Evolution of Power Electronics Engineering

A. M. Haque Power Electronics Department, Lukhdhirji Engineering College - Morbi.

haqueanwarul@yahoo.co.in

M. J. Vadhavaniya Inst. & Control Engineering Department, National Institute of Technical Teacher’s Training & Research - Chandigarh.

profmjv@yahoo.com

M. V. Makwana Power Electronics Department, Lukhdhirji Engineering College - Morbi.

shafimakwana@indiatimes.com

Shimi S. L. Inst. & Control Engineering Department, National Institute of Technical Teacher’s Training & Research - Chandigarh.

Shimi.reji@gmail.com

ABSTRACT: Power Electronics is the technology associated with the efficient solid-states conversion, control and conditioning of

electrical power. It has gone through more than four decades of intense technological revolution (a silent one, being mostly

unnoticed by the public and the decision makers!). Since the development of Thyristor it has emerged as a key technology in all the

areas of power processing viz, generation, transmission and utilization. The evolution of Power Electronics has closely followed by

the enhancement of modern power semiconductor devices, which are closely linked to the advance in fabrication techniques for

power integrated circuits and the packaging concepts. Power electronics is the field of electronics which deals with conversion,

control and switching of electrical energy for efficiently utilization of power and playing a major role in revolutionizing the industrial

processes. It provides the essential link between micro-level of electronics controllers and the mega- watt level of industrial power.

Power Electronics has gained the momentum since late1980s and early 1990s. Within the next 20 years, power electronics will shape

and condition the electricity somewhere between its generation and all its users. Power electronics, therefore, should now be

considered as a full-fledged and independent technological discipline, and should be placed with full dignity in all the university

curricula.

1.1 Introduction to Power Electronics

Power electronics is the technology associated with

the efficient solid state conversion, control and conditioning of electrical power. The advent of Thyristor

has revolutionized the art of electric power conversion and

its control and since then it has emerged as key technology

in all the areas of power processing, viz. generation,

transmission and utilization.

The fundamental of power electronics are well

established and they do not change rapidly. How-ever, the

device characteristics are continuously being improved

and new devices are added. Presently, power electronics

uses, besides SCRs, other power semiconductor devices

such as GTOs, BJTs, IGBTs, power MOSFETs and more

recently MCTs. With the emergence of the modern power devices, we have achieved saving in cost, space and

energy, reduction in maintenance, improvement of

reliability, high quality performance , complete

controllability with maximum flexibility and clean

environment. With evolution of micro-electronics and

micro-computers, power electronics is now a multi-

disciplinary technology.

Power electronics occupies an indispensable position

in the field of battery charging, UPS, electroplating,

electrolysis, galvanization and welding. It also plays an

important role in all sorts of electric drives and lighting

control. Feed drives of machine tools, multi motor drives

in rolling mills, spinning machine, wire drawing mills,

lifts and many other drives may be given the required

characteristics by means of Power electronic control.

Electronically generated high-frequency energy offers

possibilities in the wood working and plastic industries for

economical production of furniture, plywood and plastic

articles.

No boundaries can be earmarked for the application

of Power Electronics, especially with the present trend of integrated design of power semiconductor devices, micro

processors and controlled equipment. Flexible alternating

current transmission system composed of static devices

used for HVAC transmission of electrical energy. The

power rating of Power-electronic systems, range from a

few watts in lamps to several hundred mega-watts in

HVDC transmission systems. It is believed that within the

span of 10-years, almost 80% of the electric power

consumed in utility systems will passed through Power

electronics and this figure will eventually reach 100% in

the future.

• Chronology of Power Electronic:

1891 – Ward – Leonard dc motor speed control

1897 – Development of three phase diode bridge rectifier

(Graetz Circuit).

1902 - Mercury Arc Rectifier by Peter Cooper Hewitt

(U.S.A) 1904 - Vacuum diode by J.A.Fleming.

1906 - Vacuum triode by de-Forests.

