Middleton W.M. (ed.) Reference Data for Engineers: Radio, Electronics, Computer and Communications

Подождите немного. Документ загружается.

14-42

REFERENCE

DATA

FOR ENGINEERS

INPUT

CAPACITANCE

----

---8uF

EFFECTIVE LOAD RESISTANCE

ACTUAL

LOAD

RESISTANCE PLUS

FILTER-CHOKE RESISTANCE IN

OHMS

Fig.

50.

Performance of capacitor-input filter for 60-hertz full-wave rectifier, assuming negligible leakage-inductance effect.

(Adapted from

Radio Engineers Handbook,

by F.

Terman, 1st

ed.,

p. 603;

1943.

By permission McGraw-Hill

Book

CO.,

New

York.)

(F)

Fig.

51.

Effect of

on power factor for a single-phase recti-

fier.

millihenries,

is the average current, and

the

rms

voltage. (From Mohan,

N.,

al.

Power Electronics-

Converters, Applications and Design.

01989.

Reprinted by

permission of John Wiley

Sons, lnc.)

Fig.

52.

Effect

power factor for three-phase rectifier.

(From Mohan,

N.,

et al.

Power Electronics-Converters,

Applications and Design.

01989.

Reprinted by permission of

John Wiley

Sons, Inc.)

POWER ELECTRONICS

14-43

as the firing-angle delay,

is increased. Fig.

shows

the ratio

L,,/R

as a function of the percentage of max-

imum output voltage obtained from half- and full-con-

trolled rectifier types discussed

the section

thyristors. Scales are included to show

the

correspond-

ing values of

for various percentage outputs.

The ripple from a controlled rectifier is generally

larger than that obtained from a conventional diode

rectifier, and its value varies with the firing angle,

Reference

provides graphs of the ripple voltage as a

function of firing angle for the various single- and

three-phase controlled rectifier circuits.

Resonant-Filter Design

Resonant filters

are

designed to reduce a specific

frequency component of the waveform.

parallel-res-

onant section

placed in series with the load, and a

series-resonant section is placed

parallel with the

SCALE FOR CURVE

Oo200300 45"

60°

70°

80°

90"

100

SCALE FOR CURVES

AND C

30°

45O

60°

75O

90°

105O

EOo

135O

180°

LII

ISoo

IIII

I I

III

100

INFINITY

ZEROOUTPUT

o.oiJ

100

PERCENT

MAXlMUM DC OUTPUT VOLTAGE

Fig.

53.

L,,/R

as a function of the percentage of maximum

dc output voltage for thyristor rectifiers. The values of

L,,/R

given by the curves apply to a supply frequency

60 hertz.

Curve

is for full-controlled single-phase rectifiers such as

those in Fig. 22 and

Fig. 24 with the bypass diode omitted.

Curve

is for half-controlled single-phase rectifiers such as

those in Fig. 23 and in Fig. 24 with the bypass diode

included. Curve Cis for a half-controlled three-phase rectifier

such as that in Fig. 26.

load. Fig.

shows a resonant filter. Both

and

are

selected to resonate at the unwanted

frequency. These systems are applied to power-system

filters where additional losses cannot be tolerated.

DC-OUTPUT POWER SUPPLIES

The previous sections described the various types of

semiconductor devices, ac-to-dc converter circuits, and

filter circuits. This section assembles these subsystems

into complete dc power supplies. Block diagrams illus-

trate the various approaches to dc power supplies.

Unregulated Power Supplies

The most common type of unregulated power sup-

ply

the ac-to-dc rectifier with uncontrolled rectifiers

followed by a suitable filter. Polyphase power pro-

duces less dc ripple voltage, less input harmonic CLU-

rent, and reduced dc voltage regulation.

power

transformer allows for voltage matching between the

incoming ac and the dc load voltage. If the load

requires high-voltage dc, then a voltage-multiplier cir-

cuit can be chosen, since the design of the step-up

transformer is more difficult with a large step-up ratio

and severe insulation requirements. Load-voltage

adjustment can be provided by transformer taps or an

adjustable-voltage transformer.

Linear Regulated Power

Supplies

block diagram of

low-voltage linear regulated

power supply is shown in Fig.

