Week-11 Challenge: Braking

QUE 1 ANS - 1. We require some amount of power which is used for accelerating the vehicle and also for the braking of vehicle. here we consider the drive cycle which is predefined as FTP75 drive cycle.

We know kinetic energy= 0.5m*v^2

for calculating the energy the formula is E=0.5m*v^2

m=mass of vehicle=1000kg

v=velocity of vehicle= Vf - Vi ( here the veehicle is decelerating from 100 to o speed so, Vf is final velocity 100kmph and Vi is initial velocity 0 kmph )

t = time required from 100 to 0 speed is 10 sec

Power required is P = E/t

P = (0.5*1000*(100*0.277)^2)/10

= 38.36 kw

Energy required for braking of vehicle from 100 to 0 speed in 10 sec is

E = 0.0106 Kwhr

Energy required for braking of vehicle from 100 to 0 speed in 1 sec is

E = 0.106 Kwhr

QUE 2 ANS - 1. The electric motor can not develop braking torque at high speed similar to starting because once the electric supply is pulled off from the motor it act as a generator and due to the flux weakening effect of the electric generator,the generator produces low torque as expected.

2. Regenerative braking - Regenerative braking is an energy mechanism that slows down a moving vehicle or object by converting its kinetic energy into a form that can be either used immediately or stored untill needed. In this mechanism, the electric traction motor uses the vehicle momentum to recover energy that would otherwise be lost to the brake disc or heat.

3. The working of regenerative braking system depends upon the working principle of motor,which is an important component of the system. the electric motor gets activated when some electric current is passed through it. But when some external force is applied to activate the motor ( during the braking), then it behave as a generator and generate electricity. It means that whenever motor rotate in forward direction it convert electric energy into mechanicle energy and vehice gets accelerated but when motor runs in reversed direction it work as generator convert mechanicle energy into electrical energy and store energy in battery and vehicle slows down

How electric and mechanical brakes are coordinated?

1. In an electric motor, the total brake distribution is in two aspects which are electric brake which is called regenerative brake, and mechanicle brake with a hydraulic cylindricle system. Brake force distribution must be uniform, if the regegenerative braking power requirement is more than the charging limit of the battery or more than regenerative capacity of the machine we must apply mechanicle brakes as well. In a practical case, the combination of this two is applied. So usually it is a combined response of mechanicle brake and regenerative brake. The reason for how this braking force is combined, That perticular phenomena are called brake control strategies.

2. These are two brake contol strategies, which are series - in case of series, we apply mechanical brake and regenerative brake one after another. In case Parallel we apply both brake simultaneously. This perticular parallel braking is going to happen both at a time. The contol criteria such that at low speed use regenerative braking higher and at high speed or during the initial braking period we actually combined the both.

QUE 3 ANS - Syntax are

clear all;
close all;
clc;
Torque= linspace(1,250,250) %Input Torque
Speed= linspace(1,1000,250) %Input Speed
[w,T]= meshgrid(Speed,Torque) %Converting to 2D array
Kc= 0.3; %Copper loss constant
Ki= 0.009; %Iron loss constant
Kw= 0.00005; % Windage loss constant
C= 30; % constant loss
Pout= w*T; %Output Power
C_loss=Kc*(T^2); %Copper loss
I_loss=Ki*w; %Iron loss
W_loss=Kw*(w^3); %Windage loss
Pin=Pout+C_loss+I_loss+W_loss+C; %Input power
eff=Pout/Pin
contour(Speed,Torque,eff)
title('Torque-Speed-efficiency contor of the induction motor');
xlabel('RPM');
ylabel('TORQUE (N-m)');

Syntax explanation -

In this program we are plotting speed Vs torque characterstics with the efficiency values. For this, First we are defining speed and torque values of motor.

Then as we need to drew a contour, we convert this 1D array to 2D array using MESHGRID command.

Then we are defining the Cu constants for losses, like Cu loss constants, iron loss constant and windagewloss constant.

Pi=Pout+Kc*T^2+Ki*w+Kw^3+Constant loss

Using this formula, we calculate the efficiency and then plot the comntour.

Result -