eee 304 lecture notes - 1

7/25/2019 Eee 304 Lecture Notes - 1

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EEE 304

Power Electronics

Lecture Notes

D. R. Binu Ben Jose

VIT University, Chennai Campus,Chennai - 127


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Introduction

Course Name : Power Electronics

Course Code : EEE 304

L T P C : 3 0 2 4

Course

Pre-requisites : EEE102

VIT University, Chennai Campus, Chennai. 2


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Objectives

To get adequate knowledge of the power

electronic devices and their applications

To know about electric power conversion(AC to DC, DC to DC, DC to AC), control and

conditioning of electric power

To get a clear exposure on designing the

power electronic circuits



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Expected Outcome

On the completion of this course thestudent will be able to: Obtain the switching characteristic of different types of power

semi-conductor devices.

Determine the operation, characteristics and performanceparameters of controlled rectifiers.

Apply switching techniques and basic topologies of DC-DC

switching regulators

Use the different modulation techniques of pulse width

modulated inverters and to apply the harmonic reductionmethods.

Design the power electronic converters in conditioning the

power supply that suit the practical applications.



5/171

Student outcomes

An ability to apply knowledge of mathematics,

science, and engineering

An ability to design and conduct experiments, as

well as to analyze and interpret data

An ability to design a system, component, or

process to meet desired needs within realistic

constraints such as economic, environmental,

social, political, ethical, health and safety,

manufacturability, and sustainability

An ability to identify, formulate, and solve

engineering problems



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Evaluation Mode

Continuous Assessment (30 %)

Assignments / Seminars/ Projects (20 %)

Term - End Examination (50 %)



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Syllabus



8/171

Unit I

Power Semi-Conductor Devices

Structure, operation and characteristics

of SCR, TRIAC, power transistor,

MOSFET and IGBT. Driver and snubbercircuits for MOSFET - Turn-on and turn-

off characteristics and switching losses

series & parallel operationprotectionof SCRsfiring & typical control

circuitsPerformance parameter



9/171

Unit II

Phase-Controlled Converters

2-pulse, 3-pulse and 6-pulse converters

Inverter operation of fully controlled

converterEffect of source inductancesingle phase dual converter Single

phase AC voltage controllers; AC

chopper; single phase cyclo converters.



10/171

Unit III

DC To DC Converters

Step-down and step-up choppers -

Time ratio control and current limit

controlbasic oscillating choppermulti chopperquadrant operation of

chopper.



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Unit IV

Inverters

Introduction of basic series and parallel

inverters, single phase Bridge inverters

PWM techniques: Sinusoidal PWMmodified sinusoidal PWM and multiple

PWM- Voltage and harmonic control -

Series resonant inverter - Currentsource inverters.



12/171

Unit V

Applications

Regulated power supply, SMPS, UPS ,

DC Circuit Breakers , AC circuit

breakers, HVDC systems, AC and DCmotor control.



13/171

Reference Books

1. Muhammad H. Rashid, Power Electronics: Circuits,Devices and Applications, Pearson Education, Third

edition, 2004 / PHI.

2. Ned Mohan, Tore.M.Undeland, William.P.Robbins,

Power Electronics: Converters, Applications andDesign, John Wiley and sons, third edition, 2003.

3. S N Singh, A text book of power Electronics,

Dhanpat Rai and Co., New Delhi, 2000.

4.

Bimal K. Bose, Modern Power Electronics and ACDrives, Pearson Education, 2003.

5. Jaganathan, Introduction to Power Electronics,

Prentice Hall of India, 2004.



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Lecture 1, 210, 14.07.2015



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Unit I

Power Semi-Conductor Devices

Structure, operation and characteristics

of SCR, TRIAC, power transistor,

MOSFET and IGBT. Driver and snubbercircuits for MOSFET - Turn-on and turn-

off characteristics and switching losses

series & parallel operationprotectionof SCRsfiring & typical control

circuitsPerformance parameter



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Fundamentals of Devices

Semiconductors



17/171

Contd

PN Junction diodes



18/171

Transistors

Basic Structure



19/171

Contd

NPN Transistor PNP Transistor


NPN transistors are used widely than PNP transistors. Why?

Students to search and find the answer for this question


20/171

Contd

Transistor Characteristics



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Modes of operation Cutoff: In cutoff, both junctions reverse biased. There is very little current flow,

which corresponds to a logical "off", or an open switch.

Forward-active (or simply, active): The emitter-base junction is forward biasedand the base-collector junction is reverse biased. Most bipolar transistors aredesigned to afford the greatest common-emitter current gain, fin forward-active mode. If this is the case, the collector-emitter current is approximatelyproportionalto the base current, but many times larger, for small base current

variations.