55.

utility-frequency

transformer provides voltage matching between the

incoming ac voltage and

the

desired load voltage.

diode rectifier converts the secondary ac voltage to dc

voltage.

filter provides coarse filtering and fills in the

gaps in the dc voltage caused by the rectification of

single-phase power. The series transistor, operating in

its linear region, absorbs the difference between its

input voltage and

the

load voltage. The load voltage

sensed and fed back to the closed-loop voltage regula-

tor. Load current limiting can also be provided to pro-

tect the series pass transistor from excessive power

Fig. 54. Resonant filter circuit.

4-44

(RI+

Rz)

v,=

SAMPLING

NETWORK

VOLTAGE

AMPLIFIER DIFFERENCE

ANDDC

AMPLIFIER

v,n

VARIABLE

INPUTDC

VOLTAGE

LEVEL SHIFTER

REFERENCE

DATA

FOR ENGINEERS

SERIES-PASS

CONSTANT

REFERENCE

VOLTAGE

Fig.

55.

Basic series-pass voltage regulator. Transistor

electronically controlled variable resistance in series with the load.

(From

Pressman,

Switching and Linear Power

Supply,

Power Converter Design.

Rochelle

Park,

NJ:

Hayden

Book

Co..

Inc.,

1997.)

dissipation. Integrated and hybrid control circuits pro-

vide these and other functions in a single package.

Instead of sensing output voltage, the

output

current

can be sensed, and the system can provide a constant

current to a variable load.

diode is sometimes pro-

vided

prevent load-voltage reversals caused by

inductive energy in the load. Linear power supplies are

used at low power (less than

50-100

watts); where

multiple output voltages must be regulated; and where

low noise, low ripple voltage, and fast response

are

essential.

P hase-Cont rol Power Supplies

Two basic dc power-supply systems are configured

with phase-controlled thyristors either

the primary

or the secondary side of the isolation transformer. Figs.

and

show these two versions. The choice

between the two systems is dependent on the cost

thyristors as a function of their voltage and current rat-

ings. The usual configuration is for the ac input

high voltage and the dc load

be low voltage and high

current. Placing the thyristors in the primary allows

high-voltage, low-current thyristors

provide the con-

trol of the output voltage.

the thyristors are located

on the low-voltage side

the transformer, they must

be rated at high current and low voltage. The efficien-

cies of the two systems are comparable, as the double

power conversion of one system balances the losses

associated with a high-current, low-voltage phase-con-

trolled rectifier. Control of the transformer primary

voltage requires that the gating signals be symmetrical

avoid transformer saturation.

Systems without isolation transformers are used to

supply adjustable dc voltage

dc motor armatures

and field supplies. Isolation transformers are provided

in general-purpose laboratory power supplies in the

range

1-50

kW.

PHASE-CONTROLLED

THYRISTORS

AC DC

INPUT OUTPUT

ISOLATION

TRANSFORMER

DIODE LOW-PASS

RECTIFIER FILTER

Fig.

56.

Adjustable dc power supply with primary voltage control

14-45

DIODE

RECTIFIER

PULSE-WIDTH-

HIGH-FREQUENCY

INVERTER

ISOLATION

MODULATED TRANSFORMER

DIODE

INPUT

RECTIFIER

TRANSFORMER

OUTPUT

FILTER

OUTPUT

PHASE-CONTROLLED LOW-PASS

THYRISTORS FILTER

Fig.

57.

Adjustable dc power supply with secondary voltage

control.

Switching Power Supplies

Switching type power supplies are currently used

for general-purpose dc power supplies in the 100-

3000-watt range. It is expected that this range will

increase in the future as the result of the technical fea-

tures and cost reductions associated with this

approach. Table

provides the design equations and

device requirements for the most common types of dc-

to-dc converters. To achieve small size and light

weight, a 60-hertz isolation transformer is not pro-

vided. Anuncontrolled diode rectifier and small capac-

itor filter provide an approximately 130-volt dc supply

from 115-volt single-phase ac power. At light load, this

voltage can increase to approximately

170-180

volts.

A block diagram of this approach is shown in Fig.

