1. 4 Electrical actuation systems
4.1 Electrical systems
4.1.1 Switches
Types of switches:
Mechanical switch, Electromechanical switch,
Electronical solid-state device.
Mechanical switch—
Switch bounce.
4.1.2 Mechanical switches
4.1.3 Relays

3. Diode Thyristors, Triacs, Transisters.
4.1.4 Solid-state switches
Diode Thyristors, Triacs, Transisters.

7. 4.1.5 Solenoids
solenoid can be used to provide electrically operated actuators.

8. IGBT – Insulated or Isolated Gate Bipolar Transistor
IGBT combines the positive attributes of BJTs and MOSFETs.
BJTs have lower conduction losses in the on-state, especially in devices with
larger blocking voltages, but have longer switching times, especially at turn-off while.
MOSFETs can be turned on and off much faster, but their on-state conduction losses are
larger, especially in devices rated for higher blocking voltages. 
IGBTs have lower on-state voltage drop with high blocking voltage capabilities in addition to
fast switching speeds.
(+) Base
(+) Collector
(-) Emitter
NPN IGBT     
(-) Base
(-) Collector
(+) Emitter
PNP IGBT   
(+) Collector
(+) Base
(-) Emitter
NPN IGBT     
(-) Base
(-) Collector
(+) Emitter
PNP IGBT   

10. 4.2 Stepping motors
Producing rotation through equal angles, the so-called steps, for each digital pulse supplied to its input. 10

11. Solid-state electronics is used to switch the d.c. supply
between the pairs of stator windings. 11

12. Terminology: Holding torque Pull-in torque pull-out torque
Pull-in rate pull-out rate
Slew range. 12

13. Driving circuit of step motor13

14. Homework: page 128, problem 1,2,3,514

15. 4.3 Motors
Electromagnetic force (EMF)
1. Where L is the length of conductor in a magnetic field, I is the current of the conductor, and B is flux density of the magnetic field.
is the back e.m.f,
is the magnetic flux.

16. Electric Motors Basic types
DC Motors: speed and rotational direction control via voltage
Easy to control torque via current
low voltage
linear torque-speed relations
Quick response
AC Motors: smaller, reliable, and cheaper
speed fixed by AC frequency
low torque at low speed
difficult to start
直流电机：优良的调速特性，调速平滑、方便，调速范围宽广，可达1：200
过载能力大能承受冲击载荷，可实现频繁的无级快速启动、制动和反转
制造成本和维护工作量大
交流电机：结构简单，制造、使用和维护方便，运行可靠，重量轻，成本低，重量、成本为同功率转速直流电机的1/2和1/3；调速性能不如直流电机，

17. DC Motors: Principles of Operation
A wire carrying current experiences a force in a magnetic field.
Induced force
Current
(amp)
Length of wire in the direction of i (m)
Magnetic Flux Density (Tesla) q

18. Electromagnetic Force
A wire carrying current in a magnetic field. i
F = ilB
(l = wire length)
The direction of the force.

19. Electromagnetic Force
The force is perpendicular to both the magnetic field and current

20. Electromagnetic Force
A voltage is induced in a wire moved in a magnetic field
generators
Induced
voltage (volt)
Velocity of wire (m/s)
eind is also called electromotive force (EMF感应电动势)
On the contrary,
+ + +
eind
eind =vBl l
(l = the wire length) v
- - -

21. Principle of Electric Motors
Fundamental principle behind electric motors
Current running through coil in magnetic field experiences forces that cause it to rotate

22. Fundamental characteristics of DC Motors
End view
Time 0
End view
Time 0+
Shifting magnetic field in rotor causes rotor to be forced to turn

23. Nature of commutation Power is applied to armature windings From V+
Through the +brush
Through the commutator contacts
Through the armature (rotor) winding
Through the – brush
To V-
Rotation of the armature moves the commutator, switching the armature winding connections
Stator may be permanent or electromagnet

24. Diagram of a Simple DC Motor
Instructor:
The DC motor utilizes this concept by changing the direction of the current flowing through the brushes into the coiled wire in the armature. A permanent magnet creates a constant magnetic field, and when current runs through the coils, a force is created that turns the armature. When the armature has turned far enough, the brushes are now in contact with the opposite ends of the coiled wire, effectively reversing the polarity of the voltage across the coil and reversing the current flow, which create a force that spins the armature further in the same direction. This process repeats as long as voltage is supplied to the motor, creating the motor rotational force.

27. Commutator Instructor:
The brushes come into contact with the commutator, which connects to the lead wires of the armature coil. The commutator spins with the rest of the armature and the sides of the commutator change which brush they touch with every half-revolution. This reverses the current flow.

