International Journal of Applied Engineering Research

ISSN 0973-4562 Volume 10, Number 1 (2015) pp. 1243-1252

© Research India Publications
http://www.ripublication.com

A Survey On Control Strategies For Shunt Active Power

Filter For Reactive Power Compensation

S. Ravichandran*

Research scholar,
Department of Electrical and Electronics Engineering
Anna University Chennai – 600 025
Tel: +91-9489-821-541 E-mail: stravichandranphd@gmail.com

Dr. A. Senthilkumar
Professor
Department of Electrical and Electronics Engineering
Velammal Engineering College, Chennai.
E-mail: vastham@gmail.com

Dr. M. Arumugam

Director R&D, Arunai Engineering College, Tiruvannamalai-606 603

Former Director-NIT,Tiruchi.

Abstract

This paper bestows a survey on different control strategies for Shunt active
filters employed for reactive power compensation. An assortment of power
quality tribulations are instigated in the power system due to frequent use of
non-linear and inductive loads. In practical scenario, the load and source
condition may not be predicted. For effective harmonic control and reactive
power compensation, the control strategy employed in SAPF should be
enough to handle distorted, unbalanced source and load conditions. Further the
elected control strategy must handle steady state and dynamic conditions. The
cram also guides the researchers to pick the finest control strategies for SAPF
based on commitment.

Key words: Shunt Active Power Filter, Instantaneous Power Theory, Control
Strategies, Harmonics, Non Linear Load.
1244 S.Ravichandran, Dr. A.Senthilkumar, Dr.M.Arumugam

I. Introduction
Augmented use of Non linear loads introduced solemn trouble in electric power
distribution system. Customary raise in the harmonic origin and imbalance of current
with the addition of high utilization reactive power can be pragmatic. Currents with
harmonic in electric grids can introduce harmonics and disorder in voltage. Polluted
currents can interact harmfully with an ample collection of power system components,
control systems, protection circuits and non-linear loads. This review paper
significantly classifies the available control strategies for Shunt active power
conditioning system, from the view of power system conditions.
This escorts eventually to the stipulation of the key procedure for picking the
appropriate control strategy for power system applications. The power quality disquiet
can be easily solved with the application of appropriate control strategy, relevant to
source and load conditions.

II. Control Strategies for active power filters

The desired compensation properties can be arrived by an appropriate control strategy
with Shunt active power filter. There are numerous control strategies in which some
are pertinent only for normal source conditions and few are much appropriate even for
distorted and unbalanced source conditions. An instantaneous reactive power
compensator without capacitor is elaborated [1]. A control strategy based on only real
power is employed in shunt active power conditioners [2].
The various line conditioning methodologies were discussed for active power
conditioners [5].The p-q theory and properties of three phase system are revealed [7].
An instantaneous active and reactive current based compensator is employed and
performance is appraised for normal source conditions [9]. An unbalanced current
compensator was employed in three phase system for reactive power compensation
[10].
The performance analysis of a shunt active power filter based on new control
algorithm for compensation of harmonic and reactive power of a 3-phase system
under non-ideal source voltage scenarios was carried out [13]. An improved
instantaneous active and reactive current component method is employed for power
factor correction and harmonic reduction [16].
A Survey On Control Strategies For Shunt Active Power Filter 1245

PCC

3 Phase Non-Linear
3 Phase Supply
Load

SAPF

Gate pulse to SAPF

Measured Source Comparison for gate pulse

Currents generation

Reference currents
from appropriate
control strategy

Fig 1. Structure of SAPF with Control Strategy

III. Instantaneous active and reactive power (PQ) method.

Shunt active power filter compensation currents are derived from measured
instantaneous active and reactive powers of load. This is realized by computation of
supply voltages and non-linear load currents in α-β frame as given below.
 1 -1 / 2 -1 / 2   ua 

uα
uβ
= 
3 0

2

2
3
-
3   ub 

2 
  uc 
(1 )

ua ,ub and uc are the measured voltages from the source.

