POWER ELECTRONICS

1
POWER ELECTRONICS
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The Islamic University of Gaza Faculty of
Engineering Electrical Engineering Department
EELE 5450 Fall 2009-2010

• Instructor
  Eng.Moayed N. EL Mobaied

Lecture 13
2
Chapter Five
AC Line Voltage Control
Phase-Control technique give the simplest ac
regulating system and are the best known.

• There are other methods by which thyristor
  control of ac lines is possible
• Zero voltage switching
• Ac chopper control
• synchronous tap changing

Ac line voltage controllers are employed to vary
the rms value of the alternating voltage applied
to a load by using thyristors as a switch.
3
Chapter Five
AC Line Voltage Control

• The applications of ac line voltage controllers
  include the following
• Lighting controls
• Induction heating
• Industrial heating
• Transformer tap changing
• Speed control of induction motor

4
Chapter Five
AC Phase Control With resistive Load
This circuit provides a fixed half-cycle of power
and a power control range of half-power minimum
and full-power maximum, but with a strong dc
component.
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Chapter Five
AC Phase Control With resistive Load
This circuit is back-to-back SCRs which allows
symmetrical control of ac voltage during both
halves of the ac wave and eliminates and dc
component.
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Chapter Five
AC Phase Control With resistive Load
The most simple, efficient and reliable method of
controlling ac power is by using the Triac. Triac
is bidirectional device, and a single control
circuit is sufficient to control power flow in
the load during both halves of the ac input wave.
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Chapter Five
Analysis of Full-wave controller resistive Load
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Chapter Five
Full-wave controller With Inductive Load
In actual practice most loads have some amount of
inductance. Motors, solenoids, transformers, and
even some resistive heaters have inductive
components as apart of their impedance.
The effect of this reactance is that the
rms-to-average-current ratio is lowered. Higher
average current can be passed through the SCR.
With an inductive load , current flow is
maintained through the SCR even after the input
voltage has reversed polarity and goes negative.
The duration of this interval is determined bu
the load power factor.
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Chapter Five
Full-wave controller With Inductive Load
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Chapter Five
Full-wave controller With Inductive Load
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End of Lecture Eng.moayed