eee 304 lecture notes - 1
TRANSCRIPT
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EEE 304
Power Electronics
Lecture Notes
D. R. Binu Ben Jose
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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
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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.
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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
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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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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.
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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.
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Unit V
Applications
Regulated power supply, SMPS, UPS ,
DC Circuit Breakers , AC circuit
breakers, HVDC systems, AC and DCmotor control.
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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
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Contd
PN Junction diodes
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Transistors
Basic Structure
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Contd
NPN Transistor PNP Transistor
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NPN transistors are used widely than PNP transistors. Why?
Students to search and find the answer for this question
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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.
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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.
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Contd
Structure and
Two transistor
analogy
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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
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Characteristics
Three States:
Reverse Blocking
Forward Blocking
Forward Conducting
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Effects of gate current
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Estimation of anode current
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Contd...
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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
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Contd...
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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
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Contd
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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
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Contd
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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
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Switching characteristic of SCR
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Turn-on
Characteristics
on d rt t t
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Contd
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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
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Methods to Turn-on SCR
Thermal Turn-on.
Light.
High Voltage.
Gate Current.
dv/dt.
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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
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Lecture 4
21.07.2015
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Bidirectional Triode Thyristors
(TRIAC)
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Contd
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Operating modes
Mode 1(MT2 Positive, Gate Positive)
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P1
N1
N2
P2Ig
Ig
MT2 (+)
MT1 ( )GV
(+)
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Contd
Mode-II (MT2 Positive, Gate Negative)
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P1
N1
N2N3
P2
Ig
MT2 (+)
MT1 ( )GV
Finalconduction
Initialconduction
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Contd
Mode-III, MT2 Negative, Gate Positive
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P1
N1
N4
N2P2
Ig
MT2 ( )
MT1 (+)G(+)
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Contd
Mode-IV, MT2 Negative, Gate Negative
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P1
N1
N4
P2
Ig
MT2 ( )
MT1 (+)
N3
G(-)
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SCR and Triac conduction
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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
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MOSFET Structure
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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
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N-channel MOSFET
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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
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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
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G T d
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IGBT structure, operation and
characteristics
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The characteristics is similar to that of MOSFET
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C d
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Contd
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D i Ci i f MOSFET/IGBT
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Driver Circuits for MOSFET/IGBT
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S i d ll l i f d i
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Series and parallel operation of devices
Series connection of SCRs
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R = (nVdVs)/(n1)Ib
C = (n1) Qrr/ (nVdVs)
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E i 1
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Exercise 1
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E i 2
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Exercise 2
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S bb Ci it f SCR
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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
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Exercise 1
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C td
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Contd
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E r i 2
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Exercise 2
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C ntd
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Contd
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Sn bber Circ its for MOSFETs
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Snubber Circuits for MOSFETs
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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
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Switching losses of devices
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Switching losses of devices
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Exercise 1
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Exercise 1
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Contd
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Contd
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Contd
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Contd
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Exercise 3
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Exercise 3
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Exercise 4
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Exercise 4
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Contd
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Contd
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Exercise 5
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Exercise 5
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Contd
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Contd
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Contd
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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
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Sample Heat sinks
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Sample Heat sinks
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Assignment
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Assignment
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1
2
Contd
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Contd
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3
Contd
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Contd
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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
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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.
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General
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General
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Phase-ControlledConverters
Single-Phase
Semiconverter
Three-Phase
Full converter
Dual converter
Semiconverter
Full converter
Dual converter
Quadrant operation of converters
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Quadrant operation of converters
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Contd
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Co d
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Converters - classification
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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
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Contd
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Average
OutputVoltage
Maximum Average
Output Voltage
Normalized
Output Voltage
RMS o/p
Voltage
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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
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( g p
with purely resistive load)
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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
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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
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221.21592.0
3536.0
m
m
dc
rms
V
V
V
VFF
983.11221.21 22 FFRF
mVPIV
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Contd With RL Load
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Average and RMS values of single
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g g
phase full converter
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cos
2sin
2
2 mmdc
VtdtVV
2
sin2
2 22 mmrms
VtdtVV
Single-Phase
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Semiconverter
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Contd
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Average and rms values
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ttdVV
V
ttdVV
mrms
m
mdc
22
sin2
2
cos1sin2
2
Single phase dual converter
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g p
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Waveforms
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Contd.
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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
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Single-Phase Full Converter (RLE-
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load continuous conduction)
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Contd
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At t = , IL= ILo
Mode 1 = Mode 2
Contd
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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
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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
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tdiI LR
2
2
1
tdiI
LA
2
1
RRRrms IIII 2
22
AAAdc IIII 2
Discontinuous operation
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Excercises
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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.
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Exercises
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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
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60 t
CAT 1 Questions
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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.
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Contd
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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.
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Performance of 2-pulse converters
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Displacement Factor
Input power factor
Harmonic Factor
Effect of overlap
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Three phase half-wave
t ll d t
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controlled converters
(3-pulse converters)
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Continuous conduction Vav
Vrms
Dis-continuous conduction
Vav
Vrms
Three phase fully
ntr ll d n rt r
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controlled converters
(6-pulse converters)
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Contd
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Fourier analysis
Isn
I1
Irms
DF
PF
HF
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Effect of source inductance
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Assignment - 2
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Explain in detail with necessary equationsthe operation of three phase full converter
with free wheeling diode at the output
terminals.
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Contd
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Continuous conduction Vav
Vrms
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Unit III
DC T DC C
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DC To DC Converters
Step-down and step-up choppers -
Time ratio control and current limit
controlbasic oscillating chopper
multi chopperquadrant operation of
chopper.
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ContdCh i t ti d i
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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.
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Types of basic Choppers
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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.
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Contd v0V
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Vdc
V
V/R
i0
Idc
t
t
tON
T
tOFF
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Contd
B t d i t V
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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
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Contd
Eff i i i f h
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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
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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
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ContdV0V
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V
V0
t
ttON
tON tOFF
tOFF
T
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Contdv0
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V
V
v0
t
t
tON
tON
T
T
tOFF
tOFF
Current limit control
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Chopper classifications
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Quadrant operation of chopper.
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Oscillating Choppers
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Basic Circuit
Contd
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Modified Circuit
Contd
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Modified Circuit
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Unit IV
Inverters
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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.
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Current source inverters
Adding a large inductance to the dc circuit
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Adding a large inductance to the dc circuit
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Contd
C t f
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Current waveform
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Quality of an inverter Quality is evaluated in terms of the following
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Harmonic factor (HF)
Measure of individual harmonic contribution
Distortion factor (DF)
Measure of effectiveness in reducing unwanted harmonics
DF of individual harmonic is
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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
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Unit V
Applications
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Applications
Regulated power supply, SMPS, UPS ,
DC Circuit Breakers , AC circuit
breakers, HVDC systems, AC and DC
motor control.
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DC circuit breaker
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AC circuit breaker
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