Indian Journal of Science and Technology, Vol 9(30), DOI: 10.17485/ijst/2016/v9i30/99040, August 2016
ISSN (Print) : 0974-6846
ISSN (Online) : 0974-5645
Application of Static Synchronous Compensator
(STATCOM) to enhance Voltage Profile in IEEE
Standard 5 Bus Transmission System
D. Aswathi Krishna* and M. R. Sindhu
Department of Electrical and Electronics Engineering, Amrita School of Engineering, Coimbatore Amrita Vishwa
Vidyapeetham, Amrita University, Coimbatore – 641112, Tamil Nadu, India; Achu.akd.92@gmail.com,
mr_sindhu@cb.amrita.edu
Abstract
Background/Objectives: This paper presents implementation of Static Synchronous Compensator (STATCOM) which can
control reactive power through transmission lines in an IEEE standard 5 bus system to meet constraints on bus voltage
magnitude, thermal limits and power factor. Methods/Statistical Analysis: This is made possible by appropriately controlling compensation current of shunt compensator. Findings: Simulation results on performance of STATCOM are studied
in MATLAB/SIMULINK and validated the effectiveness of the controller. The results show reduction in losses, improvement
in power factor and improvement in bus voltage profile are obtained with STATCOM. Application/Improvements: Power
flow through the transmission line had improved from 0.014 p.u. to 0.154 p.u.
Keywords: FACTS, Reactive Compensation, Static Synchronous Compensation, Transmission System, Voltage stability
1. Introduction
Modernization of electrical equipment led to the increase
in the demand for power consumption. Smooth and
efficient controllers were designed for optimum use of electrical energy. Flexible AC Transmission System (FACTS)
have been initiated1,2 as an attempt to optimally utilize the
existing power system resources. Out of all the FACTS
devices implemented, Static Synchronous Compensator
(STATCOM) is the best option for controlling reactive
power flow by keeping the system stable and with minimum losses. STATCOM is capable of voltage regulation,
shunt compensation and power factor improvement3.
Several cases of FACTS devices – such as SVC4, SSSC4,
TCSC4, TSSC4, SSSC5–8 were studied in different system
configurations. These show enhancement in power transfer capability, reduction in power losses and maintenance
of voltage stability. The controllers to the inverter are
designed to operate STATCOM in reactive power injection mode. In reactive power injection mode, constant
*Author for correspondence
values of positive and negative reactive power are injected
at optimal locations in the power system network. The
amount of injected reactive power is controlled to maintain the magnitude of the bus voltage within the desired
setting.
Many research works have already been published
in steady state and dynamic modeling and control of
STATCOM. The control methods discussed are, Direct
Power Control9, Reactive Power Control4, Automatic
Voltage Control4, traditional PI/PID control4, Quantitative
Feedback Theory (QFT)10, Adaptive Neuro Fuzzy
Interference Controller (ANFIC)11, etc. Each controller
technique has its own advantages as well as disadvantages.
Traditional PI controllers were simple and easy to design
but it failed in providing good dynamic performance in
wide range and also requires tuning which can be done
only by trial and error method. QFT uses feedback for
controlling STATCOM, with which the desired system
performance can be achieved. Disadvantages of Fuzzy
controllers led to the development of ANFIC that can
Application of Static Synchronous Compensator (STATCOM) to enhance Voltage Profile in IEEE Standard 5 Bus Transmission
System
respond to real and reactive power changes at the same
time, which gives better dynamic performance of system.
By using fast controllers, STATCOM12 is used to control
line flow without violating thermal limits, stability margins etc. and keeping losses minimum. The performance
of STATCOM13 is compared with the capability of other
FACTS devices in various research papers. Some papers
already mentioned multi objective coordinated controllers for STATCOM14. However the exact relationship
between different power system quantities and general
algorithm are not explained in any of them. This paper
presents results of STATCOM15 implementation in IEEE
standard 5 bus system. The paper is organized as follows:
Section 2 explains the specifications and characteristics of
IEEE standard 5 bus system. Section 3 explains in detail
the control strategy of STATCOM. Section 4 presents
simulation results after the installation of STATCOM in
the IEEE standard 5 bus system.
