control of AC machines

1. Control of AC Machines
Pekik Argo Dahono

2. AC Machines
1. Synchronous machines
• Wound field
• Permanent magnet
• Reluctance
2. Induction machines
• Squirrel-cage rotor
• Wound rotor

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  sLl 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  sLl 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

9. Variable-Voltage Variable-Frequency
Te
V
sl
Vboost
0 

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

11. Simulated Results : VVVF System

12. Simulated Results : VVVF

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

18. Slip-Power Recovery Drives
Wound rotor
Induction motor
AC Source

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 E0 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 
*   

