Bridging Theory in Practice

1
Bridging Theory in Practice

• Transferring Technical Knowledge
• to Practical Applications

2
Introduction to Motor Control
3
Introduction to Motor Control
4
Introduction to Motor Control

• Intended Audience
• Individuals with an interest in learning about
  electric motors and how they are controlled
• A simple understanding of magnetics is assumed
• Topics Covered
• What is an electric motor?
• What are some common types of electric motors?
• How do these electric motors work?
• How these motors are controlled.
• Expected Time
• Approximately 90 minutes

5
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

6
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

7
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

8
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

9
How Do You Make an Electromagnet?

• Start with an iron bar

10
How Do You Make an Electromagnet?

• Start with an iron bar
• Wrap a wire around the iron bar

11
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
12
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
• The current induces a magnetic field creating an
  electromagnet

SOUTH
NORTH
Current
13
How Do You Make an Electromagnet?

• Reversing the current direction, reverses the
  polarity

NORTH
SOUTH
Current
14
How Do You Make an Electromagnet?

• Reversing the current direction, reverses the
  polarity
• If the current is stopped, the induced magnetic
  field decays to 0

NORTH
SOUTH
15
Electromagnets andElectric Motors

• We can use electromagnets in electric motors to
  convert electrical energy to mechanical work

Electric Motor

• Electric motors are used to perform a mechanical
  task by using electricity
• Open a sunroof
• Lift a power antenna
• Control windshield wiper

Electric Energy

-
12V
16
What Is an Electric Motor?

• An electric motor has two basic parts
• The stationary part is called the stator.
• The rotating part of the electric motor is called
  the rotor.

STATOR
17
What Is an Electric Motor?

• Electrical energy creates a rotating magnetic
  field inside the motor causing the rotor to
  rotate, creating mechanical motion

STATOR
18
Where Are Electric Motors Used?

• Electric motors are used in many different
  automotive applications

Sunroof Brakes Power steering Fuel pump Water
pump Hybrid and electric vehicles Cruise
control Throttle plate control Air vents Others
Power windows Power seats Power
mirrors Fans Windshield wipers Windshield washer
pumps Starter motor Electric radio antennae Door
locks Information gauges
19
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

20
What Is Motor Control ?

• The controlled application of electrical energy
  to a motor to elicit a desired mechanical
  response
• Start / Stop
• Speed
• Torque
• Position
• Significant amount of electronics may be required
  to control the operation of some electric motors

21
Control of Electromagnetics

• Much of the physical design of an electric motor
  and its control system 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 are arranged so that a torque is
  created, causing the rotor to rotate about its
  axis

22
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

23
Types of Electric Motors

• There are many different types and
  classifications of electric motors

Permanent magnet DC motor Stepper motor Brushless
DC motor Wound field motor Universal motors Three
phase induction motor Three-phase AC synchronous
motors Two-phase AC Servo motors torque
motors Shaded-pole motor split-phase induction
motor capacitor start motor Permanent
Split-Capacitor (PSC) motor Repulsion-start
induction-run (RS-IR) motor
Repulsion motor Linear motor Variable reluctance
motor Unipolar stepper motor Bipolar stepper Full
step stepper motor Half step stepper motor Micro
step stepper motor Switched reluctance
motor Shaded-pole synchronous motor Induction
motor Coreless DC motor Others......
24
Permanent Magnet DC Motor

• Similar in construction to the introductory
  example
• Metallic contacts (brushes) are used to deliver
  electrical energy
• Rotational speed proportional to the applied
  voltage
• Torque proportional to the current flowing
  through the motor
• Advantages
• Low cost (high volume demand)
• Simple operation
• Disadvantages
• Medium efficiency
• Poor reliability (brush, commutator wear out)
• Strong potential source of electromagnetic
  interference

