Journal of Applied Engineering (JOAE), 2 (5), May-2014 (Volume-II, Issue-V)
ISSN: 2348-4802
SSSC - Static Synchronous Series Compensator: Theory,
Modeling Controlling and Voltage Level Improvement Of
Power System
Mohsin I Sujela 1 ,Amin S Nilesh Patel2, Anas I Shikari3
1,3
PG Student, 2 Assistant Professor
Depart ment of Electrical Engineering,
Parul Institute of Technology, Limda
Abstract: The main aim of this work is to damp out power system oscillations, which has been recognized as one
of the major concerns in power system operation. In a Static Synchronous Series Co mpensator (SSSC), a
controllable A C voltage is generated by a voltage-source converter. There are two control channels for controlling
the magnitude and phase of the voltage. This work describes the damping of power oscillations by static
synchronous series compensator (SSSC) based damping controllers. The advantage of this approach is that it can
handle the nonlinearit ies, at the same time it is faster than other conventional controllers and it improve the reactive
power of the system. Simu lation studies will be carried out in Matlab/Simu link environ ment to evaluate the
effectiveness of the proposed Static synchronous series compensator (SSSC) of mu lti -area power system. Results
will show that the proposed SSSC based damping controllers improve the dampin g performance of the in the event
of a major d isturbance.
Keywords: AC transinission, FACTS, power fl ow controller, power converter, inverter, thyristor, GTO, etc .
This work will presents an analysis of Static
Synchronous Series Co mpensator (SSSC). Vo ltage
Source Converter (VSC) based FACTS is the most
recent approach in FACTS technology. The SSSC is
the series compensation devices that open up new
opportunities to control the power on transmission
systems in order to enhance their utilization, increase
power transfer capability and to improve voltage
profile. The power system is a highly nonlinear system
that operates in a constantly changing environment;
loads, generator outputs, topology, and key operating
parameters change
continually [8,9] .
When
subjected to a transient disturbance,the stability of the
system depends on the nature of the disturbance as
well as the initial operating condition. The disturbance
may be s mall or large. Small d isturbances in the form
of load changes occur continually, and the system
adjusts to the changing conditions. The system must be
able to operate satisfactorily under these conditions
and successfully meet the load demand. It is important
I. INTRODUCTION
Some of the major issues that are involved in bulk
power transmission are enhancing the level of power
transfer capability of existing transmission lines and
flexib le control over power flow through these lines.
To achieve the above goals, the current trend is to use
solid state devices for faster control and reliable
operation. Power electronic devices, wh ich are used
for power flo w control, are categorized under the
generic name of Flexib le A C Transmission Systems
(FACTS). There are three major facets of FACTS.
They are shunt compensation, series compensation and
phase angle regulation. Of these three, the series
compensation is used in this project
Among all FA CTS devices, static synchronous series
compensators (SSSC) plays much more important role
in reactive power co mpensation and voltage support
because of its attractive steady state performance and
operating characteristics.[6,7]
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Journal of Applied Engineering (JOAE), 2 (5), May-2014 (Volume-II, Issue-V)
to damp these oscillations as quickly as possible
because they cause mechanical wear in power plants
and many power quality problems. To improve the
voltage stability and the damping of oscillations in
power systems, supplementary control laws can be
applied to existing devices.
These supplementary actions are referred to as voltage
stability and power oscillation damp ing (POD) control.
In this work, voltagestability and POD control will be
applied to Static synchronous series compensator
(SSSC).The SSSC using a voltage source converter to
inject a controllable voltage is quadrature with the line
current of a power network is able to rapidly provide
both capacitive and inductive impedance compensation
independent of the power line current [12-14]. These
features make the SSSC an attractive FACTS device
for power flow control, power oscillation damping and
improving transient stability. This work will describe
the damping of power oscillations by static
synchronous series compensator (SSSC) based
damping controllers and it also improve the reactive
power of the system.
