Week-11 Challenge: Braking

1)For a defined driving cycle, calculate the energy required for braking.

Drive Cycle

A driving cycle is a series of data points representing the speed of a vehicle versus time.

For calculating power required for braking i have taken the indian urban drive cycle with the total time of 2690 sec.

Formula for consumed energy in braking is

`K.E = 1/2m.V^2`

Where M is the mass of the vehicle

and V is the velocity of the vehicle

Matlab Script

close all
clear all
clc

%mass of the Vehicle
m = 1250;
%Import Drive Cycle
Drive = readmatrix('indian_urban.xlsx');
%Total Time
Time = 2690;
% Time
T = Drive(:,1);
% Speed in Mph
Velocity = Drive(:,2);
%Mph to m/s
V = Velocity*0.447;
% Decrease in Velocity,Change in Time,Deceleration & Braking
Deceleration = zeros(1,Time);
Braking_energy = zeros(1,Time);

for i = 1:(length(V)-1)
    if V(i)>V(i+1)
        decrease_in_velocity(i)=V(i+1)-V(i);
        time_difference(i)=T(i+1)-T(i);
        Deceleration(i)=decrease_in_velocity(i)/time_difference(i);
        Braking_energy(i) = 0.5*m*((V(i))^2-(V(i+1))^2)/3600;
    end
end

%ploting
figure
subplot(3,1,1)
plot(T,V)
xlabel('Time');
ylabel('Velocity');
title ('Velocity Vs Time')
subplot(3,1,2)
plot(T,Braking_energy)
xlabel('Time');
ylabel('Braking Energy');
title ('Braking Energy Vs Time')
subplot(3,1,3)
plot(T,Deceleration)
xlabel('Time');
ylabel('Deceleration');
title ('Deceleration Vs Time')

fprintf('Total Braking Energy Required for Drive Cycle is %3f W.H',sum(Braking_energy))

here we have calculated deceleration braking energy with respect to the Indian Urban drive cycle.

In first Subplot We have shown the drive cycle

In second Subplot we have shown Braking occured with respect to deceleration

In third Subplot we have shown deceleration.

Output

For calculation Total power required in this drive cycle is calculated with the sum of all the braking force.

Output of Braking Energy

So, from the above picture the total braking force required for Drive Cycle is 1051 W.H

2) Why electric motor can’t develop braking torque at high speed similar to starting

At begining of the of the drive cycle or the motor will develop maximum torque to acheive high speed of the motor.

At high speed braking torque will be very low due to at high speed the torque will be low from the relation between the speed and torque

They are Directly Propotional to each other.

But in EV application we cant leave as like that so here we have used Regenerative Braking

When the motor is accelerated at high speed, the difference between the back EMF and the voltage from the battry is very low. And in this scenario we can't provide more voltage and the torque is only driven by the friction, because it is not possible to accelerate the power more.

So here comes the regenerative Braking

First Mechanical brakes are used in IC Engine vehicles to stop or to slow down the vehicle using frictional force, When the brake pedal is applied so that using cable,hydralic or by using pneumatic areused as a mediem to stop the vehicle by creating friction between the Disk or Drum Using Brake pads And another method to slow down by reducing gear so that the ngine brakes are applied to slow the wehicle

For stoping Electric vehicle you will be using more effective braking called electric braking using regenerative force.

And another one method is preinstalled brake in the motor to slow doen the vehicle which is connected the motor shaft by using brake pad it is stopped by creation frictional force between the motor shaft and the brake pad.

And regenerative brakes are used in electrified vehicle, the electric motor drives the wheels, either in conjunction with the gasoline engine as in a hybrid, or on its own in a battery-electric vehicle. As you drive forward, the motor runs in that direction, supplying electric power to the wheels.

But when you decelerate by taking your foot off the throttle, the electric motor stops supplying power so the vehicle will slow down. When the motor stops, it immediately disengages, and then starts running backwards. The transmission is still in Drive, so it doesn’t reverse the wheels; instead, it acts like a generator. It captures the kinetic energy from the wheels as they slow down, and converts it into electricity. It’s then stored in the battery, to be sent back to the electric motor when it’s needed to drive the vehicle’s wheels.

Control Statergy

The driver’s braking force commands are related to driving safety. The value of braking force represents the braking distance and time the driver requires to stop the vehicle. If the driver’s braking force command is large, it means the vehicle should be stopped in a short distance and time. At that time, we should decrease the proportion of regenerative braking force; when the driver’s braking force command is medium, the ratio of the regenerative braking force used should be increased; and in the last condition, the driver’s braking force command is small, so we can apply a large regenerative braking force to the vehicle. Therefore, we prefer the concourse of driver’s braking force command is: {low, middle, high}

And this above plots shows the operation of brake petal and how the regenerative brake work with both friction brake and regenerative brake.

3) Matlab script to Plot contour

Contour Plot

A contour plot is a graphical technique for representing a 3-dimensional surface by plotting constant z slices, called contours, on a 2-dimensional format.

In order to plot the contour plot of the motor torque speed and the efficent vales we need to have a motors specification which is show in the motor so let us consider those values.

Copper loss = 0.19

Iron loss = 0.0065

Windage loss = 0.000019

Constant loss = 19

Using this values

Speed varies from 0 to 1000 rpm

and the torque 0 to 250 N-M

Matlab Script

clear all 
close all
clc

%Losses in motor
C = 0.19;     %Copper Loss
I = 0.0065;   %Iron Loss
W = 0.000019; %Windage Loss
CM = 19;      %Constant Loss

%speed
S = linspace(0,1000,250);
%Torque
T = linspace(0,250,250);

%Mesh
[Speed,Torque] = meshgrid(S,T);

%Calculating Loss
copper_loss = C*(Torque.^2);
Iron_loss = (Speed).*I;
Windage_loss = (Speed.^3)*W;

%Power
output = (Speed.*Torque);
Input = copper_loss + Iron_loss + Windage_loss + output + C;
Efficient = output./Input;

%Efficiency Value
E = linspace(0.7,0.93,10);

%Plotting
grid off
contourf(Speed,Torque,Efficient,E);
colorbar
xlabel('Motor Speed');
ylabel('Torque');
zlabel('Efficiency');
title('Contour plot of Speed,Torque,Efficiency')

All the values are considered and the final result of contour plot

The most Inner value is 0.93 and respectively.