A New Hybrid Series Active Filter Configuration to Compensate Voltage Sag, Swell, Voltage and...

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IEEE International Symposium on Industrial Electronics (ISlE 2009)

Seoul Olympic Parktel, Seoul, Korea July 5-8, 2009

New Hybrid Series ctive Filter Configuration to Compensate Voltage Sag

Swell Voltage and Current Harmonics and Reactive Power

Ab. Hamadi, Student Member, IEEE, S. Rahmani and K. AI-Haddad, Fellow, IEEE

Canada Research Chair in Energy Conversion and Power Electronics CRC-ECPE

Ecole de Technologie Superieure, 1100 Notre-Dame West, Montreal, Quebec H3C 1K3, Canada.

Email: [email protected]@[email protected]

Abstract- This paper proposes a new system configuration

for a series hybrid power filter (SHPF) realized for all

harmonic types

of

loads. The series hybrid filter consists

of

a small rated series active power filter (SAPF) and a shunt

passive filter with variable inductance using a thyristor

control reactor (TCR). The DC voltage available at the load

side of a typical voltage harmonics source, such as a diode

bridge rectifier followed by a capacitor, is utilized as a

source

of

DC power for the SAPF. To increase the filtering

performance of the shunt passive filter, SAPF is control in

such a way that it increases the network impedance at the

harmonic frequency. This also helps to avoid any series or

parallel resonance that may occur. The shunt passive filter

together with a TCR is used to support the variable load

reactive power demand as well to tackle the current

harmonics generated by non-linear load. The performance

of proposed series hybrid power filter is validated through

MATLAB/Simulink simulation study and successfully

utilized to compensate the voltage sag, voltage swell,

voltage harmonics, current harmonics and load reactive

power demand.

Index Terms- Hybrid active filter, series active filter,

thyristor control reactor, voltage sag and swell, harmonics,

reactive power support.

I. INTRODUCTION

The rapid increase in the technology, especially in electric

power sector, the use of non-linear loads on a typical

distribution system has been increased significantly in

recent years. These non-linear loads are the major source of

harmonics in modem distribution system which is making

the distribution system polluted. On the other side, the

modem equipments are becoming increasingly sophisticated

and require clean power for their proper operation. Any

variation in supply voltage, such as voltage sag and swell or

even harmonics in voltage causes the sensitive equipment to

malfunction.

To improve the quality of power, several solutions have

been proposed by several authors. Among them the shunt

and series active power filters have proven as an important

and flexible alternative to compensate most important

voltage and current related power quality problems in the

978-1-4244-4349-9/09/ 25.00 ©2009 IEEE

286

distribution system [1-8]. The other alternative is the use

of

a unified power quality conditioner (UPQC) to compensate

voltage and current problem simultaneously. However, the

use of UPQC is an expensive solution [9]. A SAPF

essentially requires a source of energy, such as a DC

battery, in order to compensate for voltage sag and swell.

Generally, a separate rectifier is used to provide the

necessary DC power for the

SAPF.

A full bridge diode

rectified followed by a capacitor is extensively used in

modern plants, for example, as in adjustable speed drive.

However, such a topology is often considered as a source

of

voltage harmonics as it generates harmonics in supply

voltage. This paper proposes a new topology for a SHPF

which utilizes an existing front end diode bridge rectifier as

a source

of

DC power for the SAPF. This arrangement thus

helps to eliminate the use

of

additional rectifier require

of

the SAPF. A shunt passive filter together with a thyristor

control reactor (TCR) is used to tackle the harmonics

generated by non-linear load as well as to support the load

reactive power demand. The TCR in passive filter is used to

support the variable load reactive power demand [10-12].

Moreover, the TCR considerably reduces the size

of

overall

shunt passive filter. A hybrid detection method is added to

increase the impedance

of

the series transformer at the

harmonic frequency, which force the current harmonic to

flow in the shunt passive filter. The DC bus voltage of SAPF

is maintained at a constant level by regulating the voltage at

load bus at desired constant level.

II .

PROPOSED HYBRID SERIES ACTIVE POWER FILTER

TOPOLOGY

The system configuration

of

proposed SHPF is shown in

Fig. 1. It consists

of

- (i) small rated series active power

filter, (ii) shunt passive filter and (iii) a typical voltage and

current harmonics type

of

source. The SAPF protects the

sensitive load from variation in the supply voltage. It injects

a voltage component in series with the supply voltage and

thus considered as a controlled voltage source. The required

DC bus voltage for SAPF is provided from the load side.

The output of DC voltage of front end diode bridge rectifier,

as shown in Fig.1, is shared with the

SAPF. This

arrangement thus eliminates the need

of

additional separate

rectifier for the SAPF. The regulation

of

necessary active



power during the voltage sag and swell condition is done by

maintaining the load voltage at constant level. Thus in the

proposed configuration the need

of SAPF

DC bus voltage

regulation is also eliminated.

