SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 3 Issue 5 May 2016
Power Quality Improvement using Unified Power Quality
Conditioner
1
Rohit Saraswat, 2Jethu Singh, 3Sukha Ram
1
M.Tech Student of Power System, SKIT, Jaipur
2
B.Tech Student of Electrical Engineering, PIET, Jaipur.
3
B.Tech Student of Electrical Engineering, PIET, Jaipur.
Abstract- As the demand of electricity is increasing
day by day, it is necessary to supply
a good
quality of power to customers. In the future,
distribution system operators could decide to
supply their customers with different PQ levels and
at different prices. Due to the presence of nonlinear loads in the system many problems like
fluctuations, flickers, voltage sag, voltage swell etc.
comes in the system. The device that can fulfil these
demands is the Unified power quality conditioners
(UPQC). This paper gives a comprehensive study
of different components of UPQC along with
different control strategies used for UPQC control.
Keywords - Active power filter (APF), Power
quality, Unified Power Quality Conditioner
(UPQC), Voltage sag and swell compensation,
Active power filters, ANN, Fuzzy logic controller,
1: INTRODUCTION
The limited stretch of time Power Quality
(PQ) are most important facets of any power way of
using voice system today. feeble amount of power
quality has an effect on user and can cause loss of
producing, damage of appliances and necessary things,
increase the power loss and so forward, out, on (in
time). In present scenario the use of necessary things
based on power electronics has produce force of
meeting blow on power quality by harmonics.
Power Quality is a function of power factor
so the use of non-linear and low power factor load such
as adjustable speed drives, computer power supplies,
furnaces, power converters and traction drives are
finding its applications at domestic and industrial
levels. These nonlinear loads draw non-linear current
and degrade electric power quality. The prime
objective of power utility companies is to provide their
consumers an uninterrupted sinusoidal voltage of
constant amplitude.
The term Active Power Filter (APF) is mainly
used for the improvement of power quality. One
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modern solution that deals with both load current and
supply voltage flaws is the UPQC. The UPQC is one of
the APF family members. The main function of UPQC
is to reduce the effect of problem occurs in supply
voltage such as, sags, swells, unbalance, flicker,
harmonics, and for load current power quality
problems such as, harmonics, unbalance, reactive
current and neutral current. The UPQC is consist of
series and shunt active filters connected in cascade via
a common DC link capacitor.
2. UNIFIED POWER QUALITY
CONDITIONER
The Unified Power Quality Conditioner is a
custom power device that is consist of series and
shunt APFs for compensation of voltage and current.
It places in the distribution system to reduce the
disturbances that impact on the performance load.
UPQC is the only multi functioning device which can
reduce several problems power quality problems.
The system configuration of a 1-Φ UPQC is shown in
Fig. 1. Unified Power Quality Conditioner (UPQC)
consists of two distinct part:
• Power circuit formed by series and shunt
PWM converters
• UPQC controller
The series PWM converter of the UPQC behaves as
a controlled voltage source, that is, it behaves as a
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 3 Issue 5 May 2016
series APF, whereas the shunt PWM converter
behaves as a controlled current source, as a shunt
APF. No power supply is connected at the DC link.
It contains only a relatively small DC capacitor as a
small energy storage element.
The integrated controller of the series and
shunt APF of the UPQC to provide the compensating
voltage reference VC* and compensating current
reference IC* to be synthesized by PWM converters.
The shunt active power filter of the UPQC
can compensate all undesirable current components,
including harmonics, imbalances due to negative and
zero sequence components at the fundamental
frequency. In order to cancel the harmonics generated
by a nonlinear load, the shunt inverter should inject a
current as governed by the following equation:
Ic (ωt) = I*s (ωt) – Il (ωt)
(1)
Where Ic (ωt), I*S (ωt), and IL (ωt) represent the shunt
inverter current, reference source current, and load
current, respectively.
The series active power filter of the UPQC
can compensate the supply voltage related problems
by injecting voltage in series with line to achieve
distortion free voltage at the load terminal. The series
inverter of the UPQC can be represented by
following equation:
VC (ωt) = V*L (ωt) – VS (ωt)
(2)
Where VC (ωt), V*L (ωt), and V (ωt) represent the
series inverter voltage, reference load voltage, and
actual source voltage, respectively
continuous process industry and the information
technology services. When a disturbance occurs,
huge financial losses may happen, with the
consequent loss of productivity and competitiveness.