Simu lation studies will
be
carried out in
Matlab/Simulink environment to evaluate the
effectiveness of the proposed Static synchronous series
compensator (SSSC)
In this work the damp ing performance of a two-Area
power system will be co mpared for the cases of with
and without SSSC based damping controllers in the
event of a 3-phase short circuit faults .Simu lat ion
results show that in damp ing power system
oscillations, the SSSC with POD controller is more
effective than the SSSC without POD controll
II. THEORY
Fig. 1 shows a single line diagram of a simp le
transmission line with an inductive reactance, XL
connecting a sending-end voltage source, vs and a
receiving-end voltage source, vr respectively
To design and optimize the SSSC- based damping
controller, a mu lti area power system with SSSC, shown in
Fig is considered. It is similar to the power systems used in
references. The system consists of two generators divided
in two subsystems and are connected via an intertie.
Following a disturbance, the two subsystems swing against
each other resulting in instability. To improve the stability
the line is sectionalized and a SSSC is in between the
bus-1and 2. In the Figure, G1and G2 represent the
generators; T/F1 and T/F2 represent the transformers in the
bus-line1 and bus-line 2 respectively.
The Static Synchronous Series Compensator (SSSC) is a
series device of the Flexible A C Transmission Systems
(FACTS) family using power electronics to control power
flow and improve power oscillation damp ing on power
grids [1]. The SSSC in jects a voltage Vs in series with the
transmission line where it is connected
III A STATIC SYNCHRONOUS SERIES
COMPENSATOR
shows an SSSC connected in series with a simp le
transmission line between BUS 1 and BUS 2. The
transmission line has an inductive reactance, XL, and a
voltage source, vs at the sending-end and an inductive
reactance, Xr, and a voltage source, Vr , at the receivingend, respectively. The SSSC consists of a 24- pulse
harmonic neutralized voltage source inverter, VSZ2, a
magnetic circuit, MC2, a coupling transformer, T2, a
mechanical switch, MS2, t wo electronic switches, ES2 and
ES22, current and voltage sensors, and a controller. The
power circuit wh ich consists of a voltage source inverter
and a magnetic circu it and the controller are described
below.
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Journal of Applied Engineering (JOAE), 2 (5), May-2014 (Volume-II, Issue-V)
are cancelled by connecting filters at the AC side of the
VSC. Th is type of VSC uses a fixed DC voltage Vdc.
Vo ltage V_conv is varied by changing the modulation
index of the PWM modulator.
The SSSC (Phasor Type) block models an IGBT -based
SSSC (fixed DC voltage). However, as details of the
inverter and harmonics are not represented, it can be also
used to model a GTO-based SSSC in transient stability
studies.
B-The control system consists of:
A phase-locked loop (PLL) wh ich synchronizes on the
positive-sequence component of the current I. The output
of the PLL (angle Θ=ωt) is used to compute the direct-axis
and quadrature-axis components of the AC three-phase
voltages and currents (labeled as Vd, Vq or Id, Iq on the
diagram).Measurement systems
measuring
the q
components of AC positive-sequence of voltages V1 and
V2 (V1q and V2q) as well as the DC voltage Vdc.AC and
DC voltage regulators which co mpute the two components
of the converter voltage (Vd_conv and Vq_conv) required
to obtain the desired DC voltage (Vdcref) and the in jected
voltage (Vqref). The Vq voltage regulator is assisted by a
feed forward type regulator which predicts the V_conv
voltage fro m the Id current measurement.
The SSSC b lock is a phasor model which does not include
detailed representations of the power electronics. You must
use it with the phasor simu lation method, activated with the
Powergui b lock. It can be used in three-phase power
systems together with synchronous generators, motors,
dynamic loads and other FACTS and Renewable Energy
systems to perform transient stability studies and observe
impact of the SSSC on electro mechanical oscillations and
transmission capacity at fundamental frequency.
IV. SINGLE-LINE DIA GRAM OF A SSSC A ND ITS
CONTROL SYSTEM BLOCK DIA GRAM
As the SSSC does not use any active power source, the
injected voltage must stay in quadrature with line current.
By varying the magnitude Vq of the in jected voltage in
quadrature with current, the SSSC performs the function of
a variable reactance compensator, either capacitive or
inductive. The variation of injected voltage is performed by
means of a Voltage-Sourced Converter (VSC) connected
on the secondary side of a coupling transformer. The VSC
uses forced-commutated power electronic devices (GTOs,
IGBTs or IGCTs) to synthesize a voltage V_conv fro m a
DC voltage source. A capacitor connected on the DC side
of the VSC acts as a DC voltage source. A small active
power is drawn fro m the line to keep the capacitor charged
and to provide transformer and VSC losses, so that the
injected voltage Vs is practically 90 degrees out of phase
with current I. In the control system b lock d iagram
Vd_conv and Vq_conv designate the components of
converter voltage V_conv which are respectively in phase
and in quadrature with current. A-Two VSC technologies
can be used for the VSC: VSC using GTO-based squarewave inverters and special interconnection transformers.
