ars p es 99slides jan10

8/14/2019 ARS P Es 99Slides Jan10

1/99

1

Recommended Text Books

1) Power Electronics - circuits, devices &applications by M H Rashid

2) Power Electronics - Principles andApplications by J Vithayathil

3) Introduction to Power Electronics byDenis Fewson

Topic1: Introduction


2/99

2

This course deals with the techniques of designing high current

electronic circuits using power semiconductor devices, likeDiodes, Transistors and Thyristors.

The subject covers:

Power semiconductor devices, their working, characteristics,

protection, and drive circuits.

Power electronic converters for controlled rectification,

inversion, dc-dc conversion, and ac-ac conversion, are covered.

Applications of power electronic equipment with emphasis on

dc and ac motor drives.

Course Objectives:


3/99

3

What is Power Electronics ?

Conversion and control of electricpower using semiconductor electronicdevices and related control techniques

Conversion: ac to dc ( rectification ), dc to ac ( inversion )

Control: To vary voltage, current, Hz, power etc

Note:

In Power Electronics applications, the devices operate in

switching (ON/OFF) mode only, rather than in the linear (active)

mode.



4/99

4

What is Power Electronics? Contd.

Load

Controller

Power Circuit(Power Electronic

Converter)

Source

A C Mains ,

Battery,

etc

Motor

Power Input Power Output

Light

Heating

etc, etc

Ref Measurement

s

Control Signals

E

l

e

Electronic

Equipment

http://img.alibaba.com/photo/50160597/Waterproof_Electric_Heater.jpghttp://mirror-us-ga1.gallery.hd.org/_exhibits/light/_more2003/_more05/light-bulb-glowing-filament-light-blue-uncropped-3-AHD.jpg


6/99

6

Diodes, Transistors and Thyristors


7/99

7

Comparison of Transistors & Thyristors


8/99

8

DEVICE CLASSIFICATION according to

degree of controllability

Group I: Uncontrollable,

eg: Diodes

Group II: Semi-controllable,

eg: SCR, TRIAC

Group III:Fully-controllable,

eg: BJT, MOSFET, IGBT, GTO


9/99

9

CONTROL CHARACTERISTICS

OF POWER DEVICES


10/99

10

CONTROL CHARACTERISTICS OF POWER DEVICES (contd.)


11/99

11

CONTROL CHARACTERISTICS OF POWER

DEVICES (contd.)


12/99

12

CONTROL CHARACTERISTICS OF POWER

DEVICES (contd.)


13/99

13

Voltage and Current Capabilities

Bipolar voltage withstanding capability(e.g. SCR, GTO,TRIAC).

Unipolar voltage withstanding capability

(e.g. BJT,MOSFET, IGBT, GTO, ).

Bidirectional current capability

(e.g. TRIAC, MOSFET ).

Unidirectional current capability

(e.g. SCR, GTO, BJT, IGBT, & Diode).


14/99

14

What is Power Electronic

Converter ?

An Equipment whichaccepts electric powerfrom the existing

source (fixed V/Hz a.c,Battery etc.) andconverts it in acontrolled manner into

a suitable formcompatible with theparticular load.

Source

Converter

Set

Load

Source

Prof A Rashid, PNEC/NUST


15/99

15

Power Electronic Converters

A C

A C D C

D C

RECTIFIERS(Controlled / Uncontrolled)

DC-DCCONVERTERS

INVERTERS

AC-AC

CONVERTERS

(DC Choppers)

AC Voltage

Controllers

Cycloconverters

DC Link

Converters



16/99

16

POWER ELECTRONIC CONVERTERS

AC to DC: RECTIFIERAC to DC: RECTIFIER

DC to DC: CHOPPERDC to DC: CHOPPER

DC to AC: INVERTERDC to AC: INVERTER

AC to AC:AC to AC:

CYCLOCONVERTER, ACCYCLOCONVERTER, AC

VOTAGE CONTROLLERVOTAGE CONTROLLER

AC Input DC Output

DC Input DC Output

DC Input AC Output

AC Input AC Output



17/99

17

Why Power Semiconductor

Converters?

