Week-11 Challenge: Braking

Aim:

Braking of Motor

Objective:

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. Attach the code as a .m file attach a screenshot of all the plots.

Objective 1:

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

Theory:

Drive Cycle:

https://docs.google.com/spreadsheets/d/199N4eLn9YTuNAYip4_Xrj9hcbMmcIhh8/edit?usp=sharing&ouid=102624600894104471166&rtpof=true&sd=true

As we know that the energy can never be created or neither destroyed with the today's development

we have been able to utilize the energy which is been wasted at the time of braking. The kinetic energy which assists the vehicle to move also gets dissipated while the braking is done. Though it depends on multiple parameters on how efficient the braking would be it can be depended upon.

Number of Brake Pistons

Duration and Degree of Brake Pedal been Pressed

Road Condition

Temperature,

Brake Pad and Disc Condition

Mass of the Vehicle

Still with a basic operation where the vehicle in motion and the brakes are applied the same efficiency could be calculated by the given equations.

BE= 1/2 mv²

BE = braking energy

m = mass of the vehicle

v = velocity

In this manner the same calculation is been carried out for calculating the brake efficiency that would be required at the peak point. It being a drive cycle with speed variations the braking power required would vary but still the highest braking power required is mentioned below-

BRAKING ENERGY REQUIRED = 160 KJ FOR THE SPEED OF 57 KMPH.

Objective 2:

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

Theory:

• Why electric motor can’t develop braking torque at high speed similar to starting?

When the motor is at rest and it has to operate from standstill position to the reach the moderate speed the higher torque is required to bring the motor in 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.

• How electric and mechanical brakes are coordinated?

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 have done wonders by inventing lifesaving braking technologies such as ABS, EBD, BA and mny others. All these technologies play 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 peds 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 noth are applied one after another.

Parallel –

The Regenerative Braking or the Mechnical Breaking 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.

An example of the proposition of Regenerative Braking and the Mechanical Braking

NISSAN LEAF - EDIB (ELECTRONIC DRIVEN INTELLEGENT BRAKING):

EDIB (Electric Driven Intelligent Brake) controls the regenerative brake and friction brake to support both of these requirements. Further, it also controls the reactive force from the pedal in order to unify the feeling when stepping down on the pedal and the sense of deceleration.

Objective 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.

Theory:

MATLAB Code:

clear all

close all

clc

%Speed in rad/sec

x=linspace(1,1000,250);

%Torque in Nm

y=linspace(1,250,250);

%Motor loss constants

%Copper losses

kc=0.2;

%Iron losses

ki=0.008;

%Windage losses

kw=0.00001;

%Constant motor loss

Const_Loss=20;

[X,Y]=meshgrid(x,y); %Converting to 2D

Output_power=(X.*Y); %Power = Torque x Speed

B= (Y.^2)*kc; %Copper loss

C= X.*ki; %Iron loss

D= (X.^3)*kw; %Windage loss

Input_power = Output_power + B + C + D + Const_Loss;

Efficiency= Output_power./Input_power; %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)');

Program Description:

• Here in this program first two inputs were given. They are Speed & Torque using linspace command.
• Then the motor constant values are assigned namely Copper loss, Iron loss, Windage loss and Constant motor.
• Then meshgrid is used to evaluate functions of two variables and three-dimensional mesh/surface plots.
• Output Power is calculated by multiplying speed and torque.
• Then all the loss were calculated and the input powers were also calculated.
• Then comes the efficiency were calculated. And Contour graph is plotted between Speed, Torque and Efficiency.
• Title was given and labels were given.

Result:

This clearly shows that maximum efficiency of 93% is achieved by 691.1rad/sec and at 147Nm. The lowest Efficiency is achieved at 223 rad/sec and at torque of 105.3Nm and this Contour plot clearly gives the idea on Speed, Torque and Efficiency relationship of the motor. The colour indicates the efficiency denoted in the right side with the colorbar.

For reference check the file attached below