Final Project: Design of an Electric Vehicle

AIM:

To create a MATLAB model of electric car which uses DC motor by choosing the suitable blocks from powertrain block set.

OBJECTIVE:

To prepare a technical report about the EV models including:

1. System level configurations
2. Model parameters
3. Results
4. Conclusion.

ELECTRIC VEHICLE:

The electric vehicle type does not contain any other source of actuation other than motors and batteries. There is zero-emission in these vehicles. The battery is charged through an external source of power such as DC fast charger or AC chargers.
On average, the BEVs take around 8 hours to get fully charged using an AC charger. This time can be reduced to 1 hour using a DC fast charger.
These electric vehicles have a range from 250kms to 500kms depending upon the battery capacity and the motor.

COMPONENTS OF ELECTRIC VEHICLE:

The basic main elements of electric cars installed in almost all types of electric cars are as follows:

Traction Battery Pack

The function of the battery in an electric car is as an electrical energy storage system in the form of direct-current electricity (DC). If it gets a signal from the controller, the battery will flow DC electrical energy to the inverter to then be used to drive the motor. The type of battery used is a rechargeable battery that is arranged in such a way as to form what is called a traction battery pack.

There are various types of electric car batteries. The most widely used is the type of lithium-ion batteries.

Power Inverter (B)

The function of the inverter is to change the direct current (DC) on the battery into an alternating current (AC) and then this alternating current is used by an electric motor. In addition, the inverter on an electric car also has a function to change the AC current when regenerative braking to DC current and then used to recharge the battery. The type of inverter used in some electric car models is the bi-directional inverter category.

Controller

The main function of the controller is as a regulator of electrical energy from batteries and inverters that will be distributed to electric motors. While the controller itself gets the main input from the car pedal,(which is set by the driver), this pedal setting will determine the frequency variation or voltage variation that will enter the motor, and at the same time determine the car’s speed.

In brief, this unit manages the flow of electrical energy delivered by the traction battery, controlling the speed of the electric traction motor and the torque it produces. This component will determine how electric car work.

Electric Traction Motor

Because the controller provides electrical power from the traction battery, the electric traction motors will work turning the transmission and wheels. Some hybrid electric cars use a type of generator-motor that performs the functions of propulsion and regeneration. In general, the type of electric motor used is the BLDC (brushless DC) motor

Charger is a battery charging device. Chargers get electricity from outside sources, such as the utility grid or solar power plants. AC electricity is converted into DC electricity and then stored in the battery. There are 2 types of electric car chargers:

• On-board charger: the charger is located and installed in the car
• Off-board charger: the charger is not located or not installed in the car.

Transmission:

The transmission transfers mechanical power from the electric traction motor to drive the wheels.

DC/DC Converter:

DC/DC converter converts higher-voltage DC power from the traction battery pack to the lower-voltage DC power needed to run vehicle accessories and recharge the auxiliary battery.

Battery:

In an electric drive vehicle, the auxiliary battery provides electricity to power vehicle accessories.

Thermal System – Cooling:

This system maintains a proper operating temperature range of the engine, electric motor, power electronics, and other components.

Charge Port:

The charge port allows the vehicle to connect to an external power supply in order to charge the traction battery pack.

PROCEDURE:

1.VEHICLE BODY SYSTEM:

• The vehicle is assumed to be a front axle driven (4 wheels – 2 on each axle)
• The wheels are modeled using simple Tire(magic formula) simulink blocks.
• The N port of the tire corresponds to the normal reaction acting on it. The A port corresponds to the mechanical rotational conserving port for the wheel axle. Thus both the wheels on the same axle should form a connection through their respective A ports.
• Connection H corresponds to the Mechanical translational conserving port for the wheel hub through which the thrust developed by the tire is applied to the vehicle. Thus all 4 wheels form a connection through their respective H ports and this in turn connected to the translational hub of the vehicle body. The connection S represents the output port for slip of the tire.

• The tires are parameterized by peak longitudinal force and corresponding slip.
• The other block parameters such as rated vertical load, peak longitudinal force at rated load and slip at peak force at rated load are kept with their default values.
• The tire radius is given as 0.3m.
• The tire inertia is kept as 1Kg m^2. Also, the rolling resistance is given with a constant coefficient of 0.015.

• This block basically represents a two- axle vehicle body in longitudinal motion. The block accounts for

Body mass,

Aerodynamic drag,

Road incline

Weight distribution between axles due to acceleration

Road profile.

• Here, connection H is the mechanical translational conserving port hub. NF and NR corresponds to the output ports for the normal reaction forces on front axle and rear axle wheels respectively.
• Connection V represents the actual output translational velocity of the vehicle. Beta is the road inclination angle & W corresponds to the headwind speed.
• The gross weight is given to the 1200Kgs.

The complete subsystem is shown below:

• The input is fed to the front axle through a simple gear representing the Final Drive Ratio of 3.43.

2.DC MOTOR:

• Simulink provides an inbuilt model block DC motor which converts electrical input into mechanical rotational output.
• Here, the motor field type is kept as Permanent magnet and the model parameterization is done by rated load and speed.
• The armature inductance and mechanical parameters are given their default values.
• All the other parameters are shown in the figure:

• The connection R represents the Rotor while the connection C represents the Casing. Thus, the R port is connected to the input vehicle subsystem created earlier. The C port is connected to a mechanical rotational reference.
• The + and – terminals of the motor are connected to the motor controller. If these terminals are directly connected to the battery, the required DC motor will run on the rated capacity of the battery.
• Thus, a motor controller is very much necessary.

