Week-11 Challenge: Braking

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

• Here I created own drive cycle data as text format, then i loaded the text data into my script file in MATLAB

clear all
close all
clc

load drive_cycle.txt
time = drive_cycle (:,1);
velocity = drive_cycle (:,2);
mass = 1000;
brake_energy=(0.5*mass*velocity.^2)/1000;
fprintf('total brake energy %d',sum(brake_energy))

figure(1)
plot (time,velocity)
title('Time vs speed')
xlabel('time(sec)')
ylabel('velocity(kmph)')

figure(2)
plot(time,brake_energy)
title('Time vs brake energy')
xlabel('time(sec)')
ylabel('Brake energy(kj)')

plot results

Total brake energy

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

• During starting stage the motor draws a large current due to transient.
• Torque is proportonal to square of current, therefore torque value is also high at this moment.
• Also when speed increases torque should decrease to maintain power cocnstant.
• At the time of statrting speed is very low therefore torque value is very high.
• At the time of braking, speed value is high therefore torque value will be lower.

In order to stop the vehicle it requires electrical and mechanical braking.

There are two methods to apply this brake:

series braking

Here mechanical and electrical braking are applied one after the other.

Parallel braking

Here both braking methods are applied 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.

clear all
close all
clc

speed= linspace(0,1000);
torque= linspace(0,500);

kc= 0.2;
ki=0.006;
kw=0.000010;
k=20;

[x,y] = meshgrid(speed,torque);
copper_loss= (y.^2)*kc;
iron_loss= x*ki;
windage_loss= (x.^3)*kw;

output_power= x.*y;
input_power= (copper_loss+iron_loss+windage_loss+output_power+k);
efficiency=(output_power./input_power);

n=linspace(0.7,0.95,10);
contourf(x,y,efficiency,n);
title('speed-torque efficiency')
xlabel('speed (rad/s)');
ylabel('torque (Nm)');
colorbar