In the proposed topology a reduced size passive LC filter

alone with a TCR is connected in parallel with the load. The

SAPF controlled as a harmonic isolator, forcing the load

current harmonics to circulate mainly through the passive

filter rather than the power distribution system. The main

advantage of this scheme is that it reduces the required

power rating

of SAPF.

Where icd » ieq denote the currents in the SAPF inductors,

expressed in synchronous

(d-q)

frame. v

sd

' v

sq

represent

the voltages at the primary side of the transformer,

i

sd

'

i

Sq

are the d-q components

of

the line currents at the primary

side

of

the SAPF.

d

a»

d

q

represent the duty cycles

of

the

upper switches in the inverter topology, Vde is the DC

voltage

of

the inverter and aJ

o

is the mains angular

frequency.

III. SERIES ACTIVE POWER FILTER MODELING

IV .

REFERENCE CURRENT GENERATION

(1)

The

SAPF

is connected in series with the AC source. The

system can mathematically be represented as: [13,14]

L

diea

e -=vea - v

an

dt

L

dieb

e

veb

-v

bndt

The necessary equations to generate the reference signals

are given below:

C

d VCd C

= =

VSq-Zcd+zsd-» ; (6)

dV

cq

-ClOOV

sd

- lcq

+

lsq

u

q

dt

Applying the Park transformer to the Eqn. (1) and to the

Eqn. (2), yield to:

Using PI controller to regulate the voltage of the SAPF.

»:

=

k

p

v

cd

+k, JVeddt (7)

u

q

=k

p

v

eq

+ k

i

JV

eq

(8)

From Eqn. (4), the control law is given by

U

id

- v

ed

- Lemoi

eq

dd =

(13)

v

de

V. IMPROVING FILTER PERFORMANCE

Using PI controller to regulate the current of the

SAPF.

U

id

=kpi

cd

+k, Jieddt (11)

u

iq

=

kpi

eq

+k, Jieqdt (12)

The reference current controller is then given by

i

ed

*

=

-u

d

+

Cm

o

v

eq

+ t; (9)

i

eq

*

=

-u

q

-Cmov

ed

+i

Sq

(10)

(2)

(3)

dv;

. .

=

sc

-lee

dt

1

[

Sin(

lO

ot) -COS lOot

]

P = cos(mot) sin(mot) 0 0

3 0 0 1 3

2

L

dice

e

ee

-V

en

dt

dv

ea

. .

=

sa -lea

dt

dv

eb

. .

=

sb

-leb

dt

Where ie,a,b,e are the currents flowing through the SAPF

inductors and the

is,a,b,e

are the line currents at the primary

side

of

the

SAPF.

To reduce the system order and optimize

the mathematical representation the Park transformation is

considered. The transformation matrix P can be defined as:

1 1

~ - ~

J3 J3

2 2

3 3

2 2

(4)

(5)

The SHPF control scheme is shown in Fig. 4. The approach

uses a hybrid control; detect simultaneously the source

current

is (abc)

and the load voltage

V

L

(abc)

to get their

harmonic components. The main idea is to increase the

impedance of the series transformer at the harmonics

frequency. The reference compensation voltage of the SAPF

adopting hybrid control approach is: [15]

v

=

ki

sh

V

Lh

(15)

287



(16)

C

pF

:i CPFa

i a

iLp a

: C

pF

= .

, LpFCa):

Fig. 3. TCR equivalent circuit

The main concept behind controlling TCR is the control of

the firing instant of the thyristor to control the current in the

reactor, thus controlling the reactive power absorbed by the

TCR. Kirchoff's laws of voltages and currents neglecting

the resistor of the inductance applied to this system provide

three differential equations in the

a-b- c

frame. The TCR

control scheme is shown in Fig. 5.

Applying these transformations in dq frame to the shunt

passive filter:

d

2

i

1

J Fd J . dipFq i CI Fd

Ll lJa -- -Lp

F a

)aT UFd

=

2L

p

p(

a )(J)---- - -

dt dt

C

w

d

2

iU>q .

d i

l J' Fd i Cl' Fq

LPF a - - -LpF a)al lu FQ= 2L

PF

(a ) (JJ----= - -+ -

dt dt C

PF

FldarwiI f ttl):t2MID l14443'

-

II.

o

o 5 10 15 20 25

,...,

o

5 10 15 20

25

..

10 15

-,..

.1.1.

~ l I { I :

S 1 1 .

The compensation effects are, to a great extent, dependent

on the control gain k, which is the ratio of the compensating

harmonic voltage generated by the SAPF to the harmonic

current flowing through it. Fig. 2 shows the series voltage

harmonic versus gain k.

