Week-11 Challenge: Braking

                                   WEEK-11 CHALLENGE BRAKING

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

AIM: The Braking energy is the energy generated when the vehicle reaches to zero speed. It can be calculated when taken for deceleration is also considered.
Here we to take various time and speed values in a excel sheet and convert into graph. We taken kerb weight of the vehicle is 800kg and payload is 200kg
In the drive cycle we have taken 5 different situations (decelerations) in which total braking can calculated.
Region 1 has top speed is 20kmph
Region 2 has top speed is 31kmph
Region 3 has top speed is 42kmph
Region 4 has top speed is 60kmph
Region 5 has top speed is 70kmph
For (example) calculation purpose, we take only Region 5 where initial velocity is 9 kmph and final velocitiy is 70kmph there fore velocity vf-vi IS 70-9=61 kmph
Kinetic energy of the vehicle is given by formule:
E=1/2 MV^2
M = mass of the vehicle (kerb weight + pay load)
V = velocity of the vehicle is given by (vf-vi)
Vf is the final velocity
Vi is the initial velocity
M=1000 kg (800+200)
= 0.5*1000*(61)^2
= 1860500 or 1860.5 j
We considered last region total braking is as 1860500 j or 1860.5 kj
So for every region we can calculate the braking energy by using the above formule
                

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

AIM: 

The braking torque in Electric motor is not so high as that of acceleration torque at higher speeds due to electric motor can produce high torque at low speed but when the speed is raised to higher side produced high torque starts to decrease it is because of rotating part of the engine has higher friction. Even if you try to increase the speed of the motor the torque does not increases, because speed of the motor is already high and no extra load is applied on the motor and it is not possible to develop the torque, but in starting condition of electric motor torque is used to increase the kinetic energy (speed) of the motor.

From the above figure we can see clearly electric motor torque behaviour:
during its low (initial) speed constant torque range is high as the speed increases the torque curve decreases, at high speed motor will be at constant power range due to this high speed negitive torque production is also less.
at starting condition of the motor, the speed of the motor will be very less and at this stage and motor will be operating in constant torque range and this is the reason for high acceleration torque during starting condition of the motor.
there are also other reasons like rate of discharge of battery is higher than the charging rate. it can be said that discharge rate of the battery can be twice than the charging rate
Two types of braking systems are employed in most drive systems: electrical braking and Mechanical braking.
Braking systems are necessary for the correct and safe operation of mechatronic
Systems. Most functional braking is achieved using electrical braking, which is made
Possible by the addition of a variable speed drive system, Electrical braking is efficient and ensures smooth operation and allows the designer to recover the mechanical energy (regenerative braking).

most EVs and hybrid vehicles use regenerative braking, which utilizes the motor to convert the kinetic energy during deceleration into electrical energy. With energy regeneration, an EV is able
to run on less electricity and a hybrid vehicle on less fuel.

In any motion control system, braking is necessary for the following reasons:

In order to stop the system in cases of emergency.
In order to ensure that the system remains stationary when not in operation.

Combination of Electric and Mechanical braking.

electric vehicle is used to generate regenerative braking.
braking stability of electric vehicles with electro-hydraulic hybrid braking can be influenced by braking force and regenerative braking

However electrical braking Cannot be used as a safety braking system for the cases of emergency braking and Parking braking. It is for these reasons that mechanical braking systems are still Employed today, in order to act as emergency and parking brakes.

Brake Control Strategy:

cordination of mechanical and electric brakes is used in EV and HEVS

there are two ways to coordinate the braking system:

When ever the driver presses the brake pedal the signal is sent to both hydraulic cylinder and power converter for producing frictional and regenerative braking.

1 SERIES: in case of series braking we apply mechanical brake and regenerative brake one ofter another applying one brake at a time.

2. PARALLEL: in case of parellel braking we apply both the brakes mechanical brake and regenerative brake at a time or at the same time.

series and parellel braking are chosen is based upon the drivers comfort and efficiency.

Above parellel combination braking technology is further devloped as EDIB ( Electric Driven Intelligent Braking)

The EDIB (Electric Driven Intelligent Brake) allows and controls optimization of the regenerative brake and regular friction brake (hydraulic brake).

Here both Hydraulic and Regenerative brakes are applied at same time

Technology Functionality
After stepping on the brake pedal, the system produces natural and adequate braking force that corresponds to the operation. The amount of energy regeneration also needs to be increased as much as possible.

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.

now by using EDIB the frictional braking application is reduced and regenerative braking is increased due to more negitive torque can be produced so higher amount of power can be generated and fed back to the battery

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.

AIM:

Torque speed characteristics of induction motor

Efficiency of induction motor

close all
clear all 
clc
T=linspace(0,1000)%torque
W=linspace(0,1000)%rpm
lw=0.0005 %windage losses
li=0.0006 %iron losses
lc=0.2 %copper losses
[X,Y]=meshgrid(W,T)
windage_losses=(X.^3)*lw
iron_losses=X.*li
copper_losses=(Y.^2)*lc
constant=15
output=X.*Y
input_power=(copper_losses)+(iron_losses)+(windage_losses)+(output)+constant
Eff=(output)./(input_power)
n=linspace(0.5,0.75,10)
grid off
box off
contourf(X,Y,Eff,n)
colorbar
xlabel('rotor rpm')
ylabel('torque')
zlabel('Efficiency')
title('Torque Vs Speed curve of induction motor')
figure
surf(X,Y,Eff)
colorbar
xlabel('Rotor speed(rpm')
ylabel('Torque induced(Nm)')
zlabel('Efficiency')
% Efficiency of electric motor