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National Power

Energy

Conference

(PECon) 2004

Proceedings, Kuala

Lumpur,

Malaysia

132

SVM

Based

Hysteresis Current Controller for a

Three Phase Active Power Filter

L.

P.

Ling,

and

N

A.

Azli

Absfract-a space vector modulation

(SVM)

based *hysteresis

current controller

(HCC)

technique for a three phase shunt active

power filter is proposed. The switching control algorithms of the

proposed SVM based HCC manage to generate compensated

curre nt according to

the

reference current. Harmonics extraction

is

based

on

the instantaneous active and reactive power theorem

in t ime

domain

by

calcutating

t h e

power compensation.

A

closed

loop

control system is implemented and the error current

is

the

difference between

the

reference curren t obtained from the power

compensation and the actual current

that

needs

to be

injected

back into the line.

By

iniplementing this

control

strategy, the

active power filter

(APF)

manages

' t o

generate better

compensated harmonics curren ts

t o

the line.

I n d u

Terms-Active pow er filter, Com pens ated

harmonics

current, Hysteresis current controller, Instantaneous reactive

power, R eactive power com pensation, Space vector m odulation.

I. INTRODUCTION

S

power electronics are widely used nowadays, these

A oads seems to be the

most

common source

of

power

harmonics in the power system Passive and active power

filters

APF)

re used

in

order

to

improve this unclean power

supply. Different techniques and control strategies for

APFs

had been proposed depending on the conditioning purpose

required. Various conditioning methodologies of active power

line conditioning had been discussed

in

111.

Besides that, there

are various types

of

active power filter's configurations. The

common categories of APFs are shunt, series and hybrid

configurations. However, shunt APFs are

mostly used

in

the

commercial stage. It

i s

normally a voltage fed inverter

wth

a

current

minor

loop

[2], [3].

There are many control strategies

for

shunt APFs.

One popular

time

dom ain analysis tool is

the

instantaneous power theorem (pq theorem) by

Akagi et al.

in

1980s.

This theorem depen ds

on the instantaneous

current and

voltage.

This

theorem is applied

in

conjunction

wt a PWM

current controller

in

order

to

produce appropriate switching

signals for the harmonics current compensator

t41-163.

The

hysteresis current controller

(HCC)

is the

most

commonly

proposed control method

in

time

domain. This

method

provides instantaneous current corrective response, good

h o w

Pei Ling

is with

the Control

and

Instrumentation Engineering

Department, Faculty of Electrical Engineering, Univmih Tehologi

Malaysia,

81310

UTM Skudai, Malaysia (e-mail: leowpl@fke.utm.my).

Naziha

Ahmad Azli is with the

Energy

Conversion Department

(ENCON), Faculty

of Electrical Engineering, Universiti Telolologi Malaysia,

81 3 IO

URVl Skudai, Malaysia

(e-mail:naziha@ike.um.my).

0-7803-8724-4/04/ 20.0002004

IEEE.

accuracy and unconditioned stability to the system. Besides

that, this technique

is

the easiest and most suitable for current

controlled inverters

[l],

[ 7 ] ,

[SI.

The disadvantage of

this HCC

is

that

it

requires high switching frequency, However,

this

weakness, can be overcome by conjunction

of

the space vector

modulation (SVM) technique to the controller. SVM was

first

introduced by the German researchers in the mid of 1980s.

This

technique showed several advantages aver the traditional

pulse width modulation

fPWM)

technique.

S V M

technique

can maximize the output voltage and also reduce

the

switching

number at the same carrier frequency

of

the PWM method.

Besides

that, it can

be

easily programmed and implemented

in

digital system

[91-[12].

This

paper presents the analysis based on the combination

of

the three techniques above. The conjunction

of

the S V M

technique

wth

the HCC

generates gate switchmg pulses

for

the APF and the instantaneous active and reactive power

theory

@q

theorem)

is

used

to

generate the reference

compensated current

for

the current controller

as

this system is

implemented

in

a closed

loop

form. The three phase shunt

APF

generates

the

desired com pensated

harmonics

currents for each

phase according to the error between the reference current

from the pq

theorem and

the

generated compensated current

from

the shunt

APF.