58.

high-frequency pulse-width-modulated chopper or

inverter is provided to regulate the voltage applied to

the high-frequency transformer. The high-frequency

transformer

(20-500

kHz)

provides voltage isolation

and voltage matching at low weight, small size, and

high efficiency. An uncontrolled ac-to-dc rectifier, at

low voltages using Schottky diodes, converts from ac

to dc. A low-pass filter removes the high-frequency

(40-1000

kHz) ripple from the output voltage. A

closed-loop voltage regulator is provided by sensing

the output voltage, comparing it to a reference, and

controlling the on-off ratio of the primary transistors.

Isolation of the feedback signal can be provided by

optical couplers or voltage-to-frequency converters,

pulse transformers, and frequency-to-voltage converter

circuits.

A second approach is

separate the regulation and

transformer functions into two separate circuits. A

block diagram is shown

Fig.

59.

Voltage control is

provided by a series dc/dc chopper operating at high

frequency followed by a low-pass filter. The dc-to-ac

inverter operates with a fixed 180" waveform that

allows the use of a lightweight non-air-gap trans-

former. After rectification, the output filter needs to

provide only a small amount of high-frequency filter-

ing. This system is useful when the output voltage is

low and the current

high, so that a large filter induc-

tor is indicated.

addition to the pulse-width-modulated switching

power supplies, resonant converters based on either

zero-voltage switching or zero-current switching can

be provided. These circuits can operate a very high fre-

quency

(1-5

MHz). These circuits are generally con-

figured as dc-dc converters operating as part of a

distributed power supply.

Distributed Power Supplies

Large electronic systems composed of many circuit

cards containing digital logic chips require regulated

dc power at

volts dc. Newer types of digital logic

will require 3.3 volts dc. The connected load can

require dc currents in the range of hundreds

amperes. It is difficult to supply this amount of current

without resorting to large, heavy, and complex bus

structures. The area of conductor must be sufficient to

keep the load regulation less than the lowest voltage

required by the digital logic. A way

reduce this

VOLTAGE REGULATION LOOP

Fig.

58.

Block diagram

dc power supply with pulse-width-modulated inverter

for

voltage control.

HIGH.FREQUENCY

RECTIFIER

DIODE

TRANSFORMER

ISOlATlON

VOLTAGE

REGULATION

LOOP

Fig.

59.

Block diagram

dc power supply with dc/dc chopper for voltage control

problem has been to use distributed power supplies.

block diagram is shown in Fig.

60.

bulk ac-to-dc

converter, rated for full power, perhaps using a unity-

power-factor ac-dc circuit, provides a regulated high-

voltage dc output, in the range of

270

volts dc.

For higher reliability, multiple converters can be con-

nected to the high-voltage dc bus with diodes. This

high-voltage dc power is supplied to the back plane of

all of the electronic circuit cards and

brought

each printed circuit card. Each card has its own dc-dc

converter to convert the

volts dc to

volts dc for

that card. The power requirements for each card would

be in the range of

100

watts, resulting in greatly

reduced current demands. These "on-card" dc-dc con-

verters operate at the highest possible frequency in

order to reduce their size. Their aspect is such that

their height is generally limited to less than

0.5

inch,

that the printed circuit cards can be closely stacked

in their card rack.

Electromagnetic interference (EMI) can be con-

trolled by shielding the dc-dc converter mounted

the printed circuit card. Conducted EM1 can be con-

trolled with series and parallel connected input filters.

Heat rejection is accomplished by designing the con-

verter

have the highest possible efficiency, providing

fins for a larger heat surface, or conducting the heat

from the printed circuit card to a cold plate.