1 -1 / 2 -1 / 2   ila 

ilα
ilβ
=
2

3 0
 2
3
-
3   ilb 
 ilc 
2  
(2)

ila ,ilb and ilc are the measured currents from the load. Instantaneous active and
reactive load powers Pl and Ql are computed as

  
pl
ql
=
uα
-u β
uβ
uα   i lα
ilβ
(3 )

Which can be perished into oscillatory and average terms as pl  p l  pl .The

active filter should compensate oscillatory power components to ease the power rating
of the filter. To compensate for pc   p  l and q c   q l , a filter of second order
1246 S.Ravichandran, Dr. A.Senthilkumar, Dr.M.Arumugam

is used to extract the oscillatory component from real and reactive powers. The
compensation current is obtained by taking inverse of matrix (3) and resulting as (4)
& (5).

 ic
ic

2
u  u
1
  
u u
2 u u
pc
qc
(4)

 
 1 0 
 ic1   
  2  1 3   ic 
 ic 2   3 .   2 2  .  ic  (5)
 ic 3     
 
 1 3
  
 2 2 
Compensation currents from (5) are compared with measured grid currents for
switching signals in the active filter.

IV. Instantaneous Real Power Theory

Foundation of this theory is from the universal P-Q theory. The active filter need to
compensate the oscillating part of the instant active current of load and thereby
produces sinusoidal source current. For computation of compensation current, the
oscillating component of load real power alone is considered in this method. The real
power of the load is calculated from (1), (2), (3) as above and a filter is used to
separate oscillating component. The power loss due to DC-link capacitor also taken in
to account for computation of compensation current.
 
   kI 
PDC(loss) =  v -v  kP+  (6)
 DC,ref DC 
 s 
Now the real power need to compensate is given as,
p = P ac + P d c ( lo ss) (7 )

The compensation current is given by (8).

 ic 
ic 

u
2
1

 u
2  u u
u u  
p
0
(8 )

Compensation currents are calculated by substituting (8) in (5) and are compared
with measured grid currents for gate pulse generation to switches in the active filter.
A Survey On Control Strategies For Shunt Active Power Filter 1247

V. Reactive Power Theory

This method is also derived from universal PQ theory like instantaneous real power
theory. For computing the compensation currents, only oscillating component of load
reactive power is considered. The reactive power of the load is deliberated from
(1),(2),(3) as above and a filter is used to separate oscillating component.
The compensation current is given by (8).


ic 
ic 

u
2
1

 u
2  u u
u u   0
 
 q 
 
(9)

The Compensating currents are premeditated by substituting (9) in (5) and

compared with measured grid currents for generation of switching pulses in active
filters.

VI. Instantaneous Active and Reactive current component id-iq

method
The exploitation of control strategy is based on instantaneous active and reactive
current components to obtain compensation current [4]. From synchronous reference
frame theory the load current components are derived in d-q frame as in (6).


ild
ilq

cos  sin 
 sin  cos    il
il
1
,   tan (
u

u
) (10)

By geometric relations (10) can be written as,


ild
ilq

(u
2
1
2
 u )
.   
u u
u u
.
il 
il
(11)

ild and ilq are passed through second order high pass filter to eliminate dc value.
As a result of above, compensation currents become

icd   ild and icq   ilq

By transforming (11) from dq to αβ frame,

 
ic
ic

( u
2
1
2
 u )
 u   u
u u  
icd
icq
(12)

Substitute (12) in (5) with this above values of icd and icq we get the reference
currents as below.
1248 S.Ravichandran, Dr. A.Senthilkumar, Dr.M.Arumugam

 
 1 0 
 ic a   1 
 ic b 
 icc 

2

3
 2
 1 2
3


 
ic 
ic 
(1 3 )

3
  
 2 2 

VII. Improved instantaneous Active and Reactive current component

method
The compensation currents for SAPF are derived from measured instantaneous active
and reactive current components of load. This is realized by computation of supply
voltages and non-linear load currents in α-β frame. Computation of load currents in
rotating (dq) reference frame is attained by Park’s transformation (10).
The voltage components (direct and the quadrature) are given by,
2 2
ud = udq = uαβ = uαF + uβF

and
u q  0
By substituting,
u F uF
co s   and sin  
u F 2  u  F 2 u F 2  u  F 2

1
 ild
ilq

2
u F  u F
2  u F
u F u F
u F
 il
il 
(14)

Active and reactive currents of load in rotating reference frame, ild and ilq can be
divided into oscillatory and average terms as,
i ld  i ld  ild and i lq  i lq  ilq
The harmonic segregation of d–q transformed signal is derived by eliminating the
dc component and the reference compensator currents are achieved as.
i*cd  ild and i*cq  ilq
The reference currents for Shunt active power filter in the αβ coordinates are
computed by Inverse Park transformation as,
 i*c    i*cd 
 i* c  
  u F
2
1

 u F
2  u F  u  F
u F u F   i*cq 
 
(15)
A Survey On Control Strategies For Shunt Active Power Filter 1249

The reference currents for Shunt active power filter in the abc coordinates are
computed by Inverse Clark transformation as,
 
 1 0 
 i*ca  2  1 3   i* c 
 i* cb  
 
  i * c   (1 6 )
 i* cc  3 2 2
   1 3 
   
 2 2 
Compensation currents are computed by (16) are compared with measured grid
currents for generating switching pulses.