3. MOTOR CONTROLLER:

H-BRIDGE CIRCUIT:

• 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 PMW mode, the motor is powered if the PWM port voltage is above the enabled threshold voltage.
• In Averaged mode, the PMW port voltage divided by the signal amplitude parameter defines the ratio of On-time to the PWM period.
• Connection REF is for the reference input. This combined with the PWM connected will form the pulse input for the H-bridge.
• Connection REV corresponds to the reverse motion of the motor which means, the backward motion of the vehicle.
• Connection BRK is for the braking of the vehicle.
• Since, the PWM mode results in a huge amount of simulation time,Averaged mode is selected for this simulation.
• Load current characteristics are considered to be smoothed here.
• The brake input is connected to the Controlled Voltage Source. This will generate emf corresponding to the intensity of brakes applied and fed the power back to the battery.

• The Input threshold parameters are left with their default values.

• Simulink provides an inbuilt Controlled PWM voltage block. This block is used for providing the proper pulse inputs to the H-bridge circuits.
• Here, the PWM frequency is 1000Hz. Also, the simulation mode is Averaged as that in the H-bridge circuit.
• The input scaling parameters are given as 0V for 0% duty cycle and 5V for 100% duty cycle. Accordingly, the output voltage amplitude is 5V.
• The H-bridge circuit along with the PWM input, together form the motor controller circuit.

4. LONGITUDINAL DRIVE:

• Longitudinal driver is an inbuilt block provided by the powertrain blockset.
• It is a parametric longitudinal speed tracking controller for generating normalized Accleration and Braking commands based on reference and feedback velocities.
• The VelRef port is the reference velocity port where the input driver cycle data is fed.
• The VelFdbk port corresponds to the feedback velocity. The actual velocity output given by the vehicle body is connected here. By comparing the actual velocity with the reference velocity, the driver block generates acceleration and braking signals in order to minimize the error between the two concerned velocities.
• The selected control type is PI. Accordingly, the block implements the proportional- integral control with tracking windup and feed-forwards gains.

5. BATTERY MODEL:

• To model the Battery pack, a simple battery block is used. This is because, if the generic battery block is used instead, the simulation will run for a much longer time.
• Here, the selected option for Battery charge capacity is Finite. Accordingly, the block models the battery as a series internal resistance plus a charge-dependent voltage source.
• Also, the self- discharging of the battery and the battery dynamics are disabled.
• The Battery Nominal Voltage is 400V. The ampere- Hour rating is 50.

6. REFERENCE VELOCITY:

• The Drive cycle Source block is used to provide the reference speed for the simulation.
• It generates a standard or user specified longitudinal drive cycle.

7. BATTERY STATE OF CHARGE:

• A small subsystem is created to calculate the state of charge of the battery.
• This subsystem takes the battery current as input.

• The essential process to calculate the SOC is by subtracting the charge from the rated capacity of the battery.
• The current is integrated w.r.t time to get the charge in coulombs. Now, this coulomb is modified in to Ampere hours.
• The value obtained is now subtracted from the charging capacity of the battery. 50Ah.
• The remaining charge is now converted into percentage value of the charging capacity of the battery.

SIMULINK MODEL:

• The system is ran for simulation for 2474s which is the total time for which the input drive cycle is defined.
• A Solver configuration is added to ensure proper solving of the mathematical equations by the model.
• Scopes are connected to analyze different outputs such as SOC of the battery, the reference velocity and actual velocity of the vehicle and the distance covered by the vehicle during the total run.
• The 2 velocities are first converted from m/s to kmph. For this simple gain block is used.
• The distance is calculated by simply time- integrating the vehicle velocity.

OUTPUTS:

REF SPEED Vs ACTUAL VEHICLE SPEED:

• As can be seen from the above picture, the actual velocity of the vehicle differs from the reference drive cycle velocity.
• This is because, the chosen battery capacity and the motor are not able to propel the speed upto the required extent.
• If a battery of higher capacity is chosen, the actual velocity will tend to match with the reference velocity.
• Also, it may be noted that in certain regions, despite the drive cycle showing small decelerations, the vehicle actually is accelerating with decreasing magnitudes.

DISTANCE COVERED:

• It may be noted that, since the reference velocity of the driver cycle never becomes negative, the distance is increasing throughout.
• The total distance covered by the vehicle is approx. 9.3Kms.

BATTERY STATE OF CHARGE:

• The state of charge of the battery at the end of the simulation run is nearly about 33%.
• This means that the battery is not completely drained at the end and the vehicle can run on the same drive cycle for a few more times before the battery SOC becomes 0.
• Also, whenever the vehicle undergoes heavy deceleration, the battery SOC increases slightly.
• Again, this depends upon the generating tendency of the motor and the maximum amount of current that battery can take.

CONCLUSION:

The model was successfully run for simulation under the standard FTP75 cycle. The results have been properly analyzed and a detailed report has been done using some assumptions.