Although many efforts have been taken by utilities,
some consumers require a level of PQ higher than the
level provided by modern electric networks. This
implies that some measures must be taken in order to
achieve higher levels of Power Quality.
3. POWER QUALITY
The term ―Power Quality (PQ)‖ is defined
as ―The concept of powering and grounding
electronic equipment in a manner that is suitable to
the operation of that equipment and compatible with
the premise wiring system and other connected
equipment."
The widespread use of electronic
equipment, such as information technology
equipment, power electronics such as adjustable
speed drives (ASD), programmable logic controllers
(PLC), energy-efficient lighting, led to a complete
change of electric loads nature. These type of load are
responsible for power quality problem. Due to use of
these low power factor and their non-linearity, These
loads cause distortion and disturbances in the
waveform of voltage and current. The increased
sensitivity of the vast majority of processes
(industrial, services and even residential) to PQ
problems turns the availability of electric power with
quality a crucial factor for competitiveness in every
activity sector. The most critical areas are the
4.1: Interruption
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4: POWER QUALITY PROBLEMS
In power circuit the term power quality is very
important term that contain all the parameters
associated with amplitude, phase and frequency of
voltage and current waveform. Any problem that
occurs in power quality is due to deviation in voltage,
current and frequency that results in failure of
equipment that is by costumer is known as power
quality problems.
In now a day the equipment based on power
electronics is increase day by day that produce impact
on quality of electric power supply. Lo w q uality
po wer affects the consumer s and can cause lo ss of
production, damage of equipment or appliances,
increased
power
losses,
interference
with
communication lines and so forth. Therefore, it is
obvious to maintain high standards of power quality.
The major types of power quality problems
are:
Interruption, Voltage-sag, Voltage-swell,
Distortion,
and
Harmonics.
Figure 2. Interruption
Disappear of wave form means complete loss of
supply voltage or load current. This Interventions can be
occurring due to power system faults, equipment failures,
and control malfunction etc. On the basis of time duration
of these intervention, we can classify it in three type:
1. The momentary interruption is defined as
the complete loss of supply voltage or load current
having a duration between 0.5 second & 3 second.
2. The temporary interruption is the complete
loss lasting between 3 seconds and 1 minute,
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 3 Issue 5 May 2016
3. The long term interruption is an interruption
which has a duration of more than 1 minute
Waveform of voltage and current are
assume as non-sinusoidal shape so these waveforms
called distorted waveforms as shown in Fig 5.
4.2: Voltage Sags
Figure 3. Voltage Sags
In voltage the short-duration reduction in its
rms value is caused short-duration increment in the
current is known as voltage sags.
Normally Voltage sage (dips) occurs at the
time of motor starting, transformer energizing and
faults. A sag is decrease in voltage at the power
frequency for duration from 0.5 cycle to 1min.
Voltage sags are usually associated with system
faults but can also cause by energization of heavy
loads at starting of large motors (Fig 3).
Figure 5. Distorted
Waveform
It is defined as the steady state deviation from an ideal
sine wave, due to harmonics, which are sinusoidal
voltages or currents having frequencies that are whole
multiples of frequency at which supply system is
designed to operate (50 HZ).
4.5: Harmonics
4.3: Voltage Swells
Figure 4. Voltage Swells
Voltage swell are opposite of voltage sags. In Voltage
swell the rms value of voltage is increase in ac voltage,
At the power frequency. Time interval of voltage sage
is about half cycle to a few seconds. As shown in Fig4.
Voltage can rise above normal level for several cycles
to seconds. Normally the voltage swells is affect the
equipment such as damage of lighting, motor and
electronics loads and also cause shutdown to
equipment. The severity of voltage swell during a
fault condition is a function of fault location, system
impedance and grounding
4.4: Waveform Distortion
Distortion is the alteration of the original
shape (or other characteristic) of something, such as
an object, image, sound or waveform. Distortion is
usually unwanted,
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Figure 6. Waveform with 3rd
Harmonic
Harmonics are sinusoidal voltages or
current having frequency that are integer multiples
of the fundamental frequency. Here, 3rd harmonics
is seen in the figure 6.
5: CLASSIFICATION OF UPQC
The Unified Power Quality Conditioner are
classified on various bases like converter used,
topology, supply type and compensation method.
The UPQC is classified in two main groups which
is based on, Physical structure and Voltage sag
compensation.