1909- Steel tank mercury arc rectifier by B.Schaefer

1914-Controlled mercury arc rectifier by Langmuir

1926 – Hot cathode Thyratron

1933 – Invention of Ignitron Rectifier

1948 - Invention of Transistor.

1954 - Invention of Germanium power diode

1957 - Invention of SCR.

1960 - Use of mercury arc converter for HVDC

1971- Vector Control of AC Motor is introduced 1975- Invention of Giant Power- BJT by TOSHIBA.

1978 – Invention of Power – MOSFET

1980 – High Power GTO

1983 - IGBT Introduced

1987 – Fuzzy Logic applied in Power Electronics

1991 – ANN applied to DC Motor Drive

1996- Forward Blocking IGCT introduced by ABB.

• Revolutionary StepsRevolutionary StepsRevolutionary StepsRevolutionary Steps in in in in Power EPower EPower EPower Electronicslectronicslectronicslectronics is is is is depicted in following chart.depicted in following chart.depicted in following chart.depicted in following chart.

1.2 Power Electronic System

As shown in fig. 1 main power source may be an AC

supply or DC supply system. The output from the Power

electronic circuit may be variable DC or AC voltage, or it

may be a variable voltage and frequency. In general, the

output of a power electronics circuit depends upon the

requirements of the load.

The feedback component measures a parameter of the

load, and compares it with the command in control unit.

The difference of the two passes through the digital circuit

which finally control the instant of turn-on of

semiconductor devices forming the solid-state power

converters system. In this manner, behaviour of the load

circuit can be controlled as desired, over a wide range.

THYRISTOR

CONVERTER

CIRCUIT

DIGITAL CIRCUIT

CONTROL UNIT

LOAD

FEED BACK

SIGNAL

MAIN POWER

SOURCE

COMMAND

Fig.1. Power Electronic System.

• Diversified Applications:-

Residential: Air-conditioning; Cooking; Lighting; Space

heating; Refrigerators; Electric door opening; Dryers; Fans; Personal computer; Vacuum cleaners; Washing &

sewing machine; Light dimmers; Food mixture; Food

warmer trays; Electronic Blankets.

Commercial: Advertising; Heating; Air-conditioning;

Central refrigeration; Computer & Office equipment;

UPS; Elevator; Light dimmer & flashers.

Aerospace: Space shuttle power supplier; Satellite power

supplies; Air craft power system.

Industrial: Arc furnace; Induction furnace; Blowers &

fans; Pumps & compressors; Industrial lasers; Transformer

tap changer; Rolling mills; Textile mills; Cement mills; Sugar mills; Coal mining; Welding; Excavators.

Transportation: Traction control of electric vehicle;

Electric locomotive & battery charger; Street cars, trolley

buses, subways.

Tele-communication: Battery charger; DC power

supplies; UPS.

Utility System: HVDC transmission; HVAC transmission;

Excitation systems; Static circuit breaker; Fans and boiler;

Feed pumps; Supplementary energy system [1].

1. 3 Thyristor – Need of New Era

Until 1956, the application of semiconductor was

confined to low power circuits and electronic engineering

was also called as “light current engineering”. In

September 1956, four engineers of Bell telephone

laboratory, USA, published a paper entitled “PNPN transistor switches” in the proceedings of the institute of

Radio Engineers. This paper triggered intensive research

on PNPN device. In 1957, Gordon Hall of General

Electric Co. U.S.A developed the three terminal PNPN

silicon based semiconductor device called silicon

controlled rectifier (SCR) having characteristics similar to

that of thyratron gas tube and structure wise it visualized

as consisting of the two transistors( a p-n-p and an n-p-n,

inter-connected to form a regenerative feedback pair). The name THYRISTOR is derived by a combination of

the capital letter from THYRatron and transISTOR.

Continuous modification and improvement in its design as

well as fabrication techniques have made it more and more

economical and suitable for various control purposes.

Later on, many other power devices having characteristics

similar to that of an SCR were developed. Thyristor is a

general name given to a family of power semiconductor

switching devices, all of which are characterized by a

bistable switching action depending upon the PNPN

regenerative feedback.