AC-OUTPUT POWER SUPPLIES

REGULATED HIGH-VOLTAGE DC

_---______

CONVERTER

WITH

VOLTAGE

I-----_-

ON-CARD

REGULATION

ON-CARD

+I5

-I

REGULATION

-15

'----_--I

WITH

BACKUP AC

REGULATION

CONVERTER

VOLTAGE

REGULATION

-.---------

The previous sections have discussed the aspects of

converter and filter circuits and dc-output power sup-

plies. This section describes some of the various types

of power supplies that provide an alternating voltage

and alternating current output. Some of the specific

problem areas with an alternating output

are

associated

with

the

power factor of ac loads, ac voltage magnitude

control, polyphase output, adjustable-frequency output,

and reverse power flow. Three basic ac-output power

supplies are described, the ac voltage regulator, the dc-

to-ac inverter, and

the

ac-to-ac cycloconverter. Greater

detail and design equations for these generally complex

systems are contained

References

2,5,

and

1CL2

Voltage Regulators

The ac voltage regulator is a static circuit that

accepts a variable ac voltage input and produces a

regulated ac voltage output. The output voltage is

maintained for changes in input voltage, output load

current, and load power factor. The input frequency is

not changed, nor is the basic sinusoidal waveform

modified. Since the input and output voltage is ac,

thyristors with line commutation have been utilized.

Fig.

shows a simple ac voltage-regulator circuit.

This circuit is the static equivalent of the mechanical

on-load tap changer. The thyristors are connected in

inverse-parallel and provide a bidirectional connec-

tion from the tap

the autotransformer to the load.

One tap is at a voltage lower than the input voltage;

the other tap is at a higher voltage.

this manner, the

input voltage can be either increased or decreased to

produce a fixed voltage output. Output voltage con-

trol is provided by a closed-loop regulator that

adjusts the firing angle of the two thyristors con-

nected to the higher-voltage transformer tap. The gat-

ing

of these thyristors reverse biases the lower two

thyristors, causing them to cease conducting the load

current and transferring the load current to the

higher-tap thyristors. More than two taps can be pro-

vided to develop a regulated output voltage with

reduced harmonic content. The gating of the lower

two thyristors is accomplished at the zero crossing of

the load current.

this manner, the load current is

initially in the lower tap irrespective of the load

power factor. The transfer of load current at current

zero allows the upper-tap thyristors to turn off and

allows the lower-tap thyristors to conduct the load

current. This transfer from upper to lower tap is at

load-current zero crossing and is dependent

the

load power factor. Therefore, the output voltage

waveform and magnitude change with respect to the

load power factor, putting an additional burden

the

ac voltage regulator. Both three-phase and single-

phase circuits with full isolation transformers have

been fabricated. Where low harmonic distortion is

required,

output filter can be provided.

Fig.

60.

Block

diagram

distributed

power

supply.

14-47

UTILITY

ACIDC DCIAC

INVERTER

THREE-PHASE

BATTERY BA‘ITERY

AC INPUT

CHARGER

Fig. 61. Circuit diagram and waveforms for single-phase ac voltage regulator.

(From

Mazda, F. F.

Thyristor Control

New

York:

John

Wiley

Sons,

Inc., 1973.)

BYPASS

CRITICAL

SWITCH

LOAD

DC-AC

Inverters

This broad class of circuits is characterized by a dc

input voltage and

ac output voltage. Since the input

is dc, commutation of thyristors must be provided by

techniques other than the reversal of

the

input voltage.

Transistors

are

widely used

lower-power inverters

because of their self-commutation capability. Four

major classes of inverters are described in this section:

first, a system called an “unintermptible power supply

(UPS),”

which provides a fixed-voltage, fixed-fre-

quency output; second,

adjustable-voltage, adjust-

able-frequency system for

adjustable-speed motor

drive; third, an induction-heating supply with a high-

frequency output; and fourth, an adjustable-ac-current,

adjustable-frequency synchronous-motor drive operat-

ing at a leading power factor. These constitute typical

applications for dc-to-ac inverters. Design equations

and discussions of operating conditions

greater

depth can be obtained in References

and

10-14.

Uninterruptible Power Supply (UPShThe pur-

pose of this equipment is to provide a source

power during outages of the normal source of utility

supply. Uninterruptible power supplies are used

computer installations where power outages can mean

loss of stored data (for example,

on-line reservations

systems). Lower-power systems are provided to main-

tain continuous power to critical instrumentation (for

example, a boiler-flame detector in a power plant). The

source

power for these

UPS

installations is a battery

that is kept charged from the utility. When the utility

voltage is lost,

the

battery supplies power to the

inverter and the connected load. These installations

range in size from

kVA single-phase

1000

kVA

three-phase. The output frequency is generally

hertz, and the

output

voltage is the

normal

utilization

voltage in order to use conventional ac-operated equip-

ment and in some cases to operate

parallel with the

ac utility.

