Download Ch14 Intro to Motor Controls

Bridging Theory in Practice
Transferring Technical Knowledge
to Practical Applications
Introduction to Motor Control
Introduction to Motor Control
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
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
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
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
How Do You Make an
Electromagnet?
• Start with an iron bar
• Wrap a wire around the iron bar
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
-
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
-
How Do You Make an
Electromagnet?
• Reversing the current direction, reverses the
polarity
NORTH
SOUTH
-
+
Current
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
-
+
Current
Electromagnets and
Electric Motors
• We can use electromagnets in electric motors to convert
electrical energy to mechanical work…
Electric Motor
Electric
Energy
+
-
12V
• Electric motors are used to
perform a mechanical task by
using electricity
– Open a sunroof
– Lift a power antenna
– Control windshield wiper
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.
ROTOR
STATOR
What Is an Electric Motor?
• Electrical energy creates a rotating magnetic field
inside the motor causing the rotor to rotate,
creating mechanical motion
ROTOR
STATOR
Where Are
Electric Motors Used?
Electric motors are used in many different automotive applications:
Power windows
Sunroof
Power seats
Brakes
Power mirrors
Power steering
Fans
Fuel pump
Windshield wipers
Water pump
Windshield washer pumps
Hybrid and electric vehicles
Starter motor
Cruise control
Electric radio antennae
Throttle plate control
Door locks
Air vents
Information gauges
Others
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
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
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
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
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......
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
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
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
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
How Does a Permanent Magnet
DC Motor Work?
• "DC Motors" use magnets to produce motion
– Permanent magnets
SOUTH
NORTH
How Does a Permanent Magnet
DC Motor Work?
• "DC Motors" use magnets to produce motion
– Permanent magnets
– An electromagnet armature
SOUTH
NORTH
Permanent Magnet DC Motor
Rotating Armature
• Electromagnet armature is mounted on axle so that
it can rotate
SOUTH
NORTH
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
SOUTH
NORTH
Permanent Magnet DC Motor
Commutator Structure
• Commutator is comprised of two "nearhalves" of a ring
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
Permanent Magnet DC Motor
Commutator Structure
• Armature's windings are connected to the
commutator
Permanent Magnet DC Motor
Commutator and Brushes
• Armature's windings are connected to the commutator
• Brushes connect the commutator to the battery
Permanent Magnet DC Motor
Electromagnet Polarization
• Current flows through the armature's windings,
which polarizes the electromagnet
-
+
SOUTH
NORTH
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
-
+
SOUTH
NORTH
Permanent Magnet DC Motor
Rotation Direction?
• What direction will the armature spin?
• Clockwise? Counterclockwise?
-
+
Counterclockwise ?
SOUTH
NORTH
Clockwise ?
Permanent Magnet DC Motor
Rotation Direction?
• To determine the direction of the motor's rotation, we need
to use the "Left Hand Rule"
Left Hand Rule
• Start with two opposite
ends of a magnet
NORTH
SOUTH
Left Hand Rule:
Magnetic Field
• The magnetic field (B) is from
the NORTH pole to the
opposite SOUTH pole
• The pointing finger
follows B into
screen
NORTH
SOUTH
B
Left Hand Rule:
Current Flow
• Current flows in a wire through
the magnetic field from left
right
• The middle finger
right,
to
SOUTH
I1
follows I1
or I2 left
I2
NORTH
Left Hand Rule:
Force
• The force, F, acting on each wire
is in the direction of the
F1
thumb
SOUTH
I1
• The wire with I1
is pushed up,
I2 down
I2
NORTH
F2
Left Hand Rule:
Force
• The magnitude of F is give by:
F1
|F|=|I|**|B|
SOUTH
I1
where  is the
wire in B
length of the
I2
NORTH
F2

Left Hand Rule:
Current Loop
• If the current flows in a loop,
the force(s) will cause the F
loop to rotate
SOUTH
I
NORTH
F
Permanent Magnet DC Motor
Rotation
• Magnetic field is from right to left
• Imagine current flows out of the screen in this cross
section
-
+
SOUTH
NORTH
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
-
+
SOUTH
NORTH
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
-
+
SOUTH
NORTH
Permanent Magnet DC Motor
Rotation
• When the commutator halves reconnect with the
other brush, the current in the windings is reversed
-
+
SOUTH
NORTH
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
-
+
SOUTH
NORTH
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
-
+
SOUTH
NORTH
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
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
Turning On a PMDC Motor
in the Other Direction
• One switch is closed in each leg of the "H"
• One switch is open in each leg of the "H”
Current
Controlling a Permanent Magnet
DC (PMDC) Motor
• Unidirectional motors are controlled by a “half-H”
bridge circuit
Current
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
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
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
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
Full Step Motor Operation
Half Rotate
and Hold
`
Half Step Motor Operation
Half Rotate
and Hold
`
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
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
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
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
Example Brushless DC Motor
Operation
• 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
Example Brushless DC Motor
Operation
• This example brushless DC motor has:
– An external, electromagnet stator, with magnetic
field sensors
Brushless DC Motor
Construction
A
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com
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c
b
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C
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com
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B
Brushless DC Motor Operation
A
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1
c
b
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Brushless DC Motor Operation
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2
Brushless DC Motor Operation
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Brushless DC Motor Operation
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4
Brushless DC Motor Operation
A
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5
Brushless DC Motor Operation
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6
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Brushless DC Motor Operation
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Brushless DC Motor
Control Circuit
A1
B1
C1
A
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A2
B2
C2
C
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Brushless DC Motor
Control Circuit
A1
B1
C1
A
1
a
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A2
B2
C2
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com
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B
Brushless DC Motor
Control Circuit
A1
B1
C1
A
a
c
A2
B2
C2
com
b
B
C
2
Brushless DC Motor
Control Circuit
A1
B1
C1
A
a
c
A2
B2
C2
com
b
B
C
3
Brushless DC Motor
Control Circuit
A1
B1
C1
A
a
c
A2
B2
C2
b
com
B
C
4
Brushless DC Motor
Control Circuit
A1
B1
C1
A
a
c
A2
B2
C2
b
com
B
C
5
Brushless DC Motor
Control Circuit
A1
B1
C1
A
6
a
c
A2
B2
C2
C
com
b
B
Brushless DC Motor
Control Circuit
A1
B1
C1
A
1
a
c
A2
B2
C2
C
com
b
B
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
What Is an Electric Motor?
• An electric motor converts electric energy into
mechanical motion
Electric Motor
Electric
Energy
+
12V
-
• Electric motors are used to
perform a mechanical task by
using electricity
– Open a sunroof
– Lift a power antenna
– Control windshield wiper
Types of Electric Motors
Permanent Magnet
DC Motor
Advantages:
Disadvantages:
Stepper
Motor
Brushless DC
Motor
+ Low cost
+ Position control + High efficiency
(high volume)
(low cost
+ High reliability
+ Simple operation
control circuits) + Low EMI
+ Speed control
- Medium efficiency - Poor efficiency - Maybe higher cost
- Poor reliability
- Digital interface - Complex control
- Bad EMI
- High cost
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
Introduction to Motor Control
Thank you!
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