25
Stepper Motor

• Full rotation of electric motor divided into a
  number of "steps"
• For example, 200 steps provides a 1.8o step angle
• A stepper motor controller can move the electric
  motor one step (in either direction) by applying
  a voltage pulse
• Rotational speed is controlled by changing the
  frequency of the voltage pulses
• Advantages
• Low cost position control (instrument gauges)
• Easy to hold position
• Disadvantages
• Poor efficiency
• Requires digital control interface
• High motor cost

26
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 complex drive 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

27
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

28
How Does a Permanent Magnet DC Motor Work?

• "DC Motors" use magnets to produce motion
• Permanent magnets

29
How Does a Permanent Magnet DC Motor Work?

• "DC Motors" use magnets to produce motion
• Permanent magnets
• An electromagnet armature

30
Permanent Magnet DC Motor Rotating Armature

• Electromagnet armature is mounted on axle so that
  it can rotate

31
Permanent Magnet DC Motor Commutator and Brushes

• Electromagnet armature is mounted on axle so that
  it can rotate
• A commutator makes an electrical contact with the
  motor's brushes

32
Permanent Magnet DC Motor Commutator Structure

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

33
Permanent Magnet DC Motor Commutator Structure

• Commutator is comprised of two "near-halves" of a
  ring
• Mounted on the armature's axle to rotate with the
  rotor

Armature
34
Permanent Magnet DC Motor Commutator Structure

• Armature's windings are connected to the
  commutator

35
Permanent Magnet DC Motor Commutator and Brushes

• Armature's windings are connected to the
  commutator
• Brushes connect the commutator to the battery

36
Permanent Magnet DC Motor Electromagnet
Polarization

• Current flows through the armature's windings,
  which polarizes the electromagnet

37
Permanent Magnet DC Motor Rotation

• The like magnets (NORTH-NORTH and SOUTH-SOUTH)
  repel
• As the like magnets repel, the armature rotates,
  creating mechanical motion

38
Permanent Magnet DC Motor Rotation Direction?

• What direction will the armature spin?
  
• Clockwise? Counterclockwise?

Counterclockwise ?
Clockwise ?
39
Permanent Magnet DC Motor Rotation Direction?

• To determine the direction of the motor's
  rotation, we need to use the "Left Hand Rule"

Magnetic Field
Current
Force
40
Left Hand Rule

• Start with two opposite
  ends of a magnet

SOUTH
NORTH
41
Left Hand RuleMagnetic Field

• The magnetic field (B) is from
  the NORTH pole
  to the
  opposite SOUTH pole
• The pointing finger
  follows B
  into
  screen
  

SOUTH
NORTH
42
Left Hand RuleCurrent Flow

• Current flows in a wire through
  the
  magnetic field from left
  to
  right
• The middle finger
  follows I1
  right,
  or I2 left
  
  
  

SOUTH
I1
I2
NORTH
43
Left Hand RuleForce

• The force, F, acting on each wire
  is in the
  direction of the
  thumb
• The wire with I1
  is
  pushed up,
  I2 down
  
  
  

F1
SOUTH
I1
I2
NORTH
F2
44
Left Hand RuleForce

• The magnitude of F is give by
• F I ? B
• where ? is the
  
  length of the
  wire
  in B

F1
SOUTH
I1
I2
NORTH
F2
?
45
Left Hand RuleCurrent Loop

• If the current flows in a loop,
  the
  force(s) will cause the
  loop to
  rotate
• 
  
  

F
SOUTH
I
NORTH
F
46
Permanent Magnet DC Motor Rotation

• Magnetic field is from right to left
• Imagine current flows out of the screen in this
  cross section

47
Permanent Magnet DC Motor Rotation

• 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

48
Permanent Magnet DC Motor Rotation

• At some point, the commutator halves will rotate
  away from the brushes
• Momentum keeps the electromagnet and the
  commutator ring rotating

49
Permanent Magnet DC Motor Rotation

• When the commutator halves reconnect with the
  other brush, the current in the windings is
  reversed

50
Permanent Magnet DC Motor Rotation

• 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

51
Permanent Magnet DC Motor Rotation

• 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

52
Controlling a Permanent Magnet DC (PMDC) Motor

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

53
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"