Thyristor is a semiconductor device having three or

more junctions; four or five p and N semiconductor layers;

and 2, 3, or 4 terminals. Its maximum flexibility in

operation; faster dynamic response and lower acoustic

noise are the added advantages. This device has

revolutionized the art of solid state power conversion &

control.

The Other Members of Thyristor Family Are:

♦ SCS (Silicon Controlled Switch)

♦ LASCS (Light Activated SCS)

♦ LASCR (Light Activated SCR)

♦ PUT (Programmable Unijunction Transistor)

♦ LAPUT (Light Activated PUT)

♦ SUS (Silicon Unilateral Switch)

♦ SBS (Silicon Bilateral Switch)

♦ ASBS (Asymmetrical SBS)

♦ LAS (Light Activated Switch)

♦ Diac , Triac

Thyristor Has Replaced Industrial Devices Like:

� Thyratron

� Mercury arc converters

� Ignitrons

� Magnetic amplifier

� Motor Generator Sets

� Auto Transformers

� Induction regulator

� Contactors

� Motor starter

� Rheostats

� Mechanical speed changers � Relays , Fuses and many more others.

1.3. 1 Thyristor Manufacturing Process:

Depending upon the method of manufacturing process thyristors are classified into three types.

- Alloy diffused

- All diffused or semi-planar

- Planar

1.3.2 Principle of operation

If a positive voltage is applied to anode with respect

to cathode and with gate not connected to a triggering voltage source, a small forward leakage current flows

which increases with voltage until turn-on is initiated by

avalanche action. The corresponding voltage is called

forward break over voltage (V FBO). The voltage across the

thyristor then falls to on-stage voltage V T. when trigger

voltage applied to the gate, break over voltage is reduced

to a minimum on-stage voltage, and if the current through

the device is more than latching current the thyristor

continues to conduct even if the trigger voltage is

removed. Its main power connection is made to the anode

and the cathode, and turn-on signal is applied between the

gate and cathode.

Thyristor has three basic modes of operation:

Reverse blocking

Forward blocking

Forward conduction

In forward conduction mode, with forward bias voltage, a

thyristor can be made to conduct by any of the four

techniques:

Exceeding forward break over voltage.

Gate triggering.

dv /dt turn on.

Irradiation of gate cathode junction.

In general practice gate triggering technique is applied for

normal operation of thyristor.

1.4 Thyristor categories

The great strides taken in the industrial applications of

power electronics during recent years have demonstrated

that this versatile tool can be of great importance in

increasing production, efficiency and control. The power

electronic circuits which are also known as

``Thyristorised power controller” generally classified into

the following five broad categories [2].

1.4.1 AC – DC Converter

These controllers convert fixed ac voltage to a

variable dc output voltage. There controller circuits use

line voltage for their communication. Hence, they are also called as line commutated or naturally commutated

recifiers.

1.4.2 DC – AC Converter

An inverter converts a fixed dc voltage to an ac voltage of variable frequency and of fixed or variable magnitude.

This type of controllers use forced communication

methods to turn-off the thyristors.

1.4.3 DC – DC Converter

A chopper converts fixed dc input voltage to variable

dc output voltage. Therefore, choppers are also referred

as dc to dc converters. Forced commutation is used to

turn-off the thyristors.

1.4.4 AC – AC Converter

These circuit converters input power at one frequency

to output power at a different frequency through one stage

conversion. The Cyclo- convertors are most commonly

used for obtaining low frequency ac voltage.

1.4.5 AC Voltage controllers

These circuits convert a fixed ac voltage directly to a

variable ac voltage at the same frequency using line

communication.

1.5 Application Areas of Different Thyristor

Categories is as shown in Table 1. [3].

1.6 Enhancement in Power Electronic Devices

Evolution of microelectronics and microcomputers

has advanced the Power electronics to be a complex multi-

disciplinary technology by the synthesis of the following

diverse technological disciplines.

