ELECTRIC DRIVES

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ELECTRIC DRIVES

• CONVERTERS IN ELECTRIC DRIVE SYSTEMS
• MODULE 2
• Dr. Nik Rumzi Nik Idris
• Dept. of Energy Conversion, UTM
• 2008

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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
Current-controlled for SM converters Bridge
converter hysteresis fixed frequency 3-phase
VSI hysteresis fixed frequency SVM-based
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AC-DC controlled rectifier
Vo ?
?
90o
180o
50Hz 1-phase
Average voltage over 10ms
50Hz 3-phase
Vo ?
?
90o
180o
Average voltage over 3.33 ms
For steady state continuous current flow
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AC-DC controlled rectifier
?
va(s)
vc(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
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AC-DC controlled rectifier
linear firing angle control
Vm
Input voltage
Sawtooth compared with control signal
Results of comparison to trigger SCRs
Output voltage
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AC-DC controlled rectifier
linear firing angle control
Vm
A non-linear relation between Va and vc
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AC-DC controlled rectifier
Cosine-wave crossing control
Vm
Input voltage
Cosine wave compared with vc
Results of comparison trigger SCRs
Output voltage
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AC-DC controlled rectifier
Cosine-wave crossing control
Vscos(?t)
Vscos(?) vc
Vm
A linear relation between vc and Va
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AC-DC controlled rectifier
e.g. cosine wave crossing control
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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
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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
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AC-DC controlled rectifier Control model
Single phase, 50Hz
vc(s)
Va(s)
T10ms
Three phase, 50Hz
T3.33ms
Simplified if control bandwidth is reduced to
much lower than the sampling frequency
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AC-DC controlled rectifier
MATLAB v6.5, SIMULINK v5 SympPowerSystems
toolbox Open-loop control Closed-loop control
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AC-DC controlled rectifier Open loop
Va
controlled rectifier
vc
firing circuit
?
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scr_openloop_3phase.mdl
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AC-DC controlled rectifier Closed loop
Va
firing circuit
current controller
?
vc
iref
controlled rectifier

• To control the current current-controlled
  converter
• Torque can be controlled
• Only operates in Q1 and Q4 (single converter
  topology)

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