Study of Torque and speed characteristics

AIM:

1. To Implement DC machine torque speed characteristics equations in MATLAB script file.

2. Distinguish between power cables and signal cables in wiring of an electric vehicle.

3. To study the voltage levels for a battery pack of electric vehicle.

KEYWORDS: DC machine, Power cable, Signal cable, Electric vehicle, Battery.

SOFTWARE: Matlab

OBJECTIVE:

1. Plot Torque vs Speed by creating a code in matlab.

2. Differentiate power cable and signal cable in an electric vehicle.

3. Study the voltage level for a battery used in electric vehicle.

INTRODUCTION:

Study 1:- A brushed DC electric motor is an internally commutated electric motor designed to be run from a direct current power source. Brushed motors were the first commercially important application of electric power to driving mechanical energy, and DC distribution systems were used for more than 100 years to operate motors in commercial and industrial buildings. Brushed DC motors can be varied in speed by changing the operating voltage or the strength of the magnetic field. Depending on the connections of the field to the power supply, the speed and torque characteristics of a brushed motor can be altered to provide steady speed or speed inversely proportional to the mechanical load. Brushed motors continue to be used for electrical propulsion, cranes, paper machine and steel rolling mills. Permanent magnet brushed DC motors are the most common. These motors use permanent magnets to produce the stator field. They are generally used in applications needing fractional horsepower such as; Toys, Radio Control hobby applications, electric slot cars, etc., The DC motor consists of 2 side permanent magnets, brushes, DC voltage, armature coil, and commutator.

A simple DC electric motor. When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation.

When the armature becomes horizontally aligned, the torque becomes zero. At this point, the commutator reverses the direction of current through the coil, reversing the magnetic field. So, the torque value is negative at a certain speed of armature coil.

CODE EXPLANATION:

• Input all the data required for DC motor like, Motor speed, Armature resistance, Supply voltage.
• Calculating motor constant and flux.

• Calculating Torque Speed charcteristics equation.

clear all
close all;clc
%Speed in radians per second
Speed = [0:20:220]

%Input Motor Speed in RPM/V
m_s = input('enter the value for Motor Speed \n');

%Supply voltage in Volts
Es = input('enter the value for Supply Voltage \n');

%Armature resistance in ohm
Ra = 0.016;

%Back emf 
Eb = 1;

%Calculating motor constant and flux
Km_Phi = 60/(2*3.142*m_s)

%Calculating Torque using motor characteristics
T = ((Km_Phi * Es) / Ra) - ((((Km_Phi)^2)/Ra).*Speed);

%Converting Speed to RPM
Speed = Speed.*(60/(2*3.142));

%Plotting Speed vs. Torque
plot(Speed,T);
xlabel('Speed (RPM)')
ylabel('Torque (N-m)')
title('Torque Speed Characteristics')
axis([0 2500 0 180])

%Calculating Current in Ampere
I = (Es - Eb) / Ra

%Calculating Maximum torque in (N-m) with back emf
Tmax = Km_Phi*I 

Study 2:-

Signal cables are low power and current rated wires whereas power cables are high current rated and power. Usually, signal cables are used in test and measurement applications, where as power cables are used in powering the motors, industrial machines, large power transmitting cables.

The basic key difference between wires and cables is that a wire is a single conductor whereas a cable is a group of conductors. Although, these conductors are made of a common material- copper or aluminium. Usually, the wires are bare and are twisted. But, some of the wires are coated with thin PVC layer. And in case of cables, they run parallelly and are twisted or bonded together to form a single case. For the safety purpose, an inner and outer sheath is made.

Types of Electrical Wires

1. Solid – A solid wire has a single conductor and is either insulated or bare and it is usually protected by a coloured sheath. This wire offers a lower resistance and is best to use in higher frequencies.

2. Standard – A standard wire contains many thin wire strands that are twisted together. These wires are used where the flexibility is required, standard wire can be used over a long period of time. Comparatively, the standard wire has larger cross-sectional area than the solid wire.

Types of Electrical Cables

1. Twisted pair cable – A twisted pair cable includes 2 cables that are twisted together. This twisting can avoid the noise produced by magnetic coupling and thus it is used to carry signals. Twisted pair cable is generally used in data communication and telecommunication.

2. Multi-conductor cable – This cable has 2 or more than 2 conductors which are insulated and their purpose is to protect the signal integrity. Both twisted pair cables and multi-conductor are known as balanced line configuration cables.

3. Coaxial cable – A coaxial cable has an inner conductor which is surrounded by a parallel outer foil conductor which is protected by insulating layers. In the cable, the 2 conductors are being separated from each other by an insulating dielectric. These cables are generally used in TV cable as its performance is more stable than the twisted pair cable.

4. Fibre optic cable – The fibre optic cable transmits the signals through a bunch of glass threads and comparatively, it has a greater bandwidth than metal conductors and that means they can carry more information and data. For this reason, fibre optic cables are used instead of traditional copper cables.

Study 3:-

If the battery as 12.2 V, while driving the voltage will increases more than 12.2 V (13V - 15V) the battery is said to high voltage. If the battery voltage is less than 12.2 V, then the battery is said to be low voltage.

Interms of Phase:-

For Single Phase consists of 220 V and 3-Phase consists of 440 V. If the battery nominal voltage is less than 220 V, Single Phase is used. If the Battery nominal voltage is more than 220V, 3-Phase is used.

Modern electric cars use Lithium batteries to power their cars due to some obvious reasons. But, these Lithium batteries have only around 3.7V per cell whereas an EV Car requires somewhere near 300V. If the voltage falls down or less than 300V is said to be low voltage. If the voltage is more than 300V is said to be high voltage.

The discharge rate for lithium ion batteries are very low when compare to other batteries. Moreover, the Specific power, Specific energy is more. So the Lithium ion battery is commonly used in EV which as more efficiency.

OUTPUT:

Study 1:-

CONCLUSION:

1. As the value of motor constant and flux (Km_Phi) increases, the torque value increases.

2. When the torque becomes zero, at this point the commutator reverses the direction of current through the coil so the value of torque will be negative.

3. At the 0 speed and the max torque is obtained and vice versa.