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Unit1 Introduction (Power Electronics)


INTRODUCTION Power Electronics is a field which combines Power (Electric power), Electronics and Control systems. Power engineering deals with the static and rotating power equipment for the generation, transmission and distribution of electric power. Electronics deals with the study of solid state semiconductor power devices and circuits for Power conversion to meet the desired control objectives (to control the output voltage and output power). Control deals with the stability and response characteristics of closed loop systems using feedback on either a continuous or sampled-data basis.

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Power Electronics can be defined as the application of solid state power semiconductor devices for the control and conversion of electric power. Power Processor Controller Load measurement reference POWER INPUT POWER OUTPUT v i , i i v o , i o Source

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Importance of Power Electronics Industrial process requires control with higher productivity and improved quality factor. Energy savings by efficient usage of electricity. Environmentally clean source of electric power: photo-voltaic, wind, fuel cells


Scope of Power Electronics Power level (Watts) System 0.1 – 10 w Battery –operated equipment. Flashes/strobes 10 – 100 w Satellite power systems. Typical offline flyback supply 100 – 1 Kw Computer power supply , 1 – 10 Kw Hot tub 10 – 100 KW Electric Car eddy current braking 100 – 1 Mw Bus Micro - SMES 1 – 10 Mw SEMS 10 – 100 Mw Magnetic aircraft launch Big locomotives 100 – 1 Gw Power plant > 1 Gw sandy pond substation (2.2Gw)

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APPLICATIONS OF POWER ELECTRONICS Power supplies for communication system, telephone exchanges, satellite systems etc.. Speed control of motors which are used in traction drives, textile mills, rolling mills, cranes, lifts, pumps etc.. Power conversion for HVDC and HVAC transmission systems UPS and stand-by power supplies for critical loads such as computers medical equipments etc.. Power control in resistance welding, induction heating, electrolysis, process industry etc..


Aerospace: space shuttle power suplies, satilite power suplies. Commercial: Airconditioning, central refrigeration, computer, office equipment, and UPS. Industrial: Industrial lasers, rolling mills, and welding. Other APPLICATIONS:


Variac Failure Analysis

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Static switches Diode rectifiers Ac to Dc converters(Phase-controlled rectifiers) Dc to Dc convertors( Dc choppers) Dc to Ac convertors(Invertors) Ac to Ac convertors a). Ac voltage regulators b). Cycloconvertors TYPES OF POWER ELECTRONIC CONVERTERS

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A diode rectifier circuit converts an AC input voltage into a fixed dc voltage. The input voltage may be single phase or three phase. Applications: Battery charging, electro chemical processing, UPS. Diode rectifiers


These converts constant AC voltage to variable DC output voltage . These rectifiers use line voltage for their commutation, as such these are also called line-commutated or naturalley commutated AC to DC converters. Ac to Dc converters (Phase-controlled rectifiers)

Unit1 Introduction (Power Electronics):

12 AC-to-DC converter circuits Uncontrolled rectifiers (built with diodes) Fully-controlled rectifiers (built with SCRs) Semi-controlled rectifiers (built with both diodes and SCRs)


13 Uncontrolled Halfwave Rectifier

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14 Uncontrolled Fullwave Rectifier

Importance of Power Electronics:

15 Uncontrolled Bridge Rectifier

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16 A Controlled Rectifier


17 A Fully-controlled Rectifier


18 A Semi-controlled Rectifier

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19 A DC Power Supplier


20 A Car Battery Charger

Diode rectifiers:

21 Applications: Variable speed dc drives Battery chargers DC power supplies chemical industries.

Ac to Dc converters (Phase-controlled rectifiers) :

A DC chopper convertes fixed DC input voltage to a controllable DC output voltage. The chopper circuits require forced or load commutation to turn off the thyristors for low power circuits, thyristors are replaced by power transistors. Classification of chopper circuits is dependent upon the type of commutation and also on the direction of power flow. Dc to Dc converters( Dc choppers)

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23 Choppers ( or switch-mode power supplies ) DC-to-DC converter circuits Step-down Chopper (switch-mode power supply) Step-up chopper Fly-back converter Resonant converter

Uncontrolled Halfwave Rectifier :

24 Switched-mode Power Supply

Uncontrolled Fullwave Rectifier :