5.1: Physical structure
Classification based on parameter a r e : Type
of energy storage device used, Number of
phases, and Physical location of shunt and series
inverter.
5.1.1: Converter based classification
a) VSI (voltage source inverter)
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 3 Issue 5 May 2016
b) CSI (current source
inverter)
5.1.2: Supply system based
classification
a) 1-Φ
a1) Two H-bridge (total 8 switches)
a2) 3-Leg topology (total 6 switches)
a3) Half Bridge (total 4 switches)
b) 3-Φ
b1) Three-Wire
b2) Four-Wire
b2.1) Four-Leg
b2.2) Split Capacitor
b2.3) Three-H Bridge
5.1.3: UPQC Configuration based
classification
a) UPQC-R (Right Shunt)
b) UPQC-L (Left Shunt)
c) UPQC-I (Interline)
d) UPQC-MC (Multi-Converter)
e) UPQC-MD (Modular)
f) UPQC-ML (Multilevel)
g) UPQC-D (Distributed)
h) UPQC-DG (Distributed Generator
integrated)
5.2: Voltage Sag Compensation
To overcome the problem of voltage sag,
normally we use four methods.
a) UPQC-P (Active Power Control)
b) UPQC-Q (Reactive Power Control)
c)UPQC-Vain (Minimum VA Loading)
d) UPQC-S (Active-Reactive Power Control)
TABLE-1.1: Comparison between Voltage Source
Inverter and Current Source Inverter
Voltage Source Inverter
(VSI) based
2. VSI shares a common
energy storage capacitor
(Cdc) to form the dc-link
3. Advantages:
- Lower cost,
- Smaller physical size,
- Lighter in weight,
- Cheaper,
- Capability of multilevel
operation,
- Flexible overall control,
- High efficiency near
nominal operating point.
4. Disadvantages:
- Low efficiency when the
load power is low,
- Limited lifetime of the
electrolyte capacitor.
Current Source Inverter
(CSI) based
2. CSI shares a common
energy storage inductor
(Ldc) to form the dc-link
3. Advantages:
- Open loop current control
is possible,
- High efficiency when the
load power is low.
4. Disadvantages:
- Bulky and heavy dc
inductor,
- High dc-link losses,
- Low efficiency near
nominal operating point,
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Figure 7.
VSI
configuration
Figure 8. CSI
configuration
based
based
UPQC
system
UPQC
system
On the basis of power system, the UPQC’s are
classified into two type a) 1-Φ and b) 3-Φ.
1-Φ two-wire Two-H bridge UPQC
configuration is shown in figure 9. Next topology is
3-leg topology and it use 6 switches, in series inverter
it uses 4 switches and remaining is use in shunt
inverter. Last one is half-bridge topology (4 switches),
it uses 2 switches for series inverter and 2 switches for
shunt inverter.
Figure 9. 1-Φ Two-wire (eight switches)
Maximum non-linear load work on three
phase power supply. To improve the power quality is
fed by 3-Φ three-wire UPQC system.
The combination of 3-Φ and single- phase loads are
supplied by 3-Φ four-wire (3P4W) UPQC
configuration.
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 3 Issue 5 May 2016
3. In 1-Φ system load 3. - In 3 - Φ three- wire
reactive
current, current system apart from reactive
harmonics
are
major current, current harmonics
problems
additional problem is current
unbalance
- In 3-Φ four-wire system
additional neutral current
problem
Figure 10. 3-Φ Three-wire (3P3W) UPQC
. For neutral current compensation in threephase
four-wire (3P4W) system, various
shunt
inverter configurations are given, namely, four-leg
(4L), two split-capacitor (2C) and Three-H bridge
(3HB).
Figure 11. 3-Φ Four-wire (3P4W) UPQC
based on Four-leg (4L) shunt inverter topology
The 3HB topology use three 1-Φ H- bridge
inverter connected to same dc bus of the UPQC. The
2C topology use two split-capacitor on dc side and
the midpoint of two capacitors is at zero potential
which is used as connection point for the fourth
wire. Among all three topologies four-leg (4L) is
give better control over neutral current due to four
leg. So, in this paper 3-Φ four-wire based on four-leg
(4L) shunt inverter topology is shown in figure 11.
