Week-11 Challenge: Braking

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

Here have taken the drive cycle data from a website link is attached below. We have used NEW YORK CITY DRIVE CYCLE for calculation.

Graph is given below:

here we are going to calculate braking energy by this vehicle during this whole driving cycle.

Parameter:

M : Mass: 800 kg

Vf : Final velocity : here the minimum velocity obtained after braking is considered as final velocity.

Vi:- Initial velocity: Here the maximum velocity obtained before braking is considered as initial velocity.

excel sheet of calcualtion:

https://docs.google.com/spreadsheets/d/1qbxAa1y5FfLWA3c-1pLktiKdS7d2tuwz/edit?usp=sharing&ouid=103272420422371127018&rtpof=true&sd=true

Word file:

https://docs.google.com/document/d/1XfE8_hy3IUgKzpkeywdUXNpiAsxE-1AD/edit?usp=sharing&ouid=103272420422371127018&rtpof=true&sd=true

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

Here it is clearly shown in the first graph that till the motor reaches the critical speed it has constant torque and once it reaches the critical speed, the curve is having a down slope which is aconstant power region and this graph denotes the accelerating operation of the motor. For the deceleration or braking operation of the motor, this graph is mirrored down which will be having the speed (+ve) and torque (-ve).

For example,

an ev can achieve 0-100 kmph in 10 sec. Acceleration operation goes this way with low speed and high torque constant torque region is achieved which has accelerating power amd by reaching the critical speed it shifts to constant power region and thus it easy for an EV to reach 0-100 kmph.

As said the breaking operation graph will be mirrored image of above plot. So we can not say that the motor producing 7 Nm torque for acceleration can also produce -7 Nm for breaking. Because we are operating in the field weakening region and operating above the base speed. Thus peak acceleration torque is greater above the base speed. Thus peak acceleration torque is greater than the peal deceleration torque. For acceleration it has high torque with low speed and for deceleration it has low torque for high speed.

SERIES:

Brakes will be applied one after the another so which they are connected in series. Either one brake stretegy at a time either regenerative braking or mechanical braking at a time.

PARALLEL:-

In case of parallel both brakes are applied simultaneously, both at a time

ELECTRIC DRIVEN INTELLIGENT BRAKE:-

Nissan has developed a practical brake stretegy called ELECTRIC DRIVEN INTELLIGENT BRAKE developed by nissan leaf.

Technology Functionality:-

After stepping on the brake pedal, the system produces natural and adequate braking force that corresponds to the operation.The amount of energy regeneration also needs to be increased as much as possible. EDIB(electric driven intelligent brake) controls the regenerative brake and friction brake to support both of there requirements. Further , it also controls the reactive force from the pedal in order to unify the feeling when stepping down on the pedal and the sense of deceleration.

3) Make a MATLAB program which plots contour of given motor speed, torque and efficiency values. Attach the code as a .m file attach a screenshot of all the plots.

close all
clc
x = linspace(1,1000,250); % speed in rad/sec
y = linspace(1,250,250); % torque in nm

% motor loss constants
kc = 0.2; % copper loss constant
ki = 0.007; % iron loss constant
kw = 0.00005; % windage loss contant
Const_Loss = 20; % Constant motor loss
[X,Y] = meshgrid(x,y); % conveting to 2D
Output_power = (X.*Y); % power = torque*speed

B = (Y.^2)*kc; % copper loss
C = X.*ki; % iron loss
D = (X.^3)*kw; % windage loss
Input_power = Output_power + B+C+D+ Const_Loss;
Efficiency = Output_power./Input_power; % eff of motor
V = [0.70,0.80,0.90,0.91,0.92,0.925,0.93]; % efficiecies 
box off
grid off
contourf(X,Y,Efficiency,V);
contourcbar
title ('speed-torque-effiency characteristics of motor');
xlabel('speed(rad/sec)');
ylabel('torque(Nm)');

Prgram discription:-

• input are given with name using linspace command (Speed and torque.).
• Motor constant areassigned namely Copper loss, Iron loss, Windage loss and Constant motor.
• here, meshgrid used for evaluate functions of two variables and three dimensional mesh or surface plots.
• by using speed and torque, output power is calculated.
• contour graph is plotted speed, torque and effieciency.

we can see that maximun efficiency of 92% is achieved by 165 rad/sec and at 42 Nm. The lower efficiency is achieved at 289 rad/sec and at torque of 98 Nm. This contour plot clearly gives the idea on speed,torque and efficiency relationship of the motor. The color indicates the efficiency denoted in the right side with the colorbar.

Google drive link:

https://drive.google.com/file/d/18Dy4E-C6DD1SdpwU_3uQ6uOxEkah9ns3/view?usp=sharing