Week-11 Challenge: Braking

1)QUESTION:

Under the condition of braking,some amount of energy is required to do the same as that of energy required for accelerating the vechile.Hence to calculate energy,we use the acceleration energy equation,

                                  Ek=1/2mv^2

   Ek=Kinetic energy(J)

QUESTION1:

The driving cycle taken into consideration is the UDDS cycle which stands for Urban Dynamometer Driving Schedule.Although the data is taken for a total driving time for 1370s,for simplicity sake on 150s of driving  time is considered.The speed which is in miles per hour has been converted to meters per seconds.

The drive cycle is given below.

The euqation for kinetic energy from Braking is given as,

             E = 1/2*m(Vi-Vt)^2

where

     m=Mass of the vehicle in kg.

     Vi= initial speed of the vehicle in m/s.

      Vf = Final speed of the vehicle in m/s.

From the Drive cyccle 10 braking points were obtained.The mass is set at a constant 1500kg.The energy required for braking is given in the tabel

Therfor the total energy required for braking is 16.8KW

QUESTION 2:

Regenerative braking allows electric vehicles to use the motor as a generator when the brakes are applied,to pump vehicle energy from the brakes into an energy storage device.Regenerative braking is an effective approach to extend the driving range of an EV.

• The regenerative braking torue cannot be made large enough to provide all the required braking torque of the vehicle as iit might lead to the deterioration in stability of the vehicle.Also as compared to the torque values of acceleration torque of motor is much higher than deceleration torque.
• At high speed,the motor might be in its constant power region which causes less values of torques produced and this limits the amount of braking torque that is used for regeneration.Hence the peak value of acceleration torque and braking torque are not equal.

ELECTRICAL AND MECHANICAL BRAKES COORDINATION:

The regenerative braking system may not be used under many conditions.such as with a high state of charge(SOC)or a high temparature of the battery.In these case,the mechanical braking system works to cover the required total braking torque.

Thus,cooperation between the mechanical braking system and the regenerative braking system is main part of the design of the EV braking control stratagy and is known as torque blending.

There are 2 different control stratagies for Braking Combinations:

           1.Series control stratagy

           2.Parallel Control Stratagy

Series Control Stratagy:

•    a combination of friction-based mechanical braking system with a regenerative braking system that transfers energyto the battery with an integrated control,which distributes the required braking force between the regenerative braking system and the mechanical braking system.
• Series Stratagy could give an increase of 15-30% in fuel efficiency and has more consistent braking due to good torque blending capability.

Parallel Control Stratagy:

• Combination of mechanical and the regenerative braking system,operated simultaneously without an integrated control.
• The regenerative braking force is added to the mechanical braking force which cannot be controlled.
• The regenerative torque is determined by considering the motor capacity,battery SOC,and vehicle vlocity.The regenerative braking force is calculated from the brake controlunit by comparing the demanded brake torque and the motor torque available.

APPLICATION OF BRAKING COMBINATION EDIB(Electric Driven Intelligent Brake)inNISSAN LEAF

• EDIB allows and controls optimization of the regenerative brake and regular friction brake(hydraulic brake).
• The system produces an adequate braking force keeping energy regeneration increased as much as possible.
• At higher speeds,a combination of regenerative and friction braking is applied.
• At lower speeds,regenerative braking is given a higher proportion for maximised energy conversion.

QUESTION 3:

Motor speed -0 - 1000rpm

Motor Torqu - 0-700N.m

Motor Constants:

• copper Loss  constant, kc=0.1
• Iron Loss Constant, ki=0.001
• windage Loss constant,kw=0.0001
• Motor Loss constant, Cm=25

OUTPUT:

The contour plot for a motor with defined constants are plotted in the defined speedvs Toruqe Region based on efficiency.It can be seen that for increasing speed and torque,the efficiency of the motor gradually decreases.The level of efficiency is depicted using colorbar.

clear all
close all
clc

%Defining Speed&Torque
speed = linspace(0,1000,300);
torque = linspace(0,700,300);

%Defining Motor Constants
kc = 0.1;             %Copper Loss constant
ki = 0.001;           %Iron Loss Constant
kw = 0.0001;          %windage Loss Constant
Cm = 25;              %Motor Loss Constant


%obtaining 2-D Grid for speed&Torque
[X,Y] = meshgrid(speed,torque);

Powerout = X.*Y;                                    %calculating output power

Totalloss = ((Y.^2).*kc)+(ki*.X)+((X.^3).*kw)+Cm    %Total loss calculation

inputpower = Powerout + Totalloss;

Z = Powerout./inputpower;                            %Efficiency calculation

%Defining Efficiency levels for contouring
EL = [0.70,0.72,0.75,0.77,0.79,0.80,0.81,0.82,0.83,0.84,0.85,0.86,0.87,0.88,0.89,0.90,0.91,0.92,0.93,0.95]
%Plotting the efficiency wrt speed&Torque
contourf(X,Y,Z,EL)
colorbar
xlabel('speed(rpm)');
ylabel('Torque(N.m)');
title('Efficiency Contour');