Sri Ramakrishna Engineering College

[Educational Service : SNR Sons Charitable Trust]

[Autonomous Institution, Accredited by NAAC with A Grade]
[Approved by AICTE and Permanently Affiliated to Anna University, Chennai]
[ISO 9001:2008 Certified and all eligible programmes Accredited by NBA]
Vattamalaipalayam, N.G.G.O. Colony Post, Coimbatore 641 022.

Department of Electrical and Electronics

Engineering
12EE2603 Power Electronics
(3 1 0 4)

UNIT I Power Semiconductor Devices

Structure, operation and characteristics of SCR, TRIAC, power
transistor, MOSFET and IGBT. Driver and snubber circuits for
MOSFET - Turn-on and turn-off characteristics and switching
losses.

Third EEE (Batch 2014-2018)

18 Apr 2017 III-EEE/POWER ELECTRONICS 1
 Syllabi
UNIT - I POWER SEMI-CONDUCTOR DEVICES 9
Structure, operation and characteristics of SCR, TRIAC, power transistor, MOSFET and
IGBT. Driver and snubber circuits for MOSFET - Turn-on and turn-off characteristics
and switching losses.
UNIT - II LINE COMMUTATED CONVERTERS * 9
2,4 pulse converter with R,RL,RLE loads, effect of free wheeling diode continuous
and discontinuous conduction mode - Effect of source inductance and load inductance
introduction to 3,6 pulse converter - Dual converters- Series converters. Basic principle
of operation of single phase cycloconverter- AC voltage controllers.
UNIT - III DC TO DC CONVERTERS * 9
Step-down and step-up choppers - Time ratio control and current limit control class of
choppers - Switching mode regulators: Buck, boost, buck-boost and cuk converter -
Resonant switching based SMPS.
UNIT - IV INVERTERS 9
Single phase and three phase (both 120 0 mode and 1800 mode) inverters - PWM
techniques: Sinusoidal PWM, modified sinusoidal PWM and multiple PWM - Voltage
and harmonic control - Series resonant inverter - Current source inverters.
UNIT - V APPLICATIONS9
Uninterrupted power supply topologies - Flexible AC transmission systems - Shunt and
series static VAR compensator - Unified power flow controller- HVDC Transmission.
18 Apr 2017
III-EEE POWER Total periods (45+15T): 602
ELECTRONICS
 Course Outcome
Upon successful completion of the course, the student will be able to

CO1: Demonstrate the ability to electric and use

power semiconductor devices.
CO2: Design and Analyze the power
Converters, AC Voltage Controllers, DC-DC
Converter, Inverter.
CO3: Apply the knowledge in power electronics
to electrical drives, power systems and
renewable energies.
III-EEE POWER
18 Apr 2017 3
ELECTRONICS
 Assignments Planned
(Tentative)
Order Activity Team Title Date of
Size Submissio
n
Assg 1 Demonstration 3 per To be finalized by the students 06.01.2017
Batch (14.12.2016)
Simulating
the power Semiconductor
Devices Circuit
Assg 2 Journal 3 per Applications related Papers. 15.02.2017
Publication Batch (Disclosing of titles/Diploma)
Submitting the paper in IEEE
format
Assg 3 Written Individual 1. Voltage Source Inverter (1200) 17.03.2017
Assignment 2. Voltage Source Inverter (1800)
3. Current Source Inverter

18 Apr 2017
Deadline for Submitting
III-EEE all the Assignments 20.01.2017
POWER
4
ELECTRONICS
 Tutorial Planned (Tentative)

Order Coverage Problems Planned

Tutorial 1 Unit 1 3 Problems
Tutorial 2-Tutorial 5 Unit 2 2 Problems for each
tutorial
Tutorial 6-Tutorial 9 Unit 3 2 Problems for each
tutorial
Tutorial 10-Tutorial 13 Unit 4 1 Problem for each
tutorial
Tutorial 14 & 15 Unit 5 Application oriented
tutorial
III-EEE POWER
18 Apr 2017 5
ELECTRONICS
 Power Semiconductor
Devices
SCR (Silicon Controlled Rectifier)
TRIAC
BJT (Bipolar Junction Transistor)
MOSFET Metal Oxide Semiconductor Field
Effect Transistor
IGBT Insulated Gate Bipolar Transistor

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 SYMBOLS
SCR
(Silicon Controlled Rectifier)