25 One-Quadrant Chopper DC Drive

Uncontrolled Bridge Rectifier :

26 Applications: DC drives Battery chargers DC power supplies Trolley trucks Battery driven vehicles.

A Controlled Rectifier :

An inverter convertes fixed DC voltage to a variable AC voltage. The output may be a variable voltage and variable frequency , these converters use line,load or forced commutation for turn off tryristors. Use: Induction motor, induction heating, UPS, HVDC. Dc to Ac converters(Inverters)

A Fully-controlled Rectifier :

These convert the fixed AC input voltage nto variable AC output voltage. Two types: A) AC voltage regulators: These converter circuit convert fixed AC voltage directly to a variable AC voltage at the same frequency . B) Cycloconverters: These circiuts convert input power at one frequency to output power at different frequency through one stage conversion . AC To AC converters

A Semi-controlled Rectifier :

29 Cycloconverter Application

A DC Power Supplier:

30 Applications: The speed control of an ac traction motor Ship propulsion drives Rolling mill drives Mine winders

A Car Battery Charger:

Diagram Block of Converters

Dc to Dc converters( Dc choppers):

The power semiconductor devices can be divided broadly into five types: Power Diodes. Thyristors. Power MOSFET’s.

Choppers (or switch-mode power supplies ):

Power Diodes

Switched-mode Power Supply:

Power Semiconductor D iode Classifications Power diodes are classified according to Constructional features, Type of material used in doping process, Power ratings, Switching characteristics, Reverse recovery time, Application wise General purpose power diodes Fast recovery power diodes Schottky power diodes

One-Quadrant Chopper DC Drive :

General Purpose Power diode A general purpose power diode is a typical two-terminal pn-junction device. General purpose power diode are manufactured by Diffusion process. Used in low power applications where recovery time ( slow response) is not an issue. diode rectifiers converters for a low input frequency up to 1 KHz. Line commutated converters Alloyed type rectifier diodes are used in welding power supplies.

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On state voltage: very low (below 1V) Large t rr (about 25us) (very slow response) Very high current ratings (more than 3kA up to 5kA) Very high voltage ratings (50V to 5kV) Used in line-frequency (50/60Hz) applications such as rectifiers

Dc to Ac converters(Inverters):

Low recovery time (faster switching) , normally less than 5uS . Current ratings from 1A to 1000A. Voltage ratings from 50V to 3kV. For high rating (more than 400V), these diodes are manufactured by DIFFUSION process Recovery time is controlled by Platinum or Gold diffusion For less than 400V ratings, EPITAXIAL diodes provides very fast recovery time. Epitaxial diodes have a very narrow base width resulting in recovery time of about 50nS.

AC To AC converters:

Schottky Power diodes Schottky diode is a semiconductor diode with a low forward voltage and a very fast switching action . Reverse recovery time is almost zero (in ideal conditions). Schottky diode use a Metal–Semiconductor junction as Schottky barrier, instead of a semiconductor junction in a conventional diodes. Schottky diode is a majority carrier semiconductor device. When a Schottky diode is forward biased, free electrons on the N-side gain enough energy and travel to the metal side and cause a forward current, since the metal does not have any boles, there is no charge storage, which results in ZERO Reverse recovery time.

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Power Schottky diodes are available up to forward current ratings of 300A. The main limitation of Schottky diode is their low reverse voltage ( Limited blocking voltage) in order of 30 to 100V. Power rating are in the range of 100V/300A. Very low forward voltage drop (b arrier potential is of 0.15 to 0.45V ) typically 0.3V. Used in low voltage, high current such as switched mode power supplies. The operating frequency may be as high 100-300 kHz as the device is suitable for high frequency application.

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The Thyristor’s can be subdivided as: Forced-commutated Thyristors (Inverter grade Thyristors ) Line-commutated Thyristors (converter-grade Thyristors ) Gate-turn off Thyristors (GTO). Reverse conducting Thyristors (RCT’s). Static Induction Thyristors (SITH). Gate assisted turn-off Thyristors (GATT). Light activated silicon controlled rectifier (LASCR) or Photo SCR’s. MOS-Controlled Thyristors (MCT’s).