Fig.

shows a block diagram of a large

UPS

instal-

lation. The separate battery charger, battery, inverter,

utility bypass connection, and critical loads

are

shown.

High-power

UPS

systems use thyristors with forced

commutation circuits as

the

power switches. Systems

UTILITY

THREE-PHASE

AC INPUT

Fig. 62. Block diagram

UPS with utility bypass switch.

14-48

with ratings less than

200

kVA

now use power transis-

tors

or insulated-gate bipolar transistors as the power

switches. Fig. 63 shows a circuit diagram for a UPS

system using a three-phase, pulse-width-modulated

inverter supplied from a battery and feeding a trans-

former and filter. The transformer provides isolation

and voltage matching. The filter reduces the harmonic

content of the output voltage.

static bypass switch is

shown. If

the

inverter must be taken off-line, the criti-

cal load can be supplied directly from the utility.

Drive

for

Adjustable-Speed AC Motor-A

second

application for an ac-output system is an adjustable-

voltage, adjustable-frequency inverter operating from

a dc source and providing power to

adjustable-

speed ac motor. To operate at high efficiency over a

wide range of speed, the ac motor must be provided

with adjustable-voltage and adjustable-frequency

power. The voltage and

the

frequency are not totally

independent and

are

generally varied in such a way as

to maintain a constant ratio of voltage

frequency.

That

is,

higher ac voltage and higher frequency result

in higher motor speed. Since the source is dc and

induction motors operate at lagging power factor,

forced commutation must be provided for the switch-

ing devices used in the inverter. If thyristors are used,

they must be provided with auxiliary components

reduce the thyristor current to zero and provide a

reverse voltage

the previously conducting device.

Transistors with their self-commutation capability

are

becoming popular in inverters below

200

horsepower.

The inverter operates from a relatively fixed source

dc voltage; therefore control of the output voltage must

be provided in the inverter. The preferred technique is

to pulse-width modulate the output voltage by operat-

ing the transistors in an

on-off

mode many times dur-

ing a given half-cycle of the motor fundamental

frequency. Power transistors, with

turn-on

and

turn-off

times measured in microseconds, can be switched

and

off

many times during one half-cycle

a 60-hertz

voltage, corresponding to a 3600-rpm synchronous

speed with a two-pole induction motor.

Various

forms

of pulse-width modulation (PWM) have been pro-

posed, with a form of sine-wave shaping being a pre-

ferred approach. Rapid advancements

microprocessor-based control systems and stored-pro-

gram memory devices have reduced their cost and

complexity to

the

point where they are used

gener-

ate the pulse-width-modulation switching times.

three-phase full-bridge inverter is shown in Fig.

64. Transistors T,-T6, together with feedback diodes

D&, operate

a pulse-width-modulated manner to

generate a load voltage as shown in Fig. 65. The motor

leakage reactance acts as a filter for the motor current.

For industrial applications, the source

dc voltage

shown in Fig.

is an uncontrolled diode rectifier

from either a single-phase or polyphase ac supply.

Induction-Heating

Supply-In

this application, a

source of high-frequency ac power is converted to

localized heating for melting and heat treating metals

and ferrous parts. The frequency is relatively fixed and

is dependent

the application. Low frequency,

60-

180

hertz, is used for large ferrous heating and melting

applications, whereas

10-50

used for surface

hardening of metallic parts and in ultrasonic cleaning

tanks. This application requires that the ac power be

coupled into the load with an induction coil or trans-

STATIC

TRANSFER

TRANSFORMER

LOADS

BATFRY

DC-AC

mTER

Fig.

63.

Polyphase unintermptible power supply with static transfer switch.

POWER

ELECTRONICS

14-49

THREE

DIODE

RECTIFIER FILTER

PWM

INVERTER

Fig.

64.

Six-transistor

PWM

inverter/induction-motor

drive.

(From

Bose,

Bimal

K.,

ed.

Adjustable Speed AC Drive Systems.

New

York

BEE

Press,

1981.)

Fig.

65.

Output-voltage waveform

a pulse-width-modulated inverter with sinusoidal modulation of

the

pulse width. (From Mur-

phy,

Thyristor Control

A.C. Motors.

