Automatic Voltage Regulator Using a Novel Phase-Shifted PWM Single-phase Inverter

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The 30th Annual

Conference

of

the

IEEE

Industr ia l

Electronics

Society, November 2

-

6,2004, Busan, Korea

Automatic

Voltage Regulator Using a Novel Phase-Shifted PWM

Single-phase

Inverter

*Kuo-Kai

S h y *Ming-Ji Yang

Jing-Heng Hong

**Bau-Hung

Lin

*Department

of

Electrical Engineering, NationalCentralUniversity, E-mail : [email protected]

**Departmentof research and development,RIYE ElectricCO.,

LTD

-mail : [email protected]

Absfract-In

this

paper, a novel phase-shiftedpulse width

modulation

(PS-PWM

automatic voltage regulator (Am)

with

fast

voltage control

and reduced

total

harmonics is

proposed The novel

PS-PWM

AVR

is made up of an AUAC

converter

wth

reversible voltage control and

a

transformer for

series voltage compensation. In the active rectifier, a proper

switching operation is achieved without the problem

of

power

factor correction.

The

AVR uses a

fully

digital controller,

which is implemented by a fixed-point digital

signal

processor

DSP)

TMS320F240 DSP-based

board. Therefore, the

proposed

AVR

gives

high

efficiency and reliability.

It

is

also

shown via

some

experimental

results

that the presentednovel

PS-PWM AVR gives good performance for high quality

of

the

output voltage.

Index Terms- PS-PWM

AVR, AC/AC converter,

DSP,

active

rectifier

I. INTRODUCTION

With the modem industry advance day by

day,

he

production equipments o f automation become

more

and

more precise.

So

the requirement

of

power quality

becomes higher. Power quality problems commonly

face industrial operations including transients,

sags,

swells, surges, outages, harmonics, and impulses that

vary in quantity or magnitude of the voltage. Of these,

voltage sags and extended undervoltages have the

largest negative impact on industrial productivity, and

could be the most important factors of

power

quality

variation for many industrial and commercial customers.

Therefore, the automatic voltage regulator

AVR) of

high

stability, wide voltage regulation range, and fast

dynamic response is required

to

compensate

for

the

fault

of power

quality.

The conventional voltage regulator mainly has used

servomotor

to

change the tap-changing transformer. But

the faults are

as

follows: large size of the mechanism,

slower dynamic response, mechanical attrition and

lower

efficiency etc. Therefore, the conventional

voltage regulator cannot be used in precision equipment.

In

recent

years,

development

of

the

AC

voltage-voltage

Converter and

AC

chopperhas been used inAVR [11-[7].

There are

two

typicalconfigurations f such AVR. First,

the circuit configuration is an AC voltage-voltage

converter (AC Buck) type. Even though most faults of

the conventional voltage regulator could be improved

by AC Buck, but it cannot level down the

AC

line

voltage when the AC

line has

occurred some situations,

such as swell, surge

or

long-term overvoltage.

Secondary, the circuit configuration is a novel AC

chopper [Z]. It not

only

improves the problem of

conventional voltage regulator but also has voltage

upldown capability. But its switching sk-itegy cannot

reduce total harmonic distortion, switching loss and the

size of the LC filter.

Therefore,a novel switching strategy for single-phase

voltage regulator is

proposed in

t h i s study. The

proposed switching strategy

c n

reduce switching

loss,

total harmonic distortion, size of he LC filter etc, and

then increases the performance of the single-phase

voltage regulator.

JIDESCFUPTION

OF

THE VOLTAGE

REGULATOR TOPOLOGY

In this paper, the proposed voltage regulator topology

is shown

in

Fig. 1.

Tn

order to provide a stable AC

power supply, the transformer series in between the AC

line and the load side to compensate the variable voltage

of

AC

h e .

The

hc t ion

of

the voltage regulator is

making

AC line from unstable to stable voltage, after

the line voltage

is

regulated

and

controlled

by

power

circuit

and

digital controller.

Fig. 2 shows the voltage regulator topology, the output

voltage

of

load

is given

by

v

=

v

./;G

where vi is

the

unstable input, V, is the stable output,

Yo s the

outputof the

AC/AC

converter,

and

N

s

tur s

ratio

of

transformer.

I\

i t

v AC/AC

Converter

Fig.

1.

