Braking

Question 1:

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

The driving cycle used In here is, New York drive cycle

we know that the braking energy = `1/2*mass*(V_f-V_i)`

Approximately, we could find 30-35 decelerations from the NY city cycle graph.

To determine the Braking energy at every deceleration curve:

Total breaking energy of a drive cycle is the summation of all the calculated breaking energies at decelerating points that gives a total value of 316.197 KJ

Question 2:

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

When the motor is at rest and it has to operate from a standstill position to reach the moderate speed the higher torque is required to bring the motor into operation. Whereas when the vehicle is already at high speed the capping or the limit is reached by the motor operation and thus any further higher torque could not be obtained while braking. The braking operation happens in the motion which is been distributed as per proportion in the BRAKE ENERGY and the REGENERATIVE BRAKING.

In Mechanical braking which we usually see and experience in all vehicles, the brake pedal in the vehicle cabin helps us to engage or disengage the brakes. Currently, the braking technology has done wonders by inventing life-saving braking technologies such as ABS, EBD, BA and many others. All these technologies play a vital role in stopping the vehicle and coming back to rest from a high speed. In all these vehicles when the driver applies the brakes the brake pads come closer to the disc connected with the driving disc. The brake pads usually help in efficient braking.

There are two generic methods by which the vehicle could be braked in the ELECTRIC BRAKES.

Series - The Regenerative Braking or the Mechanical Braking both are applied one after another.

Parallel - The Regenerative Braking or the Mechanical Braking both are applied Parallely.

When the brake pedal is pressed the hydraulic fluid reaches the brake piston and created the braking pressure on the wheels and the same kinetic energy is been used by the Regenerative Braking for generating more power using the Bi-directional motor which operates as a generator while braking.

Question 3:

Make a MATLAB program that plots the 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;

w = linspace(0,1000); %speed
T = linspace(0,300);  %Torque

kc = 0.16; %copper loss const
ki = 0.008; %iron loss const
kw = 0.00002; %winding loss const
con_loss = 20; %other losses
[X,Y] = meshgrid(w,T);
Output_pw = (X.*Y);

A= (Y.^2)*kc; %Copper loss
B= X.*ki; %Iron loss
C= (X.^3)*kw; %Winding loss
Input_pw = Output_pw + A + B + C + con_loss;
Efficiency= Output_pw./Input_pw; %Eff of the motor
V = [0.70,0.80,0.90,0.91,0.92,0.925,0.93]; %Efficiencies to be plotted
box off
grid off
contourf(X,Y,Efficiency,V);
contourcbar
title('Speed-Torque-Efficiency Characteristics of Motor');
xlabel('Speed (rad/sec)');
ylabel('Torque (Nm)');

Output characteristics: