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ELECTRICAL MOTORS

D. BHAVSINGH

NITW



+

� An electric motor converts electric energy intomechanical motion

12V

-

ElectricEnergy

� Electric motors are used toperform a mechanical task by

using electricity� Mechanical energy used to e.g.

� Rotate pump impeller, fan, blower � Drive compressors

� Lift materials

� Motors in industry: 70% of electrical load

WHAT IS AN ELECTRIC MOTOR?



� There are many different types and classifications of electricmotors:

Permanent magnet DC motor

Brushless DC motor

Wound field motor

Universal motorsThree phase induction motor

Three-phase AC synchronous motors

Two-phase AC Servo motors

torque motors

Shaded-pole motorsplit-phase induction motor

capacitor start motor

Permanent Split-Capacitor (PSC) motor

Repulsion-start induction-run (RS-IR) motor

Stepper motor

Repulsion motor

Linear motor

Variable reluctance motor

Unipolar stepper motorBipolar stepper

Full step stepper motor

Half step stepper motor

Micro step stepper motor

Switched reluctance motorShaded-pole synchronous motor

Induction motor

Coreless DC motor

Others......

TOTAL ELECTRIC MOTORS



TYPE OF ELECTRIC MOTORSTYPE OF ELECTRIC MOTORS

World of Motors

DC Motors AC Motors

Brush DC

Brushless DC

Single Phase

Poly-Phase

(3 phase)

Linear

Stepper

Universal

Electric MotorsPneumatic Motors Hydraulic Motors

Servo Motors



TYPE OF ELECTRIC MOTORSTYPE OF ELECTRIC MOTORS

� classification of AC and DC motors

Electric Motors

Alternatin Current(AC) Motors

Direct Current (DC) Motors

Synchronous Induction

Three-PhaseSin le-Phase

Self ExcitedSeparatelyExcited

Series ShuntCompound



Electric MotorsElectric Motors

� DC motors still have many practical applications, suchautomobile, aircraft, and portable electronics, in speedcontrol applications

� An advantage of DC motors is that it is easy to control theirspeed.

� Most DC machines are similar to AC machines: i.e. they haveAC voltages and current within them.

� DC machines have DC outputs just because they have a

mechanism converting AC voltages to DC voltages at theirterminals. This mechanism is called a commutator;theref ore, DC machines are also called commutatingmachines



What Is a Permanent Magnet?

� A piece of iron or steel which produces a magnetic field

� Found in nature as magnetite (Fe3O4) lodestones

� Magnetic field causes the permanent magnet to attract

iron and some other materials

� Two ends of the permanent magnet are usually

designated North and South

� Opposite magnet ends attract and like magnet ends repel



What Is an Electromagnet?

� Electromagnets behave like permanent

magnets

but their magnetic field is not

permanent

� Magnetic field is temporarily induced by an

electric current



How Do You Make an Electromagnet?

� Start with an iron bar





� Wrap a wire around the iron bar






� Connecting a battery causes a current to flow

in the wire

Current

+ -






� Connecting a battery causes a current to flow in the wire

� The current induces a magnetic field creating an

electromagnet

Current

SOUTHNORTH

+ -




� Reversing the current direction, reverses the

polarity

Current

+-

NORTHSOUTH




� Reversing the current direction, reverses the

polarity

� If the current is stopped, the induced magnetic field

decays to 0

Current

+-

NORTHSOUTH



DC Motors ± Components

� Field pole� North pole and south pole

� Receive electricity to formmagnetic field

� Armature� Cylinder between the poles

� Electromagnet when current goes through

� Linked to drive shaft to drive the load

� Commutator � Overturns current direction in armature



What Is an Electric Motor?

STATOR

ROTOR

� An electric motor has two basic parts:

± The stationary part is called the stator.

± The rotating part of the electric motor is called therotor.



How Does a Permanent Magnet DC Motor Work?

� "DC Motors" use magnets to produce motion

± Permanent magnets

NORTHSOUTH



� "DC Motors" use magnets to produce motion

± Permanent magnets

± An electromagnet armature

How Does a Permanent Magnet DC Motor Work?

NORTHSOUTH



NORTHSOUTH

� Electromagnet armature is mounted on axle so that

it can rotate

� A commutator makes an electrical contact with the

motor's brushes

Permanent Magnet DC Motor

Commutator and Brushes




Commutator Structure

� Commutator is comprised of two "near-halves" of a

ring



� Commutator is comprised of two "near-halves" of a ring

� Mounted on the armature's axle to rotate with the rotor

Armature







� Armature's windings are connected to the

commutator




Commutator and Brushes

� Armature's windings are connected to the commutator

� Brushes connect the commutator to the battery



NORTHSOUTH

� Current flows through the armature's windings,

which polarizes the electromagnet

+ -


Electromagnet Polarization



NORTHSOUTH

� The like magnets (NORTH-NORTH and SOUTH-SOUTH) repel

� As the like magnets repel, the armature rotates, creating mechanical

motion

+ -

Permanent Magnet DC Motor Rotation



NORTHSOUTH

� What direction will the armature spin?

� Clockwise? Counterclockwise?

Clockwise ?

Counterclockwise ?

Permanent Magnet DC Motor Rotation Direction?

+ -



Left Hand Rule

� Start with two opposite

ends of a magnet

NORTH

SOUTH



Left Hand Rule: Magnetic Field

NORTH

SOUTH

� The magnetic field (B) is from

the NORTH pole to the

opposite SOUTH pole

� The pointing finger

follows B into

screen B



Left Hand Rule: Current Flow

NORTH

SOUTH

� Current flows in a wire through

the magnetic field from left to

right

� The middle finger follows I1right, or I2 left

I1

I2



Left Hand Rule: Force

NORTH

SOUTH

� The force, F, acting on each wire

is in the direction of the

thumb

� The wire with I1is pushed up,

I2

down

I1

I2

F1

F2



Left Hand Rule: Force

NORTH

SOUTH

� The magnitude of F is give by:

| F | = | I | * P * | B |

where P is the length of the

wire in B

I1

I2

F1

F2

P



Left Hand Rule: Current Loop

NORTH

SOUTH

� If the current flows in a loop,

the force(s) will cause the

loop to rotateI

F

F



NORTHSOUTH

� Magnetic field is from right to left

� Imagine current flows out of the screen in this cross section

� The force causes the armature to rotate clockwise

+ -




NORTHSOUTH

+ -


� At some point, the commutator halves will rotate away

from the brushes

� Momentum keeps the electromagnet and the commutator

ring rotating



NORTHSOUTH

+ -


� When the commutator halves reconnect with the

other brush, the current in the windings is reversed



NORTHSOUTH

+ -


� When the commutator halves reconnect with the

other brush, the current in the windings is reversed

� The polarity is reversed and the armature continues

to rotate + -



NORTHSOUTH

� Magnetic field is from right to left

� Imagine current flows out of the screen in this cross section

� The force causes the armature to rotate clockwise

+ -




ROTATING DC MOTOR PRINCIPLE TORQUE TAMING

This is accomplished by using a commutator (either mechanical or electronic cycle).

U0 180 360

How it Works.

Metal ring attached to shaft split in two

sections




The figure illustrates one method by which the commutation function might be

accomplished. Rather than hard wiring the current source to the coil, the current is

conducted through sliding contacts (brushes) connected to the current source. The

brushes ride on the ends of the coil wires, thus conducting current through the coil.

In this simplified motor, the brushes switch coil connections about once every 180o

of rotation. Therefore, the direction of current flow remains fixed with respect to themagnetic field.




The torque produced by this design momentarily goes to zero

every half cycle. Stall is possible, also start up may require a

small push. In addition to this the torque versus rotation angle isnot uniform



ROTATING DC MOTORPRINCIPLE FIELD TAMING

To obtain a more even

torque, the magnetic fieldlines should look somethinglike: F

X

F X

BX

BX

BX

BX

B

X

BX

And how do you get a magnetic field

with that shape?

BX



ROTATINGDCMOTORPRINCIPLE FIELD TAMING

To obtain a more even

torque, the magnetic fieldlines should look somethinglike:

B field lines follow the path of least reluctance, so the

curved poles create roughly a radial field pattern.

BX

pol s of ag t

Rotor



Redesign the permanent magnet poles.

Insert soft iron rotor




ROTATING DC MOTORPRINCIPLE FIELD TAMING

B

X

Rotor

r

Motor dimensions:

Radius r

epth N

Tor i ra ial fi l

Nr I 2!+




In a practical motor design, use many turns of wire on the rotor (rather than justone) to increase the torque.

BX

Rotor

r



� The controlled application of electrical energy to a motor toelicit a desired mechanical response

± Start / Stop ± Speed

± Torque

± Position

� Significant amount of electronics may be required to

control the operation of some electric motors

What Is Motor Control ?



Control of Electromagnetics

� Much of the physical design of an electric motor and its controlsystem are related to the switching of the electromagnetic field

� There is a mechanical force which acts on a current carrying wire

within a magnetic field

� The mechanical force is perpendicular to the wire and the magnetic

field

� The relative magnetic fields between the rotor and stator arearranged so that a torque is created, causing the rotor to rotate

about its axis



Controlling a Permanent Magnet DC Motor

� Bi-directional PM DC motors are controlled with an "H-Bridge" circuit consisting of the motor and four power switches



Current

Turning On a PMDC Motor

� One switch is closed in each leg of the "H"

� One switch is open in each leg of the "H"



Current

� One switch is closed in each leg of the "H"

� One switch is open in each leg of the "H

Turning On a PMDC Motor in Other Direction



Current

� Unidirectional motors are controlled by a half-H

bridge circuit

Controlling a Permanent Magnet DC (PMDC) Motor



DC MOTORS

� Speed control without impact power supply

quality

� Changing armature voltage

� Changing field current

� Restricted use

� Few low/medium speed applications

� Clean, non-hazardous areas

� Expensive compared to AC motors



� Relationship between speed, field flux and armature voltage

�

Back electromagnetic force: E = K * NTorque: T = K *Ia

� E = electromagnetic force developed at armature terminal (volt)

� * = field flux which is directly proportional to field current

� N = speed in RPM (revolutions per minute)

� T = electromagnetic torque

� Ia = armature current� K = an equation constant



Self-excited DC motor : series motor

� Field winding in serieswith armature winding

� Field current =

armature current

� Speed restricted to

5000 RPM

� Avoid running with

no load: speeduncontrolled

Suited for high

starting torque:

cranes, hoists



Self-excited DC motor : compound motor

Field winding in

series andparallel with

armature winding

Good torque and

stable speed

Higher %

compound in

series = high

starting torque

Suited for high

starting torque if high

% compounding:

cranes, hoists



Power flow and losses in DC machines

Unfortunately, not all electrical power is converted to mechanical

power by a motor and not all mechanical power is converted to

electrical power by a generator

The efficiency of a DC machine is:

100%in loss

in

P P

P L

! �

or100

out

in

L ! �



The losses in DC machines

There are five categories of losses occurring in DC machines.

1. Electrical or copper losses the resistive losses in the armature and field windings

of the machine.

Armature loss: 2 A A A P I R!

Field loss: 2

F F F P I !

Where I A

and IF

are armature and field currents and R A

and RF

are armature and field

(winding) resistances usually measured at normal operating temperature.



The losses in DC machines

2. Brush (drop) losses the power lost across the contact

potential at the brushes of the machine.

BD BD A P V I

!

Where I A

is the armature current and V BD

is the brush voltage drop.

The voltage drop across the set of brushes is approximately constant

over a large range of armature currents and it is usually assumed to

be about 2 V.

Other losses are exactly the same as in AC machines



THE LOSSES IN DC MACHINES

4. Mechanical losses losses associated with mechanical effects: friction

(friction of the bearings) and windage (friction between the moving parts of the

machine and the air inside the casing). These losses vary as the cube of rotation

speed n3.

3. Core losses hysteresis losses and eddy current losses. They

vary as B2 (square of flux density) and as n1.5 (speed of rotation of

the magnetic field).

5. Stray (Miscellaneous) losses losses that cannot be classified in any of

the previous categories. They are usually due to inaccuracies in modeling. For

many machines, stray losses are assumed as 1% of full load.



THE POWER-FLOW DIAGRAM

On of the most convenient technique to account for power losses

in a machine is the power-flow diagram.

for a dc

motor:

Electrical power is input to the machine, and the electrical and brush

losses must be subtracted. The remaining power is ideally converted

from electrical to mechanical form at the point labeled as P conv

.



BRUSHLESS DC MOTOR

� Similar to a permanent magnet DC motor� Rotor is always the permanent magnet (internal or external)

� Design eliminates the need for brushes by using a more complexdrive circuit

� Advantages:

+ High efficiency+ High reliability

+ Low EMI

+ Good speed control

� Disadvantages:

± May be more expensive than "brushed" DC motors

± More complex and expensive drive circuit than "brushed" DC motors



� Many of the limitations of the classic permanent magnet "brushed" DC motor are caused by the brushes pressing against the rotating

commutator creating friction

± As the motor speed is increased, brushes may not remain in

contact with the rotating commutator

± At higher speeds, brushes have increasing difficulty in maintaining

contact

± Sparks and electric noise may be created as the brushes

encounter flaws in the commutator surface or as the commutator

is moving away from the just energized rotor segment ± Brushes eventually wear out and require replacement, and the

commutator itself is subject to wear and maintenance

� Brushless DC motors avoid these problems with a modified design,

but require a more complex control system

WHY A BRUSHLESS DC MOTOR ?



How Does a Brushless DC Motor Work ?

