power electronics introduction
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MCT4320Power Electronics
2
Reference Books
Required
• Rashid M. H., (2004), Power Electronics: Circuits, Devices, and Applications, 3rd Edition, Prentice-Hall.
Recommended
• Agrawal J. P., (2001), Power Electronics System: Theory and Design, Prentice-Hall.
• Hart D. W., (1997), Introduction to Power Electronics, Prentice-Hall.
• Mohan N., Undeland T. M., and Robbins W. P., (2003), Power Electronics: Converters, Applications, and Design, John Wiley and Sons.
3
Method of Evaluation
• Quizzes 15 %
• Home Work / Project 20 %
• Midterm Examination 25 %
• Final Exam 40 %
• Total 100 %
Course Outline:
4
Contents
Definition of power electronics,
Power semiconductor devices,
Control characteristics of power semi-
conductor devices,
Power losses in switches,
Types of power electronics circuits.
Applications of power electronics.
5
Power Electronics
Control
Analog/ Digital
Electronics
Device/Circuit
Power equipment
static/rotating
6
• Power electronics involves the study of
electronic circuits intended to control the
flow and conversion of electric power.
Thus power electronics combine power,
electronics and control.
• The applications of solid-state and linear
devices for the control and conversion of
electric power.
Power Electronics
7
Power Electronics System
• Consists of an input source and a load.
• One or more converters for power conversion.
• Power semiconductor devices, which are used
as switches to perform the power conversion.
• A gating circuit to generate the gate drive signals
for the switching devices.
• A feedback control circuit implemented either in
analog and/or digital electronics.
• One or more static-switches acting as a circuit
breaker.
8
Power Electronics System
Static Applications: No rotating or moving
mechanical components. Examples: DC Power
supply, Un-interruptible power supply, Power
generation and transmission (HVDC),
Electroplating, Welding, Heating, Cooling,
Electronic ballast.
Drive Applications: for driving moving or rotating
equipment such as motors. Examples: Electric
trains, Electric vehicles, Air-conditioning system,
Pumps, Compressor, Conveyer Belt (Factory
automation).
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Control Center
Micro-Turbine
Hospital
Commercial
Building
Fuel Cell
Smart House
Performance
Building
Combined Heat and Power
Plant (CHP)
Factory
Commercial Building
House
Apartment Building
Wind Power Plants
Village
Commercial
Building
Central Power
Station Solar Power Plants
CHP House
Importance of PES
• Increasing applications of Power Electronic Equipment in Power Systems
– Availability of high power
semiconductor devices
– Decentralized renewable
energy generation sources
– Increased power transfer
with existing transmission
system
– Effective control of power
flow needed in a
deregulated environment
– Norms for Power quality Future Power System
10
Power Semiconductor Devices
Power devices are the key elements of a power
converter. The commonly used devices are:
(1) Power Diode
(2) Silicon-Controlled Rectifier (SCR) or Thyristor
(3) Gate Turn-off Thyristor (GTO)
(4) Power Bipolar Junction Transistor (Power BJT)
(5) Power Metal-Oxide Field-Effect Transistor
(Power MOSFET)
(6) Insulated-Gate Bipolar Transistor (IGBT)
(7) Mos-Controlled Thyristor (MCT)
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Power semiconductor operating regions
voltage
vs
frequency;
current
vs frequency.
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Power Electronic Applications
• Distributed generation (DG)– Renewable resources (wind and photovoltaic)
– Fuel cells and micro-turbines
– Storage: batteries, super-conducting magnetic energy storage,
• Power electronics loads: Adjustable speed drives
• Power quality solutions– Dual feeders
– Uninterruptible power supplies
– Dynamic voltage restorers
• Transmission and distribution (T&D)– High voltage dc (HVDC) and medium voltage dc
– Flexible AC Transmission Systems (FACTS): Shunt and Series
compensation, and the unified power flow controller
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Function of Power Electronics in Utility
Applications
• Enabling technology providing interface between
two (ac/dc) electrical systems
Interconnection of two asynchronous ac systems
– dc to ac conversion is required to connect fuel cells or
photovoltaic to the utility grid
Converter
Controller
Source Load
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Role of Power Electronics in Important Utility
Applications
• Distributed Generation (DG) Applications
Power electronic interface depends on the source
characteristics
AC
DC
DC
AC
Wound rotor
Induction Generator
Generator-side
Converter
Grid-side
Converter
Wind
Turbine
Isolated
DC-DC
Converter
PWM
Converter
Max. Power-
point Tracker
Utility
1f
Wind Power Generation with
Doubly Fed Induction Motors
Photo-voltaics Interface
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Role of Power Electronics in Important Utility
Applications
• Power Electronic Loads: Adjustable Speed Drives
Controller
Motor
Utility
Rectifier
Switch-mode
Converter
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Role of Power Electronics in Important Utility
Applications
• Power Quality Solutions for
– voltage distortion
– unbalances
– voltage sags and swells
– power outages
Load
Feeder 1
Feeder 2
Dual Feeders
Power Electronic
InterfaceLoad
Dynamic Voltage Restorers (DVR)
Uninterruptible Power Supplies
Rectifier Inverter FilterCritical
Load
Energy
Storage
MCT2231:A01 17
Role of Power Electronics in Important Utility
Applications
• Transmission and Distribution: DC Transmission
– most flexible solution for connection of two ac
systems
AC1 AC2
HVDC
AC1 AC2
MVDC
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Ideal PE System
To convert electrical energy from one form
to another, i.e. from the source to load with:
– highest efficiency,
– highest availability
– highest reliability
– lowest cost,
– smallest size
– least weight.