Reverse-active (or inverse-active or inverted): By reversing the biasingconditions of the forward-active region, a bipolar transistor goes into reverse-active mode. In this mode, the emitter and collector regions switch roles. Sincemost BJTs are designed to maximise current gain in forward-active mode, thefin inverted mode is several times smaller. This transistor mode is seldom

used. The reverse bias breakdown voltage to the base may be an order ofmagnitude lower in this region.

Saturation: With both junctions forward-biased, a BJT is in saturation mode andfacilitates current conduction from the emitter to the collector. This modecorresponds to a logical "on", or a closed switch.

http://en.wikipedia.org/wiki/Proportionality_(mathematics)http://en.wikipedia.org/wiki/Proportionality_(mathematics)


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Contd

Typical Transistors



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Unit IPower Semi-Conductor Devices



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Classification



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Important Parameters

Breakdown voltage and current

On-state resistance.

Trade-off between breakdown voltage and

on-state resistance.

Rise and fall times for switching between on

and off states.

Safe-operating area.



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Thyristor

Thyristor is a family of devices having 4

semiconducting layers (typically - PNPN).

Eg. SCR, Triac, Diac

Silicon controlled rectifier (SCR) is the most

powerful device in the thyristor family.

Triac is used in medium power supplies

(preferably 1 kW).

Diac is a switching device.



28/171


29/171

Contd

Structure and

Two transistor

analogy


Gate Cathode

J3

J2

J1

Anode

10 cm17 -3

10 -5 x 10 cm13 14 -3

10 cm17 -3

10 cm19 -3

10 cm19 -3

10 cm19 -3

n+

n+

p-

n

p

p+

10 m

30-100 m

50-1000 m

30-50 m


30/171

Characteristics

Three States:

Reverse Blocking

Forward Blocking

Forward Conducting



31/171

Effects of gate current



32/171

Estimation of anode current



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Contd...


1 1

1 1

1 1

1

1

Considering PNP transistor

of the equivalent circuit,

, , ,

,

1 1

E A C C

CBO CBO B B

B A CBO

I I I I

I I I I

I I I


34/171

Contd...


2 2 2

2 2

2 2

2

2

Considering NPN transistor

of the equivalent circuit,

, ,

2

C C B B E K A G

C k CBO

C A G CBO

I I I I I I I I

I I I

I I I I


35/171

Contd


2 1

2 1 2

1 2

From the equivalent circuit,

we see that

1

C B

g CBO CBO

A

I I

I I II


36/171

Contd


1 2

1 2

Case 1: When 0

1

g

CBO CBO

A

II I

I

2 1 2

1 2

Case 2: When 0

1

G

g CBO CBO

A

I

I I II


37/171

Switching characteristic of SCR


Turn-on

Characteristics

on d rt t t


38/171

Contd


Anode currentbegins todecrease

tC

tq

t

t

Commutation

di

dt

Recovery Recombination

t1 t2 t3 t4 t5

trr tgr

tq

tc

VAK

IA

tq=device off time

tc=circuit off time

Turn-off Characteristic


39/171

Methods to Turn-on SCR

Thermal Turn-on.

Light.

High Voltage.

Gate Current.

dv/dt.



40/171

Various terms Average ON state current rating

RMS forward conduction current rating Surge current rating

Holding current

Latching current di/dt rating

Peak repetitive forward blocking voltage

Forward break over voltage

Peak repetitive reverse blocking voltage

Turn OFF time

Turn ON time



41/171

Lecture 4

21.07.2015



42/171

Bidirectional Triode Thyristors

(TRIAC)



43/171

Contd



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Operating modes

Mode 1(MT2 Positive, Gate Positive)


P1

N1

N2

P2Ig

Ig

MT2 (+)

MT1 ( )GV

(+)


45/171

Contd

Mode-II (MT2 Positive, Gate Negative)


P1

N1

N2N3

P2

Ig

MT2 (+)

MT1 ( )GV

Finalconduction

Initialconduction


46/171

Contd

Mode-III, MT2 Negative, Gate Positive


P1

N1

N4

N2P2

Ig

MT2 ( )

MT1 (+)G(+)


47/171

Contd

Mode-IV, MT2 Negative, Gate Negative


P1

N1

N4

P2

Ig

MT2 ( )

MT1 (+)

N3

G(-)


48/171


49/171

SCR and Triac conduction



50/171

MOSFET

Symbols



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MOSFET Terminals

The voltage applied to the GATE terminal determineswhether current can flow between the SOURCE & DRAINterminals.

