S. Arulkumar et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
Research Paper
PERFORMANCE OF UNIFIED POWER QUALITY
CONDITIONER WITH DIFFERENT CONTROLLER
S.Arulkumar1 and P.Madhavasarma2
Address for Correspondence
Research Scholar, Anna University, Chennai, India.
2
Principal, Saraswathy College of Engineering and Technology, India.
1
ABSTRACT
The quality of the power is affected by many factors like harmonic contamination, due to the increment of non-linear loads,
such as large thyristor power converters, rectifiers, voltage and current flickering due to arc in arc furnaces, sag and swell
due to the switching of the loads etc. Recent times due to increased usage of loads, maintaining the quality of power is major
challenging for control engineer. Unified Power Quality Conditioner (UPQC) can be used for effectively improving the
power quality of an electrical power system. It is having shunt APF (Active Power Filter) and series APF (Active Power
Filter). The shunt part for compensate the source current and series parts for compensate the load voltage. In this paper
presents the reduction of Total Harmonic Distortion (THD) with the help of UPQC using PI controller, improved UPQC
controller (IUPQC) and Fuzzy logic controller. The output results are carried out and compare by using MATLAB software.
KEY WORDS: UPQC, Power quality, IUPQC, Fuzzy Logic Controller.
1. INTRODUCTION
Nowadays Power quality is the major issue in the
power system area. E.W.Gunther, et al., developed a
new power quality monitoring instrument. This can
be used to monitor the steady state quantities and
disturbances [1]. In UPQC the active power filters to
compensate current and reactive power for voltage
compensation [2]. The power electronics based
equipment’s are used to improve the power quality
issues and power enhancement [3]. In [4, 5] UPQC
SCR controlled capacitor banks achieving load
compensation by current control method. A new
method proposed [6] for power quality improvement
and it needs actual sinusoidal power supply. In this
paper [7] the universal power quality conditioning
system with various compensation are discussed with
recent development. The ANN with hysteresis
control give assurance for power quality issues like
swell, sags etc. [8, 9].Artificial intelligence based 3ɸ
UPQC implemented for control purpose [10]. The
improvement of power quality issues are discussed in
[11, 12]. The authors presented PI based power
quality improvement system [13] to improve the
THD level. Various control schemes are discussed
and applied for synchronous rotating frame to
maintain the constant voltage [14]. Thus, the DC
Link voltage control unit is intended to keep the
average dc bus power absorbed by the shunt inverter
.By varying the amplitude of the fundamental
component of the reference current, small amount of
real power is regulated. The ac source offers some
active current to recharge the dc capacitor [15].In this
proposes improvement of power quality issues and to
compensate the sag, imbalance condition, support the
real and reactive power and to eliminating the
harmonics in the distribution network with different
controller (PI, IUPQC and FUZZY controller).
2. UNIFIED POWER QUALITY CONDITIONER
The UPQC is a custom power device that combines
the series-and shunt active filters, connected back-toback on the dc side and sharing a common DC
capacitor [15] as shown in Fig.1. It’s having two
VSIs that are connected to a common DC energy
storage capacitor. Among these two VSIs one is
connected in series with the feeder and another one is
connected in parallel to the same feeder. The series
component of the UPQC is responsible for mitigation
of the supply side disturbances viz. voltage
sags/swells, flicker, voltage unbalance and
harmonics. It inserts voltages for to maintain the load
voltages at a constant level, balanced condition and
harmonic distortion free. The shunt component is
accountable for reducing the power quality problems
caused by the consumer. They are poor power factor,
load harmonic currents, load unbalance and DC
offset. It injects currents to the ac system such that
the source currents become balanced sinusoidal
waveform and in phase with the source voltages. The
major advantage of UPQC is that it does not require
any energy storage. It can be designed to lessen any
sag above certain magnitude, independent of its
duration. The main difficulty of UPQC is the huge
current rating required to mitigate deep sags. For low
power, low-voltage equipment this will not be a
severe concern, but it might limit the number of large
power and medium-voltage applications.
