International Journal of Innovative and Emerging Research in Engineering
Volume 3, Issue 4, 2016
Available online at www.ijiere.com
International Journal of Innovative and Emerging
Research in Engineering
e-ISSN: 2394 - 3343
p-ISSN: 2394 - 5494
SRF BASED CONTROL FOR POWER QUALITY
IMPROVEMENT USING D-STATCOM
Riya B. vasava
ME ELECTRICAL SCET, SURAT
Abstract:
Three phase three wire distribution system are facing severe power quality problems such as poor voltage
regulation , high reactive power and harmonics current burden , load unbalancing , etc. For the improvement of
power quality FACTS devices are used. FACTS devices are SSSC, UPFC, SVC , D-STATCOM etc. In this paper
D-STATCOM is used to solve power quality problems. There are many different control strategies are used to
control the D-STATCOM. Different control strategies are Instantaneous power theory (IRP) , Synchronous
Reference frame theory (SRF) , Symmetrical component theory (SC), modified p-q theory etc. In this SRF control
strategy is used to control the D-STATCOM. MATLAB simulation is presented with D-STATCOM using SRF
control strategy.
Keywords: power quality, D-STATCOM, voltage source converter , control strategy (SRF), Hysteresis control
INTRODUCTION
Initially for the improvement of power quality or reliability of the system FACTS devices like static synchronous
compensator (STATCOM), static synchronous series compensator (SSSC), inter line power flow controller (IPFC), and
unified power flow controller (UPFC) etc are introduced. These FACTS devices are designed for the transmission system.
But now a day as more attention is on the distribution system for the improvement of power quality, these devices are
modified and known as custom power devices. The term“ custom power” describes the value-added power that electric
utilities will offer to their customers. The value addition involves the application of high power electronic controllers to
distribution systems, at the supply end of industrial, commercial consumers. The main custom power devices which are
used in distribution system for power quality improvement are distribution static synchronous compensate or
(DSTATCOM). A DSTATCOM is utilized to eliminate the harmonics from the source currents and also balance them in
addition to providing reactive power compensation to improve power factor or regulate the load bus voltage. The
compensating type custom power devices can be classified on the basis of different topologies and the number of phases.
For power quality improvement the voltage source inverter (VSC) bridge structure is generally used for the development
of custom power devices, while the use of current source inverter (CSI) is less reported. The topology can be shunt
(DSTATCOM).A DSTATCOM is a custom power device which is utilized to eliminate the harmonics from the source
currents and also balance them in addition to providing reactive power compensation to improve power factor or regulate
the load bus voltage. A Distribution Static Compensator is in short known as D-STATCOM. It is a power electronic
converter based device used to protect the distribution bus from voltage unbalances. It is connected in shunt to the
distribution bus generally at the PCC. The schematic diagram of a D-STATCOM is as shown in Fig.1.1 [1]
Fig.1.1 Schematic Diagram of D-STATCOM [2]

Operating principle: A D-STATCOM is capable of compensating either bus voltage or line current. It can operate
in two modes based on the parameter which it regulates .They are,[2]
 Voltage Mode Operation: In this mode, it can make the bus voltage to which it is connected a sinusoid.
This can be achieved irrespective of the unbalance or distortion in the supply voltage. [2]
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Current Mode Operation: In this mode of operation, the D-STATCOM forces the source current to be
a balanced sinusoid irrespective of the load current harmonics.
The basic operating principle of a D-STATCOM in voltage sag mitigation is to regulate the bus
voltage by generating or absorbing the reactive power. Therefore, the DSTATCOM operates either as an
inductor or as a capacitor based on the magnitude of the bus voltage.[2]
Inductive Operation: If the bus voltage magnitude (VB) is more than the rated voltage then the DSTATCOM acts as an inductor absorbing the reactive power from the system. The circuit and phasor
diagram are shown in Fig.1.2. [2]
Fig.1.2 inductive mode operation [2]
Capacitive Operation: If the bus voltage magnitude (VB) is less than the rated voltage then the DSTATCOM acts as a capacitor generating the reactive power to the system. The circuit and phasor diagram
of this mode of operation are shown in Fig 1.3. [2]
Fig.1.3 capacitive mode [2]
I.
