Voltage profile Improvement Using Static Synchronous Compensator STATCOM

International Journal of Advanced Engineering, Management and Science (IJAEMS) [Vol-2, Issue-11, Nov- 2016]
Infogain Publication (Infogainpublication.com) ISSN : 2454-1311
www.ijaems.com Page | 1830
Voltage profile Improvement Using Static
Synchronous Compensator STATCOM
Mohammed Y. Suliman
Technical Power Engineering Dept., Northern Technical University
Abstract—Static synchronous compensator (STATCOM)
is a regulating device used in AC transmission systems as
a source or a sink of reactive power. The most widely
utilization of the STATCOM is in enhancing the voltage
stability of the transmission line. A voltage regulator is a
FACTs device used to adjust the voltage disturbance by
injecting a controllable voltage into the system. This
paper implement Nruro-Fuzzy controller to control the
STATCOM to improve the voltage profile of the power
network. The STATCOM controller has simulated for
some types of abnormal conditions. The simulation results
show improves the system voltage profile. The
performance of compensator with its new controller was
very close to the nominal value, which was 98% of the
busbar voltage.
Keywords— FACTS, STATCOM,VSI, d-q theory, park
transformation, FLC, Sinusoidal Pulse Width
Modulation (SPWM).
I. INTRODUCTION
Power quality is defined of electrical limits that permit
the part of the equipment to use function in its intended
manner without loss of the performance or life
expectancy. The electrical device like generator,
transformer, motor, computer, printer, communication
equipment, or a house machines. All of these devices
react negatively to the power quality, depending on the
severity of the problems. Reactive power unable to be
transmitted when large load angle even with essential the
magnitude of voltage gradient [1]. Instability of Voltage
may cause partial or complete interruption in the power
system. Static Synchronous Compensator is a voltage
source inverter (VSI) based on shunt device generally
used in transmission system to enhance the compensator
and power quality. The advantage of STATCOM is that,
it has a very advanced power electronics based control
that can efficiently regulate the injection current into the
transmission bus [2]. The second advantage is that, it has
different applications, e.g. i. controlling the voltage of
distribution bus against sag/swell conditions. ii.
Suppressing the harmonics content in line currents iii.
Modified poor load power factor, and compensating the
reactive power of the transmission line and the load [3].
STATCOM with an energy source on the DC side, it is
advisable to control the magnitude and phase angle of the
injected voltage by the VSC in order to control the active
power and reactive power output. A shunt compensator
enables to mitigate voltage fluctuations at the point of
common coupling (PCC) [4].
II. COMPENSATION AND VOLTAGE
REGULATION
The principle and theoretical effects of shunt reactive
power compensation in AC system for voltage regulation
are shown in figure 1. This includes a source (V1), a
power line and a typical inductive load. Figure 1a, shows
the system without compensation and it is related to the
phasor diagram. From the phasor diagram, the angle of
the line current has related to the side of the load, this
means that active current (IP) is in phase with (V2) the
load voltage. Since assumed the load is inductive and
requires reactive power for suitable operation and hence,
the source must supply it; thus increasing the current from
the generator and through power lines. If reactive power
is supplied near the load, the line current can reduce
power losses and improve voltage regulation at the load
terminals [5]. This can be done in three ways: 1) with a
capacitor [6]; 2) with a voltage source inverter [7]; or 3)
with a current source inverter [8]. In figure1b, a current-
source device is used to compensate the reactive
component of the load current by inject/absorb current
(IC) to/from system. As a result, the system voltage
regulation is improved and the reactive current
component from the source is reduced or almost
eliminated. If the load needs leading compensation, then
an inductor would be required. In addition, a current
source or a voltage source can be used for inductive shunt
compensation.
The STATCOM is providing voltage support under large
system disturbances during which the voltage excursions
would be well outside of the linear operating range of the
compensator. The main advantage of using voltage or
current-source Var generators (instead of inductors or
capacitors) is that the reactive power generated is
independent of the voltage at the point of connection as
shown in figure 2 [9].

