Transcript Speed Control of AC motors (AC Drives) Dynamics of Motor Load Systems dm TJ  TL dt TJ dm  Tm  Bm dt J moment of inertia kg-m2 m instantaneous angular.

Speed Control of AC motors
(AC Drives)
Dynamics of Motor Load Systems
dm
TJ
 TL
dt
TJ
dm
 Tm  Bm
dt
J moment of inertia kg-m2
m
instantaneous angular velocity rad/sec
T developed torque of the motor N.m.
TL
Bm
The load torque.
Viscous Friction torque.
B Viscous Friction coefficient.
Steady State Stability
dTL
dT

dm dm
d m
0
dt
m
T
A
Unstable
TL
TL
B
Stable
T
Torque
Four-quadrant operation.
Pulsed Resistor Braking
Rectifier Regenerative Front End
Pulse-width-modulated inverters
Pulse-width modulate inverter used to shape the
output ac voltages to be as close to a sine wave
as possible.
One-leg switch-mode inverter.
Vˆcontrol
ma 
Vˆ
tri
fs
mf 
f1
vcontrol  vtri
vcontrol  vtri
T A is on ,
T A is on ,
1
v Ao  Vd
2
v Ao
1
  Vd
2
 
Vd
ˆ
VAo 1  ma
2
for ma  1
 
Vd
ˆ
VAo 1  ma
for ma  1
2
Vˆcontrol
Vd
Vd
v Ao 1  ˆ sin 1t  ma sin 1t
for ma  1
2
2
V
tri
v AN
1
 v Ao  Vd
2
VˆAN h  VˆAo h
 
Vd
V
4
d
ˆ
 V Ao 1 
2
 2
ma  1
 
4 Vd
 Vd 
ˆ
VAo 1 
 1.273 
 2
 2 
Simulation of one leg PWM Inverter
Single-phase full-bridge inverter.
PWM with Bipolar Voltage Switching
PWM with Unipolar Voltage Switching
PWM with Bipolar Voltage Switching
ma  1.0
Vˆo1  maVd
4
ˆ
Vd  Vo1  Vd

ma  1.0
PWM with Unipolar Voltage Switching
vcontrol  vtri
TA on
and
VAN  Vd
vcontrol  vtri
TA on
and
VAN  0
 vcontrol  vtri
TB  on
and
VBN  Vd
 vcontrol  vtri
TB  on
and
VBN  0
Vˆo1  ma Vd
4
ˆ
Vd  Vo1  Vd

ma  1.0
ma  1.0
Waveforms
THREE-PHASE INVERTERS
Waveforms
THREE-PHASE INVERTERS driving 3-phase induction motor
3phase INVERTERS driving variable 3-phase induction motor
Fig.4.22 Three-phase PWM waveforms and harmonic spectrum.