When the AC

l ine

input terminal has occurred voltage

variation, the

load

terminal

still

outputs a stable voltage after

regulating the AC/AC converter. It can be

noted

that the power

specification of

AC/AC

converter is reduced to IN of the

output power because

of

using a hnsfor mer. That is,

Topology

of

the proposed novel

PS-PWM

AVR

where

output power, and

N

s the t u r n s ratio of the transformer.

is

the power of the AClAC converter,Po,,

is

the

0-7803-8730-9/04/ 20.002004 EEE

1851



I

Inverter :

Fig.2.

Power circuit of

he proposed

AC/AC converter

with

1_- 9k?Rec ?L~- i .--.--...... .....

novelPS-PWM ontrol.

111.PROPOSEDSWITCHING STRATEGYFOR

AVR

The main power circuit

of

system is

shown in

Fig. 2 i s

based on the same circuit structure as 121, but the

switching strategy is innovative. Fig.2 shows two parts

of

the

power circuit, the left dotted line block

and

the

right

one

are the active rectifier and the inverter,

respectively.

In

the following, their operational

principles and functions will be illustrated.

A. DESCRIPTION OF THEACTIVERECTIFIER

Consider the active rectifier shown in Fig. 2. When

switchesS,, SJR

re

tumed

on,

the waveforms ofAC

inputare changed

from

negative to positive.Thus, he

sine wave ofAC input is rectified to a signal greater

than

zero. Because the active switches

are

substituted

for the passive ones, it is called active rectifier. The

forward voItages on the active switch and the passive

one re 0.2volt and 0.7 volt, respectively.Hence, the

forward voltage of active switch is lower as compared

with the passive diode rectifier.

However, using he active rectifier not only reduces

power loss on

the

switches, but also increases the power

factor at the AC line input. Therefore, it is suitably used

high

power applications.

Fig.

3

Equivalent circuit of the reversible voltage

inverter

B. PROPOSED SWITCHING STRATEGY

FOR

Fig. 3 shows the equivalent circuit of the reversible

voltage inverter

[ 8 ] . T h i s

circuit schematic is identical

with general inverters. To compare the switching

strategies

of

the proposed method and the conventional

one, Figs.

4

and

5

show the conventional switching

strategy

and the proposed method, respectively. These

figures show the sequences of all driving

signals

and

output voltage waveform at the fullbridge inverter. It

can

be seen that the proposed switching strategy only

FULLBRIDGE INVERTER

uses half the switching frequency of the conventional

one. But he proposed switching strategy outpuM the

same switchpattern

as

the conventional

one.

However, it should be noticed that during the

positive period of A C line input, the duty

ratio

is limited

to

greater

than 50%for

the

switchesSi and

S4.

On he

contrary, during the negative

period of

AC line input,

the

duty ratio

is

limited to less than 50 for

the

switches

SI

and

S4.

To clearly

explain

the operational concepts o f the

switchingstrategy, in the following, more details

will be

given. For convenient illustration, the input voltage will

be assumed to be a

DC

value and the characteristics

of

all

components will be considered

in

ideally.

Fig.

4.

Conventional switching strategy for

single-phase full-bridge inverter

t

t

f

t

Fig. 5. Proposed switching strategy of the novel

PS-PWM

for single-phase full-bridge inverter

(1) Duty ratio

0 2 5 0

1852



From Fig. 6, it canbe observed that the

signal

of S , is

phase-shifted

90 to the

signal

of S,,

and the switching

signal of high side is complementary

o

that of the low

side in the full-bridgeinverter.During the interval I 5,

and S4 are turned on and

S2

and

S3

are turned

off.

The

switching output voltage Vsw is the same

as

the input

voltage Vi. Therefore,

the

inductor voltage VLis given

by

VL = y

v

3)

Duriog the interval 2, SI and

S,

are tumed on, and 2

and S are turned off.

In

this case, Vm equals

zero.

VL

becomes

Similarly, same

results

can be obtained during inteivals

3

and

4. Therefore, he average inductor voltage can be

derived by the volt-second balance theorem during one

switching cycle [SIas

v =-v

(4)

Accordingly

5-v,). T + -v, ) . Tw-Tm)=O 6 )

D = ? k

(7)

v

= V , . 2 0 - l ) ; D L 0 . 5

(8)

m

Define be the ratio between the turn-on ime and the

cycle time of he switch during a switching cycleas

T m

Thus

nserting 7)

into

(6)gives

(2) Duty ratio D S O W

In t h i s condition, interval

5

is

fmdy

discussed.