1) High efficiency

2) Long Life

3) Low maintenance

4) Compact size

5) Low Cost

6) Fast response7) Low power consumption in their

control circuits


18/99

A Si l Ph F ll W U t ll d R tifi Ci it (Di d F ll


19/99

19

A Single Phase Full Wave Uncontrolled Rectifier Circuit (Diode Full

Wave Rectifier) using a Center Tapped Transformer


20/99

20

Half-WaveControlled Rectifier

(a) Cicuit

V

(b) Waveforms


21/99

21

A Single Phase Full Wave Controlled Rectifier

Circuit using a Center Tapped Transformer


22/99

22

Full-Wave


23/99

23

Single-Phase ac-ac converter


24/99

24

CHOPPERS


25/99

25

INVERTERS


26/99

26

Static Switches

bidirectional

voltage blocking

and current

conduction


27/99

27

INVERSIONUncontrolled and half-controlled rectifiers will

permit power to flow only from the a.c systemto d.c load and are therefore referred to asunidirectionalconverters.

In case of fully controlled rectifiers, it ispossible to transfer power from d.c side of therectifier back into the a.c system by controllingthe phase angle .

Such mode is known as inverting mode. Thefully controlled converter may therefore be

called as a Bidirectional converter.


28/99

28

Inductive Smoothing of D.C Without L, the voltage waveform at M and N

has Ripple Voltage component in additionto dc component.

L will smooth out Ripple Voltage and makeit negligibly small.

Capacitor can also be connected in parallel,but in high power applications the capacitorwill draw too much charging current fromsupply band cause other problems.

In electronic circuits( light current)application capacitor is preferred.

(Ref. VIT p. 142)


29/99

29

Applications of Controlled Rectifiers

1) DC Motor speed control

2) Electrochemical andElectrometallurgical

processes

3) Magnetic power supplies

4) Converters at the input end of dc

transmission line

5) Portable handtool drives


30/99

30

Generalized Power Converter System


31/99

31

Design of Power Electronics Equipment

1) Design of power circuits( Devices,

their ratings and configuration)

2) Protection of power devices (Fuse,Heat-Sink etc.)

3) Determination of control strategy

(Phase-angle control, ON-OFF control etc)

4) Design of logic and gating circuit.