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 TRIAC

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 BJT (Bipolar Junction Transistor)

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MOSFET
(Metal Oxide
Semiconductor Field Effect
Transistor)

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 IGBT
Insulated Gate Bipolar Transistor

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 THYSITOR

SCR
(Silicon Controlled
Rectifier)

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 Simplified model of a Thyristor
The silicon control rectifier (SCR)
consists of four layers of
semiconductors, which form NPNP
or PNPN structures have three P-N
junctions labeled J1, J2 and J3, and
three terminals.
The anode terminal of an SCR is
connected to the p-type material of a
PNPN structure, and the cathode
terminal is connected to the n-type
layer, while the gate of the SCR is
connected to the p-type material
nearest to the cathode

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 SCR - STRUCTURE
G a te C a th o d e

n
+
10
19
cm
-3
n
+
10
19
cm
-3
1 0 m

J3 - 17 -3
p 10 cm 3 0 -1 00 m

J2

n 10
13
-5 x 1 0
14
cm
-3 5 0 -1 0 0 0 m

J1
p
+
10
17
cm
-3
3 0 -5 0 m
19 -3
p 10 cm

Anode
18 Apr 2017 III-EEE/POWER ELECTRONICS 14
 Modes of operation
Forward Blocking Mode (Off State)
Anode-Positive, Cathode-Negative, Gate Zero
Potential, J1 & J3 Forward Biased, J2
Reverse Biased
Forward Conduction Mode (On State)
Increase the voltage across anode to cathode
beyond breakover voltage/ apply positive
pulse to gate.
Reverse Blocking Mode (Off State)

18 Apr 2017 III-EEE/POWER ELECTRONICS 15

 An SCR has two states i.e. either it does not conduct or it conducts
heavily. There is no state in between. Therefore, SCR behaves like a
switch.
There are two ways to turn on the SCR. The first method is to keep the
gate open and make the supply voltage equal to the breakover voltage. The
second method is to operate SCR with supply voltage less than breakover
voltage and then turn it on by means of a small voltage applied to the gate.
Applying small positive voltage to the gate is the normal way to close an
SCR because the breakover voltage is usually much greater than supply
voltage.
To open the SCR i.e. to make it non-conducting, reduce the supply voltage
to zero.

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 Principle of Operation
Forward Biased SCR

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 Circuit diagram of thyristor
(Driver)

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 VI Characteristics (Static)

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 VI Characteristics (Static)

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Breakover Voltage
It is the minimum forward voltage, gate being open, at which SCR starts
conducting heavily i.e. turned on.
Peak Reverse Voltage
It is the maximum reverse voltage (cathode positive w.r.t. anode) that can be
applied to an SCR without conducting in the reverse direction.
Holding Current
It is the maximum anode current, gate being open, at which SCR is turned
OFF from ON condition.
Forward Current Rating
It is the maximum anode current that an SCR is capable of passing without
destruction.
Circuit Fuse (I2t) Rating
It is the product of square forward surge current and the time of duration of
the surge i.e.,Circuit fusing rating =I2t
The circuit fusing rating indicates the maximum forward surge current
capability of SCR.

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 Two Transistor Model of
SCR

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 Two Transistor Model of
SCR

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 Turn ON & Turn OFF
Methods of SCR
Turn ON Methods Turn OFF Methods
forward-voltage triggering Natural Commutation
gate triggering Reverse Biased
dv/dt triggering
temperature triggering
light triggering

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 Switching Characteristics of SCR
(dynamic)

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Inference from the Characteristics,

Time tc must be greater than tq for reliable turn-off,

otherwise the device may turn-on at an undesired
instant, a process is called commutation failure.

SCRs with slow turn-off time (50-100s) are called

converter grade SCR.

SCRs with fast turn-off time (3-50s) are called

inverter grade SCR.