New York Pergamon Press,

1973.)

ducer. Because of the lagging power factor of the work

coil, a capacitor, either fixed or adjustable in steps, is

provided to increase the power factor. High-power

applications require the use of thyristors, and forced

commutation is required because the operating fre-

quency is higher than

hertz. The inductance of the

work coil, an external capacitance, and

the

load resis-

tor

are

selected to form an underdamped resonant cir-

cuit. Changes

the load resistance only change the

damping ratio and barely affect the resonant fre-

quency. The sinusoidal current waveform in the thyris-

tors allows them to operate at higher frequencies with

reduced losses. Fig.

shows

induction-heating

inverter operating from a three-phase ac supply and

supplying a single-phase load. High-power systems

use this technique to balance the load on

the

three-

phase supply.

Synchronous-Motor Drive-This system illus-

trates a fourth commutation technique for thyristors. In

this

case, the synchronous machine

operated at a

leading fundamental-frequency power factor provided

by overexciting the field of the machine.

adjust-

able-speed drive system of

this

type is shown

Fig.

67.

The source of supply is an adjustable dc current

supply. Thyristors

TI-T,

steer the dc current into the

motor windings in sequence to provide the ac-motor

line current.

suitable control system turns on the thy-

ristors at the proper time with respect to the back elec-

tromotive force in the motor to provide a reverse

voltage for commutation of the thyristors. Shaft-posi-

tion sensors or electrical signal processing is used to

determine the correct time

gate the thyristors. The

source of adjustable dc current for the inverter is an ac-

to-dc phase-controlled rectifier. Special commutating

14-50

REFERENCE

DATA

FOR ENGINEERS

...

Fig. 66. Modified frequency multiplier with load commutation. (From Dewan,

B., and Straughen,

Power Semiconductor Cir-

cuits.

New

York:

John

Wiley

Sons,

Inc., 1975.)

THKEE-PHASE

AC SUPPLY

RECTIFIER INVERTER

Fig. 67. Six-thyristor load-commutated

inverter/synchronous-motor

drive.

(From Bose, Bimal

K.,

ed.

Adjustable Speed AC Drive

Systems.

New York

BEE

Press,

1981.)

circuits or turn-off intervals in the dc supply current

are necessary to provide thyristor commutation during

initial start-up and low-speed operation of the motor

when the back emf is insufficient to commutate the

thyristors. These drives have been fabricated to supply

large synchronous machines up to

000

horsepower.

Cyc

oco

nver

The preceding sections have described power-con-

version systems that operate from dc power and pro-

duce an ac output.

industrial applications, the source

usually ac, thereby requiring a two-step conversion

process from ac to dc to ac. The cycloconverter allows

for a one-step conversion process from ac of a given

voltage and frequency to adjustable-voltage ac (within

limits) and adjustable-frequency ac (also within lim-

its). This system uses the reversal of the line voltage to

commutate the thyristors. The output voltage can be

controlled by retarding the thyristor firing angle as in

the phase-controlled rectifier.

second set of thyris-

tors provides a path for the negative half-cycle of the

load current.

three-phase to single-phase cyclocon-

verter is shown in Fig. 68. The firing angle of the thy-

ristors is modulated in a sinusoidal manner to generate

a cycle of the desired output frequency. The inverse-

parallel connection of the thyristors provides a bidirec-

tional path for current flow at any power factor. Since

the commutation of the thyristors is provided by the

input frequency, the maximum

output

frequency must

be less than the input frequency. The maximum output

voltage is also less than the input voltage because of

the need to generate a sinusoidal output voltage wave-

form.

There are

two

major applications for cycloconvert-

ers. The first is very high horsepower, very low speed,

multiple-pole induction and synchronous motors. The

maximum frequency for these motors can be less than

hertz

the case of an 8000-hp motor enclosing a

rotary cement ball mill. The second application is for

variable-speed constant-frequency (VSCF) systems in

aircraft. The speed of the aircraft generator, and hence

its generated frequency, is a function of the engine

speed.

cycloconverter is provided at the

output

of the

POWER

ELECTRONICS

14-51

NEGATIVE

GROUP

POSITIVE

GROUP

A!-

NEUTRAL

Fig.

68.

