7117171-A-New-Method-for-Power-Factor-Correction-and-Harmonic-Elimination-in-Power-Systems.pdf

8/17/2019 7117171-A-New-Method-for-Power-Factor-Correction-and-Harmonic-Elimination-in-Power-Systems.pdf

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810

-

A

New Method for Power Factor orrection and Harmonic Elimination

in Power Systems

I. Kasikci, MIEEE, VDE

University

of

Applied

Sciences

of

Mannheim,

Germany

TeVFax: +49-620

1

I 82301, E-mail: I m a i l .~ ~ s i ~ c i i u r h ~ i n i i i ~ i n . ~ ~. i n i l

Abstract : The influence of power electronics-based

technology, which is increasingly used, has disadvantageous

effect on the quality of electric power supply. Pure sinuso idal

voltage supply does not exist anymore. Low and medium

voltage power systems are polluted to an increasing extent

by

harmonic currents and voltages, voltage fluctuation, voltage

unbalance, voltage sags, voltage swells and flicker This paper

presents an new configuration for power factor co rrection and

harmonic current elimination in electrical power systems. A

single-phasecontrol concept is discussed for simplicity. It also

presents a brief discussion of the main problems in the

distribution power systems.

Keywords: Reactive power compensation, Harmonics, Active

Filters, Control

,

EM1

I.

INTRODUCTION

The increased use of non-linear devices cause voltage

distortion in the network. This leads to malfunctions of

the electric facilities and to costly interruptions of

production.

The filter circuit parameters are analysed and described.

This filter configuration provides an alternative

approach to the existing one. According to the test

results, the proposed approach can achieve a complete

elimination of harmonics.

The sw itched-capacitor active filter was first presented

in 19 82 by C.C. Marouchos

[ I ]

and

is

fundamentally

different fiom the inverter configuration. T he switched-

capacitor configuration removes the requirement for a

large current or voltage source, which leads, not only to

a reduction in cost but also in physical size [2,3].

Another configuration of shunt active filter was

developed in [4]. The major drawback of these circuit is

that the control algorithm is very complicated, time

consuming and produces itself resonances.

As

described in [5] a sampling control is used and a load

is applied to the inverter which requires only the control

of the fundamental current for power factor correction.

In this paper, it is shown that the circuit is capable of

correcting not only the power factor of the

fundamentals but also of eliminating the harmonics and

ver easy to control. In recent years the proliferation of

non-linear loads has lead to the development

of

active

filters designed to eliminate current harmonics from the

power supply network.

0-

78C3-

49 ?-6:00:$18. O 20901EEE

This paper examines shunt active filter inverter and

passive filter, highlighting the co mplexity of the control.

Two different approaches are investigated, with the aim

of

reducing the computational requirements associated

with the control technique and hence increase the

applicability of the propos ed system.

A significant simplification is presented which eases the

somewhat laborious, but never the less unavoidable

computational requirements. A new control unit is also

developed providing

an

alternative to the dominated

computer controlled very complicated techniques.

The main characteristics of a non-linear supply are the

voltage interruptions, harmonic pre-distortions and

unbalance in the three phase systems. O n the other side,

the main characteristics of a non-linear loads are the

harmonics, hndamental reactive current, unsymmetrical

parts and the stochastic fluctuations called flicker.

There is a strong coupling between reactive power

balance and of a power system and the voltages. Today,

many techniques are used to compensate the reactive

power. Shunt and series com pensation is widely used in

the industry.

Two possible loads can be discussed in this point of

view. The non-linear supply voltage which influences

the loads behaviour and non-linear loads which cause

voltage distortions in other supply feedings.

Fig.1 represents the proposed active power filter

configuration. The proposed new control block diagram

shows nine main sections constituting the power active

filter structure. The harm onic cu rrent generated by non-

linear load is detected and fed back to the reference

current estimator, in conjunction with the other system

variables. The resulting reference signal drives the

overall system controller, which, in turn, generates the

control effort necessary for the switching pattern.