'

11. S YS T E M

CONFIGURATION

Fig.

1

shows the fimdaniental blocks

of

the proposed closed

loop

control

strategy for a three phase

APF. The

configuration

for

the APF

is

in

the f o rm

of

a current regulated voltage source

inverter. Power compensation technique

in

conjunction

wt

the SVM based HCC is

used

to generate appropriate gate

switching signals

for the

three

phase APF.

Reactive power compensation technique is used to isolate

the desired compensated harmonics

it*

with the fundamental

signal. The desired compensated harmonics

i,

is used as the

reference current

in

the

system This

allows the proposed

APF

to

produce

the

output current according to the reference

current i,

from

the pq calculation. Besides that, the feedback

current signal is the output current

i of

the

inverter whch

needs

to

be injected back

into

the power line.

The current

error signal is

acquired

from

the difference

between the reference current and the feedback current. This

current error signal is then fed

into two

sets

of

hysteresis

comparators

to

determine

the

region and the vector

of

the

reference current.

The

status

of the

outer and inner ban d errors

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133

are sent into

the

region detector and

the

switching function

table. Six sets of appropriate gate switching signals are

generated and are sent

to

the voltage source inverter. The

desired compensated current is generated by the three phase

inverter and i s injected back into each power line

to

compensate the distorted Lines current.

The transformation coordinates of the related space vectors

are

shown as follows:

1 -0.5

-0 .5

‘:,“ 1 -

Fig.

1

Block diagram

of

the proposed

APF

As a

result, he conventional pow er for thee phase circuits

be derived as follows:

’

= - - - -,

. -k e p . p =

e

+ epip

(3)

and the instantaneous reactive power is defined as follows:

(4)

- - -

= Fa x p+ ep x ia

=

evia -ea’,

From (3) and (4), the equation can be expressed as

5)

can

A

Reactive power

compensalion

The instantaneous active and reactive power theory deals

with the voltages and currents mathematically to calculate the

imaginary power

of

the three phase power circuits. The

instantaneous imaginary power

is

the reactive power which

needs

to

be

eliminated.

This

pq theorem performs

and

from S) ,

the instantaneous compensating currents can be

derived

by

6 )

instantaneously

as

the calculation

is

based

on

th

nstantaneous

voltages and currents

of

the three phase circuits

[4].

The instantaneous voltages,

e,, eb ,e,

,

and

currents, ,

b

,

aS

the

compensator will only compensate the instantaneous

reactive power,

the

real power

is

always

set to zero. The

instantaneous reactive power is set into opposite vectors in

iC

I

are

expressed as instantaneous ’pace Fig’

shows

order to cancel the

the transfomutions Of the

three phase

and

component in the line current, The

t h e e

phase

compensated currents are defined

as follows:

vectors in

~ 4 - c

oordinates

into

orthogonal coordinates,

coordinates.

i

(7)

These instantaneous compensating currents

for

each phase

icn*,

icb*,

and

ice*

are

used as

the

reference currents for

the

current

Fig. 2.

Orthogonal coordinate transformation

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134

controller.

3

S

VM Bused HCC

The S V M echnique treats the inverter as a whole unit,

which

is different when compared to P W M echnique. The

inverter

can

be driven to one of the eight unique switching

states, where each state corresponds to

a

space vector

[lo],

[12].

Fig.

3 

shows

the space voltage vectors according

to

the

eight switching states.

Vo is

the

zero

voltage vector,

and

it

normally has

two

switching pattems

Vo (000) and V,

(1

11).

However,

in this

paper, the zero voltage vector is always set

to

vo (000).

v4 (011)

I

v3

010)

v2 (1

IO)

Fig.

3.

Space vectors and derivative vectors

of

current

error

in

region

I

The derivative vectors deidt

o f

the current error determines

the correct or deslred space voltage vectors

VI: or

each state.

Fig,

3

shows the desired output space voltage vectors

V,*

is

located in region I. The derivative vectors of the current error

respect to

the

output space.voltage vector

in

region

I

shows

that del/dt and de2/dt provides the mini values

of

derivative

vectors of

t h e

current

error. Hence, the correct

space voltage vectors

for V,*

are

V,,

Vz and Vo.