VIII. Improved instantaneous PQ theory

The universal instantaneous reactive power (p–q) theory is reprehensible under non-
ideal voltage conditions. In order to improve the performance, the new algorithm is
proposed in [5].The d – q reference transformation is applied for reducing number of
filters used.
From (3),


i
i

u
2
1

 u
2 u  u
u u 
  p
q
(17)

Measured voltages are converted to αβ frame and filtered as shown in the block
diagram below.

LPF

Vabc v vd vd v v
v

v v vq vq v v

LPF

Fig 2. Block diagram for filtering voltages.

  
u
u

cos 
sin 
 sin 
cos    udF
uqF
(18)

*i c 
*   2 2
1

i c  u   u 
 
 
u u
u u
p
q
(19)
1250 S.Ravichandran, Dr. A.Senthilkumar, Dr.M.Arumugam

Compensation currents are calculated by substituting (22) in (13) and are compared
with measured grid currents for generation of pulses in the active filter.

IX. Average Power method

To obtain fundamental component of mains voltage a PLL is preferred. The mains
voltage possess fundamental and distorted component. Unit vector templates of
voltage is obtained by sensing the input voltage and multiplied by 1/ vpk, where vpk is
maximum value of fundamental voltage. By passing the Unit vectors via PLL,
synchronization of signals is achieved. The fundamental frequency components from
PLL are multiplied by vpk to get fundamental mains voltage.
The reference for load current component I*smp is computed with the help of
sensed average load power Pavg. The sensed load currents(Ila, Ilb, Ilc) and bus voltages
(Va, Vb, Vc) through PLL are used to obtain the instantaneous power PL ,
P L  u a .i L a  u b .i L b  u c .i L c (20)
The average power Pave is computed by taking the average of instantaneous power
for 1/6 th of supply frequency. The peak current component of load I*smp,
*
P avg  1 .5 V p k . I sm p (21)

The reference peak current required to compensate the losses in APF is I* smd and
computed by comparing the reference voltage and actual capacitor voltage. Average
voltage of capacitors used in each phase is taken as the actual capacitor voltage. The
peak reference source current I*sm is calculated as in(16).
* * *
I sm  I sm p  I sm d (22 )
The reference source currents (i*sa,i*sb,i*sc ) are calculated by the product of peak
value I*sm with unit current templates(usa ,usb ,usc)obtained from bus voltages(va,vb,vc)
through PLL. The APF desired references currents (i*ca,i*cb,icc) are as follows,
* *
i ca  i s a  isa (23)
* *
i cb  i s b  isb (24 )
* *
i cc  i s c  is c (25 )
The equations (23),(24),(25) are compared with measured grid currents for gate
pulse generation to switches in the active filter.

From various control methodologies, the comparison has been established in

table 1
A Survey On Control Strategies For Shunt Active Power Filter 1251

Table 1 Comparison of control strategies

Unbalanced
Normal& Normal& Balanced
Distorted
Balanced Unbalanced Distorted
Source
Source Voltage Source Voltage Source Voltage
S.No control strategy Voltage
Condition Condition Condition
Condition
Excellent
1 PQ theory Incompatible Incompatible Incompatible
Compensation
Excellent
2 P theory Incompatible Incompatible Incompatible
Compensation
Excellent
3 Incompatible Incompatible Incompatible
Q theory Compensation
Excellent
4 Incompatible Incompatible Incompatible
id-iq method Compensation
Improved Excellent Excellent Excellent Excellent
5
id-iq method Compensation Compensation Compensation Compensation
Excellent Excellent Excellent Excellent
6 Improved PQ theory
Compensation Compensation Compensation Compensation
Excellent Excellent Excellent Excellent
7 Average power method
Compensation Compensation Compensation Compensation

X. Conclusion
This literature assessment has given prominence to describe the effectiveness of
suitable control strategy for SAPF to augment power quality under various source
voltage conditions in three phase system supplying non-linear load. Seven different
control strategies for SAPF are discussed and their suitability for different source
voltage scenarios have been elaborated. From the table1, the effectiveness of control
strategy for various source voltage conditions is determined.

XI. References
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