a Without Reactive Compensation
b Compensation with a Current Source
Fig.1: Principles of Shunt Compensation
Fig.2: Q-V characteristics of the STATCOM
The STATCOM connected between the source and load
as shown in figure 3.
Fig.3:Fundamental connection of STATCOM
III. MEASURING LINE VOLTAGE AND
REACTIVE POWER
For measuring line voltage and reactive power, d-q theory
has been used. D-q theory is based on time-domain, and it
is valid for operation in different state (steady or transient
state), also this theory can applied for generic voltage and
current waveforms, this will simply allow to control the
reactive power in real time. Another advantage of this
theory is the simplicity of the calculations, which include
algebraic calculation and simply to separating the mean
value and alternated value respectively when calculated
the components of power system [10]. The d-q theory
implements by transformation to quadrant coordination
known “park transformation” from a stationary reference
coordinates abc to dq rotating coordinates[11].The
transform applied to time-domain voltages in the natural
frame (i.e. va, vb and vc) is as follows:
=
2
3
cos(∅) cos( ∅ −
2
3
) cos(∅ +
2
3
)
−sin (∅) −sin (∅ −
2
3
) − (∅ +
2
3
)
1
2
1
2
1
2
!
"
(1)
=
2
3
cos(∅) cos( ∅ −
2
3
) cos(∅ +
2
3
)
−sin (∅) −sin (∅ −
2
3
) − (∅ +
2
3
)
1
2
1
2
1
2
!
"
(2)
∅
= (#$
+ %) (3)
Where is the angle between the rotating and fixed
coordinate system at any time and θ the phase shift of
the voltage. Then the compensated active power and
reactive power calculated by:
&
= ' (
+ ' ( (4)
*
= ' ( − ' ( (5)
The resultant voltage is:
,
= -,.
/ + ,0
/ (6)
IV. CONTROL SCHEME OF STATCOM
Block diagram of the STATCOM control system is
shown in Figure 4. The three phase line voltages are
sensed then filtered to eliminate high frequency noise and
the quadrature voltage components (vd and vq) the are
calculated by park transformations. The measured voltage
is calculated and works as a feedback for the closed loop
control system. The measured voltage is compared with
the reference voltage of the busbar ( set point ) vref to
generate error signals verorr. This error signal is processed
in controller where:

'23343
= + '325 (7)
Fig.4: Block diagram for STATCOM control system
V. FUZZUY CONTROL SYSTEM
Fuzzy logic control are suitable for approximate
reasoning, especially for the system that have
mathematical model is difficult to derive. Fuzzy system
controllers perform an important role in different practical
applications. There are many inference mechanism
systems in fuzzy logic control which Takagi-Sugeno type
is chosen in this paper. To tune the membership functions
of the Takagi-Sugeno (TS fuzz-like-PI controller),
Artificial Neural Network (ANN) will be used in this
paper. The TS fuzzy controller have a highly non-linear
variable gain controller. it makes wide differences of the
gain of the controller. The selection of controller
parameters may lead to an adequate system response or
instability [12]. First the controller build using mamdani-
type then transfer it to TS fuzzy type to get a better
system response by using Neuro-Fuzzy control to adjust
the parameters of fuzzy and rules by employing ANN
learning algorithm. Since it integrates the qualitative of
fuzzy approach with the capabilities of adaptive learning
of ANN, this system can trained without need great expert
knowledge that usually required for the mamdani fuzzy
logic [13]. Results, the fuzzy rule base is reduced.
The membership parameters of the output and input
functions are determined through the training step. The
designed Fuzzy system consists of five layers, each one
have parameters no need to tune or have parameters need
to tune during the training stage. The output of five layers
that emulate the fuzzy design steps is given in reference
[14] for more details. The objective of the learning
algorithm is to set the parameters of the membership
functions for output and input so that the output of
adaptive fuzzy matching the training data. Gradient
Descent-GD and Lease Squares Estimate-LSE (hybrid
learning) applied for identify the parameters of network.
The use of GD method updates the antecedent
membership function parameters. In this work The input
universe of discourse is split into 5 gaussian membership
function with 50% overlapping, therefore, for two inputs
(error and Δerror), 25-control rule resultant linear
functions required to be determined as shown in Figure 5.
To tune the rules using adaptive fuzzy, two group of data
are generated. Two vectors of input data: Verror and ΔVerror
the output m the modulation index. Figure6 shows the
validation test of Fuzzy logic system. To perform the
procedure the GUI of ANFIS file included in the
MATLAB/FUZZY Logic Toolbox is used.
Fig.5: Fuzzy logic validation test and surface
VI. SIMULATION STUDY
system consists of feeder with two branches changeable
load. the STATCOM system installed in busbar 2 (BB2)
to compensate the voltage in BB2. the test start by change
the load and measure the load voltage at BB2 without
compensation as shown in figure 10. From the result it
can be notice that the drop voltage increased
proportionally with increasing the load, the maximum
drop was 0.94 pu between 0.6 and 0.8 sec. Figure 11
shows the action of STATCOM to compensate the load
voltage where the voltage at BB2 was restored and
mitigate the drop voltage from 0.94 to 0.985 pu, this
compensation done by inject compensated voltage
VSTATCOM with respect to phase voltage as shown in
Figure 12. Figure 13 shows the p-v curve, it can notice
that the voltage with STATCOM more stable and
enhanced the stability margin. To investigate the
performance of the adaptive controller for step change of
the load condition, a PI controller is used for the sake of
comparison. Figure 14 shows the results of the system
response to step change in rms of the line voltage. From
the results, it is clear that the Fuzzy controller has a
smoother in response and faster than the PI controller to
reach the steady state.
Fig.6: System model for simulation