Based

on the

SVM

principles,

o n l y

correct and adequate

vectors

will be

applied

in

each switching state.

By

implementing this

technique

to the HCC, this

can reduce the

unnecessary number of switching. HCC is used to denote

further information

of

the derivative vectors

of

the current

error.

Two

sets

of

different tolerance band hysteresis

comparators

are

used. Each

set

consists

of

three individual

hysteresis comparators. The wider tolerance band hysteresis

comparator

is called the outer

band

controller

which is

used to

denote the region

of the

output vectors. And the comparator

wth

narrow

band

or

the inner band comparator

is

used to

denote the proper sp ace voltage vectors. The

output signais of

the outer band

HCC,

Bo Bb

B

aad the

output

signals

of

the

inner band

HCC, BairBbi Bci,

provides

the

information to a

programmable logic array to produce appropriate gate

switching signals

to the

three phase APF.

The

signals

of

each sets

of

the hysteresis comparator fo r all

regions are arranged

in

Table 1

to show

the output

of

the

desired space vectors

Vk and the

related

regions of

each state.

To

avoid confusion, each

Vk of

each state is represented

by

three

output

parameters,

y l

y2 and y3

w h c h a re

set

according

to the output signals of the inner

band hysteresis comparators.

These three parameters are then used to generate

gate switching signals of

the

APF.

TABLE

I

SVM BASED WITCHINGUNCTIONAELE

six sets

of

111 SIMULATION RESULTS

The

performance of the proposed control strategy

is

evaluated

through

digital simulation using Matlab Simulink

program.

The

outer tolerance bands and

the inner

tolerance

bands are set to roughly 8 and

4

of the maximum

harmonics current respectively. However, as the applied loads

are dynamic,

the

settings

of

the tolerance band have to be

reconsidered.

This is

because the magnitudes

of

the

harmonics

current are changing according to

t h e

loads applied.

Fig. 4(a) shows

the

compensated

harmonics current in

phase

A

which

is

injected

to

the

line by the

APF with the

outer

and inner bands tuned to

3.0

and 1.2A respectively.

T h s

tolerance bands are tuned in

wt

respect to the initial

harmonics loads

current. These bands produced

smooth

and

fine compensated harmonics current for the whole simulation

of

dynamics

loads. Fig.

4(b)

and (c) shows a wider range

of

tolerance bands settings for outer and inner bands. However,

the outputs obtained are not satisfactory. Wider tolerance

bands failed to produce accurate output signals for

the SVM

switching function table.

Fig.

5(a) shows

the

distorted

line

current

of

dynamic

load's change

in

phase A. The

desired com pensated harmonics

current

due

to the changing loads is

shown

in

Fig.

5(b).

This

compensated harmonics current is regenerated and injected

back

into

the

line by the

SVM

based

HCC

active power filter.

Fig.

5(c ) shows

the compensated supply current

of

phase

A

wth dynamically changing oads. Analysis

of

10cycles

of

the

signals

in Fig. 5 shows

that the proposed APF reduces the

THD

of the supply line current

from 30.11

to 5.32% which

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135

the comparison of the harmonics spectrum for uncompensated

and compensated fine currents'are shown inFig. 6 .

C o m m s a l e d Harmonics Currenl

- ~ . 1 3

0.t35

0.14 0.145 0.15

0.155 0.18 0,185

(al

IiamonIcs Spectrum br the Uncmpensaled Line

Currenl

Fundament4 ( 5M Z) = 210.7, THO= 30.11%

t I

8 83;

I

(a)

Hannmic$Spectmmbr the Compensated Line

Current

Fundamental 50Hr)=

210.5,

M O = 5.32%

Fig.

6.

Ilarmonics spectrum

(a)

distorted line current,

(b) compensated line current.

(E)

l l m e

8)

Fig. 4.

Compensated

harmonics

current with outer and inner

Loleraiice bands are

set

to

(a)

3.0 and 1.2

A

respectively,

(b) 6.4 and

3.2

A respectively, (c ) 14.4 and

7.0 A

respectively.