CONTROL STRATEGY
DSTATCOM has been used extensively for reactive power compensation, load balancing and harmonic mitigation
in the distribution system. The objective of the compensating scheme is to supply the oscillating component of power such
that the dc component can be supplied by the source. The performance of DSTATCOM depends on the control algorithm
used for extraction of reference current components. For this purpose, many control algorithms have been reported in
literature, and some of these are, Instantaneous Reactive Power theory (IRP) , interpretations and modifications on IRP,
Synchronous Reference Frame theory (SRF), Symmetrical Component theory (SC), current compensation using dc bus
voltage regulation ,computation based on per phase basis and scheme based on neural network techniques.[3,4,5]
The aim of control scheme is to generate the reference current waveforms which are to be injected to serve the
required objective. The compensator would produce desired results as long as its bandwidth is sufficient to follow the
fluctuations in the load. There are many control approaches available for the generation of reference source currents for
the control of VSC of three-phase, four-wire DSTATCOM system. [3,4,5]
(A) SRF THEORY:
The synchronous reference frame (SRF) theory is used in this investigation for the control of three phase threeleg VSC of the DSTATCOM. A block diagram of the control scheme is shown in fig 2.2 [3]
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Volume 3, Issue 4, 2016
A
AC
Zs
B
AC
AC
i_sa
i_La
i_sb
i_Lb
i_sc
C
i_Lc
Linear/non
linear load
Zs
3 phase AC source
Lf
V_dc
C_dc
isa
control
isb
isc
VSa VSb VSc
iLa
iLb iLc Vdc
Fig.2.1 Basic circuit diagram of the DSTATCOM system.[3]
cos 𝜃
− sin 𝜃
iLd
2𝜋
2𝜋
2
[iLq ] = cos (𝜃 − 3 ) − sin (𝜃 − 3 )
3
2𝜋
2𝜋
iL0
cos (𝜃 + ) sin (𝜃 + )
3
3
[
∗
𝑖𝑠𝑎
∗
[𝑖𝑠𝑏
]
∗
𝑖𝑠𝑐
cos 𝜃
= cos (𝜃 −
[
cos (𝜃 +
3
2𝜋
3
)
sin (𝜃 −
) sin (𝜃 +
2
1
𝑖𝑙𝑎
[𝑖𝑙𝑏 ]
𝑖𝑙𝑐
2
1
2
(2.1)
]
1
sin 𝜃
2𝜋
1
2𝜋
3
2𝜋
3
)
)
2
1
2
1
2]
𝑖𝑑∗
[𝑖𝑞∗ ]
𝑖0∗
(2.2)
The DSTATCOM can be operated for power factor correction at the supply side or to regulate the voltage at the
PCC to the reference value. The source current is controlled in-phase with the voltage, when it is operated in the power
factor correction mode. In the voltage regulation mode, DSTATCOM injects a current such that the voltage at the PCC
(vsa , vsb , vsc ) and source voltage (𝑣𝑚𝑎 , 𝑣𝑚𝑏 , 𝑣𝑚𝑐 )are equal in magnitude. The load currents (𝑖𝑙𝑎 , 𝑖𝑙𝑏 , 𝑖𝑙𝑐 ), the PCC voltages
(vsa , vsb , vsc ) and dc bus voltage (vdc) of DSTATCOM are sensed and used as feedback signals. The load currents in the
three phases are converted into the d-q-0 frame using the Park’s transformation as given in equation.[3]
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Volume 3, Issue 4, 2016
Vs(abc)
PLL
theta
Clarke’s
transformation
iL(abc)
Park’s
transformation
Switching signals
to VSC
filter
Reverse park’s
transformation
Hysteresis
current
controller
Reverse
clarke’s
transformation
Is(abc)
Fig.2.2 Basic block diagram of SRF method.[4]
A three-phase PLL (phase locked loop) is used to synchronise these signals with the PCC voltage. These d-q current
components are then passed through low pass filters to extract the dc components of iLd and iLq. A SRF controller extracts
dc quantities by a low pass filter and hence the non dc quantities (harmonics) are separated from the reference signal. The
d-axis and q-axis currents consist of fundamental and harmonic components as, [3]
ild = id dc + id ac
ilq = iq dc + iqac
(2.3)
(2.4)
The compensation strategy for DSTATCOM considers that the source must deliver the dc component of the
direct-axis component of the load current (𝑖𝑑𝑑𝑐 ) along with the active power current component for maintaining the dc bus
and meeting the losses (𝑖𝑙𝑜𝑠𝑠 ) in DSTATCOM. Moreover, the source must deliver the dc component of the quadrature axis
current (𝑖𝑞𝑑𝑐 ) and the component obtained from the PI controller (𝑖𝑞𝑟 ) used for regulating the voltage at PCC. The output
of PI (proportional-integral) controller at the dc bus voltage of DSTATCOM is considered as the current (𝑖𝑙𝑜𝑠𝑠 )for meeting
its losses. [3]
iloss(n) = iloss(n−1) + k pd (vde(n) − vde(n−1) ) + k id vde(n)
(2.5)
∗
Where, vde(n) = vdc
− vdc(n) is the error between the reference (vdc*) and sensed (𝑉𝑑𝑐 ) dc voltage at the nth
sampling instant. 𝑘𝑝𝑑 and 𝑘𝑖𝑑 are the proportional and the integral gains of the dc bus voltage PI controller. The reference
direct axis source current, [3]
i∗d = id dc + iloss
(2.6)
∗
The amplitude of ac terminal voltage (𝑉𝑠 ) at the PCC is controlled to its reference voltage (𝑉𝑑𝑐
) using a PI
controller. The output of PI controller is considered as the reactive component of current (𝑖𝑞𝑟 ) for zero voltage regulation
of ac voltage at PCC. The amplitude of AC voltage (VS) at PCC is calculated from the ac voltages
(vsa , vsb , vsc ), [3]
2
vs = ( )
3
1⁄
2
2
2
2
(vsa
+ vsb
+ vsc
)
(2.7)
Then, a PI controller is used to regulate this voltage to a reference value as,
iqr(n) = iqr(n−1) + k pq (vte(n) − vte(n−1) ) + k iq vte(n)
vte(n) = vs∗ − vs(n)
i∗q = iqdc − iqr
(2.8)
(2.9)
(2.10)
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Three-phase reference source currents are obtained by reverse Park’s transformation using eqn. In an indirect
current controller, the sensed (isa, isb, isc) and reference source currents (isa*, isb*, isc*) are compared and a proportional
controller is used for amplifying these current errors in each phase before comparing with a triangular carrier signal to
generate the gating signals for six IGBT switches of VSC of DSTATCOM. The generated gating signals control the IGBT
switches to inject a current such that the sensed source currents exactly follow the reference source currents. [3]
II.