29. Commutator Brush Brush wear Brushless Excitation of motors:
Armature Armature conductors Field coil Field pole
Commutator Brush Brush wear Brushless
Excitation of motors:

30. (a) Series: highest starting torque and greatest no-load speed.
(b) shunt: lowest starting torque, a much lower no-load speed
and has good speed regulation.
(c) compound: high starting torque
and good speed regulation.
(d) separate:a special case
of the shunt wound motor and
ease to revert the direction.
The speed of such d.c motors can be changed by either changing the armature current or the field current. The variable voltage is often obtained by an electronic circuit.

31. DC motor wiring topologies

35. Permanent magnet DC motors

36. Permanent Magnet DC Motors
Have permanent magnets rather than field windings but with conventional armatures. Power only to armature.
Short response time
Linear Torque/Speed characteristics similar to shunt wound motors. Field magnetic flux is constant
Current varies linearly with torque.
Self-braking upon disconnection of electrical power
Need to short + to – supply, May need resistance to dissipate heat.
Magnets lose strength over time and are sensitive to heating.
Lower than rated torque.
Not suitable for continuous duty
May have windings built into field magnets to re-magnetize.
Best applications for high torque at low speed intermittent duty.
Servos, power seats, windows, and windshield wipers.

37. Single phase (low power) and Poly phase (high power)
4.4 A.C. motors
Single phase (low power) and Poly phase (high power)
Induction (Cheaper) and Synchronous motors
Single-phase squirrel-cage induction motor: not self-starting, the rotor rotates at a speed determined by the frequency of the alternating current applied to the stator (synchronous speed), there is difference between the rotor speed and synchronous speed (slip).

38. Three-phase induction motor: there is rotating magnetic field which completes one rotation in one full cycle of the current, self-starting, the direction of rotation is reversed by interchanging any two of the line connections.
Synchronous motors: its rotor is a permanent magnet, not self-starting, used in the case when the precise speed is required.

39. Inducing magnetism in the rotor
Difference between angular velocity of rotor and angular velocity of the field magnetism causes squirrel cage bars to cut the field magnetic field inducing current into squirrel cage bars.
This current in turn magnetizes the rotor

40. Torque/speed curve

41. A.C. motor is cheaper, more rugged, reliable and maintenance free.
Speed control of A.C. motor is more complex than with d.c. motors.

42. 4.4.1 Brushless permanent magnet d.c. motors
High performance, reliability and low maintenance.
Current-carrying conductors are fixed and the magnet moves. The current to the stator coils is electronically switched, the switching being controlled by the position of the rotor so that there are always forces acting on the magnet causing it to rotate in same direction.

43. 4.4.2 Speed and position control of D.C motors
PWM modulation：

48. Position servo system of D.C. motor

49. 4.4.3 A.C servo system
D.C./A.C. Inverter

50. PWM Variable Frequency Drives
AC to DC converter and a DC to AC converter (inverter)
Inverter frequency and voltage output can be varied to allow motor speed to be varied.
Very efficient and cost effective variable speed

51. SPWM Modulation

54. 改变脉冲宽度调节平均电压

56. Speed servo control of synchronous A.C. motor

58. Direct Vector Control Introduction
Scalar control of ac drives produces good steady state performance but poor dynamic response. This manifests itself in the deviation of air gap flux linkages from their set values. This variation occurs in both magnitude and phase.
Vector control (or field oriented control) offers more precise control of ac motors compared to scalar control. They are therefore used in high performance drives where oscillations in air gap flux linkages are intolerable, e.g. robotic actuators, centrifuges, servos, etc.

59. Introduction (cont’d)
Why does vector control provide superior dynamic performance of ac motors compared to scalar control ?
In scalar control there is an inherent coupling effect because both torque and flux are functions of voltage or current and frequency. This results in sluggish response and is prone to instability because of 5th order harmonics. Vector control decouples these effects.

60. Torque Control of DC Motors
There is a close parallel between torque control of a dc motor and vector control of an ac motor. It is therefore useful to review torque control of a dc motor before studying vector control of an ac motor.

61. Torque Control of DC Motors (cont’d)
A dc motor has a stationary field structure (windings or permanent magnets) and a rotating armature winding supplied by a commutator and brushes. The basic structure and field flux and armature MMF are shown below:

62. Torque Control of DC Motors (cont’d)
The field flux f (f) produced by field current If is orthogonal to the armature flux a (a) produced by the armature current Ia. The developed torque Te can be written as:
Because the vectors are orthogonal, they are decoupled, i.e. the field current only controls the field flux and the armature current only controls the armature flux.

63. Torque Control of DC Motors (cont’d)
DC motor-like performance can be achieved with an induction motor if the motor control is considered in the synchronously rotating reference frame (de-qe) where the sinusoidal variables appear as dc quantities in steady state.
Two control inputs ids and iqs can be used for a vector controlled inverter as shown on the next slide.

