Challenge

Final Project: Design of an Electric Vehicle

SSagar Nemade26 Jan 2022

Question

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:

Objectives:

1. System level configurations

2. Model parameters

3. Results

4. Conclusion

Answer :-

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

OBJECTIVES: To prepare a technical report about the EV model including -

System level configurations
Model parameters
Results
Conclusion

THEORY:

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.

Components of an EV -

EVs have no need for the fuel engine and gear transmission, the two of the most crucial components for internal combustion vehicles.
An electric powered car has three primary components - Battery, motor controller, and the electric motor.

(1) Battery: The battery of an electric car can be charged through the use of ordinary grid electricity at a specialized power station. But aside from the conventional lithium-ion battery technologies, there are also other major battery technologies which can be used for electric cars

Lithium-Ion Batteries: This battery technology gives extra performance and range. However, it also

carries the highest price tag. Lithium-ion batteries are lighter than Lead acid and Nickel metal. These are also the batteries used in digital cameras and smartphones.

Lead Acid Batteries: This battery technology is the most popular. It is also the cheapest among

battery technologies. What's good about it is it's 97% recyclable

Nickel Metal Hydride Batteries: This battery technology provides higher output and better

performance but it costs much more than lead-acid batteries.

(2) Motor Controller: The motor controller of an electric car administers its complete operation and the distribution of its power at any given moment. It acts as a floodgate between the motor and batteries. It helps monitor and regulates all key performance indications such as the vehicle's operator, motor, battery, and accelerator pedal. It has a microprocessor which can limit or redirect current. It is used to either improve the mechanical performance of the car or suit the operators driving style. There are also more refined controllers which are capable of greater accuracy and thus, higher efficiency.

(3) Electric Motor: Unlike a gasoline engine with lots of moving parts, a motor only has one moving part. This makes it a very reliable source of motive power. Choosing an electric motor depends on the car's system voltage. They can be structured to use either AC or DC current. AC motors are less expensive and lighter compared to DC motors. They are also more common and they tend to suffer from less mechanical wear and tear. However, AC technology requires a more refined or sophisticated motor controller.

PROCEDURE

(1) Vehicle Body Subsystem:

The vehicle is assumed to be a front axle driven (4 wheels-2 on each axie). • The wheels are modelled using simple Tire (Magic formula) simulink blocks.

The N port of the tire corresponds to the Normal Reaction acting on it.

The A part 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 parts. 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 the 4 wheels form a connection through their respective H ports and this is 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 0.3 m. • The tire inertia is kept as 1 kg-m^2. Also, the rolling resistance is given with a constant coefficient of 0.015.

This 2 axle (4 wheel) assebly is now connected to a Velocity Body simscape block.
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, the connection H is the mechanical translational conserving port hub.

NF & NR correspond to the output ports for nomral 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 (headwind - direction opposite to that of vehicle).

The gross weight is given to be 1200 kg.
The geometric parameters of the vehicle are given as –

To account for proper drag force on the vehicle, the related parameters are kept as –

The pitch dynamics for the vehicle are not considered for this simulation.

The complete subsystem is shown below

2) DC Motor;-

Simulink provides an inbuilt bodel block for DC motor which converts electrical input into mechanical . rotational output.

Note: Here, the blue colour corresponds to the electrical side of the motor and the green colour corresponds to the mechanical side.

Here, the motor field type is kept as Permanent magnet and the model parameterization is

rated load and speed. The armature inductance and the mechanical parameters are given their default values. All the other parameters are changed as shown below

The connection R represents the Rotor (rotational output) while the connection C is for the Casing (stationary). Thus, the R port is connected to the input of the 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 a battery, the required DC motor will run on the rated capacity of the battery. This will eventually result into no control over the DC motor and the vehicle will run at top speed throughout the simulation.

Thus, a motor controller is very much needed.

3) Motor Controller:-

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 enabled threshold

voltage. .

In Averaged mode, the PWM port voltage divided by the PWM signal amplitude parameter defines the • Connection REF is for the reference input. This combined with the PWM connected will form the

ratio of the on-time to the PWM period.

pulse input for the H-Bridge.

Here, the REF input is connected to the Electrical Reference (ground).

Connection REV corresponds to the reverse motion of the motor which essentially means, the

backward motion of the vehicle.

Here, the backward motion of the vehicle is not accounted for and so, the port is connected to the

electrical reference.

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.
Also, the regenerative braking is anabled for the simulation. This means, when the vehicle starts

decelerating, corresponding amount of charge will be fed back to the battery. Accordingly, the BRK input is connected to a Controlled Voltage Source. This will generate emf corresponding to the intensity of brakes applied and fed the power back to the battery.

4):-Longitudinal driver

It is a parametric longitudinal speed tracking controller for generating normalized Acceleration and Braking commands based on reference and feedback velocities, • The VelRef port is the reference velocity port where the input drive 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 (feedback) velocity with the reference velocity, the driver block generates acceleration and braking signals in order to minimise the error between the two concerned velocities.

Grade corresponds to the grade angle. For this simulation, no inclination is considered and hence, a constant block with value O is connected.

Info gives the output for the bus signal for different block calculations like difference in reference

vehicle speed and vehicle speed, etc.

AccelCmd & DecelCmd correspond to the acceleration and deceleration commands generated respectively and are connected to the corresponding ports of the Controlled PWM Voltage block. • Here, the selected control type is PI. Acordingly, the block implements proportional-integral (PI)

control with tracking windup and feed-forward gains.

5):- Battery

To model the Battery pak, 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. If the chosen option had been Infinite, the voltage source would have been constant.

Also, the self-discharging of the battery and the battery dynaics are disabled. • The Battery Nominal Voltage is given as 400V.

The Ampere-hour rating is assumed to be 50. The rest all paramaters are left with their default values.

6):- Referance velocity cycle

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.