PWM Voltage:

produces Pulse-Width modulated signals to control voltage fed to H-Bridge as per requirements.

ref+ ------>positive reference voltage signal

portref-  -----> negative reference voltage signal port 

PWM ------> Pulse-Width modulated electrical signal 

REF ------>  Port associated with zero voltage reference

The simulation model is set to PWM and output voltage amplitude is set similar to the input signal amplitude of the H-Bridge

Along with all these, a solver configuration block is used as is necessary for simulation and is connected to the physical network of the motor controller.

3. Battery:

It represents the powerhouse of the model which supplies the power required by the motor as controlled by the controllers. SOC calculation of battery is done to trace the battery reliability and range of the vehicle model. SOC is calculated by reducing the usage from the nominal SOC value on a timely basis.

SOC calculation:

4.Longitudinal driver:

It Represents a longitudinal speed controller which produces acceleration and deceleration commands based on input and feedback speed variables provided using a Proportional Integral (PI) control.

VelRef - input port associated with the input reference velocity of the vehicle (m/s)

VelFdbk - input port associated with velocity feedback from the vehicle which helps in smooth control of the system.

Grade - input port associated with an inclination of surface in degrees.

Info - output port associated with a bus signal for acceleration, deceleration, error in velocity etc

AccelCmd - Output port associated with acceleration commands with reference to the input signal.

DecelCmd - Output port associated with deceleration commands with reference to the input drive signal.

proportional integral type is selected and other control variables are kept as default values.

5.Drive cycle source:

Generates a standard or user-specified longitudinal drive cycle. The block output is the vehicle longitudinal speed.

By default, the FTP75 drive cycle is selected. The wide-Open-Throttle condition can also be selected. Drive cycle data can also be taken from spreadsheet data or through a glider block or a signal builder block.

The simulation default time for FTP75 is 2474 seconds.

Results:

The velocity values of the reference FTP75 and velocity in the feedback is shown in the plot using the scope.

FTP75 Drive cycle is used to perform the simulation. The speed comparison curve shows that the actual velocity(blue curve) of the vehicle almost follows the Reference curve (yellow curve) throughout the simulation. During peak decelerations, the Speed comparison curve shows a difference in velocity which is encountered due to inertial effects of the vehicle and instantaneous velocity drops in the reference curve.

soc of the battery:

The FTP75 drive cycle is having several accelerations and deceleration profiles that vary randomly which depicts a real-life driving scenario that helps to track the nature of battery discharge while different acceleration profiles and regenerative charging effects on deceleration profiles. The SOC scope block helps in keeping track of the remaining battery capacity.