For an n-channel MOSFET, the SOURCE is biased at a lowerpotential (often 0 V) than the DRAIN

(Electrons flow from SOURCE to DRAIN when VG> VT)

For a p-channel MOSFET, the SOURCE is biased at a higherpotential (often the supply voltage VDD) than the DRAIN

(Holes flow from SOURCE to DRAIN when VG< VT )

The BODY terminal is usually connected to a fixedpotential.

For an n-channel MOSFET, the BODY is connected to VDDV

For a p-channel MOSFET, the BODY is connected to 0 V



52/171

MOSFET Structure


A GATEelectrode is placed above (electrically insulated from)

the silicon surface, and is used to control the resistance

between the SOURCE andDRAINregions

NMOS:N-channel Metal

Oxide Semiconductor

L

L= channel length

Metal (heavily

doped poly-Si)

W

W= channel width

SOURCE

DRAIN

GATE


53/171

N-channel MOSFET


Without a gate-to-source voltage applied, no current can

flow between the source and drain regions.

Above a certain gate-to-source voltage (thresholdvol tageVT), a conducting layer of mobile electrons is

formed at the Si surface beneath the oxide. These

electrons can carry current between the source and drain.

n

p

oxide insulatorgate

n

Drain

Source

Gate

ID

IG

IS


54/171


55/171


56/171

Insulated gate bipolar transistor

(IGBT)

Posses the advantages of both BJT and

IGBT such as less Vce ONand voltage

controlled.

Better characteristics at high voltages

High power rating


G T d


57/171

IGBT structure, operation and

characteristics


The characteristics is similar to that of MOSFET


58/171


59/171

C d


60/171

Contd


D i Ci i f MOSFET/IGBT


61/171

Driver Circuits for MOSFET/IGBT


S i d ll l i f d i


62/171

Series and parallel operation of devices

Series connection of SCRs


R = (nVdVs)/(n1)Ib

C = (n1) Qrr/ (nVdVs)


63/171

E i 1


64/171

Exercise 1


E i 2


65/171

Exercise 2



66/171

S bb Ci it f SCR


67/171


Snubber Circuits for SCRs (Protection)

Turn on snubber

di/dt protection

Limits inrush

switching Current

Inductance

Turn off snubber

dv/dt protection

Limits voltage spikes

Series RC network

E i 1


68/171

Exercise 1


C td


69/171

Contd


E r i 2


70/171

Exercise 2


C ntd


71/171

Contd


Sn bber Circ its for MOSFETs


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Snubber Circuits for MOSFETs


Turn on snubberdi/dt protection

Limits inrush

switching Current

Inductance

Turn off snubberdv/dt protection

Limits voltage spikes

Series RC network

Exercise 3


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Exercise 3


Switching losses of devices


74/171

Switching losses of devices


Exercise 1


75/171

Exercise 1



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77/171

Contd


78/171

Contd


Contd


79/171

Contd



80/171

Exercise 3


81/171

Exercise 3



82/171

Exercise 4


83/171

Exercise 4


Contd


84/171

Contd


Exercise 5


85/171

Exercise 5


Contd


86/171

Contd


Contd


87/171

Contd



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Thermal Protection


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Thermal Protection

Switching and conduction losses increases thejunction temperaturesometimes beyond 100oC

Maximum operating case temperature is 60oC

This keeps the junction temperature less than

100oC

Use heat sinks for medium power

Use coolant for high power


Sample Heat sinks


90/171

Sample Heat sinks


Assignment


91/171

Assignment


1

2

Contd


92/171

Contd


3

Contd


93/171

Contd


4 Design a heat sink (dimensions and Heat sink part number

available in internet) for an IGBT CT60AM based simple boostconverter. Heat sink temperature not to exceed 60oC. CT60AM

carries an average current of 30 A and a peak current of 60 A

at a switching frequency of 10 kHz and duty ratio 50 %. Use

appropriate thermal pad and heat sink compound. Assume no

core saturation occurs in the boost inductor.

CT60AM

Unit II


94/171

Unit II

Phase-Controlled Converters

2-pulse, 3-pulse and 6-pulse converters

Inverter operation of fully controlled

converterEffect of source inductance

single phase dual converter Single

phase AC voltage controllers; AC

chopper; single phase cyclo converters.