Dlning the interval 5, SI

and

S3 are turned on, and SI

and S4 re

urned

off. It is seen that V, is

equal to

zero

and

VL

is:

v

=

-v

9)

Next, during the

interval

6,

because

52

and

S,

are

turned on, and S, and & are turned

off.

Vswreverses to

Vi.As a result, VLis given by

Following similar discussions, same results can be

obtained for intervals 7

and

8. Accordingly, the average

inductor

voltage during one switching cycle is obtained

as

v

=

-vi v

10)

+T

Consequently, one obtains

v

=

P i . ( 2 0

1 ;

D

5 0 . 5 (13)

C TRANSFER

FUNCTION

OFTHE

PROPOSED

P S P W M INVERTER

Synthesizing analysis of above discussions

DZO.

5

and

D S U . 5 ) ,

one

can

easily have the relation between

Viand V. for the whole duty

ratio

range as

follows:

v = v i . ( 2 ~ - I ) ; 0 S D I I

(14)

v

Postive

Y Y R

A

i

Negative

1

Fig. 6. Vd v ,contrasts with the

D

Fig.

6 shows he relation,

which

contrasts the F Pi

witb the

duty

ratio D. When

D

50 , the output

voltage is in phase to the input. When D=50%, he

output voltage is zero. When

D

<50 , the output

voltage

is reverse to the input.

Accordingly, it is obvious that one only need to adjust

the

duty

ratio to

obtain an

in phase or reverse voltage

to

the input waveform. From

B e

foregoing analysis, the

waveforms are repeated for V,, and VL

during

one

switching cycle (intervals

1-4

or intervals5-6).

In other

words, the output k p n c y will be double to

the

switching fiequencyof the each switch. That is

where fo is the oufput fiequency and fm is the actual

switchingfiequency.

Consequently, it can be concluded that the proposed

novel switching strategy can reduce the switching

fkequency of the switch to reduce the

switching

losses.

The

most important is that it doubles the

output

fkquency;

as

a result,

the

total harmonic distortion and

the

specification

of

LC

filter

are reduced.

Fig.

7

shows

the corresponding signal waveforms

of

the inverter

using

the proposed novel switching

strategy.

f

=2 . f (15)

inphase

voltage I reverse vattage

Fig.

7.

Waveforms diagram of the power circuit.

1853



Turns

ratio

of the

transformer

5

6

7

8

9

1

11

12

Voltage

disturbances

a.Momentary voltage

b. Transient

Vervoltage

Freauencv variation

VoltageTHD

Power factor

Switching frequency

PWM output

fkequency

Input voitage

Load

power

Inductance of the

output filter

Capacitance of

the

output filter

neters and conditions

Rang or maximum

N , :N , = 5 : l

-20% to +20 (ANSI

C84.1-1970

k+6.

-13 )

-20

to

-25

for

less

O S s , with -100%

acceptable

for

5-25111s

+120 to 160 for less

than 0 . lm

60- fO.5Hz to flHz

3-4 wthlinear load)

0.95-0.98

f .=20kHz

AC llOV,, 1 4

10

kVA

Lo= 1mH

CO= ouF

Fig.

8.

Structureblock

diagram

of

he

pmpased

navel

AVR

system

Fig. 9.

Photo

of

the novel single-phase PS-PWM

AVR

+ 5.514 m

Freq(1I

28.8885 k l h

FreqQ)

n 28.8885

klh

FreqlQ) M

48.8855

k l h

Fig. 10. Chi: Switching waveform of SI,

Ch2:

Switching waveform of

SI,

Ch3: Waveform of

the

P W M

utput.

24-tlov-83

23:32:2B

7 IRj

mxi rum(1 I 131

F r eq t l l M

59

99

mx1ru

155

F r e q W

M

59

99

tb

18 ffi

Fig.

11.

Input

and output voltage waveform when

input is long-term undervoltage.

1 9 - k - 8 3

13

56

I4

I- ---.

1

Fig.

12. Input and output voltage waveform when

input s long-term overvoltage.

prototype

1854



I l l

I I I I

I I I I I t I I

I I I I I I I I I

Eh2:b

Fig. 13. Input and output voltage waveform when

input is voltage sag.

I I I I l I I l l i

I I I I I I O I

I

I

I

I

I l l

i

I

I I50 l s

Fig. 14 Input and output voltage waveform when

input is voltage swell.