The resulting filter current is also detected and fed back

to the controller. The power and filter circuit is then

connected to the PCC. Shunt active filter is connected to

the main power circuit as shown in the single-line

diagram of Fig.2.

I t

is mainly aim ed towards cancelling

the load current harmonic as it has the ability of

controlling the amount of current flowing in the circuit.

It can also contribute to reactive power compensation

and balancing of three-phase currents, transients and

flicker.


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PCC Measurements

-

r l

ilter elements

..................... .............. ................................................................................ t r

I

_.................. .... .........

Switching Overall

i Controller

Strategy System

.............................................

Detector I

%. " .......-

. .

.

Reference

current

Estimator

1 1

Actual current

.... . .................. ............

........... ........

Fig.1 Complete Control Diagram

for

the proposed System

v cy

C D C

...................

VSI

s

s

r

........................... ...................................... .....-.....

c

lComp

V F

AC-Passive F ilter

T-Network

PCC

ion-linear Load Supply Voltage

N LL

Non-

linear

Load

Current C ontroller

i

Actual current , Reference current, Switch condi tions, P W nd H ysterisis controller, Supply

voltage, Load current)

L

..

................

.....................................................................................................

Fig.2: S ingle-phase

Full

Bridge Inverter-Filter Scheme

- 8 1 1


3/6

- 812 11. ANALYSIS OF

THE

FILTER

The problem relating to current harmonics is very

important in lo w and medium power applications. It is the

value of the current and its waveform that determines many

of the power system design criteria Fig. 3 . Due

to

the

non-linear nature of the load, the load current

iL

, consists

of a fundamental component i as well as harmonic

components ihormwhich in the absence of the active filter

are present within the supply current i s , polluting the

power system. Therefore if i = i,, then is = i where

i, contains only the fundam ental component.

Most active filters designed for this purpose are voltage or

current fed inverter configurations, using various switching

techniques to control the compensation signal. The inverter

configuration relies on the availability of a constant dc

voltage

or

current source in order to generate the required

compensation signal. This is accomplished by the use of

large reservoir capacitors or inductors, which are not only

expensive but are also physically very large.

Network

m

Fig.3: Basic structure of shunt-active power-

filter configurations

The parallel connected active filter generates a

compensation signal i, ,which then supplies the harmonic

components required by the load, shown below:

(1 )

. . .

is

= i L

- 1 ,

= i i, -i

The energy required to maintain this constant dc level is

obtained from the supply via the inverter, this limits the

performance of the filter.

Using Fig. 4 as an example, the rate of change of current

within the inverter inductor

L,

is controlled

as

follows:

tr. 11

t

t

Fig.4: PW M-hysterisis switching technique

For the top boundary

For the bottom boundary

.

Idv

-

= 2 Ts

+T,)

3)

To achieve a hysteresis control band w idth

1

the current,

which is controlled, can be calculated fiom:

4)

To

avoid the harmonics in the main power current and

supply voltage a filter is designed and applied to a single

VSI.

The filter resistance R is inserted to restrain the

oscillation of the capacitor of the network and inverter

inductance.

A

lower value

of R ,

gives the best results of

the smoothing of the network current and supply voltage.

On the other hand, the filter capacitor C Fm us t be large

enough to absorb the current and vo ltage ripples. In order

to limit the failure current the following equation gives:


4/6

813

-

The resonance frequency is:

fr -


5/6

814

25,

23-

15-

10-

:C111..:0 20 3 4

5

Fig.

6 :

Current harmonic spectrum before comp ensation

2

l

e 10

20 30 40

5

Fig.

7:

Current harmonic spectrum after compensation

4,682"

. .

: 10A

_ I

......................

...

. . .

. ?

......................

. . +-++A

. . . . . . . .

. . . .

.

,:

.

.:

....

x _: .....

x . ....... 3 ......:vi.. ..