Three-phase

single-phase cycloconverter

power

circuit.

(From

Murphy,

Thyristor

Control

A.C.

Motors.

New

York:

Pergamon

Press,

1973.)

generator to convert the varying frequency into a fixed

400-hertz frequency for the aircraft power system. The

adjustment

the thyristor gating times generates a

sinusoidal output voltage waveform with minimum fil-

tering. Output voltage regulation is provided by both

the adjustment in thyristor gating times and adjustment

the field excitation on the synchronous generator.

REFERENCES

1. Jahns,

M.,

et al. “Circuit Utilization Character-

istics of MOS-Controlled Thyristors.”

IEEE

Trans.

Ind. Appl.,

Vol. 27, No. 3, May/June 1991, pp.

589-597.

2. Mohan, N., et

al.

Power Electronics-Converters,

Applications and Design.

New York: John Wiley

Sons, Inc., 1989.

3. “Harmonic Voltages in the Outputs of Controlled

Rectifier Circuits.”

Electronic Engineering,

Vol.

36,

No.

442, December 1964.

4. Baliga, B. J., and Chen, D. Y., Eds.

Power Traizsis-

tors: Device Design and Applications.

New York:

IEEE Press, 1984.

Rashid,

Power Electronics-Circuits,

Devices and Applications.

Englewood Cliffs, NJ:

Prentice-Hall, Inc., 1988.

Mazda,

Power Electronics Handbook.

Lon-

don:

Buttenvorths, 1990.

7. Hnatek,

Design

Solid State Power

Sup-

plies,

3rd ed. New York:

Van

Nostrand Reinhold

Co., 1989.

Billings,

Handbook

Switchmode Power

Supplies.

New York: McGraw-Hill Book Co.,

1989.

9. Chryssis, G. C.

High-Frequency Switching Power

Supplies,

2nd ed. New York: McGraw-Hill Book

Co., 1989.

10.

Murphy, J.

D., and Turnbull,

Power Elec-

tronic Control

AC Motors.

Oxford Pergamon

Press, Inc., 1988.

11. Bose, B.

Power Electronics andAC Drives, Inc.

Englewood Cliffs, NJ: Prentice-Hall, Inc., 1986.

12. Kenjo, T.

Power Electronics for the Microproces-

sor Age.

Oxford Oxford University Press, 1990.

13. Bose, E.

K.,

Ed.

Microcomputer Control

Power

Electronics and Drives.

New York IEEE Press,

1987.

14. Dewan,

B., and Straughen, A.

Powev Semicon-

ductor Circuits.

New York

John

Wiley

Sons,

Inc., 1975.

15. Sen,

Thyristor DC Drives.

New York John

Wiley

Sons,

Inc., 1981.

16.

Moltgen,

Line Commutated Thyristor Convert-

ers.

London: Pitman Publishing, 1972.

17. Felly, B.

Thyristor Phase-Controlled Convert-

ers and Cycloconverters.

New York: John Wiley

Sons, Inc., 1971.

18. McMurray, W.

The Theory and Design

Cyclo-

converters.

Cambridge, MA: M.I.T. Press, 1972.

19. Gyugyi,

L.,

and Pelly,

Static Power Fre-

quency Changers.

New York: John Wiley

Sons,

Inc., 1976.

20. Harnden,

D.,

Jr., and Golden,

B., Eds.

Power

Semiconductor Applications,

Vol.

and Vol. 2.

New York: IEEE Press, 1972.

21. Bose, B.

K.,

Ed.

Adjustable Speed AC Drive Sys-

tems.

New York: IEEE Press, 1981.

22. Brown, M.

Practical Switching Power Supply

Design.

San

Diego: Academic Press, Inc., 1990.

23. Brown, M.

Power Supply Cook Book.

Newton,

MA: Butterworth-Heinema, 1994.

24. Mammano,

R.,

Niedorf,

R.,

Improving Input

Power Factor-A New Active Controller Simplifies

the Tusk.

Unitrode

Corp.,

Merrirnack, NH.

25. Tenti, P., Spiazzi, G.,

Harmonic Limiting Stan-

dards and Power Factor Correction Techniques.

Sevilla, Spain: EPE Conference Tutorial, Septem-

ber

1995.