IV.

EXPERIMENTALRESULTS

The proposed novel switching

strategy

has been

implemented in a novel AVR according to the structure

block diagrams for this system shown in Fig.

8.

Fig.

9

shows

the real hardware experimental system of a 10

RVA novel single-phasePS-PWM

A I R

prototype. Table

I shows the experimental parameters and conditions for

this

system.

Figs.

10-14

show the experimental results.

In

Fig. 10, one

c n

see the output

P W M

iequency

doubles the switching lkquency. Fig. 11 shows the

compensated output voltage when AC

line

had occurred

long-term undervoltage. However, if the AC line had

occurred long-term overvoltage, Fig. 12 shows

this

system can still works well. For the case when the AC

line had occurred the voltage sag, Fig. 13 shows the

output voltage can

be

fast

compensated.

Also,

Fig.

14

shows this

system

fastly cut down the input voltage

when the

AC

line had occurred he voltage swell.

V.CONCLUSIONS

In

this study,a

fixed-point, high-speed cost-effective

DSP (TMS320F240) is

used

to implement the

fully

digital controller of the proposed voltage regdator. It

has been

demonstrated

through experimental results that

the proposed novel switching strategy can lower the

switching fiequency of the switch to reduce the

switching

losses.

The most important is that it doubles

the output frequency; as a result, the total h o n i c

distortion and the specification

of

LC filter are reduced.

The

proposed novelPS-PWMAVR has the following

features:

allows any schemes of the single-phase

full-bridge inverter.

fast dynamic response

for

AC voltage

regulation.

reduces switching

losses

and total harmonic

distortions.

reduces the LC filter

size.

improves the input power factor

and

power

quality.

a

fully

digital design to lower total system cost

and improves

reliability.

VI.REFERENCE

[l] Steven M. Hietpas,

Mark

Naden, “Automatic

Voltage Regulator Using an AC Voltage-Voltage

Converter,” IEEE

Tranractions

on Industry

Applicafions, Vol. 36, No.1, pp. 33-38,

Jan 2000.

[2]

Bong-Hwan

Kwon, Gang-You1 Jeong, Sung-Hoon

Han, and Duk-Ho Lee, “Novel Line Conditioner

with Voltage UplDown Capability,” IEEE

Trunsuctiom on Industrial Electronics,

Vol.

49,

No.

[3] Do-Hyun Jang and Gyu-Ha Choe,

“Step-

Up/Down

AC Voltage Regulator Using Transformer with Tap

Changer and

P W M

AC Chopper,” IEEE

Transactions on Industrial Electronics,

Vol.

45,

No.

6, pp. 905-911, Dec., 1998.

141

Han-Woong Park, Sung-Jun Park,Jin-Gil Park and

Cheul-U Kim, “A Novel High-Pedormance Voltage

Regulator for Single-phase AC Sources,’’ IEEE

Transactions on Industrial Electronics, Vol. 4S, No.

[SI T.W. Kim, J.H. Choi and B.H. Kwon,

“High-performance line conditioner with output

voltage regulation and power Factor correction,”

IEE

Proc.-EIecfr

Power Appl., Vol. 151,No. 1, pp.

[ ]

B.R.

Lin,

T.L.

Hung

and C.H. Huang, “Single-phase

AC/AC converter with capacitor-clamped scheme,”

IEE

Proc-Electr

Power Appl., Vol. 150, No. 4, pp.

91-97, July, 2003.

[ 7 ] B.H. Kwon, B.D. Min

and

J.H.

Kim

‘Wove1

commutation technique of AC-AC converters,” IEE

Proc.-Electr:

Power

Appl., Vol.

145, NO. , pp.

[8] N. Mohan,

T.

M. Undeland,

W.

P. Robbins, “Power

Electronics: Converters, Applications,

and

Design.”

Second Edition, John Wiley & Sons, nc., 1996.

5 , pp. 1110-1119, Oct., 2002.

3, pp. 554-562, Ju. 2001.

91-97, Jan., 2004.

295-300, July, 1998.

Achowledgment:

and the National Science Council of Taiwan under

contract

NSC

92-2622-E-008-027-CC3.

This study was supported

by

the

RIYE

ElectricCO.

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Documents

Automatic Voltage Regulator Using a Novel Phase-Shifted PWM Single-phase Inverter