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 dv/dt & di/dt protection

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 Snubber Circuit of SCR
When the supply is closed to the circuit, sudden
voltage appears across SCR.
Now, as the thyristor current is zero it can be
considered as an open switch.
At this moment, the capacitor C behaves like a
short-circuit and therefore voltage across the SCR
is zero.
With the passage of time capacitor C gets charged
at a slow rate such that dv/dt across the capacitor
and therefore across SCR is less than the
specified maximum dv/dt rating of the device.
Thus the capacitor protects the SCR against high
voltages and high dv/dt.
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 Driver Circuit/Firing circuit

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 RC Firing circuit

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Parallel Operation of SCR

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 Thyristor ratings
Voltage ratings
Working peak off state forward voltage
Repetitive peak off state forward voltage
Non- Repetitive peak off state forward voltage
Working peak reverse voltage
Repetitive peak reverse voltage
Non-Repetitive peak reverse voltage
On state voltage
Gate trigger voltage
Voltage safety factor
Forward dv/dt rating

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 Current ratings
Average On state current
RMS On state current
Surge current rating
I2t rating
di/dt rating
Holding current
Latching current
Gate current

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 TRIAC
TRIode & AC

18 Apr 2017 III-EEE/POWER ELECTRONICS 34

 TRIAC
A Triac is another 4-layer, 3-terminal device similar
to the SCR.
The Triac can be triggered into conduction in either
direction.
There are four possible triggering modes for a Triac.

18 Apr 2017 III-EEE/POWER ELECTRONICS 35

 TRIAC

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 TRIAC - Structure

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 VI Characteristics
(Static)

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 VI Characteristics

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 Modes of Operation
1. MT2 is positive and Gate current is also positive.
2. MT2 is positive but Gate current is negative.
3. MT2 is negative but Gate current is positive.
4. Both MT2 and Gate current are negative.

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 Modes of Operation

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18 Apr 2017 III-EEE/POWER ELECTRONICS 42
1. MT2 is positive and Gate current is also positive.
When MT2 is positive with respect to MT1, junction
P1N1, P2N2 are forward biased but junction N1P2 is
reverse biased.
When gate terminal is positive with respect to MT1, gate
current mainly flows through P2 N2 junction.
When gate current has injected sufficient charge into P2
layer, reverse biased junction N1P2 breaks down.
As a result, triac starts conducting through P1N1P2N2
layers.

18 Apr 2017 III-EEE/POWER ELECTRONICS 43

 2. MT2 is positive but Gate current is negative.
when gate terminal is negative with respect to MT1, gate
current flows through P2 N3 junction and reverse biased
junction N1P2 is forward biased as in a normal thyristor.
As a result, triac starts conducting through P1N1P2N3
layers initially ( Pilot SCR).
Later the main structure P1N1P2N2 begins to conduct.
3. MT2 is negative but Gate current is positive.
The gate current Ig forward biases P2N2 junction.
When gate current has injected sufficient charge into P2
layer, reverse biased junction N1P1 breaks down.
As a result, P2N1P1N4 is completely turned ON.

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4. Both MT2 and Gate current are negative.
The gate current Ig flows from P2 to N3 as in normal
thyristor.
Reverse-biased junction N1P1 is broken and finally, the
structure P2N1P1N4 is turned ON completely.
The device is more sensitive under this condition.

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 TRIAC Phase Control
Circuit

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 Power Transistor
BJT
(Bipolar Junction
Transistor)
18 Apr 2017 III-EEE/POWER ELECTRONICS 47
 BJT
A Bipolar transistor is a three-layer, two junction npn
or pnp semiconductor device.
The term bipolar denotes that the current flow in the
device is due to the movement of both holes and
electrons.
It has three terminals named Collector(C), Emitter(E),
Base (B).

18 Apr 2017 III-EEE/POWER ELECTRONICS 48

 BJT (Bipolar Junction Transistor)

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 Steady State Characteristics

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 Input Output
Characteristics Characteristics

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 Switching Characteristics of NPN
Power Transistor

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 BJT - SAFE OPERATING AREA

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 MOSFET
Metal Oxide
Semiconductor Field
Effect Transistor
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 MOSFET

Enhancement Depletion
MOSFET MOSFET

n-Channel p-Channel n-Channel p-Channel

EMOSFET EMOSFET DMOSFET DMOSFET

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MOSFET
(Metal Oxide
Semiconductor Field Effect
Transistor)

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 MOSFET - STRUCTURE

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 MOSFET - Characteristics

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 MOSFET - Characteristics

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 MOSFET Driver Circuit

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 MOSFET - Safe Operating Area

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 IGBT
Insulated Gate Bipolar
Transistor

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 IGBT
Insulated Gate Bipolar Transistor

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 IGBT - Structure

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 Static Characteristics - Circuit

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 Static Characteristics

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 Switching Characteristics

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 IGBT - Safe Operating Area

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 THANK YOU

18 Apr 2017 III-EEE/POWER ELECTRONICS 72