Week-11 Challenge: Braking

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

consider UDDS for calculation of breaking energy

kinetic energy of vehicle while moving is converted into breaking enegy hence

Breaking energy =0.5*m*v^2

calculations are done in excel sheet with apropriate formulae.

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

Electric Motor Braking :

Eectric motor can’t develop braking torque at high speed similar to starting,Electric motor can't develop braking torque at high speed similar to starting, because Braking Torque of an EV Motor is not as high as the Acceleration Torque. Therefore Regenerative braking is cannot happen so effectively that we can get all the power back to the battery.

Braking is the process of controlling the velocity of an object by inhibiting its motion. An object in motion possesses kinetic energy and to bring the object to a stop this kinetic energy must be removed. Removing the kinetic energy can be accomplished by dissipating the energy to the atmosphere through friction or by converting it into another form of energy. The most common type of braking is a mechanical brake which inhibits motion through friction brake pads. A mechanical brake applies a friction force to convert the kinetic energy of the vehicle into thermal energy which then dissipates into the atmosphere. Braking systems which don't use friction are referred to as Regenerative Braking System (RBS). In RBS, the kinetic energy is converted into other forms of useful energy, which can be stored for later use, increasing fuel efficiency.

As with any system, the process of braking must follow the principal of conservation of energy. Energy cannot be created or destroyed but only converted from one form to another,

Einput=Eoutput

The energy present in an object in motion is given by the following equation:

KE=1/2m*v^2

where,

m- mass of the object in Kilogram(Kg),

v - velocity of the object in meters per second(m/s),

From this above equation, and assuming the mass of the object is constant, it is clear the in order to remove the kinetic energy from the system, the velocity must be brought to zero. which is difficult with electrical breaking .

clear all

clc

% Plotting Efficiency Contour for Electric Motor

%Input of Speed & Torque

Speed=linspace(1,1000);

Torque=linspace(1,250);

%Losses

kc=0.2; % For Copper Loss

ki=0.008;% For Iron Loss

kw=0.00001;% For Windage Loss

C=20;% For Constant Motor Loss

%Meshing

[S,T]=meshgrid(Speed,Torque)

%Calculating Power = Speed * Torque

Outputpower=(S.*T);

%Calculating Losses

Cu=(T.^2)*kc;%Copper Losses

Fe=S*ki;%Iron Losses

W=(S.^3)*kw;%Windage Losses

Inputpower = Outputpower+Cu+Fe+W+C;

Efficiency = Outputpower./Inputpower;

%Now Set the Efficiency to plot Contour

V=[0.70,0.80,0.85,0.90,0.91,0.92,0.925,0.93];

box off

grid off

contour(S,T,Efficiency,V)

xlabel('Speed(rad/s)')

ylabel('Torque(Nm)')

title('Motor Speed-Torque Efficiency Contour Plot')

hold on

The above Plot shows the Motor Speed-Torque Efficiency Contour Plot. A Point is denoted in innermost contour line is group of efficiencies which is highest value of the efficiency as 93%, because where the height is maximum and another point is denoted outermost contour line is contain group of efficiencies which is the lowest value of efficiency as 70%, because where the height reduces. Increasing efficiency order as going inward and Decreasing efficiency order as going outward.