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.

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Method of Evaluation

• Quizzes 15 %

• Home Work / Project 20 %

• Midterm Examination 25 %

• Final Exam 40 %

• Total 100 %

Course Outline:

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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.

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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

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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

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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

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Control Characteristics

Thyristors （SCR）：

Controlled turn on and

uncontrolled turn off

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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

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Control CharacteristicsBJT, MOSFET, IGBT, SIT：

Continuous gate signal requirement

VO

VS

VB

++

VOVS

+

VB

++

VOVS

+

VGS

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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

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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.

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DC-DC converter

It converts the dc voltage into variable dc, by

controlling the conduction time of transistor.

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DC-AC Converter

It converts the dc voltage into ac, by controlling the

conduction time and sequence of transistors.

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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.

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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.