Week-11 Challenge: Braking

Aim :

1. For a defined driving cycle, calculate the energy required for braking.
2. Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?
3. Make a MATLAB program which plots contour of given motor speed, torque and efficiency values.

Objective 1:

Choosing an UDDS cycle for the calculations

Results for the calculations is attached to following file.

https://docs.google.com/spreadsheets/d/1VyUQFcHv6DOisBe-RHV4ZCkDJz_5Z1_M/edit?usp=sharing&ouid=115623907811535897228&rtpof=true&sd=true

Objective 2:

Starting Torque

At starting of the vehicle speed is lower and that's why torque is high.

Braking Torque

But during braking when the speed is high it is unable to generate high torque.

• Braking power of the motor depends upon the battery recovery, Battery composition as well as motor rated power.
• Regenerative braking is only applicable when the batter is low on the charging so that barking power will recharge the battery, but if the is full or not enough to recover that energy then the battery will charge above the safe level and thus motor will limit the renegerative torque.

Co-ordination of the mechanical and electrical brakes:

Pure Electrical Braking:

When the motor is braking clutch I is engaged and clutch II is disconnected. The engine and the hydraulic braking systems do not participate in the braking action and the required braking torque is provided by the motor.

Objective 3 :

MATLAB script for motor speed, torque and efficiency values.

close all
clear all
clc
Tq = linspace(1,300); %torque values stored in variables
Ve = linspace(1,2000); %Speed values stored in variables

[V,T]=meshgrid(Ve,Tq); %creating the square matrix for the calculation ease
Outp = (V.*T);

Cu = 0.2; %copper loss constant
Fe = 0.009; %Iron loss constant
w = 0.00001; %winding loss constant
c = 20; %constant

Copp_Loss= (T.^2)*Cu; %calculation of copper loss
Iron_Loss= V.*Fe; %calculation of Iron loss
Wind_Loss= (V.^3)*w; %calculation of Winding loss

InP = Outp+Copp_Loss+Iron_Loss+Wind_Loss+c; % Total input power

X=[0.7,0.75,0.80,0.85,0.90,0.95]; %efficiency block

Eff =Outp./InP; %efficiency calculation

box off
grid off
contour(V,T,Eff,X); %plotting of the contour
colorbar

figure
surf(V,T,Eff); %plotting of the 3point graph
colorbar

Result of the 3 point graph for efficiency range accross the velocity and torque values.

Result of the plotting for the contour .

Conclusion:

1. Result for the braking energy is obtained.

2. Theory for the motor braking and mechanical braking is studied thorougly

3. Efficiency, speed and torque contour is plotted.