INTRODUCTION TO POWER ELECTRONICS

Power Electronics is a field which combines Power (electric power), Electronics and Control systemsPower 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).

Power Electronics???Power electronics may be defined as the subject of applications of solid state power semiconductor devices (Thyristors) for the control and conversion of electric power.

BRIEF HISTORY OF POWER ELECTRONICS

The first Power Electronic Device developed was the Mercury Arc Rectifier during the year 1900. Then the other Power devices like metal tank rectifier, grid controlled vacuum tube rectifier, ignitron, phanotron, thyratron and magnetic amplifier, were developed & used gradually for powercontrol applications until 1950.

The first SCR (silicon controlled rectifier) or Thyristor was invented and developed by Bell Labs in 1956 which was the first PNPN triggering transistor.The second electronic revolution began in the year 1958 with the development of the commercial grade Thyristor by the General Electric Company (GE). Thus the new era of power electronics was born. After that many different types of power semiconductor devices & power conversion techniques have been introduced.

POWER ELECTRONIC APPLICATIONS

COMMERCIAL APPLICATIONSHeating Systems Ventilating, Air Conditioners, Central Refrigeration, Lighting, Computers and Office equipments, Uninterruptible Power Supplies (UPS), Elevators, and Emergency Lamps.DOMESTIC APPLICATIONSCooking Equipments, Lighting, Heating, Air Conditioners, Refrigerators & Freezers, Personal Computers, Entertainment Equipments, UPS.

POWER ELECTRONIC APPLICATIONS

INDUSTRIAL APPLICATIONSPumps, compressors, blowers and fans. Machine tools, arc furnaces, induction furnaces, lighting control circuits, industrial lasers, induction heating, welding equipments.AEROSPACE APPLICATIONSSpace shuttle power supply systems, satellite power systems, aircraft power systems.

POWER ELECTRONIC APPLICATIONSTELECOMMUNICATIONSBattery chargers, power supplies (DC and UPS), mobile cell phone battery chargers.TRANSPORTATIONTraction control of electric vehicles, battery chargers for electric vehicles, electric locomotives, street cars, trolley buses, automobile electronics including engine controls.

POWER ELECTRONIC APPLICATIONSUTILITY SYSTEMSHigh voltage DC transmission (HVDC), static VAR compensation (SVC), Alternative energy sources (wind, photovoltaic), fuel cells, energy storage systems, induced draft fans and boiler feed water pumps.

POWER SEMICONDUCTOR DEVICES

Power Diodes.Thyristors.Power BJTs.Power MOSFETs.Insulated Gate Bipolar Transistors (IGBTs).Static Induction Transistors (SITs).

Thyristors Types

Forced-commutated Thyristors (Inverter grade Thyristors)Line-commutated Thyristors (converter-grade Thyristors)Gate-turn off Thyristors (GTO).Reverse conducting Thyristors (RCTs).Static Induction Thyristors (SITH).Gate assisted turn-off Thyristors (GATT).Light activated silicon controlled rectifier (LASCR) or Photo SCRs.MOS-Controlled Thyristors (MCTs).

Types of Power Electronic ConvertersDiode Rectifiers It converts AC input voltage into fixed DC voltage . The input voltage mat be single phase or three phase AC supply.AC to DC converters/Phase controlled converters The phase controlled rectifier provides a variable d.c. load voltage from a fixed voltage and frequency a.c. source.

Types of Power Electronic ConvertersDC to DC Converters / DC Choppers The D.C. to D.C. chopper provide variable D.C. load voltage from a fixed D.C. source voltageDC to AC Converters / Inverters The d.c. to a.c. inverters produce a variable a.c. voltage and requency from a fixed voltage d.c. source.

Types of Power Electronic ConvertersAC to AC Converters These provide variable A.C. load voltage from a fixed A.C. source voltage

They are of two types AC voltage controller Cycloconverter

(DC to DC CONVERTERS)

The functions of dcdc converters to convert a dc input voltage into a dc output voltage to regulate the dc output voltage against load and line variations; to reduce the ac voltage ripple on the dc output voltage below the required level;to provide isolation between the input source and the load (isolation is not always required);to protect the supplied system and the input source from electromagnetic interference (EMI);to satisfy various international and national safety standards.

Main TypesThe dcdc converters can be divided into two main types: 1, Hard-switching pulse width modulated (PWM) converters, and 2, Resonant and soft-switching converters.

The PWM convertersThe PWM converters have been very popular for the last three decadesThe output voltage of dc choppers is controlled by adjusting the on time of a switch which in turn adjusts the width of a voltage pulse at the output.This is so called pulse-width modulation (PWM) control. The dc choppers with additional filtering components form PWM dcdc converters.

Advantages of PWM convertersAdvantages of PWM converters include low component count, high efficiency, constant frequency operation,Relatively simple control and commercial availability of integrated circuit controllers, and ability to achieve high conversion ratios for both step-down and step-up application

Disadvantage of PWM convertersA disadvantage of PWM dcdc converters is that PWM rectangular voltage current waveforms cause turn-on and turn-off losses in semiconductor devices which limit practical operating frequencies to a megahertz range. Rectangular waveforms also inherently generate EMI.

Basic DC Choppers

Basic dcdc converter topologiesFour basic dcdc converter topologies presented in Sections are 1, buck, 2,boost,3, buckboost, and4, C` uk converters.

Buck converterThe step-down dcdc converter, commonly known as a buck converterDuring ON time VL= VS-VODuring OFF time VL= -VO

Waveform

Boost ConverterThe step-up dcdc converter, commonly known as a boost converterDuring ON time VL= VSDuring OFF time VL= VS-VO

Waveform

Buck Boost ConverterOutput is either higher or lower than the input voltageDuring ON time VL= VSDuring OFF time VL= -VO

Wave form

Cuk ConverterOutput is either higher or lower than the input voltageDuring ON time VL1= VS VL2= VC1-VODuring OFF time VL2= -VO VL1= VS-VO

Waveforms