REACTIVE POWER COMPENSATION USING UNIFIED POWER FLOW CONTROLLER(UPFC)

1. REACTIVE POWER COMPENSATION
USING UNIFIED POWER FLOW
CONTROLLER(UPFC)

2. CONTENTS
 Introduction to flexibleAC transmission systems(FACTS)
 Literature survey
 Basic types of FACTS controller
 Merits/demerits of FACTS controller
 UPFC: introduction, configuration and working
 Active and reactive power flow control
 Performance analysis of UPFC
 Comparison between FACTS devices
 Applications of UPFC
 Conclusion
 References

3. Introduction to flexible AC transmission
systems(FACTS)
• Electrical power systems are frequently accommodating numerous electromechanical
disturbances caused due to different reasons such as sudden application of load or escape
out of load, environmental causes etc. Such disturbances are responsible for creation of
harmonics and oscillations affecting system stability which may further lead to system
failure.
• Different technologies are used to compensate these disturbances and to provide quality
power. One of the technologies is the implementation of Flexible AC Transmission
System (FACTS) devices.
• This technology was implemented in the year 1980, was launched by Electric Power
Research Institute(EPRI).
• A Flexible Alternating Current Transmission System(FACTS) is defined by the IEEE as a
power electronics based system and additional static equipment that provide control
of one or more AC transmission system parameters to enhance controllability and
increase power transferAbility

4. Literature survey
Firstly, I studied the introduction to FACTS technology, their conventional method and modern
technology and basic operation of it. Then studied the various techniques to improve reactive
power. There are many FACTS controllers such as Fixed Capacitor-Thyristor Controlled
Reactor (FC-TCR), Static synchronous compensator (STATCOM), Thyristor controlled Series
Capacitor (TCSC), Static synchronous Series Compensator (SSSC) and Unified Power Flow
Controller (UPFC) for power system stability enhancement and improvement of power transfer
capability.
So, I have studied, how power flow control and system stability is improved using UPFC and
studied the uncompensated system model, compensated system model & waveforms which are
done in MATLAB/SIMULINK environment.
And then compare with other FACTS controller with respect to variation in power flow with
change in capacitance.
So, I can conclude that there are numerous equipments which are capable for power flow
control but there is only one which can control the power flow optimally is UPFC.[1-5]

5. Basic types of FACTS controller
In general, FACTS controller can be divided into four categories:
 Series controllers: -
Static Synchronous Series Compensator (SSSC)
Thyristor Controlled Series Capacitor (TCSC)
Thyristor Controlled Series Reactor (TCSR)
 Shunt controllers: -
Static Synchronous Compensator (SSC/STATCOM)
Static VAR Compensator (SVC)
Thyristor Controlled Resistor (TCR)
 Combined series-series controllers: -
Interline Power Flow Controller (IPFC) , also referred as unified series-series
controller
 Combined series-shunt controllers: -
Unified Power Flow Controller (UPFC)

6. (a) General symbol for FACTS controller
(b) Series controller
(c) Shunt controller
(d) Unified series-series controller
(e) Coordinated series and shunt controller
(f) Unified series and shunt controller

7. ⦿ Merits of facts devices
1) Enhancement of dynamic & transient stability
2) Voltage stability & security improvement
3) Line compensation
4) Power factor improvement
5) Loss minimization
6) Voltage & power profile improvement
7) Good voltage regulation
8) Line capacity improvement
9) Reliability of Transmission system increases
10) These devices are also employed for congestion
management and loss optimization
⦿ Demerits of facts devices
1) High initial cost
2) High repair cost

8. UPFC: introduction, configuration and working
 UPFC, concept was proposed in 1991
 It was invented for real-time control & dynamic compensation of AC transmission system
providing multifunctional flexibility required to solve many of the problems facing the
power industry.
 A Unified Power Flow Controller (UPFC) is a FACTS device for providing fast acting
reactive power compensation on high voltage electricity transmission networks.
 It is able to control, simultaneously or selectively, all the parameters affecting power flow in
the transmission lines(i.e voltage, impedance, phase angle) & hence, it is called UNIFIED.
 It can independently control both real and reactive power flow in the line.
 The unified power flow controller (UPFC) is one of the most favourable Flexible AC
Transmission Systems (FACTS) devices used for the load flow control.

9. Configuration of UPFC: -
Schematic diagram of UPFC
UPFC consists of two converters. One converter (SSSC) is connected in series with the
transmission line through the series transformer and other converter (STATCOM) is
connected in parallel with the transmission line through the shunt transformer. The two
converters are coupled through a common dc link which provides bidirectional flow of real
power between series o/p SSSC and shunt output STATCOM respectively. For balancing of
power between series and shunt controller it is necessary to maintain constant voltage
across the dc link. Each converter is capable of generating or absorbing reactive power at its
AC terminal.

10. Working of UPFC: -
The two VSIs can work independently of each other by separating the dc side.
 Series connected converter, converts demand or excess of real power of transmission line to
common dc bus as supply or absorb the real power.
 Shunt converter converts the demand at dc link to ac and feeds back to the line with the help
of shunt connected transformer
 So in that case, the shunt inverter is operating as a STATCOM that generates or absorbs
reactive power to regulate the voltage magnitude at the connection point.
 Instead, the series inverter is operating as SSSC that generates or absorbs reactive power to
regulate the current flow, and hence the power flows on the transmission line.