32/99


33/99

33

(c) Appearance

SCR Structure, Symbol and Appearance

A

K

G

PJ1

N

P

NJ2

J3

(a) Structure

Lesson Plan Topic 2.1

(b) Symbol

Anode

Cathode

Gate

Low

Power

Medium

Power
http://images.google.com.pk/imgres?imgurl=https://www.alliedelec.com/Images/Products/Small/935-3546.jpg&imgrefurl=https://www.alliedelec.com/Search/ProductDetail.aspx%3FSKU%3D9353546%26MPN%3DNTE5569%26R%3D9353546%26SEARCH%3D9353546%26DESC%3DNTE5569&h=200&w=200&sz=6&hl=en&start=38&usg=__n6jdEoIXLreFjd9x7wKShkZcdeQ=&tbnid=3_54I90sV8ksOM:&tbnh=104&tbnw=104&prev=/images%3Fq%3Dsilicon%2Bcontrolled%2Brectifier%26start%3D20%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DNhttp://images.google.com.pk/imgres?imgurl=https://www.alliedelec.com/Images/Products/Small/935-3546.jpg&imgrefurl=https://www.alliedelec.com/Search/ProductDetail.aspx%3FSKU%3D9353546%26MPN%3DNTE5569%26R%3D9353546%26SEARCH%3D9353546%26DESC%3DNTE5569&h=200&w=200&sz=6&hl=en&start=38&usg=__n6jdEoIXLreFjd9x7wKShkZcdeQ=&tbnid=3_54I90sV8ksOM:&tbnh=104&tbnw=104&prev=/images%3Fq%3Dsilicon%2Bcontrolled%2Brectifier%26start%3D20%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DNhttp://images.google.com.pk/imgres?imgurl=http://www.smcelectronics.com/SCR1.JPG&imgrefurl=http://www.smcelectronics.com/semi.htm&h=187&w=90&sz=11&hl=en&start=85&usg=__5KOZr_-rIlOpqij_Jd6Y4BbWrEg=&tbnid=8hDPhSof7S37pM:&tbnh=102&tbnw=49&prev=/images%3Fq%3Dsilicon%2Bcontrolled%2Brectifier%26start%3D80%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DNhttp://images.google.com.pk/imgres?imgurl=https://www.alliedelec.com/Images/Products/Small/935-3546.jpg&imgrefurl=https://www.alliedelec.com/Search/ProductDetail.aspx%3FSKU%3D9353546%26MPN%3DNTE5569%26R%3D9353546%26SEARCH%3D9353546%26DESC%3DNTE5569&h=200&w=200&sz=6&hl=en&start=38&usg=__n6jdEoIXLreFjd9x7wKShkZcdeQ=&tbnid=3_54I90sV8ksOM:&tbnh=104&tbnw=104&prev=/images%3Fq%3Dsilicon%2Bcontrolled%2Brectifier%26start%3D20%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DN


34/99

34

Thyristor Construction

C


35/99

35

BJT Characteristics

T f Ch t i ti f NPN


36/99

36

Transfer Characteristics of NPN

Transistor

Lesson Plan Topic 2.2


37/99


38/99

EFFECT OF GATE CURRENT


39/99

39

EFFECT OF GATE CURRENT on

FORWARD BLOCKING VOLTAGE


40/99

40

TURN-ON CHARACTERISTICS

on d r t t t= +


41/99

41

Reverse Recovery Characteristic of

Diode

t1

t2

tr r

0 . 2 5 IR R

t

IR R

IF


42/99


43/99

43

Methods of Thyristor Turn-on

1) Gate Current : Normal method

2) Light: Normal method for LASCR ( Light

Activated SCR)

3) High Voltage: False Turn-on (If appliedvoltage exceeds the rated value)

4) dv/dt :False Turn-on (If applied dv/dt exceedsthe rated value)

5) Thermal Turn-on: False Turn-on

Zener Diode


44/99

44

Zener Diode


45/99

45

Zener-Diode Application

Uni Junction Transistor


46/99

46

Uni-Junction Transistor

E

B 2

B 1B 1

A

B 2

E

R B 2

R B 1n - t y p e

p - t y p e

E t a - p o i n t

B a s i c S t r u c t u r e S y m b o l

1 2 BB B B R R R= +


47/99


48/99

48

UJT Relaxation Oscillator

R R 2

V B B

R 1C

E

B 2

B 1V e v o

V e

V p

V V

V o

t

t

C a p a c i t o r

c h a r g i n g

1 = R C

T

V + V

B B

V P

2 1= R C

C a p a c i t o

d i s c h a r g

Vv


49/99

49

UJT Firing Circit

(Synchronised UJT Oscillator)

R

C

+

-

D 1 D 3

D 4 D 2

V d c

R 1

V Z

+

-

Z

i 1

v c

+

-

R 2

G 1

C 1

G 2

C 2

P u l s e T r a nE

B 2

B 1

T o SG a t e

V lt f A


50/99

50

Voltage-waveforms Across

Zener, Capacitor, Output

1 2 1 2 1 2

P u l s eV o l t a g e

v c ,

v d c

v c v c v c

V d cV Z

V Z

t

t


51/99

51

UJT FIRING CIRCUIT

Triggering Circuits Using ICs


52/99

52

Triggering Circuits Using ICs

Resistance Firing Circuit (Half-Wave)


53/99

53

Resistance Firing Circuit (Half Wave)