Fig. 8: Load Current waveform

226,Ou::

ms 22911-2 ~ ~ :RX

in

SO ,OH ~

'gqo ?

.-. ;R.

...

$?

...... I 2. . . . . . . . . :%........

;

. ;

? ' .

I

::

:

0.

i

i 1 ::. :

: : : : : : i

.... : :....>,.,I

.......:... ... ..5,..:..

\ :

%

S J

: .t

. .

; i

. -

a) Inverter Current

2.1 572

b) Compensated C urrent

1 4 lb

10.2 P

4995

HZ

2140 C

995

Xr

00

2.154

7

13 K

4

4 13 17 21 25 29 33 37 41 45 49

c) Harmonic Spectrum

Fig.9: Loading condition


6/6

IV.

EMC COMPATIBILITY

Th e EM1 generated by the proposed system was m easured

when employing both hysterisis and PWM techniques.

Permissible level of electromagnetic emissions of the

switching power devices is given in Fig.

10,

in conjunction

with the emitted harmonics. These indicate that the passive

filter and the proposed switching technique meet the EM1

regulations.

The emitted interference is decreased about 30 dBN. The

passive filter designed traps the high fkequency harmonics

as shown in the Bode plots of Fig.

11.

It stops these

harmonics ffom penetrating into the supply and hence

hr the r reduces the EM1 generated by the system.

. lr

Fig. 10: Permissible level of the electromagnetic emissions

I I

Fig. 1 1 : Bode

diagram

of the transfer hnc tion

successfu lly filters unwan ted harmon ics generated by a

non-linear load.

8

15

-

By using PWM and hysterisis control method outlined

above the switching patterns required to control the filter

can rapidly be determined, and therefore the filter can

respond to varying load.

The main advantage of this technique is that it does not

require very complicated computer algorithms and

microprocessors. Simulation and experimental results show

that this new method can eliminate a wide range of

harmonics currents, flicker and transients. Power factor

correction is also possible.

Further, the response time

of

the controller much faster

comparing to the existing comm ercial power conditioner.

VI. REFERENCES

[1] Marouchos C.C., “Switched Capacitor Circuits For Reactive

Power Generation”, PhD Thesis, 1982.

[2] Mehta P., Darwish

M.,

Thomson T., “Switched Capacitor

Filters”, IEEE trans on Power Electronics, Vo1.5, No.3, July

1990

Koozehkani Z.D., Mehta P., Darwish M.K.,”An active filter

for retrofit applications”, in PEVD-96, Nottingham, UK.

El-Habrouk M., Mehta P., Darwish M.K., ‘‘ A new active

filter for power sytem applications”; I N P O W E R 9 8 ,

October 1998

Masaaki Ohshima, Eisuke Masada: Novel error tracking

mode ac current waveform control method and ac filter

design procedure, Sevilla EPE 95 , page 2.472-2.477.

[3]

[4]

[5]

VII. BIOGRAPHY

Ismail Kasikci was bom in Turkey, on September

1,

1952. He

received two Dipl.-Ing. degrees from the University of Applied

Sciences of Darmstadt in Germany and the MPhil and PhD

degree from Brunel University London. He has been working in

the industry more than 15 years as a Chief Design Engineer. He

is responsible for design and development of electrical power

including power distribution networks, transformer stations,

protection and control of electrical systems. He is also a Lecturer

at University of Applied Sciences of Mannheim Germany and

VDE in Berlin. His special fields of interest is reactive power

compensation and harmonics, design, protection and control of

electrical power systems, VDE and IEC regulations. He is an

author

of

tree books in electrical engineering being published

in

2000 in German and another tree books in Turkish. He is a

member

of

VDE and IEEE.

V.

CONCLUSIONS

The results presented show that the shunt active power

filter configuration combined with a passive filter

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7117171-A-New-Method-for-Power-Factor-Correction-and-Harmonic-Elimination-in-Power-Systems.pdf