General


95/171

General


Phase-ControlledConverters

Single-Phase

Semiconverter

Three-Phase

Full converter

Dual converter

Semiconverter

Full converter

Dual converter

Quadrant operation of converters


96/171

Quadrant operation of converters


Contd


97/171

Co d


Converters - classification


98/171


Semiconverter..is a one-quadrant converter and it has one polari ty

Full converter

..is a two-quadrant converter and the polari ty of its output

can be either positive or negative. However

the output current of ful l converter has one polari ty only

Dual converter

..can operate in four quadrants ; both the output voltage

and cur rent can be either positive or negative


99/171

Contd


100/171

Average

OutputVoltage

Maximum Average

Output Voltage

Normalized

Output Voltage

RMS o/p

Voltage


cos1

2

sin

2

1m

mdc

VttdVV

mdm

VV

cos15.0 dm

dc

n

V

VV

2

2sin1

2sin

2

1 22

m

mrms

VttdVV

Exercise 1 (Single pulse converter


101/171

( g p

with purely resistive load)


A single pulse converter has a purely

resistive load of R and a delay angle of =

/2,determine the rectification efficiency

the form factor FF

the ripple factor RF the peak inverse voltage PIV of thyristor T1

Contd


102/171


2

2cos1

2sin

2

1 mmdc

VttdVV

mdc VV 1592.0

mm

rms VV

V 3536.02

22

sin2

1

2

%27.203536.0

1592.02

2

2

2

m

m

rms

dc

V

V

V

V

Contd


103/171


221.21592.0

3536.0

m

m

dc

rms

V

V

V

VFF

983.11221.21 22 FFRF

mVPIV


104/171


105/171


106/171

Contd With RL Load


107/171


Average and RMS values of single


108/171

g g

phase full converter


cos

2sin

2

2 mmdc

VtdtVV

2

sin2

2 22 mmrms

VtdtVV

Single-Phase


109/171

Semiconverter


Contd


110/171

Average and rms values


ttdVV

V

ttdVV

mrms

m

mdc

22

sin2

2

cos1sin2

2

Single phase dual converter


111/171

g p


Waveforms


112/171



113/171

Contd.


114/171

Input harmonic factor

Total harmonic current (upon) fundamentalcurrent

DC voltage ratio

Mean dc voltage to maximum dc voltage

Voltage ripple factor

Net harmonic content of output voltage to

average voltage

Current ripple factor Net harmonic content of output current to

average current


Single-Phase Full Converter (RLE-


115/171

load continuous conduction)


Contd


116/171


At t = , IL= ILo

Mode 1 = Mode 2

Contd


117/171

VIT University, Chennai Campus, Chennai.117

tL

R

S

L

S

L eZ

V

R

E

IR

E

tZ

V

I

sin

2

sin

2

0

R

L 1tan 22 LRZ

where

At the end of mode 1, t = + , IL1= ILo, Solving ILofor gives,

Contd


118/171

The critical value of at which Io becomes zero can

be solved by iterative method for known values of ,

R, L and E.

RMS Current

for Thyr istor is

AVG Current

for Thyristor is

RMS Output

Current AVG Output

Current

VIT University, Chennai Campus, Chennai.118

tdiI LR

2

2

1

tdiI

LA

2

1

RRRrms IIII 2

22

AAAdc IIII 2

Discontinuous operation


119/171


Excercises


120/171

A single-phase full converter has an RL load of R

= 2.5 , L = 6.5mH. The input voltage is VS= 100V(rms) at 50 Hz. Determine

(a) the average and rms values of output voltage

and current.

(b) The conversion efficiency.

(c) The conduction losses if VAK ON= 1 V per

device.

(d) The average switching loss if tr= tf= 2 S.Assume td= ts= 0 and sinusoidal loss curves.


Exercises


121/171

Asingle-phase semiconverter has an RL load

of L = 6.5mH, R = 2.5 Ohm, and E = 10 V. Theinput voltage is VS= 120 V(rms) at 50 Hz.

Determine

(a) the load current IL0at(b) the average thyristor current IA

(c) the rms thyristor current IR

(d) the rms output current Irms

(e) the average output current Idc


60 t

CAT 1 Questions


122/171

1. Explain the VI characteristics of a four layer, semi-controlled unidirectional power

electronic device which is used in phase controlled ac-dc conversion.

2. Design a snubber (L1, Rs, Cs) for the thyristor in Fig. 1. The supply voltage is 400 V,

allowable di/dt and dv/dt are 50 kA/ms and 200 kV/ms respectively.

3. A series thyristor string with ratings 3 kV and 750 A uses thyristors with 800 V and 175 A

rating. Find the number of SCRs to be connected in series and in parallel. Use a derating

factor of 30 %. Determine the values of R and C of static and dynamic equalizing circuits.

Assume the maximum forward blocking current and maximum difference in recovery

charge as 8 mA and 30 Crespectively.