L O A D

v Oa b

i R 1

R 2

D

R V g

V T

v = V s i n tS m


54/99

54

Waveforms for Resistance Firing Circuit (Half-Wave)

V S

2 3 4

t

V s i n tm

V g V g t

t

t

t

t

V o

i o

V T

V g p V g tV g p

( a )

t

t

t

t

t

t

t

t

t

t

2 3 4

2 3 4

V S

V g

V o

i o

V T

V S

V g

V o

i o

V T

V = Vg p g t

2 7 00

2

3 4

9 00 = 9 0

0

( c )( b )

< 9 00

V > Vg p g t


55/99

55

R C Half-Wave Trigger Circuit

L O A D

v O

R

C

V T

v = V s i n tS m

D 2

V C

+

-

D 1


56/99

56

Waveformsfor R C Half-Wave Trigger Circuit

v s

0

V s i n tm

0 t

t t

av c

- / 2

a

v c

Vg t

v o

v T

2 3

V m

- Vm

v s

0

V s i n tm

0 t

av c

- / 2

a

v c

Vg t

0

0

v o

v T

V m V m

2 3 - Vm

( 2 + )

( a ) ( b )

t t


57/99

57

RC Triggering

L O A D

v O

R

C

V T

v = V s i n tS m

D 2

V C

+

-

D 1


58/99

58

R C Full-Wave Trigger Circuitv O

R

C

V T

v = V s i n tS m

+

-

L O A D+

-

D 1 D 3

D 4 D 2

v d

Waveforms of RC full-wave triggering


59/99

5959

v s

v d

v o

v T

t

t

t

V s i n tm

v d

v c v c v cv g t

gg gwith Rat high value

Waveforms of RC full-wave triggering( ) ith R HIGH l (b) ith R LOW l


60/99

60

(a) with R, HIGH value (b) with R, LOW value

v s

vd

v o

v T

t

t

t

t

V s i n tm

v d

v c v c v cv g t

V s i n tm v s

vd

v o

v T

t

t

t

v g t

( a ) ( b )

Triggering Device


61/99

61

Triggering Device

A device is classified as triggering device

if it changes from one stable off-state toanother stable on-state upon sensing a

particular voltage level called the Trigger,

FiringorPeak-Pointvoltage.

In most applications triggering devices

sense voltage magnitude across a

capacitor. When the capacitor voltage

reaches the trigger voltage, the deviceturns on and provides a discharge path

for capacitor.

Si l G t T i


62/99

62

Simple Gate Trigger


63/99

63

SCR Triggered by Light Pulse

PhotoTransistor

Light

V I Ch t i ti f TRIAC


64/99

64

V-I Characteristics of TRIAC

C


65/99

65

DIAC is a two terminal five layer semi-conductor bi-directional switching device.

P

N N

N

N

P

PP

T 1

T1

T2

T 2

DIAC can conduct in both directions when the


66/99

66

DIAC can conduct in both directions when thevoltage applied across the device terminals

exceeds its break over voltage.

T1

T1T 2 T 2

RL

RL

V V

I

I


67/99

67

Diac Characteristics

V B 0 2

V B 0 1

B l o c k i n g s t a t e

F o r w a r dc o n d u c t i o n

R e v e r s ec o n d u c t i o n r e g i o n

I

V

Circuit Turn-off Time t


68/99

68

Circuit Turn-off Time tc

It is the turn-off time that the circuit

presents to the SCR.

The circuit turn-off time tc must always be

greater than the turn-off time of SCR

(tqor toff), otherwise the SCR may revert to

the on-state.

Losses in Thyristor


69/99

69

y

1) Load current forward conduction loss

= IA x VF

2) Forward leakage power loss = IFB x VS

( due to forward leakage current)

3) Reverse leakage power loss ( only in a.c;

due to reverse leakage current )

4) Gate power loss: It is due to energy input

from firing circuit. Pulse firing reduces

this loss.