TABLE-1.2: Comparison between 1-Φ UPQC
and 3-Φ UPQC
1-Φ UPQC
4. Voltage related power
quality problems are similar
for both single and threephase system except voltage
unbalance compensation is
required in 3-Φ system
UPQC’s farther classify on the basis of position of
shunt is location. If the shunt is located in right the
it called UPQC-R. similar if shunt is located in left
side the it called UPQC-L. UPQC-R is commonly
used because current flow through series
transformer. The UPQC-L is rarely used when to
avoid interference between shunt inverter and
passive filters.
TABLE-1.3: Comparison between Interline UPQC
and Multi-converter UPQC
Interline UPQC (UPQC-I)
Multi-converter UPQC
(UPQC-MC)
1. In Interline UPQC two
1. In UPQC-MC third
inverters
are
connected converter is added to
between two distribution support dc bus.
feeders.
2. One inverter is connected 2. The third converter is
in series with one feeder connected either series or
while other inverter is parallel with feeder.
connected in shunt with
other feeder.
3. UPQC-I can control and
3. To
improve system
manage flow of real power
performance, use of storage
between two feeders.
battery or super capacitor at
third converter.
TABLE-1.4: Comparison between Modular UPQC
and Multi-level UPQC
3-Φ UPQC
1. 1-Φ UPQC is possible in 1Φ two-wire (1P2W)
1. 3-Φ UPQC is possible in 3Φ three-wire or 3-Φ four-wire
(3P3W or 3P4W)
2. 1-Φ UPQC is
further classified on:
(I) Two H-bridge
(ii) 3-Leg topology
(iii) Half Bridge
2. 3-Φ four-wire
UPQC is further classified
on:
(I) Four-Leg
(ii) Split Capacitor
(iii) Three-H Bridge
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4. Voltage related power
quality problems are similar
for both single and threephase system except voltage
unbalance compensation is
not required in 1-Φ system
Modular UPQC (UPQC- Multi-level UPQC
MD
(UPQC-ML
1. In UPQC-MD several
H-bridge modules are
connected in cascade
in each phase.
1. UPQC-ML is based
on 3level neutral point
clamped topology.
2. UPQC-MD can be
useful to achieve higher
power levels.
2. UPQC-ML can also
be
useful to achieve
higher power levels.
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 3 Issue 5 May 2016
TABLE-1.5: Comparison between UPQC-D
UPQC-DG
and
Distributed UPQC
(UPQC-D)
Distributed Generator
Integrated UPQC
(UPQC-DG)
1. UPQC-D topology is also
known as 3 P3W to 3 P4W
Distributed U P Q C
b ec a us e
3P4W system is realized by
2. In U P Q C-D s y s t e m t h e
neutral of series transformer
is used as neutral of 3P4W
system.
1. The UPQC can be
integrated w it h one or
several DG systems which is
known as UPQC-DG.
3. Fourth l e g i s a d d e d t o
3P3W
UPQC
to
compensate neutral current
flowing
towards
transformer neutral point.
3. In UPQC-DG battery can
be added at dc bus which is
used as stored power and
used as backup which give
benefit
for
removing
voltage interruption.
2. The output of DG system
is connected to dc bus of
UPQC to compensate voltage
and current related problems.
Finally, we can classify UPQC’s on the basis of
voltage sag compensation. There are four methods.
TABLE-2.1: Comparison between Active Power
Control and Reactive Power Control.
Active Power Control
Reactive Power Control
(UPQC-P)
(UPQC-Q)
1. The voltage sag is
mitigated
by
injecting
active power through series
inverter of UPQC.
2. In Active Power Control
P is referred as active
power.
3. To compensate equal
percentage of sag UPQC-P
requires smaller magnitude
of series injection voltage
compared to UPQC-Q
1. The voltage sag is
mitigated
by
injecting
reactive power through series
inverter of UPQC.
2.
In Reactive P o w e r
Control Q is referred as
reactive power.
3. To compensate equal
percentage of sag UPQC-Q
requires smaller magnitude
of series injection voltage
compared to UPQC-P
TABLE-2.2: Comparison between Minimum
VA loading and Active & Reactive Power Control
Minimum VA loading Active & Reactive
(UPQC-Vain)
Power
Control
(UPQC-S)
1. This method is used 1.In UPQC-S the series
which is injected certain inverter is delivered
optimal angle with respect both active and reactive
power.
to source current.
2.The
series
voltage
injection and the current
drawn by shunt inverter
must need for determining
Minimum VA loading of
UPQC.
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2. The series inverter
of UPQC-S perform
voltage sag and swell
compensation
and
sharing reactive power
with shunt inverter.