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Power Semiconductor Devices
BJT MOSFET Thyristor IGBT
GTO
Diode
Inductor
Capacitor Transformer
Ferrite core
Powerdered ion core
2200£gF 250 V 85 ¢J
Electrolytic capacitor
104/250V
Metalizedpolypoyester capacitor
102
Ceramiccapacitor
20
Inductors and Capacitors in PE
Inductor: V = L di/dt
• The current in an inductor cannot change
instantaneously!
Capacitor: i = C dV/dt
• The voltage across a capacitor cannot change
instantaneously!
These passive components are fundamental to
the operation of all power electronics.
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Control Characteristics
Diode
Uncontrolled turn on
and off
++
VOVS
VS
VO
VS
VO
22
Control Characteristics
Thyristors (SCR):
Controlled turn on and
uncontrolled turn off
23
Control Characteristics
Thyristors:
Once it is in conduction
mode, it cannot be
turned off by gate signal
++
VOVS
VO
VS
Vg
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Control CharacteristicsGTO, BJT, MOSFET,
SITH, IGBT, SIT, MCT:
Controlled turn on and
off.
VO
VS
Vg
++
VOVS
+
Vg
25
Control CharacteristicsBJT, MOSFET, IGBT, SIT:
Continuous gate signal requirement
VO
VS
VB
++
VOVS
+
VB
++
VOVS
+
VGS
26
Other CharacteristicsBidirectional current capability: TRIAC, RCT
Unidirectional current capability: SCR, BJT, MOSFET, etc
See table 1.3 and Figure1.9 of the text book for more information.
Self Study: Characteristics of Ideal switches
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The Practical Switch
1. Limited power handling capabilities, limited conduction
current in the on-state, and limited blocking voltage in the
off-state.
2. Limited switching speed caused by the finite turn-on and
turn-off times. This limits the maximum operating
frequency of the device.
3. Finite on-state and off-state resistances, that is, forward
voltage drop exists when in the on-state, and reverse
current flow (leakage) exists when in the off-state.
4. Because of characteristics 2 and 3, the practical switch
experiences power losses in the on- and off-states
(known as conduction loss), and during switching
transitions (known as switching loss).
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Losses in Power ElectronicsIn semiconductor components:
• Switching losses
• Conduction losses
In passive components (C & L):
• Effective series resistance
Typical efficiencies are in the range of 90-
99% for each conversion stage, depending
on the exact converter topology.
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Power switch losses
• Why it is important to consider losses of power switches?
– to ensure that the system operates reliably under prescribed ambient conditions,
– so that heat removal mechanism (e.g. heat sink, radiators, coolant) can be specified. Losses in switches affects the system efficiency
– Heat sinks and other heat removal systems are costly and bulky. Can be substantial cost of the total system.
– If a power switch is not cooled to its specified junction temperature, the full power capability of the switch cannot be realized.
Main losses:
– forward conduction losses,
– blocking state losses
– switching losses
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Switching Power Losses
31
Types of PE Circuits
• Diode Rectifier
• AC-DC Converter (controlled rectifier)
• AC-AC Converter (ac voltage controller)
• DC-DC converter (dc chopper)
• DC-AC Converter (inverter)
• Static Switches
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Diode Rectifier
It converts ac voltage into a fixed dc voltage.
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AC-DC Converter
It converts ac voltage into dc voltage of variable
magnitude by varying the conduction time of a
Thyristor.
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AC-AC Converter
It converts ac voltage into variable ac voltage by
varying the conduction time of a TRIAC.
35
DC-DC converter
It converts the dc voltage into variable dc, by
controlling the conduction time of transistor.
36
DC-AC Converter
It converts the dc voltage into ac, by controlling the
conduction time and sequence of transistors.
37
Static Switches
Static Switches:
Uninterruptible Power Supply (UPS): Mains1 supplies the
normal power to the load. The ac-dc converter charges the
standby battery. The dc-ac converter supplies the
emergency power to the load.
38
Conclusions
• Power electronic System and its scope,
applications and importance
• Control Characteristics of PE devices.
• Losses in solid state switches
• Types of Power Electronic Circuits.
• Properties of Capacitor and Inductor in PE
circuits.