Power electronics devices, components and materials

Converter circuit topologies

Control of the motor drives and power systems

Control theory-analysis and simulation

Analog and digital electronics

Micro-electronics/micro-computers/digital-signal

processors

Computer aided simulation and design tools

Application specific integrated circuits (ASIC)

Each of these component disciplines are developing

very rapidly and providing a tremendous challenge to the

research and development in power electronics. The

present power electronic devices use exclusively silicon as

the basic material. However, new type of materials like

gallium arsenide, silicon carbide and diamond show

tremendous promise for future generation of devices. Silicon carbide and diamond in synthetic thin film-form

are particularly interesting because of their large band

gape, high carrier mobility and high electrical and thermal

conductivity.

A diamond power – MOSFET for example, can have

sixth order magnitude of power, fifty (50) times higher

frequency, less conduction drop and 6000 C junction

temperature compared to a silicon power device.

It is seen that the trends are in the invention of new and

improved switching devices. In new enhanced power

integrated circuits (PICs), the control and Power Electronics are integrated on the same chip called “Smart

Power”. This results in reduction in cost, size, EMI

(Electro-magnetic interference) and improvement in

reliability. A PIC is often differentiated from a high

voltage integrated circuit (HVIC) where the voltage is

high but current is small. Recently a large family of new

enhanced PICs that include power-MOSFET smart switches, half bridge inverters, two-phase step motor

drives, one quadrant choppers for the dc motor drives,

three-phase diode rectifier, PWM Inverters, application-

specific PICs (ASPICs) have become available.

1.6.1 Power Electronic Devices

Power electronic devices operating in the switching

mode from the heart of the power electronic drives and

they have gone through a dynamic revolution in recent

time. Since the birth of SCR, gradually other devices such

as Triac, light-activated SCR (LASCR), inverter-grade fast

thyristor, asymmetrical SCR (ASCR) reverse-conducting

thyristor (RCT), gate-assisted turn-off thyristor (GATT)

were introduced. during the last 10 years , SCR have been

challenged by the enhancement of the self- commutating

devices like Gate Turn Off Thyristor(GTOs), Power- BJTs (Bipolar Junction Transistor), Power-MOSFETs(Metal

Oxide Semi-conductor field Effect Transistors), IGBTs

(Insulated Gate Bipolar transistors) etc. Presently Power

Electronics uses, besides SCRs, other power semi-

conductor devices such as GTOs, Power BJTs, Power

MOSFETs, IGBTs and more recently MCTs (MOS –

Controlled Thyristors) [4].

1.6.2 Power Devices Performance Parameters

Power electronic devices are used as a switch should

ideally possess the following performance parameters.

Unlimited voltage and current ratings.

Instant turn-on and turn-off times.

Zero leakage current.

Zero switching and conduction losses.

Zero gate/base drive power requirement

Ability to withstand current over-loads and voltage

transients.

Ease of protection against spurious turn-on and fault

conditions,

Low cost and ease of assembly

1.6.3 Selection of Switching Devices

In actual practice, none of the power electronic device

satisfies the entire performance parameter requirement.

Many devices have relative merits which make them

suitable for one application than other. In some areas there

is overlapping options available for the choice of devices.

The important criteria in selecting devices for circuit

application mostly include the parameters of the rating,

switching times, switching and conduction losses, control strategy and finally the cost of the circuit.

1.6.4. Modern Power Devices

The development of power semiconductor devices

can be related to the handling of high voltage and currents

as dictated by the load and supply constraints. The

evolution of power electronics has closely followed by the

enhancement of power semiconductor devices, since the

invention of transistors and Thyristors. Progress in their

growth has been closely linked to the advances in

fabrication techniques for integrated circuits and in

packaging concepts. A variety of these devices are presently available covering a large power spectrum

ranging from a few watts to several hundreds of kilowatts.

Presently available power devices can be classified

into three groups according to their degree of

controllability:

• Diodes-on and off states controlled by power circuits.

• Thyristors-turned-on by a control signal but must be

turned-off by the power circuit.

• Controllable switches- turned on & off by control

signals.