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Thyristors: Are 4-layer silicon semiconductors. Use low input power to control large load currents. Are very common in industrial power & motor control. Are inherently nonlinear devices. Have two states: ON and OFF. A (Anode) K (Cathode) + V ak _ I a Thyristor: Symbol G (Gate) I g Static V-I characteristic of an SCR

Power Diodes:

Two-transistor model of an SCR SCR (hokey-puck-type) on power pack kits SCR (stud-type) on air-cooled kits

Power Semiconductor Diode Classifications:

TURN ON: If the forward breakover voltage ( V bo ) is exceeded, the SCR “self-triggers” into the conducting state. The presence of gate current will reduce V bo . “Normal” conditions for thyristors to turn on: The device is in forward blocking state ( i.e V ak is positive) a positive gate current ( I g ) is applied at the gate. Once conducting, the anode current is latched. V ak collapses to normal forward volt-drop, typically 1.5-3V.

General Purpose Power diode :

TURN OFF: In reverse -biased mode, the SCR behaves like a diode. Thyristor cannot be turned off by applying negative gate current. It can only be turned off if I a goes negative (reverse). This happens when negative portion of the of sine-wave occurs (natural commutation). Another method of turning off is known as “forced commutation”, The anode current is “diverted” to another circuitry

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THYRISTOR CONDUCTION + v s _ i g i a w t v o a i g w t w t v s

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Characteristics of DIAC

Schottky Power diodes:

Phase Control Thyristors

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Metal Oxide Silicon Field Effect Transistor ( MOSFET ) Can be turned “ON”and “OFF” by relatively very small control signals. Operated in SATURATION and CUT-OFF modes only. No “linear region” operation is allowed due to excessive power loss. In general, power transistors do not operate in latched mode.

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I D V DS + V GS _ + V DS _ I D D (drain) G (gate) S (source) + V GS _ MOSFET: symbol ( n -channel) v-i characteristics Turning on and off is very simple. To turn on: V GS = +15V To turn off: V GS = 0 V to turn off. Gate drive circuit is simple Ratings: Voltage V DS <500V, current I DS <300A. Frequency f >100KHz. For some low power devices (few hundred watts) may go up to MHz range.

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MOSFET characteristics Basically low voltage device. High voltage device are available up to 600V but with limited current. Can be paralleled quite easily for higher current capability. Internal (dynamic) resistance between drain and source during on state, R DS(ON), , limits the power handling capability of MOSFET. High losses especially for high voltage device due to R DS(ON) . Dominant in high frequency application (>100kHz). Biggest application is in switched-mode power supplies.

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Insulated Gate Bipolar Transistor (IGBT) Combination of BJT and MOSFET characteristics. 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). Ratings: Voltage: V CE <3.3kV, Current,: I C <1.2kA currently available. Latest: HVIGBT 4.5kV/1.2kA. Switching frequency up to 100KHz. Typical applications: 20-50KHz.

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IGBT: symbol + V CE _ I C C (collector) G (gate) E (emitter) + V GE _ V CE V GE v-i characteristics V CE (sat) IGBT-Module type: Full bridge and three phase

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10Hz 1kHz 1MHz 100kHz 10MHz 1kW 100kW 10kW 10MW 1MW 10MW 1GW 100W MOSFET IGBT GTO/IGCT Thyristor

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High efficiency High reliablity Long life Less maintanence Fast dynamic responce Small size Less weight Advantages:


Generate harmonics Input power factor is low(ac/dc or dc/ac) Power regenaration is difficult High cost Disadvantages:

Characteristics of DIAC:

8/17/2013 60 Devices Symbols and Characteristics

Phase Control Thyristors:

8/17/2013 61 Devices Symbols and Characteristics

Metal Oxide Silicon Field Effect Transistor (MOSFET):

8/17/2013 62 Devices Symbols and Characteristics

PowerPoint Presentation:

8/17/2013 63 Devices Symbols and Characteristics

MOSFET characteristics:

8/17/2013 64 Devices Symbols and Characteristics

Insulated Gate Bipolar Transistor (IGBT):

8/17/2013 65 Control Characteristics of Devices

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8/17/2013 66 Control Characteristics of Devices

PowerPoint Presentation:

8/17/2013 67 Control Characteristics of Devices

PowerPoint Presentation:

8/17/2013 68 Control Characteristics of Devices



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