4. A single phase fully controlled converter is connected to a 20 resistance load. Estimate

the average load voltage, average load current and rms load current for a triggering angle

of 300, if the supply voltage is 230V, 50Hz. Derive the formula used. Draw the load

current and load voltage waveforms for the above single phase converter.

5. Explain the symbol, basic structure and transfer characteristics of different types of

MOSFETs with neat diagrams. Compare an IGBT with MOSFET.



123/171


124/171

Contd


125/171

4. Vav= 193.3 VIav= 9.66 A

Vrms= 226.1 V

Irms= 11.305Draw the voltage and current waveforms

5. Explain the required items for four types ofMOSFETS.


Performance of 2-pulse converters


126/171

Displacement Factor

Input power factor

Harmonic Factor

Effect of overlap


Three phase half-wave

t ll d t


127/171

controlled converters

(3-pulse converters)


Contd


128/171


Continuous conduction Vav

Vrms

Dis-continuous conduction

Vav

Vrms

Three phase fully

ntr ll d n rt r


129/171

controlled converters

(6-pulse converters)



130/171

Contd


131/171

Fourier analysis

Isn

I1

Irms

DF

PF

HF



132/171


133/171

Effect of source inductance


134/171


Assignment - 2


135/171

Explain in detail with necessary equationsthe operation of three phase full converter

with free wheeling diode at the output

terminals.



136/171

Contd


137/171

Continuous conduction Vav

Vrms



138/171

Unit III

DC T DC C


139/171


DC To DC Converters

Step-down and step-up choppers -

Time ratio control and current limit

controlbasic oscillating chopper

multi chopperquadrant operation of

chopper.


140/171

ContdCh i t ti d i


141/171

Chopper is a static device.

A variable dc voltage is obtained from a constant dcvoltage source.

Also known as dc-to-dc converter.

Widely used for motor control.

Also used in regenerative braking. Thyristor converter offers greater efficiency, faster

response, lower maintenance, smaller size and

smooth control.

MOSFET/IGBT based converter offers high switchingfrequency, lesser filter requirements, faster response,

lower maintenance, smaller size and smooth control.


Types of basic Choppers


142/171

Step-down choppers. output voltage is less than input voltage.

output current is more than input current.

Step-up choppers.

output voltage is more than input voltage.

output current is less than input current.



143/171


144/171

Contd v0V


145/171


Vdc

V

V/R

i0

Idc

t

t

tON

T

tOFF


146/171


147/171

Contd

B t d i t V


148/171


2

0

2

But during ,

Therefore RMS output voltage

1

.

.

ON

ON o

t

O

ONO ON

O

t v V

V V dt T

tVV t V

T TV d V


149/171

Contd

Eff i i i f h


150/171


Effective input resistance of chopper

The output voltage can be varied by

varying the duty cycle.

i

dc

i

VR

I

RRd

Methods of Modulation/Control


151/171

The output dc voltage can be varied by thefollowing methods.

Constant frequency operation with variable

ON time or Pulse width modulation control

with constant frequency operation.

Variable frequency control.

With constant ON time

With constant OFF time Current limit control



152/171

ContdV0V


153/171


V

V0

t

ttON

tON tOFF

tOFF

T


154/171

Contdv0


155/171


V

V

v0

t

t

tON

tON

T

T

tOFF

tOFF

Current limit control


156/171


Chopper classifications


157/171


Quadrant operation of chopper.


158/171


Oscillating Choppers


159/171


Basic Circuit

Contd


160/171


Modified Circuit

Contd


161/171


Modified Circuit


162/171

Unit IV

Inverters


163/171

Inverters

Introduction of basic series and parallel

inverters, single phase Bridge inverters

PWM techniques: Sinusoidal PWM

modified sinusoidal PWM and multiple

PWM- Voltage and harmonic control -

Series resonant inverter - Current

source inverters.


Current source inverters

Adding a large inductance to the dc circuit


164/171

Adding a large inductance to the dc circuit


Contd

C t f


165/171

Current waveform



166/171

Quality of an inverter Quality is evaluated in terms of the following


167/171


Harmonic factor (HF)

Measure of individual harmonic contribution

Distortion factor (DF)

Measure of effectiveness in reducing unwanted harmonics

DF of individual harmonic is

Contd


168/171

Total harmonic distortion Measure of closeness of shape between a waveform and

its fundamental

Lower order harmonic

Harmonic component which is closest to the fundamental


Unit V

Applications


169/171

Applications

Regulated power supply, SMPS, UPS ,

DC Circuit Breakers , AC circuit

breakers, HVDC systems, AC and DC

motor control.


DC circuit breaker


170/171


AC circuit breaker


171/171

eee 304 lecture notes - 1

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