SIMULATION RESULTS
Discrete ,
Ts = 1e-005 s
powergui
Scope 1
Scope
700
Constant
PI
Fo=45 Hz
g1
Vdc
g2
VS_a
theta
v _abc
g3
Fo=10000 Hz
IL_b
g4
I_d
I_d
VS_b
IL_a
g5
Out3
VS_c
i_sabc
Is_b
I_q
theta
IL_c
g6
PLL
D-STATCOM
Is_a
I_q
i_abc
Fo =10000 Hz
theta
I_0
Scope 2
I_0
Is_c
Subsystem4
Subsystem2
Subsystem1
Out1
Out2
IS_abc*
Out3
Out4
Out5
IS_abc
Out6
Fig.3.1 Matlab simulation model of SRF control
Fig.3.2 Voltage Vrms(p.u) at the load point (a) without D-STATCOM 22.4% voltage sag (b) with DSTATCOM 5% voltage sag
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Fig.3.3 Voltage Vrms(p.u) at the load point
(a) without D-STATCOM 29% voltage swell (b) with D-STATCOM 5.6% Voltage Swell
Fig.3.4 Voltage Vrms(p.u) at the load point (a) without D-STATCOM 33% voltage sag
(b) with D-STATCOM 9% voltage sag for Single phase to ground fault
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Fig.3.5 Voltage Vrms(p.u) at the load point (a)without D-STATCOM 66.5% voltage sag
(b)with D-STATCOM 20% voltage sag for Two phase to ground fault
Fig.3.6 Voltage Vrms(p.u) at the load point (a)without D-STATCOM 98.7% voltage sag (b) with DSTATCOM 28% voltage sag for Three phase to ground fault
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Fig.3.7 Voltage Vrms(p.u) at the load point (a) without D-STATCOM 98.75% voltage sag
(b) with D-STATCOM 30% voltage sag for Three phase fault

Voltage improvement table
Before
compensation(p.u)
Voltage sag
Voltage Swell
Single phase to ground
fault
Two phase to ground
fault
Three phase to ground
fault
Three phase fault
0.776
1.29
0.67
After
compensation(p.u)
SRF
0.95
1.056
0.91
0.335
0.8
0.013
0.72
0.0125
0.7
Table.3.1 Voltage improvement table
 Appendix
Parameters
Supply voltage
Frequency
Coupling transformer
Dc bus voltage of DSTATCOM
Dc bus capacitance of DSTATCOM
Values
230 kv
50 Hz
230/11/11 kv
700 v
750 µF
Table.3.2 system parameter [6]
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Volume 3, Issue 4, 2016


III.
CONCLUSION
From above simulation results conclude that D-STATCOM is promising device which is used for voltage sag,
swell and phase to ground fault mitigation at distribution side.
SRF theories have demonstrated the satisfactory behaviour of DSTATCOM.
REFERENCES
[1] Yash pal ,Bhim singh, “A Review Of Compensating Type Custom Power devices for power quality improvement
”IEEE power india conference,pp,1-8,2008.
[2] D.R.PATIL, KOMAL K.MADHALE, “DESIGN AND SIMULATION STUDIES OF D-STATCOM FOR
[3]
[4]
[5]
[6]
VOLTAGE SAG, SWELL MITIGATION ” , International Journal of Power System Operation and Energy
Management ISSN, pp 2231 – 4407, Volume-2, Issue-1,2
P. Jayaprakash , Bhim Singh, “DSP Based Implementation of a Three-Phase Four- Wire DSTATCOM for Voltage
Regulation and Power Quality Improvement” industrial Electronics, annual conference of IEEE,pp,3660-3665
,IEEE 2009.
Tejas Zaveri, Bhalja Bhavesh, “ Control Techniques for Power Quality Improvement in Delta Connected Load
using DSTATCOM”,IEEE international Electric machines & Drives Conference(IEMDC) ,2011
Bhim Singh, “A Comparison of Control Algorithms for DSTATCOM”, IEEE TRANSACTIONS ON
INDUSTRIAL ELECTRONICS, VOL. 56, NO. 7,July 2009.
P. Jayaprakash, Bhim Singh, “ A T-Connected Transformer and Three-leg VSC Based DSTATCOM for Power
Quality Improvement”, IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 6, NOVEMBER
2008
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