Design of an Electric Vehicle using MATLAB and Simulink

Abstarct:

An electric vehicle is a vehicle that uses one or more electric motors or traction motors for propulsion.An electric vehicle may be powered through a collecter 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.In this project,We discuss about mechanical parameters such as rolling resistance,aerodynamic drag force,payload,tractive force etc.,Also a DC motor is used for this vehicle with H-bridge connections and this model is tested under various driving cycles.

Theory:

Some of the factors considered during this simulation are,

1.Rolling resistance force:

Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. 

`F_(rr)=mu_(rr)mg`

where m=mass,

`mu_(rr)`=rolling resistance co-efficient.

which depends on tire condition,road material.

`mu_(rr)=0.01(1+0.001v)<128kmph`

2.Aerodynamic drag force:

In fluid dynamics, drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid.This can exist between two fluid layers (or surfaces) or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag force depends on velocity.there are two types i.e., shape drag,skin friction.\

`F_(ad)=1/2rhoAc_dv^2` in N

`rho=`air density

A=Frontal area

`C_d`=Drag co-efficient

V=Velocity

3.Drive Cycle:

A driving cycle is a series of data points representing the speed of a vehicle versus time. Driving cycles are produced by different countries and organizations to assess the performance of vehicles in various ways, as for instance fuel consumption, electric vehicle autonomy and polluting emissions.

Some types of driving cycles are,NEDC,UDC & EUDC etc.,

Driving cycles look like this,

Components used:

1.Batteries

2.Power controllers

3.Transmission system

4.Wheels

5.Motor/generator

Simulink model:

Wheel and transmission system is defined first.

We have used magic tires from simulink block.

Represents the longitudinal behavior 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

I have used this block becausse this will allow us to model the longitudinal behaviour of vehicle tires on highways.

Connection A is the mechanical rotational conserving port for the wheel axle. Connection H is the mechanical translational conserving port for the wheel hub through which the thrust developed by the tire is applied to the vehicle. Connection N is a physical signal input port that applies the normal force acting on the tire. The force is considered positive if it acts downwards. Connection S is a physical signal output port that reports the tire slip.

These wheels should be connected to vehicle body.Vehicle body in simulink platform looks like this.

This 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.

Connection H is the mechanical translational conserving port associated with the horizontal motion of the vehicle body. The resulting traction motion developed by tires should be connected to this port. Connections V, NF, and NR are physical signal output ports for vehicle velocity and front and rear normal wheel forces, respectively. Wheel forces are considered positive if acting downwards. Connections W and beta are physical signal input ports corresponding to headwind speed and road inclination angle, respectively.

Then a simple gear block is connected to wheel axles with a gear ratio of2.

So representation of the vehicle body with tyres and gearboxes are included in a subsystem as shown below.

Given values in this model is 

Gear ratio=2

Rolling radius=0.3m

mass=800kg

Frontal area=3m^2

Drag co-efficient=0.4

We have selected a DC motor to model this vehicle because DC motors are easier to control than AC induction motors.

Parameters for DC motors are as

H-Bridge:

An H-bridge is an electronic circuit that switches the polarity of a voltage applied to a load. These circuits are often used in robotics and other applications to allow DC motors to run forwards or backwards.

The term H-bridge is derived from the typical graphical representation of such a circuit. An H-bridge is built with four switches (solid-state or mechanical). When the switches S1 and S4  are closed (and S2 and S3 are open) a positive voltage is applied across the motor. By opening S1 and S4 switches and closing S2 and S3 switches, this voltage is reversed, allowing reverse operation of the motor.

Using the nomenclature above, the switches S1 and S2 should never be closed at the same time, as this would cause a short circuit on the input voltage source. The same applies to the switches S3 and S4. This condition is known as shoot-through.

MATLAB model for H-bridge is, 

I have taken internal power supply so external voltage or battery is not required.Parameters taken is given below.

A controlled PWM source is used to provide controlled voltage modulation to H-bridge.For a PWM controller duty cyle is given by,

`delta=T_(on)/(T_(on)+T_(off))`

To control all of this inputs, driver is required for our simulink model.For that,a longitudinal driver is used in Simulink..

A parametric longitudinal speed tracking controller for generating normalized acceleration and braking commands based on reference and feedback velocities.

So velocity feedback from Vehicle body is connected to  longitudinal driver.

Velocity inputs are given by drive cycles through multiports and checked for velocity feedbacks using scope.

For SOC,Charge is integrated to get current.From that we get SOC.

Performance:

Plot for Velocity is given below.

Here the velocity feedback follows almost the same as input velocity except in some areas where the drive cycle takes sudden drop in speed.As this is practically impossible for shorter intervals,there is a change in velocity of the vehicle.

Plot for SOC of battery:

The state of charge is the current amount of charge that is left in the battery in required time.So for a 400V battery,Depth of discharge is around 95%.Pulses in graph line shows regenerative braking of vehicle.

Current in the model:

Current has frequent fluctuations as it follows drive cycle of the car.It is reduced in some of point because of speed fall in drive cycle.

Conclusion:

• Feedback velocity is almost same as input velocity.
• Current consumption increases with increase in accelaration.
• During regenerative braking,SOC of the battery is increased.

References:

Google,Wikipedia

Google drive link:

https://drive.google.com/file/d/1I4M6qija1tpsPnugngTs2kpRmesvyNTn/view?usp=sharing