Week-11 Challenge: Braking

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

Ans-

Here we have taken the drive cycle data from the internet to calculate the braking energy of the vehicle for that drive cycle.

The table is as below

By using the formula we can calculate the braking energy required to stop the vehicle

BE=1/2 *m* V2

Where,

m=Mass of the vehicle

V=Velocity of the vehicle.

We have to calculate the braking power at different speed but highest energy to stop the vehicle is at the highest speed.

So in considered drive cycle the highest speed is about 57kmph.

to convert it into the mps 57*5/18=15.83 mps.

so that braking power is

BE=0.5*800*15.83*15.8

BE=100235.56

BE=100.235 kJ

So the braking energy to stop the vehicle for 57 kmph is 100.235 KJ

2.Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?

Ans-

We can not developed the braking torque as high as the starting torque because in braking we have to developed the in the opposite direction of rotation.But by using mechnical and electrical braking we can

brake the motor.

In electrical braking we can used the regenerative braking.

Regenerative Braking-

In regenerative braking the motor works as the generator and generate the power .In regeneative motor in motor the back emf is greater than the supply voltage and motor works as the generator.

In regenrative braking mode supply from the battery get cuts off and then only input to the motor in running condition is roatating wheel which is kinetic input and then motor works as generator and converts the

mechanical input into the electrical output.Ans battery start charging.The graph of regenerative braking is as shown below

In regenerative the torque of motor becomes the negative and the speed of motor remains the positive from motoring to regenerative braking.It is also called as decond quadrant operation of motor.In electrical

motor torque is very low when acceleration is very high and torque is high when the deceleration start we an say that the torque of electrical motor is not same at start and at braking we required more power to

stop the vehicle in deceleration.So to stop the vehicle we required combination of electrical and mechnical braking is required.

Combination of electrical braking and mechanical braking-

1.Series Braking

2.Parallel Braking

Series Braking-

In case of series of braking we apply the brake one after another mean we press the electrical regenerative braking after the mechanical braking.

Parallel Braking-

In case of parallel braking the both the brakes pressed simultneously at the same time.

3.Make a MATLAB program which plots contour of given motor speed, torque and efficiency values. Attach the code as a .m file attach a screenshot of all the plots.

Ans-

The MATLAB program for the plotting the contour is as follow

clear all;
clc;
S=linspace(0,1000);
T=linspace(0,300);
Kc=0.18;
Ki=0.006;
Kw=0.000015;
ConL=20;
[X Y]=meshgrid(S,T);
outputpower=(X.*Y);
B=(Kc)*(Y.^2);
C=Ki*X
D= Kw*(X.^3);
Inputpower=outputpower+B+C+D+ConL;
Z=outputpower./Inputpower
V=linspace(0.70,0.95,10);
box off;
grid off;
contour(X,Y,Z,V);
xlabel('Speed/rad.s^-^1'),ylabel('Torque/Nm');
title('SPEED TORQUE CHARACTERISTICS');
hold on

Where

Ki represent the iron loss

Kc represents the copper loss

kw represents the windage loss

S is represent speed and T represents torque.