The controllable switch category includes several

power devices such as Bipolar Junction Transistors (BJT),

gate turned off Thyristors (GTO), Power-MOSFET,

IGBT, and SIT/SITH and MCT. A concise discussion is

cited over here one after another [5],[6],[7].

Table 2- Modern Power Devices with Ratings

Sr.

No.

Power

Semiconductor

Devices

Maximum

Voltage in

(volt)

Maximum

Current in

(Amp)

Maximum

Frequency

in (Hz)

1 Power Diode 3000 3500 1

2 Thyristor 6000 3500 1

3 SITH 4000 2200 20

4 GTO 4000 3000 10

5 Triac 1200 300 0.4

6 BJT 1200 400 10

7 Power MOSFET 1000 50 100

8 SIT 1200 300 100

9 IGBT 1200 400 20

10 MCT 1000 100 20

Table-3 Modern Power Devices with Conditions

Device Switching Condition

SCR,GTO ,SITH,MCT Pulse gate signal for Turn- ON state

BJT, Power-MOSFET

IGBT,SIT

Continuous gate signal in Turn-ON

state

SCR,GTO Withstand Bipolar voltage

BJT, Power-MOSFET

IGBT,MCT Withstand uni-polar voltage

TRIAC, RCT Bi-directional current devices

Power Diode ,Power-

MOSFET,SCR,GTO

BJT,IGBT,SITH,SIT,MCT

Uni-directional current devices

1.7 Modern Control of Power Electronics

In the Performance of a power electronic system,

control plays a key role. The recent advent of

microelectronic components and chips has reduces he size

and cost to the controller and has improved the performance.

In a particular power electronic system, the control used

depends on the desired system performance, the driving load

and the converter topology [8].

1.7.1 Microcontroller and Microcomputer Control

Microcontroller and microcomputer control improves

system reliability, eliminates electromagnetic interference

and drift problems and provides significant const reduction

in control hardware in addition to hierarchical control

capability, information storage, monitoring and diagnostics. A micro-controller is a single integrated circuit,

commonly with the following features:

• central processing unit - ranging from small and

simple 4-bit processors to complex 32- or 64-bit

processors.

• volatile memory (RAM) for data storage.

• ROM, EPROM, EEPROM or Flash memory for

program and operating parameter storage.

• discrete input and output bits, allowing control or

detection of the logic state of an individual package

pin.

• serial input/output such as serial ports (UARTs).

• other serial communications interfaces like I²C, Serial

Peripheral Interface and Controller Area Network for

system interconnect.

• peripherals such as timers, event counters, PWM

generators, and watchdog.

• clock generator - often an oscillator for a quartz

timing crystal, resonator or RC circuit.

• many include analog-to-digital converters, some

include digital-to-analog converters.

• in-circuit programming and debugging support [8].

The advance microcomputer functions in control may

be on-line estimation of parameter and state, performance

optimization, fault tolerant control, optimal and adaptive

control, expert and fuzzy control, etc [9].

1.7.2 FPGA and VLSI Control

FPGA stands for Field Programmable Gate Array

(FPGA). It is an integrated circuit that can be configured

by the user in order to implement digital logic functions of varying complexities. FPGA can be very effectively used

for control purposes in processes demanding very high

loop cycle time. The implementation of a digital controller

in a FPGA can be parallel, resulting in very high speeds of

operation [10].

A VLSI chip can be defined as a chip typically

containing more than 100 000 devices. This chip works in

conjunction with other VLSI chips or works alone. The

VLSI control have advantages like improved speed, higher

reliability, parallel signal processing, low power

consumption and low cost for high volume applications

[9].

1.7.3 Artificial Intelligence (AI) Control

In artificial intelligence, an expert system is a

computer system that emulates the decision-making ability

of a human expert. Expert systems are designed to solve

complex problems by reasoning about knowledge, like an

expert, and not by following the procedure of a developer

as is the case in conventional programming [11].