70/99

70

Losses in Thyristor ( contd.)

5) Switching loss (or Dynamic loss)

Loss during turn-on and turn-off periods.

At high frequency ( above 1 kHz ) this

loss is significant.

For high frequency operation, thyristors ofInverter-grade are used.

H t Si k


71/99

71

Heat Sinks


72/99

Comparison between different types of Diodes


73/99

73

p ypGeneral PurposeDiodes

Fast Recovery DiodesSchottky Diodes

Upto 6000V &3500A Upto 6000V and1100A Upto 100V and300A

Reverse recoverytime High

Reverse recoverytime Low

Reverse recoverytime Extremely

low.

Switching frequency Low

(Max 1KHz)

Switching frequency High

(Max 20KHz)

Switching frequency Very high. (Max

30KHz)

0.7 to 1.2VF

V = 0 . 8 t o 1 . 5 VFV =

25rr

t s 0.1 s to 5 srrt = a few nano sec

rrt =

73

0.4 to 0.6VFV


74/99

74

POWER DIODES APPEARANCE


75/99

Bipolar Junction Transistor (BJT)Bipolar Junction Transistor (BJT)


76/99

76

Bipolar Junction Transistor (BJT)Bipolar Junction Transistor (BJT)

Ratings: Voltage: VVCECE


77/99

77

Ratings: VoltageVoltage VVDSDS


78/99

78

Combination of BJT and MOSFET characteristics.

Compromises include:

Gate behaviour similar to MOSFET - easy to turn on and off. Low losses like BJT due to low on-state Collector-Emitter

voltage (2-3V).

IGBT


79/99

79

IGBT

Ad f IGBT


80/99

80

Advantages of IGBT

Combines the advantages of BJT & MOSFET

High input impedance like MOSFET

Voltage controlled device like MOSFET

Simple gate drive, Lower switching loss Low on state conduction power loss like BJT

Higher current capability & higher switching speed

than a BJT. ( Switching speed lower than MOSFET)

Gate-Turn-Off Thyristors (GTO)


81/99

81

Gate-Turn-Off Thyristors (GTO)

Slow switching speeds

Used at very high power levels

Require elaborate gate control circuitry

Switching Waveforms for


82/99

82

Switching Waveforms for

GTOs

tt

tt

iiGG

tt

iiAA

vvSS

large in magnitude ~ 1/3 ilarge in magnitude ~ 1/3 iAA

Neededtoturn-offNeededtoturn-off


83/99

8383

di/dt Protection

S

S

Vdidt L

=


84/99


85/99

8585

Static & Dynamic Equalization


86/99

8686

PARALLEL OPERATION

Switches comparison


87/99

87

Switches comparisonDevice Type Year

madeRated

VoltageRated

CurrentSwitchingFrequency

RatedPower

DriveCircuit

Comments

SCR 1957 6kV 3.5kA 500Hz 100s MW Simple Cannot turn-off usinggate signal

GTO 1962 4.5kV 3kA 2kHz 10s MW VeryDifficult

King in very highpower

BJT 1960s 1.2kV 400A 5kHz 1 MW Difficult Phasing out in newproduct

MOSFET 1976 500V 200A 1MHz 100 kW VerySimple

Good performance inhigh frequency

IGBT 1983 3.3kV 1.2kA 100kHz 100s kW VerySimple

Best overallperformance

Harmonics


88/99

88

( )

=

++=1

0 )sin()cos()(n

nn tnbtnaatf

=

tdtntfan )(cos)(1

=

tdtntfbn )(sin)(1

It can be defined as a sinusoidal component of a periodic waves or quality

having frequencies that are an integral multiple of the fundamental frequency.

