DC Motor PWM Techniques

Motor Drive and
PWM Techniques
Eng:Mohamed Loay Ali
1

Contents
 DC Motor
1. Introduction to DC motor and its parameters.
2. PWM 8 bits modes (Fast PWM &Phase Correct).
3. PWM 16 bits modes (Fast PWM & Phase Correct).
4. Speed Control of DC motor.
 Stepper motor.
1. Stepper motor basics.
2. Main Components of Stepper motor.
3. Types of Stepping Motors
4. Unipolar and Bipolar Stepper Motors
5. Driving Stepper motor.
2

DC motor
 A direct current motor one of the most widely used motors.
 By connecting the motor terminal to dc source it rotates in one direction,
and by reversing the polarity it rotates to the opposite direction.
 The maximum speed of a dc motor is indicated with the rpm and is
given in the data sheet.
 The dc motor control can be unidirectional or bidirectional as shown in
the following figure
3

DC motor
 The speed of the motor depends on three factors
1) Load.
2) Voltage.
3) Current.
 The rpm of the motor can be controlled by varying the voltage
terminals.
 For a given fixed load a steady speed can be maintained by using
Pulse width modulation (PWM) to change the voltage across the DC
terminals.
 Although the PWM has a fixed amplitude, it has a variable duty
cycle. That means the wider pulse the wider the higher the speed.
 By varying the duty cycle the power fed to the motor speed is
changing as shown in the following
4

DC motor
5

DC motor
6

DC motor
7

DC motor
PWM 8 bits modes : Fast PWM
8

DC motor
9

DC motor
10

DC motor
11

DC motor
12

DC motor
13

DC motor
14

DC motor
15

DC motor
 The counter counts up like it does in the normal mode.
 It counts up until it reaches its maximum value 0xFF.
 Then it rolls over to from 0xFF to 0x00 ,it set the TOV
 The fast PWM differs from the other PWM option by its single-slope operation.
 In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared
on the compare match between TCNT0 and OCR0x, and set at BOTTOM.
 In inverting Compare Output mode, the output is set on compare match and
cleared at BOTTOM.
16

DC motor
PWM 8 bits modes :PWM 8 bits modes : Fast PWM
17

DC motor
For non-Inverted mode
For Inverted mode
18

DC motor
19

DC motor
PWM 8 bits modes : Phase Correct
 The phase correct PWM mode (WGM02:0 = 1 or 5) provides a high resolution.
 The counter counts repeatedly from BOTTOM to TOP and then from TOP to
BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1and OCR0A when
WGM2:0 = 5
 In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared
on the com-pare match between TCNT0 and OCR0x while up counting, and set
on the compare match while down counting.
 In inverting Output Compare mode, the operation is inverted. The dual-slope
operation has lower maximum operation frequency than single slope operation
20

DC motorDC motor
21

DC motor
For non-Inverted mode
For Inverted mode
22

DC motor
23

DC motor
 PWM 16 bits modes (Fast PWM & Phase Correct).
 Speed Control of DC motor.
DO IT Yourself
24

Stepper Motor
Stepper Motor are motors that moves one step at a time.
 A digital version of an electric motor
 Each step is defined by a Step Angle
25

Stepper Motor
 Relatively inexpensive
 Ideal for open loop positioning control
 Can be implemented without feedback
 Minimizes sensing devices
 Just count the steps!
 Torque
 Holds its position firmly when not turning
 Eliminates mechanical brakes
 Produces better torque than DC motors at lower speeds
 Positioning applications
26

Stepper Motor
2.Main Components of Stepper motor.
Consists of
1.Stator:
Holds multiple
windings/phases
27

Stepper Motor
Consists of
2.Rotor:
Magnetized
or non-magntized
28

Stepper Motor
Voltage applied to winding initiates current flow
Magnetic flux begins to flow
29

Stepper Motor
Rotor rotates to minimize flux path (or reluctance)
30

Stepper Motor
3.Types of Stepping Motors
 Permanent Magnet
Magnetic rotor
 Variable Reluctance
Non-magnetic, geared rotor
 Hybrid
Combines characteristics from PM and VR
Magnetic, geared rotor
31

Stepper Motor
 Permanent Magnet
32

Stepper Motor
 Variable Reluctance
Non-magnetic, geared rotor
33

Stepper Motor
 Hybrid
Combines characteristics from PM and VR Magnetic, geared rotor
34

Stepper Motor
35

4.Unipolar and Bipolar Stepper Motors
Stepper Motor
Leads on each coil can
be brought out in two
ways:
−Each lead taken separately
−Bi-directional current flow
through entire winding
36

4.Unipolar and Bipolar Stepper Motors
Stepper Motor
A center tap added
between the two leads
−Unidirectional current flow
in each ½ of winding
Unipolar
37

5.Driving Stepper motor(Bipolar Full Step).
Stepper Motor
38

Stepper Motor
39

Stepper Motor
40

Stepper Motor
41

Stepper Motor
42

Stepper Motor
43

Stepper Motor
44

Stepper Motor
45

5.Driving Stepper motor(Bipolar Full Step two phase on).
Stepper Motor
46

Stepper Motor
47

Stepper Motor
48

Stepper Motor
49

Stepper Motor
50

Stepper Motor
51

Stepper Motor
52

Stepper Motor
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Stepper Motor
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5.Driving Stepper motor(Bipolar half Step).
Stepper Motor
 Combines “One Phase On” and “Two Phase On”
algorithms
 Improves rotational resolution
 Minimizes anti-resonance
55

Stepper Motor
56

Stepper Motor
57

Stepper Motor
58

Stepper Motor
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Stepper Motor
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Stepper Motor
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Stepper Motor
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Stepper Motor
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Stepper Motor
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Stepper Motor
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Stepper Motor
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Stepper Motor
5.Driving Stepper motor(Unipolar half Step).
 Center Tap
connected to
Ground or Voltage
Source.
 Current flows in ½
winding at a time.
67

Stepper Motor
5.Driving Stepper motor(Unipolar).
68

Stepper Motor
69

Stepper Motor
70

Stepper Motor
71

Stepper Motor
72

Stepper Motor
73

Stepper Motor
5.Driving Stepper motor(Bipolar Drive Circuit).
74

Stepper Motor
75

Stepper Motor
76

Stepper Motor
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Stepper Motor
78

Stepper Motor
79

Stepper Motor
5.Driving Stepper motor(Uni-polar Drive Circuit).
80

DC Motor PWM Techniques

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