11. Active and reactive power flow control: -
a simple two machine system with sending end voltage Vs, receiving end voltage Vr and line
impedance X as shown in fig (a):
The system voltage phasor and transmission angle ɗ as shown in fig (b)
both the power transmitted through sending end of the line against transmission angle ɗ as
shown in fig (c)
TheActive and Reactive power of the sending end as well as receiving end can be control
using UPFC.

12. Above figure Shows UPFC can be included in two machine power system in series
with the line.
• To represent the UPFC properly, the series voltage source is designed to generate
only the reactive power Qpq it exchange with the line.
• Generator of sending end must be fed with real power Ppq for perfect coupling.
• The dc link of UPFC circuit has been placed between two inverters which has
bidirectional coupling for the flow of active power between sending end bus and
injected voltage source.
• It is assume that UPFC shunt inverter is operating at unity power factor.
• The prime duty of UPFC circuit is to delivered active power demand of series
inverter to generator of sending end.

13. Performance analysis of UPFC
Uncompensated system model: -

14. Real power flow Reactive power flow
Load voltage Load current

15. UPFC compensated model: -

16. Real power flow Reactive power flow
Load voltage Load current

17. Variation of power flow with change in capacitance
S.no. Capacitance
(µF)
Real power
(MW)
Reactive power
(MVAr)
1 50 0.0254 0.036
2 200 0.975 1.38
3 350 2.08 2.95
4 500 1.64 2.33
5 600 1.4 1.98
6 800 1.13 1.60
7 1000 1.0 1.40
8 1200 0.91 1.285
9 1400 0.85 1.20
10 1500 0.83 1.17
From the above table, it is seen that both power flow is improved up to a certain limit of
capacitance (350µF). In this point, injection of real and reactive power to the system is
maximum. Beyond this, if we increase the value of capacitance then power profile is
deteriorates.

18. Comparison between FACTS devices
FACTS
Devices
Capacitance(350µF) Capacitance(1500µF)
Real power
(MW)
Reactive
power
(MVAr)
Real power
(MW)
Reactive
power
(MVAr)
FC-TCR 0.86 1.21 2.70 3.80
STSTCOM 0.85 1.20 2.70 3.82
TCSC 0.772 1.085 2.66 3.70
SSSC 2.08 2.93 0.83 1.18
UPFC 2.08 2.95 0.83 1.17
Comparison of power flow between FACTS devices
• From the above table, it is seen that reactive power improvement will vary with change in
capacitance in all the five cases. At a capacitor value of 350μF UPFC is seen to give best
performance and at capacitor value 1500μF, STATCOM gives better performance.
• Since, increased rating of capacitor means increase the cost of equipment. So, from the
above comparison table we can conclude that UPFC FACTS controller will give optimum
performance at capacitor rating of 350μF.

19. Variation of power flow between FACTS devices with change in
capacitance (50-1500μF)
 The above graph shows, the behaviour of all the FACTS devices for different capacitor
values.
 From this graph, it is observed that, of all FACTS devices, UPFC gives best performance
for a capacitor value of 350μF after which its performance deteriorates.
 Again we see, that the performance of STATCOM continues to improve with increasing
capacitance. But, increasing the capacitor rating means increasing the overall cost of the
equipment.

20. Applications of UPFC
FACTS
devices
Load
Flow
control
Voltage
control
Transient
stability
Dynamic
stability
SVC + +++ + ++
STATCOM + +++ ++ ++
TCSC ++ + +++ ++
UPFC +++ +++ +++ +++
Where: - Good +, Better ++, Best +++
• Load flow control
• Voltage control
• Transient stability
• Dynamic stability
• Reactive support
• Power quality improvement
• Fast adjusting the parameters of transmission system
• Expanding the capacity of transmission
• Optimizing the operation of power system
Benefits of FACTS devices for different applications

21. Conclusion
• UPFC performs the functions of different FACTS devices like STATCOM,
TCSC, and the phase angle regulator and it also provides additional flexibility by
combining some of the functions of these controllers.
• In grid transmission system, UPFC has control over various line parameters such
as voltage amplitude, phase angle and power. Thus it improved overall power
system stability.
• Hence, the UPFC is a versatile FACTS device which can be used to control
active and reactive power flows in a transmission line
• Hence, it can be concluded that UPFC provides most desirable performance
when connected to the system as compared to other FACTS devices.

22. References
1Samima Akter, Anulekha Saha & prof. Priyanath Das, “modelling, simulation and
comparison of various FACTS devices in power system”, International Journal of
Engineering Research & Technology (IJERT), vol.1, issue 8, october-2012.
2Mausam Yadav, Ankur Soni, “improvement of power flow and voltage stability using
unified power flow controller”, International Conference on Electrical, Electronics, and
Optimization Techniques (ICEEOT) – 2016.
3Smitkumar D. Choudante, A. A. Bhole, “A Review: Voltage Stability and Power Flow
Improvement by using UPFC Controller”, International Conference On Computation Of
Power, Energy, InformationAnd Communication (ICCPEIC)-2018
4 Electrical power systems byAshfaq Hussain
5 Understanding FACTS: CONCEPTS AND TECHNOLOGY OF FLEXIBLE AC
TRANSMISSION SYSTEMS by Narain G. Hingorani & Laszlo Gyugyi