International Journal of Advanced Engineering,
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Fig.7: The 3-ph phase waveforms output of the inverter
Fig.8: Fourier analysis of inverter
Fig.9: Fourier analysis of line current after STATCOM
voltage injected
Fig.10: The BB2 voltage without compensation
VBB2
VBB1
International Journal of Advanced Engineering, Management and Science (IJAEMS)
Infogainpublication.com)
ph phase waveforms output of the inverter
inverter output
Fourier analysis of line current after STATCOM
The BB2 voltage without compensation
Fig.11: The BB2 voltage with compensation
Fig.12: The injected compensated
versus phase voltage
Fig.13: P-V curve of the system
VII. CONCLUSION
In this paper, a STATCOM based
adaptive controller has been
and some abnormal conditions have
simulation. The results of
STATCOM with adaptive controller improve the voltage
profile of distribution system
conditions. The model of STATCOM
the required controller and
performance in fast regulation at load
simulation compared with and without compensation.
Also the simulation results
ability to restore the load voltage for increased the load
with satisfactory performance. Th
performance with the controller was very close
nominal value of the busbar voltage
these tests the conventional PI controller has been used
for the seek of comparison. Also controller algorithm is
0.5 1 1.5 2 2.5
0.8
0.85
0.9
0.95
1
1.05
1.1
LineVoltage
VBB1
[Vol-2, Issue-11, Nov- 2016]
ISSN : 2454-1311
Page | 1833
BB2 voltage with compensation
injected compensated voltage VSTATCOM
versus phase voltage
V curve of the system
CONCLUSION
based three phase PWM with
controller has been integrated in the load bus,
abnormal conditions have been studied through
simulation have shown the
controller improve the voltage
system through the abnormal
STATCOM is developed with
and components to prove its
in fast regulation at load voltage. The of
simulation compared with and without compensation.
results of STATCOM show the
ability to restore the load voltage for increased the load
with satisfactory performance. The STATCOM
controller was very close to the
nominal value of the busbar voltage (within 98%). In
these tests the conventional PI controller has been used
for the seek of comparison. Also controller algorithm is
2.5 3 3.5 4 4.5 5 5.5 6
Power in pu
Load Voltage without STATCOM
Load voltahe with STATCOM
VBB2
V
TATCOMV
phase

used to control the STATCOM for voltage profile
improvement. The Neuro-Fuzzy System was tuned the
algorithm off-line. The rules determine by training the
error and change of error for voltage for initiating the
process. The computation time was small, this important
notice for implementation in real time. Simulation results
show the adaptive controller provide an good
performance for the operation of STATCOM. Nero-
Fuzzy controller is used to control the STATCOM for
voltage profile improvement. the results show that the
used controller smoother and fast response compared with
the conventional PI controller.
Fig.14: The line voltage versus injected compensated
voltage
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Fuzzy Controller
PI Controller

Voltage profile Improvement Using Static Synchronous Compensator STATCOM

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Voltage profile Improvement Using Static Synchronous Compensator STATCOM