Thc

sccond

niost

sigtiificant hannotiics uf h c distorted linc

current which is about 20 of the fundamental component

is

reduced to 4% of the fundamental component. As a result, the

THD

o f

the line current is improved.

r

0 05 0.l

(a)

0.15

0.2

300,

0.05

0.1 b)

0.15

0.2

0.1

(cl

0.15

0.2

T i m i i s

Fig.

5 . Current

waveform

(a) distorted

line

current,

(b)

Compensated harm onics current, (c) Compensated

suppIy

current.

IV . CONCLUSlON

The

proposed APF has managed to produce compensated

harmonics

current regardless to the changing

of

loads. The

SVM

based HCC has provided proper switching vectors tu the

APF

by

detecting the region and vectors of each states. Better

compensated harmonics current is obtained by setting snialler

tolerance bands for the hysteresis comparators.

v.

REFERENCES

W. M . rady, M

Samotyi,

and A. H

Noyola, Survey of

active line

conditioning methodologies;' f6E.E

Transnclions

011 Power D d i i w y

H Akagi, ''Trends

in

active power line conditioners, IEEE

TransacIiorrs on Power Electronics, vu]. 9 pp.

263-268,

ay 1994.

H. Akagi, New trends

in active

fi l ters

for

power conditioning,

IKEE

ransactions on

Industry Applicarions, vol.

32,

pp. 1312-1322,

Nov/Dcc 1936.

H. Akagi.

Y.

Kanewa, and A. Nabae. Instantaneous reactive power

compensators comprosing switching devices without energy storage

components,

IEEE Pans .

Indus l ry Applications.

vol.lA-20,

pp. 625-

630, May/June 1984.

F. 2

Peng,

H. Akagi, rnd

A. Nabae, A Novel

Harmonics Power

Filter.

IEEE Transactions Power Electronicr Specinlisfs Conference, PGSC

8 8

Record, pp. 1151-1 159, 11 -14 ApriI 1988.

M. redes,

and

L

F.

C. Monteira, A control slratcgy for shunt active

filter, presented at the 10

ln temat ional

Conrerence: llarmonics and

Quality of Power, vol . 2, pp.

4 7 2 4 7 7 ,

2002.

vol. 5, pp.1536-1542, July 1990.

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David M.

E.

Ingram, and S. D. Round, “A

novel

digital hysteresis

current controller for

s n

active power filter,” in

f r o c .

1997

international Conlerence

on

Power Electronics

and

Drive Sysfems,

May 26-29, vol. 2, pp.

IEEE

744-749.

S . Buso,

S.Fasolo,

and

I-.

Malesani, “A dead-beat adaptive hysteresis

current control,” IEEE Transactions on

Industry

Applicofions, vot. 36,

pp, 1174-1180, uly/August

2000.

M.

P. Kazmierkowski, M. A. Dzieniakowski, and W ulkowski, ‘Wove1

Space vector based current controllers for

PWM-Inverters,”

IEEE

Transactions on Power Elecrronics,

vol.

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pp.

158-166,

Jan

1991.

[lo] B. H.

Kwon, T. W

Kim. and

J.

H

Youm,

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[ I l l M. I. Marei, E. F. El-Saadany, and M. M. A. Salama, “ A new

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[I21 R

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VI. BIOGRAPHIES

Leow l’ei Ling

was born in

the

state of Selangor in

Malaysia, on August 5*, 1980. She paduated from

Universiti

Teknologi

Malaysia

in

the year of 2003.

She is currentiy

undergoing her

master’s degree in

electrical engineering majoring in Mechatmnics and

Automation Control in the Faculty

of

Electrical

Engineering, Univeniti Teknologi Malaysia.

Naziha

Ahmnd Arli has

been serving for 16

years as

a lecrurer at the Faculty

of

Electrjcal

Engineering,

Universiti

Teknologi

Malaysia.

She

received

h r

l3.Sc.E.E. degree from the University of Miami,

Florida,

U S A

and her M.E.E. and Ph.D degrees from

Universiti

Teknologi

Malaysia in 1986, 1992 and

2002 respectively. She currently teaches power

electronics at both undergraduate and

masters level.

Her research interests include pow er converters

sta t ic

applications,

power quality and PVifuei

cell power

systems.