Uploaded by Cabdi wali Gabeyre

LEC- 1a

Power electronics
• Power Electronics refers to an interdisciplinary
subject within electrical engineering that deals
with the design, control and conversion of
power in its electric form. A system that
converts electric energy to an electric load
through a control circuit is known as a Power
Electronic System.
• The purpose of this tutorial is to introduce and
explain the main concepts in Power
Electronics, which include Power SemiConductor Devices, Phase-Controlled
Converters, DC to DC Converter, Inverters and
AC to AC Converters.
• Power Electronics refers to the process of
controlling the flow of current and voltage and
converting it to a form that is suitable for user
loads. The most desirable power electronic
system is one whose efficiency and reliability
is 100%.
Take a look at the following block diagram. It
shows the components of a Power Electronic
system and how they are interlinked.
• A power electronic system converts electrical
energy from one form to another and ensures
the following is achieved Maximum efficiency
Maximum reliability
 Maximum availability
 Minimum cost
 Least weight
 Small size
Applications of Power Electronics
are classified into two types:
Static Applications and Drive
Static Applications
• This utilizes moving and/or rotating
mechanical parts such as welding, heating,
cooling, and electro-plating and DC power.
Drive Applications
• Drive applications have rotating parts such as
motors. Examples include compressors, pumps,
conveyer belts and air conditioning systems.
• Air Conditioning System
• Power electronics is extensively used in air
conditioners to control elements such as
compressors. A schematic diagram that shows
how power electronics is used in air
conditioners is shown below.
Power semiconductor
• Materials that permit flow of electrons are called
conductors (e.g., gold, silver, copper, etc.).
• Materials that block flow of electrons are called
insulators (e.g., rubber, glass, Teflon, mica, etc.).
• Materials whose conductivity falls between those
of conductors and insulators are called
• Semiconductors are “part-time” conductors
• whose conductivity can be controlled.
• Some common power devices are the power
diode, thyristor, power MOSFET and IGBT
(insulated gate bipolar transistor). A power
diode or MOSFET, for example, operates on
similar principles as its low-power
counterpart, but is able to carry a larger
amount of current and typically is able to
support a larger reverse-bias voltage in the
• Silicon is the most common material used to
build semiconductor devices.
• • Si is the main ingredient of sand and it is
estimated that a cubic mile of seawater
• contains 15,000 tons of Si.
• Germanium is another semiconductor
material with four valence electrons.
Control characteristics of power device
• The power semiconductor devices can be
operated as switches by applying control
signals to gate terminals of thyristors (and to
the base of bipolar transistors).
• The required output is obtained by varying the
conduction time of these switching devices.
• Showing the figure [Pdf]
Classification of power semiconductor
• Uncontrolled turn on and off (diode)
• Controlled turn on and uncontrolled turn off (SCR).
• Controlled turn on and off characteristics
• Continuous gate signal required (BJT,MOSFET.IGBT,SIT);
• Pulse gate requirement (SCR,GTO,MCT)
• Bipolar voltage withstanding capability (SCR,GTO);
• Unipolar voltage withstanding capability (BJT,MOSFET,GTO,IGBT,MCT)
• Bidirectional current capability (TRIAC,RCT)
• Unidirectional current
Ideal characteristics
The characteristics of an ideal switch
In the On state when the switch on, it must have :
1- Able to carry any value of forward current .
2-has zero voltage drop.
3-has zero on state resistance.
4-has zero power dissipation.
In the Off state when the switch off, it must have :
1-Able to withstand infinite open- circuit voltage
2- has zero leakage current.
Has infinite off state resistance
Types of power electronic circuit
1) diode rectifiers
2) Ac to Dc converters (controlled rectifier)
3)Ac to Ac converters (Ac voltage controllers)
4)Dc to Dc converters (Dc choppers)
5) DC to Ac converters (inverters)
6) Static switches