Week-11 Challenge: Braking

Ans.1)

In any vehicle acceleration and declaration is much important. I we need to drive the vehicle from one place to another we need acceleration but to stop the vehicle we need brakes which acts deceleration on vehicle. As we required to stop the vehicle in stipulated time, but we are not allow to stop the vehicle at its inertia value so we need to apply brakes .When we apply the brakes amount energy is utilized by vehicle, this energy utilization is depends on the driving cycle in which vehicle is driven at that moment.

The formula for Energy reqired for braking is same as of acceleration.

Energy(dec)=12*MV2Energy(dec)=12*MV2

Where,

M= total mass of vehicle

V=speed of vehicle

The EUDC (Extra Urban Driving Cycle) segment has been added after the fourth ECE cycle to account for more aggressive, high speed driving modes. The maximum speed of the EUDC cycle is 120 km/h. An alternative EUDC cycle for low-powered vehicles has also been defined with a maximum speed limited to 90 km/h.

Figure: EUDC Cycle

Figure: EUDC Cycle for Low Power Vehicles

Emissions are sampled during the cycle according to the constant volume sampling (CVS) technique, analyzed, and expressed in g/km for each of the pollutants.

The following table includes a summary of selected parameters for the ECE 15, EUDC and NEDC cycles.

Characteristics	Unit	ECE 15	EUDC	NEDC†
Distance	km	0.9941	6.9549	10.9314
Total time	s	195	400	1180
Idle (standing) time	s	57	39	267
Average speed (incl. stops)	km/h	18.35	62.59	33.35
Average driving speed (excl. stops)	km/h	25.93	69.36	43.10
Maximum speed	km/h	50	120	120
Average acceleration1	m/s2	0.599	0.354	0.506
Maximum acceleration1	m/s2	1.042	0.833	1.042

For calculation of braking energy of vehicle in Extra Urban Driving Cycle

Total Weight of vehicle =1200 Kg

Initial velocity (speed) = 80 kmph

Final velocity (speed) = 0 kmph

Declaration time = 10 sec and 20 sec

Calculating with these inputs vehicle exibits 0.01235 kWh for 10 sec of time duration and 0.00617 KWh for 20 sec of time duration.

In time duration of 10 sec 0.1235 KWh energy is utilize in 1 sec by the vehicle.

https://1drv.ms/x/s!AgID4ew-wDzNgT0G5I1pM6Uk0ne-?e=dcbuIm

Ans.2)

The electric motor can't develop braking torque at high speed similiar to starting because once the electric supply is pulled off from the motor,it acts as a generator and due to the flux weakening effect of the electric generator,the generator produces low torque as expected.

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 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.

Ans.3)

https://drive.google.com/file/d/1lXqPAky4ceYbX39EIWOaBEgo0QQRl3YS/view?usp=sharing

MATLAB program to plots contour of given motor speed, torque and efficiency values:-

%Creating speed and torque matrices
Speed = linspace(0,1000);
Torque = linspace(0,250);

%Inputs for losses coefficients
Kc = 0.2;
Ki = 0.008;
Kw = 0.00001;
cons = 20; %Constant losses

%Creating a mesh of speed and torque values and calculating losses at every
%point along with output power available
[X,Y] = meshgrid(Speed,Torque);
output_power = X.*Y;
A = Kc.*(Y.^2); %Copper losses
B = Ki.*X; %Iron losses
C = Kw.*(X.^3); %Windage losses

%Input power calculation and plotting of contour for efficiencies
Input_power = output_power + A + B + C + cons;
n = output_power./Input_power;

%Creating a matrix for efficiencies values for which the contours are to be
%plotted
v = [0.7 0.8 0.85 0.88 0.90 0.92 0.94 0.96 0.98 1];

%Plotting the contour
contour(Speed,Torque,n,v,'ShowText','on');
box on
grid on
colorbar
xlabel('Speed(rad/sec)');
ylabel('Torque(N-m)');
title('Efficiency contour of electric motor');

• x,y values are given as speed (rad/s) and Torque (Nm) respectively.
• Motor parameters like motor losses, input power , Output Power, Efficiency are given.
• Efficency=output power / input power

Results:-