One can observe that by deceasing

k, from 5 to 2, reduce the amplitude of the series

transformer voltage harmonics which affects negatively the

filtering performance. For k =

5

the reflected impedance

of

SAPF becomes high and therefore load current harmonic

flows through the shunt passive branches.

k =5(THD

1S

=3%) k=3(THD

1S

=10%) k=2 (THD

1S

=30%)

Fig. 2 voltage harmonic of series active filter versus gain

k

One knows that:

Only the reactive part is chosen:

(17)

(19)

(18)

The following relation is obtained

A.

Sag and

swell compensation

The extractions of three phases voltage references signals

are based on Unit Vector Template Generation. A Phase

Locked Loop (PLL) is used to extract the sinusoidal signal

at fundamental frequency. The PLL gives signal in terms

of

sine and cosine functions. The obtained v Ca ,b,c) are

compared with the measured

VLCa ,b,

c ) As shown in Fig. 4,

the error signal is feed forwarded to the V

hd

and the

v

hq

signal and compared to the compensator voltages

v

cd

and v

cq

' The feedforward signal enhances the filtering

performance by compensating sag, swell and voltage

harmonics.

To regulate the current i

PFq

a model reference adaptive

control is used. The reactance of the inductance can be

modeled as: [10,11]

Jr

L

Pl

.. {

a ) =

L

pF

,

(20)

2J r

- 2a +

sm(2a)

VI.

SHUNT PASSIVE FILTERMODELING

Thyristor controlled reactor for continuously variable

reactive power can be obtained across the entire control

range, with full control

of

both inductive and capacitive

of

the compensator. The principal benefit is its optimum

performance during major disturbances in the system such

as sudden load change and load rejections. This type of

TCR is characterized by continuous control, low losses,

redundancy, and flexibility. Fig. 3 shows the TCR

equivalent circuit. [16,17].

i

CPFq •

u

j

=

B a - -+

oll

Ll

Fq

C

pF

(

2, C

pF

U 1 -OJ

I

LPFq

-

= B

a

I

CPFq

(21)

(22)

The shunt passive filter presents great impedance at the

fundamental frequency and very low impedance at the

harmonics frequency. This filter combined with the series

active filter is able to absorb practically all the current

288



harmonics generated by the nonlinear load. The passive

filter is reduced in term of components and is very robust

when its parameters change.

VII. SIMULATION RESULTS

The proposed series hybrid power filter configuration is

simulated under MATLAB-PSB environment to estimate

its' performance. The set of loads consists

of

current-source

type

of

nonlinear load and voltage-source type

of

nonlinear

load to study of the effectiveness of the proposed scheme.

The SHPF system was tested for several different operating

conditions such as - steady-state, transient condition,

voltage sag, voltage swell, and under balanced

nonsinusoidal utility voltages, intending to validate the

SHPF system performance. The simulation results are

shown in Figs. 6 - 8 and discussed in the following

subsections.

A. Dynamic performance under load change condition

In order to verify the performance of the SHPF during

transient response, two types of three phase nonlinear loads

are used simultaneously (diode bridge rectifier followed by

R-L load and diode bridge rectifier followed by R-C load).

Fig.6 shows the transient response of SHPF system. The

load current is abruptly increased and decrease. As viewed

from the simulation results, the changeover from one

operating condition to the other is quite smooth,

maintaining the perfect compensation. The sudden increase

(decrease) in the load though causes a small decrease

(increase) in the DC link voltage.

It was observed that this

decrease (increase) in DC link voltage was around 10V for

nov DC link. Consequently as the load on the system

changes, the control algorithm takes minimum two cycles to

compute the new steady-state load active power demand.

This proves that the SHPF system compensates the

harmonics and reactive power of the load during steady

state as well as transient operating conditions without losing

its performance.

The harmonics spectrums befor and after compensation are

shown in the Fig.7. The compensated source current and

load voltage profile show that the SHAF system was

working effectively, reducing the source current THD from

22.34 % to 1.94 % and the load voltage THD from 18.03 %

to 3.31 %, respectively.

B. Voltage sag, swell

and

harmonics compensation

The performance

of

SHPF system is also tested under

voltage swell, voltage sag and balanced non-sinusoidal

utility voltages. The simulation results are shown in Fig.8.

The source voltage has a voltage THD of 18.03% with

dominant 5

th

and 7th harmonics of 15 % and 10 %,

respectively. In consecutive cycles, the voltage swell is

introduced voluntarily in the utility voltage (20%). And

after that, the voltage sag is also introduced in the utility

voltage (-40%). The SHPF system does not show any

significant effect

of

distortion present in the utility voltages

on its compensation capability and, the source current and

the load voltage THD under this condition, are found pure

sinusoidal. Since the load voltage is maintained constant.