64. Torque Control of DC Motors (cont’d)
With vector control:
ids (induction motor)  If (dc motor)
iqs (induction motor)  Ia (dc motor)
Thus torque is given by:
where is peak value of sinusoidal space vector.

65. Torque Control of DC Motors (cont’d)
This dc motor-like performance is only possible if iqs* only controls iqs and does not affect the flux , i.e. iqs and ids are orthogonal under all operating conditions of the vector-controlled drive.
Thus, vector control should ensure the correct orientation and equality of the command and actual currents.

66. Equivalent Circuit of Induction Motor
The complex de-qe equivalent circuit of an induction motor is shown in the below figure (neglecting rotor leakage inductance).

67. Equivalent Circuit of Induction Motor (cont’d)
Since the rotor leakage inductance has been neglected, the rotor flux = , the air gap flux.
The stator current vector Is is the sum of the ids and iqs vectors. Thus, the stator current magnitude, is related to ids and iqs by:

68. Phasor Diagrams for Induction Motor
The steady state phasor (or vector) diagrams for an induction motor in the de-qe (synchronously rotating) reference frame are shown below:

69. Phasor Diagrams for Induction Motor (cont’d)
The rotor flux vector is aligned with the de axis and the air gap voltage is aligned with the qe axis. The terminal voltage Vs slightly leads the air gap voltage because of the voltage drop across the stator impedance. iqs contributes real power across the air gap but ids only contributes reactive power across the air gap.

70. Phasor Diagrams for Induction Motor (cont’d)
The first figure shows an increase in the torque component of current iqs and the second figure shows an increase in the flux component of current, ids. Because of the orthogonal orientation of these components, the torque and flux can be controlled independently. However, it is necessary to maintain these vector orientations under all operating conditions.
How can we control the iqs and ids components of the stator current Is independently with the desired orientation ?

71. Principles of Vector Control
The basic conceptual implementation of vector control is illustrated in the below block diagram:
Note: The inverter is omitted from this diagram.

72. Principles of Vector Control (cont’d)
The motor phase currents, ia, ib and ic are converted to idss and iqss in the stationary reference frame. These are then converted to the synchronously rotating reference frame d-q currents, ids and iqs.
In the controller two inverse transforms are performed:
1) From the synchronous d-q to the
stationary d-q reference frame;
2) From d*-q* to a*, b*, c*.

73. Principles of Vector Control (cont’d)
There are two approaches to vector control:
1) Direct field oriented current control
- here the rotation angle of the iqse vector with respect to the stator flux qr’s is being directly determined (e.g. by measuring air gap flux)
2) Indirect field oriented current control
- here the rotor angle is being measured indirectly, such as by measuring slip speed.

74. Direct Vector Control
In direct vector control the field angle is calculated by using terminal voltages and current or Hall sensors or flux sense windings.
A block diagram of a direct vector control method using a PWM voltage-fed inverter is shown on the next slide.

75. Direct Vector Control (cont’d)

76. Direct Vector Control (cont’d)
The principal vector control parameters, ids* and iqs*, which are dc values in the synchronously rotating reference frame, are converted to the stationary reference frame (using the vector rotation (VR) block) by using the unit vector cose and sine. These stationary reference frame control parameters idss* and iqss* are then changed to the phase current command signals, ia*, ib*, and ic* which are fed to the PWM inverter.

77. Direct Vector Control (cont’d)
A flux control loop is used to precisely control the flux. Torque control is achieved through the current iqs* which is generated from the speed control loop (which includes a bipolar limiter that is not shown). The torque can be negative which will result in a negative phase orientation for iqs in the phasor diagram.
How do we maintain idsand iqs orthogonality? This is explained in the next slide.

78. Direct Vector Control (cont’d)

79. Direct Vector Control (cont’d)
Here the de-qe frame is rotating at synchronous speed e with respect to the stationary reference frame ds-qs, and at any point in time, the angular position of the de axis with respect to the ds axis is e (=et).
From this phasor diagram we can write:
and

80. Direct Vector Control (cont’d)
Thus,
, , and
The cose and sine signals in correct
phase position are shown below:

81. Direct Vector Control (cont’d)
These unit vector signals, when used in the vector rotation block, cause ids to maintain orientation along the de-axis and the iqs orientation along the qe-axis.

82. Summary of Salient Features of Vector Control
A few of the salient features of vector control are:
The frequency e of the drive is not controlled (as in scalar control). The motor is “self-controlled” by using the unit vector to help control the frequency and phase.
There is no concern about instability because limiting within the safe limit automatically limits operation to the stable region.

83. 4.5 Design method
Transient response will be fast because torque control by iqs does not affect flux.
Vector control allows for speed control in all four quadrants (without additional control elements) since negative torque is directly taken care of in vector control.