� A brushless DC motor uses electronic sensors to detect the positionof the rotor without using a metallic contact

� Using the sensor's signals, the polarity of the electromagnets is

switched by the motor control drive circuitry

� The motor can be easily synchronized to a clock signal, providing

precise speed control

� Brushless DC motors may have:

± An external PM rotor and internal electromagnet stator

± An internal PM rotor and external electromagnet stator



� This example brushless DC motor has: ± An internal, permanent magnet rotor

Example Brushless DC Motor Operation



� This example brushless DC motor has: ± An external, electromagnet stator




� This example brushless DC motor has: ± An external, electromagnet stator, with magnetic

field sensors


hl i



Brushless DC Motor Construction

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Brushless DC Motor Operation

B hl DC M O i



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B hl DC M t O ti



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Brushless DC Motor



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A1 B1 C1

A2 B2 C2

Control Circuit

Brushless DC Motor



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A2 B2 C2

Control Circuit

Brushless DC Motor



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Control Circuit



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BRUSHLESS DC MOTOR CONTROL CIRCUIT

Brushless DC Motor



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Control Circuit

Brushless DC Motor



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Control Circuit

Brushless DC Motor



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Control Circuit

Brushless DC Motor



Control Circuit

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A2 B2 C2



Permanent Magnet Stepper Brushless DC

DC Motor Motor Motor

Advantages: + Low cost + Position control + High efficiency

(high volume) (low cost + High reliability

+ Simple operation control circuits) + Low EMI

+ Speed control

Disadvantages: - Medium efficiency - Poor efficiency - Maybe higher cost

- Poor reliability - Digital interface - Complex control

- Bad EMI - High cost

Types of Electric Motors



Brushless DC Motor

� Similar to a permanent magnet DC motor� Rotor is always the permanent magnet (internal or external)

� Design eliminates the need for brushes by using a more complexdrive circuit

� Advantages:

+ High efficiency+ High reliability

+ Low EMI

+ Good speed control

� Disadvantages:

± May be more expensive than "brushed" DC motors ± More complex and expensive drive circuit than "brushed"

DC motors



Modeling a DC motor

if

Replaced by a

permanentpermanent

magnetmagnet

Electrical Part Mechanical Part

Electromechanical part



M d li th A t C t ll d DC M t



Modeling the Armature Controlled DC Motor



SIMULINK MODEL

100Ravi Kumar Jatoth, Asst Prof, Dept of ECE



3 assumptions in modeling DC motor

Assumption 1:Assumption 1: The air gap flux is proportional to the field current

f iw* f ik 1

!*

Assumption 2:Assumption 2: The torque developed on the motor shaft is proportional to theproduct of armature current and the air gap flux

ai*wX f aa iik k ik 212 !*!X

2 configurations can be made in controlling DC motor2 configurations can be made in controlling DC motor

(1) Armature-controlled DC motor (if = constant)

(2) Field-controlled DC motor (ia = constant)

Our focus





(cont.)

Assumption 3:Assumption 3: The back-emf is proportional to the velocity of the motor shaft

mbvy

w U

Our objective is to find the transfer function of

)()(

s E

s

a

mU

ll d



Armature-Controlled DC motor

Electrical part:Electrical part:

By applying KVL, we obtain the differential equation:

baaa

aa vi Rd t

d i Lt e !)(

Take the Laplace transform yields to:

)()()( sV s I R s L s baaaa ! EquationEquation 11

Mechanical part:Mechanical part:

d t

d

d t

d J t

mm

mmm

UUX !

2

2

)(

In Laplace

? Ammmmmmmm

s B s J s B s J s UUUX !!22)( EquationEquation 22

ll d ( )



Armature-Controlled DC motor (cont.)ElectroElectro--Mechanical part:Mechanical part:

a f m iik k 21!X

mk Motor torque constant

)( s I k amm !X

mbvy

wU mbb k vy

! U

Relationship between Torque & armature current

Relationship between back-emf & angular speed

Equation 3Equation 3

EquationEquation 44

Back-emf constant

mbb sk V U!

? A)()(

1)( sV s E

Rs s I baa

! Equation 1Equation 1



R saa

? A)(1

2s

s s J m

mm

m X U

! EquationEquation 22

amm I k !X Equation 3Equation 3

EquationEquation 44mbb sk V U!

aa R sL

1m

k s B J s

mm2

1

b sk

)( smU)( s I a )( smX )( sa

)( sV b

We can draw in term of block diagram

)(1

sG )(2 sG)(3 sG



aa R sL 1 mk

s D J s mm 2

1

b sk

)( smU)( s I a )( sm

X )( sa

)( sV b

)( s H

)()()()(1

)()()(

)(

)(

321

321

s H sG sG sG

sG sG sG

s

s

a

m

!

U

Thus, the transfer function for DC motor



� .



Thank

You

saranya bhavsingh motors

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