54
Turning On a PMDC Motorin the Other Direction

• One switch is closed in each leg of the "H"
• One switch is open in each leg of the "H

55
Controlling a Permanent Magnet DC (PMDC) Motor

• Unidirectional motors are controlled by a
  half-H bridge circuit

56
Controlling a PMDC Motor Options

• DC operation
• Rotational speed of the DC motor is fixed at a
  given voltage and load
• PWM Operation
• Average voltage (and rotational speed) can be
  controlled by opening/closing the switches
  quickly
• Braking
• Shorting the terminals or momentarily reversing
  the drive
• Others

57
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

58
Why a Stepper Motor ?

• Unlike the permanent magnet DC motor, stepper
  motors move in discrete steps as commanded by the
  stepper motor controller
• Because of their discrete step operation, stepper
  motors can easily be rotated a finite fraction of
  a rotation
• Another key feature of stepper motors is their
  ability to hold their load steady once the
  require position is achieved
• An example application for stepper motors is for
  implementing traditional "analog" instrumentation
  gauges on a dashboard

59
How Does a Stepper Motor Work ?

• A stepper motor often has an internal rotor with
  a large number of permanent magnet teeth
• A large number of electromagnet "teeth" are
  mounted on an external stator
• Electromagnets are polarized and depolarized
  sequentially, causing the rotor to spin one
  "step"
• Full step motors spin 360o/( of teeth) in each
  step
• Half step motors spin 180o/( of teeth) in each
  step
• Microstep motors further decrease the rotation in
  each step

60
Full Step Motor Operation

Half Rotate and Hold
61
Half Step Motor Operation

Half Rotate and Hold
62
Stepper Motor Control

• The stepper motor driver receives square wave
  pulse train signals from a controller and
  converts the signals into the electrical pulses
  to step the motor
• This simple operation leads stepper motors to
  sometimes be called "digital motors"
• To achieve microstepping, however, the stepper
  motor must be driven by a (quasi) sinusoidal
  current that is expensive to implement

63
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

64
Why a Brushless DC Motor ?

• 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

65
How Does a Brushless DC Motor Work ?

• A brushless DC motor uses electronic sensors to
  detect the position of 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

66
Example Brushless DC Motor Operation

• This example brushless DC motor has
• An internal, permanent magnet rotor

67
Example Brushless DC Motor Operation

• This example brushless DC motor has
• An external, electromagnet stator

68
Example Brushless DC Motor Operation

• This example brushless DC motor has
• An external, electromagnet stator, with magnetic
  field sensors

69
Brushless DC Motor Construction
A
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Brushless DC Motor Operation
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Brushless DC Motor Operation
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Brushless DC Motor Operation
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Brushless DC Motor Operation
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Brushless DC Motor Operation
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Brushless DC Motor Operation
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Brushless DC Motor Operation
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Brushless DC Motor Control Circuit
A1
B1
C1
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A2
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C2
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Brushless DC Motor Control Circuit
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A2
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Brushless DC Motor Control Circuit
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Brushless DC Motor Control Circuit
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Brushless DC Motor Control Circuit
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Brushless DC Motor Control Circuit
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Brushless DC Motor Control Circuit
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Brushless DC Motor Control Circuit
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85
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

86
What Is an Electric Motor?

• An electric motor converts electric energy into
  mechanical motion

Electric Motor

• Electric motors are used to perform a mechanical
  task by using electricity
• Open a sunroof
• Lift a power antenna
• Control windshield wiper

Electric Energy

-
12V
87
Types of Electric Motors
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
88
Agenda

• Introduction to Electromagnets and Electric
  Motors
• What Is Motor Control?              
• What Are Some Common Types of Motors?          
• Permanent Magnet DC Motors
• Stepper Motors
• Brushless DC Motors
• Summary of Motors and Motor Control Circuits    
  

89
Introduction to Motor Control
90
Thank you!

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