Table 1. Bus data
Node
Q (p.u)
(demand)
1
1.526
0.6584
0
0
2
0.3
–0.6512
0
0
3
0
0
0.45
0.20
4
0
0
0.80
0.30
5
0
0
0.50
0.25
Table 2. Transmission line parameters
2. Test System
IEEE standard 5 bus system shown in Figure 1 is used as
test system. It consists of 3 load buses, 1 PV bus, 2 generating plants and 7 transmission lines. Bus 1 is the swing
bus. Base kV and base MVA for the system is selected as
100 kV and 100 MVA. The impedance and base current
are 100Ω and 1000A respectively.
Bus data, Transmission line parameters and load flow
analysis results in IEEE 5 bus system are shown in Tables 1
and 2.
Load flow analysis is performed in single iteration
with a power mismatch tolerance of 100% and load flow
analysis flow chart is shown in Figure 2.
P (p.u)
Q (p.u)
P (p.u)
(generated) (generated) (demand)
Line, p-q
Impedance (p.u)
Line Charging (y/2)(p.u)
1-2
0.02 + j0.06
j0.03
1-3
0.08 + .j0.24
j0.025
2-3
0.06 + j0.18
j0.020
2-4
0.06 + j0.18
j0.020
2-5
0.04 + j0.12
j0.015
3-4
0.01 + j0.03
j0.010
4-5
0.08 + j0.24
j0.025
Bus voltages and power flow through each line are
shown in the Figures 3, 4 and Table 3.
From the above results, it is seen that the power generation and power demand are balanced and the system
attains steady state. The bus voltage angle difference
between two neighboring buses exceeding 6˚ will result
in overloading16. Hence from the results, line 2 - 4 is overloaded. Here, STATCOM is implemented to enhance its
power transfer capability.
3. Control Strategy of STATCOM
Load flow equations that regulate power system are:
PGi − PDi −
n
∑ |V ||V ||Y
QGi − QDi −
j =i
i
j
| cos(qij + di − d j ) = 0
ij
n
∑ |V ||V ||Y
j =1
i
j
ij
(1)
|sin(qij − di + d j ) = 0
Where,
PGi = Real power generation at ith bus.
PDi = Real power demand at ith bus.
QGi = Reactive power generation at ith bus.
QDi = reactive power demand at ith bus.
Figure 1. IEEE 5 bus system.
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The load flow in the system should satisfy a set of constraints on real and reactive generator power outputs, bus
Indian Journal of Science and Technology
D. Aswathi Krishna and M. R. Sindhu
Figure 4. Power flow through transmission lines –
Graphical representation.
Table 3. Power flow in transmission lines
Figure 2. Load flow analysis – Flow chart.
Node 1
Node 2
S12 (p.u)
S21 (p.u)
1
2
1.0087 + 0.5250i
–0.9846 – 0.5158i
1
3
0.5173 + 0.1333i
–0.4960 – 0.1210i
2
3
0.3376 + 0.0087i
–0.3307 + 0.0099i
2
4
0.4022 + 0.0149i
–0.3925 + 0.0049i
2
5
0.5448 – 0.1118i
–0.5326 + 0.1188i
3
4
0.3768 – 0.0691i
–0.3752 + 0.0545i
4
5
–0.0323 – 0.0727
0.0326 + 0.0250i
voltage magnitude constraints, constraints on tap setting
transformers, capacitor bank reactive power specifications, loading limit on transmission lines and voltage
stability limits. The constraints17 are mathematically
­represented as:
• Generator real and reactive power output constraints:
PGi min ≤ PGi ≤ PGi max ; i = 1, 2,....N G
QGi min ≤ QGi ≤ QGi max ; i = 1, 2,....N G
(2)
• Voltage magnitude of each bus:
max
| Vi |0min
.9 p
u ≤| Vi |≤| Vi |1.1 p
u ; i = 1, 2,... N (3)
• Tap setting of transformers:
Ti min ≤ Ti ≤ Ti max ; i = 1,2....N (4)
• Capacitive bank reactive power output limits:
Figure 3. Bus voltages in IEEE 5 bus system.
