ELECTRIC DRIVES - Universiti Teknologi Malaysia
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Transcript ELECTRIC DRIVES - Universiti Teknologi Malaysia
ELECTRIC DRIVES
CONVERTERS IN ELECTRIC DRIVE SYSTEMS
MODULE 2
Dr. Nik Rumzi Nik Idris
Dept. of Energy Conversion, UTM
2006
CONVERTERS - Module 2
AC-DC controlled rectifier
approximate model
SIMULINK examples
open-loop
closed-loop
Switch Mode DC-DC
converter
2-Q and 4-Q converters
Small signal modeling
unipolar
bipolar
SIMULINK example
Assignment 1
Current-controlled for SM
converters
Bridge converter
hysteresis
fixed frequency
3-phase VSI
hysteresis
fixed frequency
SVM-based
AC-DC controlled rectifier
2Vm
+
50Hz
1-phase
Vo
Vo
2Vm
cos
90o
180o
90o
180o
Average voltage
over 10ms
2 Vm
3VLL,m
50Hz
3-phase
+
Vo
Vo
3VLL,m
cos
Average voltage
over 3.33 ms
3VL L,m
For steady state continuous current flow
AC-DC controlled rectifier
+
vc
firing
circuit
controlled
rectifier
Va
–
vc(s)
?
va(s)
DC motor
The relation between vc and va is determined by the firing circuit
It is desirable to have a linear relation between vc and va
AC-DC controlled rectifier
linear firing angle control
Vm
0
vc
2
3
Input voltage
4
vt
Sawtooth compared with control signal
Results of comparison to trigger SCRs
Output voltage
AC-DC controlled rectifier
linear firing angle control
vt vc
Vm
0
2
3
4
vt
vc
vc
vt
vc
vc
2Vm
Va
cos
vt
A non-linear relation between Va and vc
AC-DC controlled rectifier
Cosine-wave crossing control
Vm
0
vc
3
2
vs
Input voltage
4
Cosine wave compared with vc
Results of comparison trigger SCRs
Output voltage
AC-DC controlled rectifier
Cosine-wave crossing control
cos(t)= vc
Vscos()
Vm
0
2
vc
3
v
cos1 c
vs
4
vs
Va
2Vm v c 1 v c
coscos
vs
vs
A linear relation between vc and Va
AC-DC controlled rectifier
e.g. cosine wave crossing control
AC-DC controlled rectifier
Control model
Va is the average voltage over one period of the waveform
- sampled data system
Delays depending on when the control signal changes – normally taken
as half of sampling period
AC-DC controlled rectifier
Control model
Va is the average voltage over one period of the waveform
- sampled data system
Delays depending on when the control signal changes – normally taken
as half of sampling period
AC-DC controlled rectifier
Control model
T
s
2
G H (s) Ke
Single phase, 50Hz
vc(s)
Va(s)
K
2Vm
Vs
T=10ms
Three phase, 50Hz
K
3VLL,m
Vs
T=3.33ms
Simplified if control bandwidth is reduced to much lower than the
sampling frequency
AC-DC controlled rectifier
MATLAB v6.5, SIMULINK v5
SympPowerSystems toolbox
SIMULINK EXAMPLES
Open-loop control
Closed-loop control
AC-DC controlled rectifier
Open loop
+
vc
controlled
rectifier
firing
circuit
Va
–
DC motor
modeled with
R-L and Vdc
Step
+
-
v
Voltage Measurement1
i
Controlled Voltage Source
-
+
+
Current Measurement1
-
signal
Scope2
Scope
A
+
B
C
pulses
+
-
Series RLC Branch
Universal Bridge
v
Scope1
+
-
v
alpha_deg
AB
BC
+
-
v
i
pulses
CA
Block
Synchronized
6-Pulse Generator
acos
Step1
Trigonometric
Function
-KGain
+
-
Current Measurement
Three-phase AC source
Step
+
-
v
Voltage Measurement1
i
Controlled Voltage Source
-
+
+
Current Measurement1
-
signal
Scope2
Scope
A
+
B
C
pulses
-
Series RLC Branch
Universal Bridge
+
v
Scope1
+
-
v
alpha_deg
AB
BC
+
-
v
i
pulses
CA
+
Current Measurement
Block
Synchronized
6-Pulse Generator
acos
Step1
Trigonometric
Function
-KGain
Controlled rectifier
‘Firing circuit’
scr_openloop_3phase.mdl
-
Load
AC-DC controlled rectifier
Closed loop
+
current
controller
iref
vc
controlled
rectifier
firing
circuit
Va
–
Step
+
+
-
-
v
v
• To control the current – current-controlled converter
• Torque can be controlled
• Only operates in Q1 and Q4 (single converter topology)
i
-
+
+
A
+
B
C
pulses
-
Series RLC Branch
Universal Bridge
+
v
+
-
v
alpha_deg
AB
BC
+
-
v
i
pulses
CA
Block
Synchronized
6-Pulse Generator
PID
Signal
Generator
5
Constant1
PID Controller1
acos
-K-
+
-
-
signal
Scope2
Scope
Open-loop system from previous simulation
Step
+
+
-
-
v
v
i
-
+
+
A
+
B
C
pulses
+
-
Series RLC Branch
Universal Bridge
v
+
-
v
alpha_deg
AB
BC
+
-
v
i
pulses
CA
Block
Synchronized
6-Pulse Generator
PID
Signal
Generator
acos
-K-
PID Controller1
5
Constant1
Closed-loop elements
closed_loop_unipolar_4q_with_id.mdl
+
-
-
signal
Scope2
Scope