Fuzzy logic is a mathematical system that analyzes

analog input values in terms of logical variables that take

on continuous values between 0 and 1 [11]. The fuzzy

control is more suitable in the process where the model is

ill defined or complex, has high nonlinearity with a

parameter variation problem and feedback sensor signals

are imprecise. Thee fuzzy control and expert system

techniques have hardly been applied in power electronics

systems [9]. The term Neural network has been derived from the

analogy of the nervous system of the human brain in

which neurons are interconnected by input dendrites and

output axons. A neural computing network can be realised

as distributed computing system with parallel-input

parallel-output where a set of first order nonlinear

differential equations are solved parallel. The neural

network algorithm can be implemented on a cluster of

DSP’s or a special purpose analog computer [9].

1.8 Application

1.8.1 Power Electronic Drives

Solid state power electronics has opened up new vistas

in the motor control. Thyristor drives has been widely used

throughout industry and, for normal industrial applications,

a dc motor powered by a Thyristor converter is now a

popular choice as a variable speed drive. The static

variable-frequency ac drive uses a cage-rotor induction

motor or synchronous reluctance motor powered by a static

frequency converter. This gives a versatile and robust

variable-speed machine which has the advantage over

conventional variable speed drives of higher accuracy,

better reliability, reduced maintenance and higher

efficiency. The main objection to the static ac drive has

been on economic grounds, since the cost of the static

frequency converter has often been considered excessive.

However, power semiconductor prices are steadily decreasing as production volume grows and manufacturing

techniques improve, and the future of the solid-state ac

drive is assured.

The replacement of dc machine by an ac motor also

has economic benefits, since increasing labour and

material costs are weakening the position of the dc motor

with its elaborate commutator construction. The

disadvantages of mechanical commutation are well known

and the Thyristor controlled dc motor drive also produces a

greater degree of ac mains distortion than certain types of

solid-state ac motor drive.

Because of these factors, and a growing awareness of

the performance possibilities, a more widespread

application of the solid-state ac drive is inevitable. When extremely precise speed control or precise speed matching

is demanded, the solid-state ac drive is being used to

provide standards of accuracy and reliability which have

never before been achieved. The improving economic

position of the solid-state ac drive also means that, in the

future, it will be increasingly considered for general -

purpose applications [3],[4].

1.8.2 Power Electronics on the Pavement of HVDC

Transmission

Large consumption of electrical energy is an index of

the industrial growth and prosperity of a nation. The

demand of electrical power is increasing through out the

world and in developing country like India, the demand of

electrical power is doubling every five to ten years. In

some countries excellent hydro-power sites are available, but at far distance from load centres. To avoid pollution

hazards and also from economical consideration, the

thermal power plants are now located near mouth of the

coal mines. All these problems involve the transmission of

large block of power over long distances which can be

done more economically by using H.V.A.C. transmission

lines. However, Voltage regulation associated with

reactive power balance, Steady state, Transient state &

Dynamic stability are the main technical problems

associated with long AC power transmission. These

problems of AC transmission have led to the development

of DC transmission [12]. However, as generation and utilization of power remain at alternating current, the use

of an HVDC link requires converter at each end station of

the line. The transformers and thyristors are the main

equipments in a converter station. At sending end the

Thyristor operate as rectifiers to convert AC in DC which

is transmitted over the line as shown in fig 2.a.

Fig. 2 .a Converter System

At the receiving end the Thyristor operate as inverters

to convert DC into AC which is utilized at receiving end.

The physical process of conversion is that the same

converter station can switch from rectifier to inverter by

simple control action and, thus, power can be transmitted

in either direction as shown in fig.2.b.

Fig. 2 .b Control Characteristics.

The first commercially used HVDC link in the world

was built in 1954 between the mainland of Sweden and the

island of Gotland. This was a monopolar, 100KV, 20MW,

cable system making use of sea return. Since then more

and more HVDC systems have been set up. In 1970

Thyristor replaced the valves based on mercury- arc

technique. At present the biggest HVDC link is ITAIPU in

Brazil (two bipoles, ±300KV, 6300MW). The highest

system voltage reached is ±600KV [13].