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QCi min ≤ QC ≤ QCi max ; i = 1,2..... N C (5)
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Application of Static Synchronous Compensator (STATCOM) to enhance Voltage Profile in IEEE Standard 5 Bus Transmission
System
• Loading on transmission line:
S i ≤ S i max ; i = 1,2...N L (6)
Here STATCOM is used to improve power transfer
­capability of transmission line 2-4. The control strategy
should also satisfy the limits on STATCOM shunt injected
voltage limits.
| Vsh |min ≤| Vsh |≤| Vsh |max
Qsh min ≤ Qsh ≤ Qsh max Figure 6 shows the flow chart for implementation of
shunt controller.
Closed loop control strategy by reactive power injection mode is explained as follows:
ctual reactive power injection by shunt conQinjact = A
verter.
spec
Qinj
= Specified value of reactive power injection by
shunt converter.
(7)
∆Q(inj ) = Qinjspec − Qinjact
Figure 5 shows the location of STATCOM in IEEE 5
bus system. According to Table 3, without any compensation, flow of real and reactive power in transmission line
is 0.4022 p.u. 0.0149 p.u.
3.1 Shunt Converter Control for Reactive
Power Injection Mode
STATCOM is operated in reactive power flow control
mode by applying proper control signals for shunt controller. Shunt compensator injects/absorbs suitable value
of reactive power such that constraints on bus voltage are
satisfied. Shunt converter has two functions:
During ith iteration,
∆Qijk( inj ) = ∆Qijk(−inj1 ) − Bi ∆eik eik
where
∆eik = eik − eik −1
eik = Vi spec cos q ik −1
 f k −1 
q ik −1 = a tan  ik −1 
 ei 
(9)
• Maintain transmission line voltage at its reference
value by absorbing or injecting reactive power to the
transmission line.
• To retain voltage level of DC link capacitor at its reference
value by drawing real power from transmission line.
Shunt Current to be injected per phase =
Desired Reactive Power − Actual Reactive Power
(8)
3Vph
Figure 5. STATCOM connected IEEE 5 bus system.
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Figure 6. Flow chart for implementation of shunt controller.
Indian Journal of Science and Technology
D. Aswathi Krishna and M. R. Sindhu
k = kth power flow iteration.
i = Bus at which reactive power is injected
∆Q(inj ) = Change in reactive power injection needed to
control bus voltage at bus i.
e = Tolerance in controlled voltage.
Bii = Bus admittance of ith bus
Figure 7 shows the block diagram of a shunt controller. To improve voltage profile at bus 4, shunt voltage
source inverter is controlled to inject 0.0145 p.u. of reactive power. After shunt compensation, real power and
reactive power transferred through line 2-4 are 0.436 p.u
and 0.14 p.u respectively. The bus 4 voltage has improved.
The simulation results with shunt compensation are plotted in Figures 8–12.
Figure 9. DC link capacitor voltage of shunt controller.
Figure 10. Comparison between injected current and
actual current in the system.
Figure 7. Control block of shunt controller.
Figure 8. Reference current injected by the shunt controller.
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Figure 11. Second
compensation.
bus
voltage
before
and
after
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Application of Static Synchronous Compensator (STATCOM) to enhance Voltage Profile in IEEE Standard 5 Bus Transmission
System
7. References
Figure 12. Power flow through the tranismission lines in
STATCOM connected system
6. Results and Discussions
The simulation results shown in Table 3 and Figure 12
show that:
• STATCOM can improve the bus voltages so as to make
the desired amount of power through the transmission line.
• STATCOM reduces load angle difference between two
neighboring buses so as to avoid the overloading condition of the system.
• The DC link capacitor has changed to the nominal
value and shown in Figure 9.
7. Conclusion
This paper presented the performance characteristics of
STATCOM installed in IEEE 5 bus system. Line 2-4 shows
overloading without the installation of STATCOM. By
installing STATCOM in the line, shunt controller injects
reactive power so as to get the desired amount of power
flow through transmission line as 0.43 p.u. and 0.154 p.u.
respectively. The compensation system shows reduction
in loading of the line. Shunt compensation at bus 4 is also
done to improve voltage profile of bus 4. In both the cases,
all the bus voltages are in nominal voltage limits. Real
and reactive power losses in the system are reduced with
STATCOM compensation.
8. Acknowledgement
The authors would like to thank Amrita Vishwa
Vidyapeetham and Department of Science and Technology
for the support for carrying out this project work.
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