6: CONTROL STRATEGIES OF UPQC
For control the UPQC’s we normally us
three type of control strategy:
6.1: Voltage and current signals are sensed:
In this strategy we use power
transformer and voltage sensor for sense
voltage signal and for sense the current
signal we use current sensor and power
transformer.
6.2:
Compensating commands in terms
of voltage and current levels are derived:
this is based on mainly two type of
domain method: a) Frequency domain
method, b) time domain method.
6.3: The
gating
signals
for
semiconductor switches of UPQC are
generated using PWM, hysteresis or
fuzzy logic based:
6.3.1: FUZZY LOGIC CONTROLLER
A fuzzy control system is a control system based on
fuzzy logic which is much closer in spirit to human
thinking and natural language than classical logical
systems —a mathematical system that analyses
analog input values in terms of logical variables that
take on continuous values between 0 and 1, in
contrast to classical or digital logic, which operates
on discrete values of either 1 or 0
Fuzzy system transforms a human knowledge into
mathematical formula. Therefore, fuzzy set theory
based approach has emerged as a complement tool
to mathematical approaches for solving power
system problems. Fuzzy set theory and fuzzy logic
establish the rules of a nonlinear mapping.
In present scenario the fuzzy logic is use in all sector.
The fuzzy logic controller designed can be of the
form
shown
in
Fig.
2
Figure 13: Fuzzy Logic Controller
The fuzzy logic controller is comprised of four main
components [1]: the fuzzification, the inference
engine, the rule base, and the defuzzification, as
shown
in
Fig.
3
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 3 Issue 5 May 2016
Figure 14: Components of Fuzzy Controller
The fuzzifier transforms the numeric/crisp value into
fuzzy sets; therefore, this operation is called
fuzzification. The main component of the fuzzy logic
controller is the inference engine, which performs all
logic manipulations in a fuzzy logic controller. The
rule base consists of membership functions and
control rules. Lastly, the results of the inference
process is an output represented by a fuzzy set,
however, the output of the fuzzy logic controller
should be a numeric/crisp value. Therefore, fuzzy set
is transformed into a numeric value by using the
defuzzifier. This operation is called defuzzification.
6.3.2: ARTIFICIAL NEURAL NETWORK
Artificial intelligence based gain scheduling is an
alternative technique commonly used in designing
controllers for non-linear systems.
The rapid detection of the disturbance signal with
high accuracy, fast processing of the reference signal,
and high dynamic response of the controller are the
prime requirements for desired compensation in case
of UPQC.A recent study shows that ANN-based
controllers provide fast dynamic response while
maintaining stability of the converter system over
wide operating range. The ANN is made up of
interconnecting artificial neurons. It is essentially a
cluster of suitably interconnected nonlinear elements
of very simple form that possess the ability to learn
and adapt. It resembles Improvement of Power
Quality by UPQC Using Different Intelligent
Controls:
A literature Review
the brain in two aspects: 1) the knowledge is acquired
by the network through the learning process and 2)
interneuron connection strengths are used to store the
knowledge. These networks are characterized by
their topology, the way in which they communicate
with their environment, the manner in which they are
trained, and their ability to process information. ANN
has gain a lot of interest over the last few years as a
powerful technique to solve many real world
problems. Compared to conventional programming,
they own the capability of solving problems that do
not have algorithmic solution and are therefore found
suitable to tackle problems that people are good to
solve such as pattern recognition. ANNs are being
used to solve AI problems without necessarily
creating a model of a real dynamic system. For
ISSN: 2348 – 8379
improving the performance of a UPQC, a multilayer
feed forward- type ANN-based controller is
designed. This network is designed with three layers,
the input layer with 2, the hidden layer with 21, and
the output layer with 1 neuron, respectively.
7: CONCLUSION
The power quality problems in distribution
systems are not new but customer awareness of these
problems increased recently. It is very difficult to
maintain electric power quality at acceptable limits.
One modern and very promising solution that deals
with both load current and supply voltage
imperfections is the Unified Power Quality
Conditioner (UPQC). This paper presented review on
the UPQC to enhance the electric power quality at
distribution level. The UPQC is able to compensate
supply voltage power quality issues such as, sags,
swells, unbalance, flicker, harmonics, and for load
current power quality problems such as, harmonics,
unbalance, reactive current and neutral current. In
this paper several UPQC configurations have been
discussed. Among all these configurations, UPQCDG could be the most interesting topology for a
renewable energy based power system.
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