FUTURE SCOPE

The on-going development of interconnection

standards and regulations will present both market

opportunities and technology challenges for the Power

Electronics industries. Future trends and development

efforts will need of focus on improving efficiency and

reliability, communication and interface, thermal

management, reduce parts and points of failure, packaging

and bringing down the cost.

REFERENCES

[1] Rai Haris C., (2006) “Industrial & Power Electronics”, Umesh Publications, Delhi.

[2] Ned Mohan, (2011) “Power Electronics Converters,Applications and

Design”, Wiley India Pvt. Ltd. [3] Sen P.C., (2010) “Thyristor DC Drive”, John Wiley & Sons. New

York.

[4] Mittal R. (1993) “Electronic Devices”. G.K. publishers, Jabalpur.

[5] Berde M. S. (2009) “Thyristor Engineering”, Khanna Publications,

Delhi.

[6] Dr. .Bimbhra P. S., (2007) “Power Electronics”, Khanna Publication,

Delhi.

[7] Rashid M.H., (2006) “Power Electronics circuits, devices and

applications”, Prentice- Hall of India, Delhi.

[8] Wikipedia: http://www.wikipedia.org. Microcontroller control.

[9] B. K. Bose, “ Recent Advances in Power Electronics”, IEEE Trans.

Power Electronics, Vol. 7, pp. 12-14, January 1992. [10] Wikipedia: http://www.wikipedia.org. Field programmable gate

array.

[11] Wikipedia: http://www.wikipedia.org. Artificial Intelligence.

[12] Hingorani Narain G. (2011) “Understanding FACTS”.

[13] Vadhera S.S. (2009) “Power system Analysis & stability”, Khanna

Publisher, Delhi.

[14] Murphy J.M.D. (2001) “Thyristor control of AC motors”, Umesh Publications, Delh.

[15] Sugandhi / K.K.Sugandhi, (1998) “Thyristor Theory and

Applications”, Wiley Eastern Limited. Delhi.

[16] Singh S.N., (2007) “A text book of Power Electronics”, Dhanpat Rai

& Company (P) Ltd., Delhi.

Table 1- Power Devices Area of Applications

Sr.

No.

Categories of

thyristors Applications

1. AC – DC

Converter

(Rectifiers)

DC drives – rolling mills, printing press, printing mills, textiles, Wire winders, machine tools,

electric traction; slip power energy recovery scheme; power supplies-low power radio and

electronic equipment, stabilized and uninterrupted supply, dc supply ac inverter systems;

electrochemical and electrometallurgical process- electroplating, anodizing, galvanizing,

aluminium reduction, metal refining, chemical gas production; battery charging; rectifier

substation for traction system; HVDC systems; X-ray & welding equipment; reflectors and

theatre dc lightning systems; adjustable reactive lightning systems; adjustable reactive load.

2. DC – AC

Converter (Inverters)

A.C. Drives – motoring and regenerative, electric traction; slip energy recovery; power supplies

– general purpose, uninterruptible emergency; HVDC transmission and transformers; High frequency melting furnace; surface heat treatment; Tempering; Dielectric drying; Medium

frequency tools; Electronics of vehicles – shop and aircraft; ultra -centric fuses.

3. DC – DC

Converter

(Choppers)

D C Drives – Electric traction, battery operated vehicles, regenerative drive; Slip ring induction

motor rotor resistance control; Regulated dc power supplies; AC welding equipment;

Electrostatic gas purifier; Temperature control in electric furnace; DC Static switch; Advertising

Display and light dimming in theatres.

4. AC – AC

Converter

(Cyclo-

Converters)

AC Drives – Induction and synchronous motor drives, Electric traction, Gearless rotary kiln;

rolling mills, Air craft generators; Heating converters for furnaces; propulsion drive for electric

locomotives.

5. AC Voltage

Controllers

AC Drives – Large pump and fans; motor starters and fan regulators; Induction and resistance

heating and control; static reactive power compensation; power supplies; Lamp dimmers.