3. Equivalent Circuit of Induction Machines
is Rs Lls Llr
is Rs Lls Llr
ir
ir
vs Rc Lm Rr
vs Lm Rr
s
s
is Rs Ll is Rs Ll
iR iR
vs Ls RR vs LM RR
s s
4. Analysis of Induction Machines
Torque :
Rotor current :
3P E 2 RR
Te Pg / m
E
Ir 2 s RR / s 2 Ll 2
RR / s 2 Ll 2
3P E 2 RR s
Te
Airgap power :
2 RR sLl 2
2
3E 2 R R
Pg 3I r2 RR / s
s RR / s 2 Ll 2 Maximum Torque :
2
3P E 1
Rotor losses : Tem
4 Ll
Pr 3I r2 RR
RR
Output Mechanic : at s m
Ll
1 s
Pm 3I r2 RR
s Normal operating conditions RR sLl 2
2
Airgap power : Rotor losses : Output 1 : s :1 - s 3P E 2 s
Te
2 R R
5. Torque and Current Characteristics
of Induction Machines
Torque
Current
Slip
1 0 1
I FL
Slip
1 0
6. Pole Changing of Induction Machines
• Discrete and limited
speed control.
Low speed
Torque
• Suitable for some
applications. High speed
• Can be designed with Load
constant torque,
constant HP, and
variable torque.
• Available up to Speed
medium HP motors.
7. Voltage Control of Induction Motors
• Percent losses is increased
when the speed is decreased. AC source IM
• Suitable for soft-start control.
• Why-delta, autotransformer,
part-winding, primary resistor
starters are commonly used to
limit the starting current.
• Suitable for speed control of V1 V2 V3
small HP motors.
Torque
V3
• Voltage control can be done by
using TRIAC or antiparallel
thyristors. Load
• Wide speed control range is V2
achievable by using high slip V1
motors.
Speed
8. Variable-Voltage Variable-Frequency
Torque :
E6 E5 E4 E3 E2 E1
RR sl
2
3P E f 6 f 5 f 4 f3 f 2 f1
Te
Torque
2 RR sl Ll 2
2 Load
3P E sl
2
Te
2 RR
Speed
Maximum Torque :
2
3P E 1
Tem
4 Ll
10. Scheme of VVVF System
Smoothing
inductor
AC Motor
AC source
3
Smoothing
capacitor
vout
Controlled Square - wave
rectifier inverter
VVI System
AC Motor
AC source
3
Smoothing
capacitor
vout
Uncontrolled PWM inverter
rectifier
PWM System
13. Slip-Controlled Induction Motor Drives
V
va
va V sin
Te*
sl
*
vb V sin 23
vb
GT vc V sin 23
vc
r
3P E sl
2
Te
2 Rr
14. Vector Control
Pg 3EI r
E Lm I m
Pg 3P
Te Lm I m I r
Im iR m 2
RR Im
Is LM E Is 2
Im I r2 tan 1
s Ir
Rr
Lm I m I r
s
R I
s sl r r
Lm I m
15. Vector Control
*
Is *
ia 2 I s sin
ia
*
Ir I s I m I r2
Te* 2
2 *
2 I s sin 23 *
:
Im s
ib ib
3P s tan 1
Ir ic
*
2 I s sin 23
*
*
Im
ic
Lm
g
sl
Rr :
r
16. Vector Control
Ed
Three - Phase
VSI Inverter IM
Current
Controller ia , ib , ic
* * *
ia , ib , ic
I R2
*
I m2
*
Signal
Generator
*
Im
I*
tan 1 m
I* et
* R
r
* Speed
Controller
IR
*
RR I R sl e r
*
LM I m
17. Wound-Rotor Induction Motor Drives
AC source
R1 Rr Rr Rr
r
2 3 4
Torque
4 3 2
Rr Rr Rr
R1
r
Load
Speed
19. Variable-Speed Power Generation
Wound rotor
Induction motor
Ps , s Psl , sl
AC Source
cycloconverter
Pm , m
s m sl
Ps : Psl : Pm 1 : s : 1 s
20. Synchronous Motor Drives
Synchronous
Machine
AC source PG
Triger Triger
circuit circuit
Id * Current
controller
21. Self-Controlled Principle
N P EI s1 cos
T he phase angle of E is detected by using
S
a position sensor. T he emf is
E K m I f
If the field current is constant hen the
t
magnitude of emf E is also constant.
T orque is
I s1 E0 Te P / m KI f I s1 cos
22. Synchronous Motor Drives
Synchronous
Machine
PG
Gate driver
Current
Controller
ia I s sin
*
ib I s sin 23
*
Is *
ic I s sin 23
*