VIII.

CO

NCLUSION

To improve the power quality and to reduce the overall cost

of compensator, in this paper a new hybrid series active

power filter configuration has been proposed. The most

important power quality problems, such as, voltage sag,

voltage swell, voltage harmonics, current harmonics and

load reactive power are compensates effectively utilizing

the proposed system configuration. Thus it could be an

economical solution over a UPQC to tackle similar power

quality problems. Moreover, this configuration requires

reduced size of series active power filter. The

MATLAB/Simulink results show that the voltage sag and

swell are compensates effectively providing a regulated

voltage at load terminal. Additionally , the harmonics

present in the load current (load current THD= 22.34%) and

source voltage (source voltage THD= 18.03%) are

significantly reduced to 1.94% in source current and 3.31%

in load voltage. This proposed system configuration thus

eliminates the need of additional energy source required for

the series active power filter.

11

v / .

VLb

VL c

i l , a :

u l h l C s u u r ce typ e HO

li n

e r

lo t

~

u n t

p s si v e filter

Fig. I Proposed series hybrid power filter configuration

289



P

V

s(abc) { re f )

vc(abc)

e

+

U

iq

i

cq

ti l

VI

c:

tlZ

:U 0>

0>

:= .S

(l 3

LL

.i;

C

Fig. 4 SHPF control scheme

V

sa

_

i u

. • u q t j3

I

q 0 - .1 H

H

r

__y cont rol ler Eq.22 oo k up

table

c=7..r

PF q

0. 4

.3 5

.3

.1 5

0 .2 0 .2 5

Fig.6 Sudden load variation

0. 1

.0 5

Fig. 5 TCR control scheme

~

f \ . J C A

A 7 \

n

A 7 \

n

f \ . J C A __

\ J C A ~

- A

A A ~

-200

.

__ 0 .1 0 .1 5 __ 0 .2

__

__ 0 .4

~ -20g

o 0 .0 5 0 .1 0 .1 5 0 .2 0 .2 5 0 .3 0 .3 5 0 .4

o

0

.0 5

0 .1 0

.1 5

0

.2

0

.2 5

0

.3

0

.3 5

0

.4

~ ~

o

0

.0 5

0 . 1 0

.1 5

0

.2

0

.2 5

0 .3 0 .35 0. 4

:g

o 0 .0 5 0 .1 0 .1 5 0 .2 0 .2 5 0 .3 0 .35 0 .4

2 0

.

~ g ~

o 0 .0 5 0 .1 0 .1 5 0 .2 0 .2 5 0 .3 0 .3 5 0 .4

~ ~

o 0

.0 5

0 .1 0

.1 5

0

.2

0

.2 5

0 .3 0 .35 0. 4

~ ~ ~ ~ ? = S F ±

: : :

3

o

THD=1 8.03%

SourceVoltage HarmonicSpectrum

i

80

-36 0

'0 40

to

1

20

o

_ L ~ _

5 10 15

Harmonicorder

THO

=

3.31%

10 15

HarmonICO.de.

Load

Voltag

e Har mon ic Spectrum

THO 22.34%

Load Current Harmonic Spectrum

THO;;1.94%

10 15

Harmonlco rtler

Source Current HarmonicSp

ectrum

a) Source current b) Load current d) Load voltage c) Source voltage

Fig.? Harmonics spectrum a) source current b) load current c) load voltage d) source voltafe

290



0 .4 5.4.3 5.3.2 5.2.1 5.1

~

2000

0.05 0. 1 0.15

0. 2_ _

0.25 0.3 0 .35

0. 4

0 .45

~ ~ 0 ? L n ~ n ~ f ~

200

0.05

0 .1

0.15

0. 2

0 .25 0.3 0 .35

0. 4

0 .45

,_20

•

. e s -2g ~

o 0 .0 5 0 .1 0 .1 5 0 .2 0 .2 5 0 .3 0 .35 0 .4 0 .45

~

1000 0.05 0. 1 0.15 0.2 0 .25 0.3 0 .3 5

0. 4

0 .45

~ ~ _ 1 0 ~ ~

200 0 .0 5

0. 1

0.15 0.2 0 .25 0 .3 0 .3 5 0. 4 0 .4 5

~

_ 5

: : ~ - 2 0

0.05

0. 1

0 .1 5 0 .2 0 .2 5 0. 3 0 .3 5 0. 4 0 .4 5

g

~

E

l i

. . ; ; : ;; ;; 1 : j @

o

0.05

Fig. 8 Voltage sag, voltage swell and voltage harmonics compensation

IX. REFER ENCES

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291

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