=

2

0

0 )(2

1tdtfa =

2

0

)(cos)(1

tdtntfan=

2

0

)(sin)(1

tdtntfbn

For Odd Functions: =

0

)(sin)(2

tdtntfbn00 == naa

For Even Functions: =

0

)(cos)(2

tdtntfan=

0

0 )(1

tdtfa 0=nb

A Simple Circuit (R-L Load) Current continues to flows for a while even after the input


89/99

89

Current continues to flows for a while even after the input

voltage has gone negative

ADVANTAGES OF THYRISTORISED


90/99

90

POWER CONTROLLERS

1) High efficiency due to low losses in the Thyristors.

2) Long life and reduced/minimal maintenance due to

the absence of mechanical wear.

3) Control equipments using Thyristors are compact in

size.4) Easy and flexibility in operation due to digital

controls.

5) Faster dynamic response compared to the electro

mechanical converters.6) Lower acoustic noise when compared to electro

magnetic controllers, relays and contactors.

DISADVANTAGES OF THYRISTORISED

POWER CONTROLLERS


91/99

91

POWER CONTROLLERS

1) All the thyristorised power controllers generate

harmonics (unwanted frequency components) due to theswitching ON and OFF of the thyristors. These harmonics

adversely affect the performance of the load connected to

them. For example when the load are motors, there are

additional power losses (harmonic power loss) torqueharmonics, and increase in acoustic noise.

2) The generated harmonics are injected into the supply

lines and thus adversely affect the other loads/equipments

connected to the supply lines.

3) In some applications example: traction, there is

interference with the commutation circuits due to the

power supply line harmonics and due to electromagnetic

radiation.

DISADVANTAGES OF THYRISTORISED


92/99

92

POWER CONTROLLERS( contd.)

4) The thyristorised AC to DC converters and AC to ACconverters can operate at low power factor under some

conditions.

5)Special steps are then taken for correcting the line supply

power factor (by installing PF improvement apparatus).

6) The thyristorised power controllers have no short time over

loading capacity and therefore they must be rated for

maximum loading conditions. This leads to an increase in the

cost of the equipment.

7) Special protection circuits must be employed inthyristorised power controllers in order to protect and safe

guard the expensive thyristor devices. This again adds to the

system cost.

Synchronous Speed


93/99

93

Synchronous Speed

pfNs

120=

s is syncronous speed [rad/sec]

Ns is syncronous speed [rpm]

p is numbers of poles

is the supply frequency [rad/sec]f is the supply frequency [Hz]

Nm is motor speed

A t d N i l th th d f th t ti fi ld N


94/99

94

Armature speed N is less than the speed of the rotating field Ns

by an amount equal to theslip speed s.

The frequency of an induction machine at the rotor side isnt

the same as the frequency at primary side.

Rotor Frequency,

where fr

and fs

are rotor current frequency and mains supply

frequency, respectively.

s

s

N

NNs =

sr sff =

TorqueSpeedCharacteristic


95/99

95

Characteristic

For small values of slip,developed torque is proportional

to slip.

TORQUE-SPEED CHARACERISTIC

f I d ti M t


96/99

96

of Induction Motor

Tmax

Smax

Tst

Td

S=0sNs

S=1

TL

S=SmmNmNm =0

Tm=TLOperating point

Stator Voltage Control


97/99

97

gControlling Induction Motor Speed by Adjusting The Stator Voltage

Tmax

S=0sNs

S=1

TL

Nm =0

Td

Vs1Vs Vs2> >

1 2

Tst

Tst1

Tst2

Varying supply voltage and supply


98/99

98MZS

FKEE, UMP

98

The best method since supplyvoltage and supply frequency is

varied to keep VV//ff constant

Maintain speed regulation

uses power electronics circuit forfrequency and voltage controller

Constant maximum torque

y g pp y g pp y

frequency

T

nNL1

T

nr1nr2nr3 n

f

decreasing

nNL2nNL3

Frequency Voltage Control


99/99

Frequency Voltage ControlControlling Induction Motor Speed by Adjusting The Frequency Stator Voltage

Tmax

S=0

TL

Td

ars p es 99slides jan10

Documents