Typically four three-level inverters are used to build a 48step
voltage
waveform.Special
interconnection
transformers are used to neutralize harmon ics contained in
the square waves generated by individual inverters. In this
type of VSC, the fundamental co mponent of voltage
V_conv is proportional to the voltage Vdc. Therefore Vdc
has to varied for controlling the injected voltage. VSC
using IGBT-based PWM inverters. This type of inverter
uses Pulse-Width Modulation (PWM) technique to
synthesize a sinusoidal waveform fro m a DC voltage with a
typical chopping frequency of a few kilohertz. Harmon ics
V SIMULATION A ND RESULT
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Journal of Applied Engineering (JOAE), 2 (5), May-2014 (Volume-II, Issue-V)
capacitive reactance in series with the transmission line.
The transition fro m one mode of operation to the other
mode takes place in a sub-cycle time. The operation of the
model is verified by connecting the model in series with a
simp le transmission line which can easily be rep laced by
the utility’s existing mo re co mplex power system network.
.
VI. REFERENCES
[1]. N.G. Hingorani, “Flexible AC transmission”. IEEE Spectrum, v. 30,
n. 4, pp. 40-44, 1993.
[2]. N.G. Hingorani and LGyugyi, “Understanding FACT S Concepts and
Technology of Flexible AC Transmission Systems”, IEEE Press, New
York, 2000.
[3]. Y.H. Song and A.T. Johns, Eds., “Flexible AC T ransmission Systems
(FACT S)”, IEE Press, London, 1999.
[4]. R.M. Mathur and R.K. Varma, “Thyristor-Based FACT S Controller
for Electrical Transmission Systems”, IEEE Press and Wi-ley Interscience, New York, 2002.
Vqinj Vqref (pu)
0.2
0.15
[5]. R. Gru¨nbaum, M. Noroozian, and B. T horvaldsson, “ FACT S
Powerful systems for flexible power transmission”, ABB Rev., May 1999,
4–17.
0.1
0.05
0
-0.05
[6]. K. Stahlkopf and M. Wilhelm, “Tighter controls for busier systems”,
IEEE Spectrum, 1997, 34(4), 48–52.
P_B2 (MW)
900
850
800
[7]. K.K.Sen, “SSSC-static synchronous series compensator: theory,
modelling and applications”, IEEE Trans. on Power Delivery, v. 13, n. 1,
1998, pp. 241-246.
750
700
650
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
[8]. K.R. Padiyar, “Power System Dynamics - Stability and
Control”,Second Edition, Hyderabad: B.S. Publications, 2002.
[9]. G. Guo, Y. Wang and D.J. Hill, “Nonlinear output stabilization
controlof multi-machine power systems”, IEEE Trans. on Circuits and
Systems,Part I, v. 47, n.1, 2000, pp. 46-53.
[10]. K.R. Padiyar, “Analysis of Sub-synchronous Resonance in
PowerSystems”, Kluwer Academic Publishers, Boston, 1999.
[ 11 ]Transmission Line Dynamic Impedance Compensation System,L.
Gyugyi and C. D. Schauder, US Patent No. 5,198,746.
[12] Static Synchronous Series Compensator: A Solid-stateApproach to
the Series Compensation of Transmission Lines, L. Gyugyi, C. D.
Schauder and K. K. Sen, 96 WM 120-6 PWRD, IEEE PES Winter
Meeting, 1996.
V. CONCLUSION
The SSSC wh ich is a voltage source inverter injects an
sinusoidal voltage in series with the transmission line. This
almost injected voltage is almost in quadrature with the line
current, thereby emulating an inductive reactance or a
capacitive reactance in series with the transmission line.
The power flow in the transmission line always decreases
when the injected voltage by the SSSC emu lates an
inductive reactance in series with the transmission lime and
the power flo w in the transmission line always increases
when the injected voltage by the SSSC emulates a
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