Week-11 Challenge: Braking

1.

Driving cycle is a set of data represented by velocity with respect to time. accelaration also deaccelarations are the part of driving cycle. In driving cycle the accelation deaccelaration happen regarding to user driving ways, traffics , envioremental effects and many more.

Braking is the important thing for life and vehicle safty. It used for deaccelarate the vehicle and for diveting the accidents. in urban driving a huge amount of energy lost in the braking effect. In EV's builders tried to utilise and recover the loss occuring in the braking and charging the battery.Hybrid braking are designed for saving braking energy loss and as fast possible to slow down the vehile in no time.

Braking energy:

1/2*m*v^2

m = mass

v = velocity

MATLAB code for braking energy calculation

Mass=1000;%Mass of Vehicle in Kg

Drivecycle = xlsread('drivecycle.xlsx')

Time = Drivecycle(:,1);%Time in sec

Vel = Drivecycle(:,2);% Velocity in m/s

for i = 1:(length(Drivecycle)-1)

if Vel(i)>Vel(i+1)

E(i) = 0.5*Mass*(Vel(i)-Vel(i+1))^2;

end

end

fprintf('Total Braking energy is %d',sum(E))

fprintf('\nAverage Braking energy is %d',mean(E))

figure(1)

subplot(2,1,1)

plot(Time,Vel,'linewidth',3,'color','r')

xlabel('Time(sec)')

ylabel('Velocity(m/s)')

title('Drivecycle')

hold on

subplot(2,1,2)

plot(E,'linewidth',3,'color','g')

xlabel('Time(s)')

ylabel('Energy(J)')

title('Brakingenergy')

total breaking energy calculated in watt

the first graph for the drive cycle generated from xlsx file.

Second graph is for generated energy for breaking energy required in terms of deaccelaration . as you can see the rapid dacelartion consume more energy.

2.

The electrical motor can't develope braking torque at high speed similarly statring torque.The reason behind is once the supply pulled off from motor,it acts like generator due to flux weaking effectof generator, as generator produced low torque

Regerative Braking:

Regenerative braking is an energy recovery 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 until needed. In this mechanism, the electric traction motor uses the vehicle's momentum to recover energy that would otherwise be lost to the brake discs as heat. This contrasts with conventional braking systems, where the excess kinetic energy is converted to unwanted and wasted heat due to friction in the brakes, or with dynamic brakes, where the energy is recovered by using electric motors as generators but is immediately dissipated as heat in resistors. In addition to improving the overall efficiency of the vehicle, regeneration can significantly extend the life of the braking system as the mechanical parts will not wear out very quickly.

The most common form of regenerative brake involves an electric motor functioning as an electric generator. In electric railways, the electricity generated is fed back into the traction power supply. In battery electric and hybrid electric vehicles, the energy is stored chemically in a battery, electrically in a bank of capacitors, or mechanically in a rotating flywheel. Hydraulic hybrid vehicles use hydraulic motors to store energy in the form of compressed air. In a hydrogen fuel cell powered vehicle, the electrical energy generated by the motor is used to break waste water down into oxygen and hydrogen which is recycled back into the fuel cell for later reuse.

The most common form of regenerative brake involves using an electric motor as an electric generator. The working of the regenerative braking system depends upon the working principle of an electric 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 behaves as a generator and generates electricity. This means that whenever the motor runs in one direction, the electric energy gets converted into mechanical energy, which is then used to accelerate the vehicle, and whenever the motor runs in the opposite direction, it performs functions of a generator, which then converts mechanical energy into electrical energy, which makes it possible to utilize the rotational force of the driving axle to turn the electric motors, which results in regenerating electric energy for storage in the battery and simultaneously reducing the speed of the car with the regenerative resistance of the electric motors. This electricity is then used for recharging the battery.

Coordination of Electric and Mechanical Brake :

In an electric Motor, the Total Brake distribution is in two aspects which are Electrical Brake which is called Regenerative Brake, and Mechanical Brake or Classical Brake with a hydraulic cylindrical system. Brake Force distribution must be uniform, If the Regenerative braking power requirement is more than the charging limit of the battery or more than the regenerative capacity of the machine we must apply Mechanical brakes as well. In a practical case, the combination of these two is applied. So usually it is a combined response of Mechanical brake and Regenerative brake. The reason for how this braking force is combined, that particular phenomena are called Brake Control Strategies. There are two Brake Control Strategies, which are Series - In case of Series, we apply Mechanical brake and Regenerative electric brake one after another. We can apply only one brake strategy at a time either apply Regeneratively or apply Mechanical brake. The Series Brake Control Strategy has a further classification, that is based on whether we want the comfort of driver or Brake behavior compared to energy efficiency. Parallel - In the case of Parallel, we apply both brakes simultaneously. This Particular Parallel braking is going to happen both at a time. Electric Driven Intelligent Brake (EDIB) is a combination of Hydraulic brake or Mechanical brake along with a Regenerative brake. It is a Parallel braking technique. The Control criteria such that at low speed use regenerative braking higher and at high speed or during the initial braking period we actually combine the both.

3.

For ploting contour graph we need to determine the losses happining in a motor like

Copper loss:

can say it I^2R loss,R defined as armature resistance and torque is directly proposnal to current.

and defined as from torque

copper loss = Kc*T^2

Iron loss:

can say it magnetic loss.It based on magnetic field. Iron losses are given per weight and depend on the frequency and the maximum flux density.

Iron loss:Ki*w

windage loss:

can say it mechanical friction loss.Windage loss is the reduction in efficiency due to windage forces. For example, electric motors are affected by friction between the rotor and air. Large alternators have significant losses due to windage. To reduce losses, hydrogen gas may be used, since it is less dense.

windage loss:Kw.W^3

constant loss: as denenoted as C

Total loss =