Fig.1 System configuration of UPQC
3. CONTROL STRATEGIES
3.1. COMPENSATING CURRENT
GENERATION
The magnitude of three phase reference current is
considered from the output, isp. The unit current
vectors (usa,usb,usc) are in phase with the three phase
supply voltages(vsa,vsb,vsc).These current vectors are
in phase with the three phase reference current. On
multiplying the isp magnitude with the current vectors
it results in three phase reference supply
currents(isa*,isb*,isc*).On subtracting the load
currents(ila,ilb,ilc) from the reference supply
current(isa*,isb*,isc*) it gives three phase reference
currents(isha*,ishb*.ishc*) for shunt inverter.
3.2.
VOLTAGE
GENERATION
AND
COMPENSATION
The series inverter operates in current control mode,
introduces a voltage source which isolates the load
from the supply. This voltage source gives for the
deviation of voltages. In closed loop control of series
inverter, the 3ɸ load voltages are subtracted from the
3ɸ supply voltages and it is compared with the
reference supply voltage.
Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/1293-1300
S. Arulkumar et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
These reference supply voltages are injected to the
voltages and hence compensating the voltage sag.
load. By suitable transformation of the resource, the
The current iref are compared with iact in PWM
reference currents of the series inverter are obtained
current controller, six switching signals are obtained
from the 3ɸ reference voltages. The 3ɸ reference
for series inverter’s IGBTs.
currents along with their sensed counterparts are
3.4. CONTROL OF DC VOLTAGE
given to a current (PWM) controller. The current
For maintain constant dc current in the energy
(PWM) controller gating signals, assure that the
storage capacitor. Usually a PI Controller is used for
voltage deviations are meet by the series inverter and
determining the magnitude of this compensating
hence giving sinusoidal voltage to load.
current from the error between the average voltage
across the dc capacitor and the reference voltage. In a
3.3. THE EQUATIONS OF UPQC
practical approach (Ziegler-Nichols tuning rules) for
3.3.1. Shunt Inverter Control Quantities
From the three phases sensed value the amplitude of
tuning the PI Controller is proposed. As an
the supply voltage is enumerated as:
alternative to PI Controller, IUPQC Controller and a
vsm = [2/3(vsa2+vsb2+vsc2)] 1/2
(1)
simple linear control technique of Fuzzy Controller is
The 3ɸ per unit current vectors are given as:
proposed.
usa = vsa/vsm; usb = vsb/vsm; usc = vsc/vsm
(2)
The active power which is necessary to keep dc
The three phase supply current is obtained by the
voltage constant in steady state or transient
product of three phase unit current vectors (usa, usb
condition. The voltage fluctuations of the dc
and usc) and the amplitude of three phase supply
capacitor are affected by three principal factors; to
current (isp). Multiplication of 3ɸ per unit current
compensate the alternating power, imbalance
vectors with the supply current gives the 3ɸ reference
during transient and active power absorbed.
supply currents as follows:
The FLC contains three parts: fuzzification,
isa* = isp.usa; isb* = isp.usb; isc* = isp.usc
(3)
inter fer ence engine and defuzzification. The FLC
The reference current is obtained by
is characterized as: i. for each input and output 7
subtracting the three phase load currents from the
fuzzy set ii. Triangular membership functions for
three phase supply currents: The reference current
simplicity iii. Continuous universe of discourse for
obtained from the difference between 3ɸ load
fuzzification. iv. Implication using mamdani’s‘min’
currents 3ɸ supply currents:
operator v. defuzzification using the ‘height’ method.
isha* = isa* -ila; ishb* = isb* - ilb
The knowledge bases are designed in order to get a
ishc* = isc* -ilc
(4)
good dynamic response under uncertainty in process
In Direct current control technique of shunt inverter
parameters and external disturbances. Dc voltage
these are the iref. Shunt inverter gives the switching
control using fuzzy logic is shown in figure2. In our
signals, the irefare compared with iactin PWM current
application, the fuzzy controller is based on
controller.
processing the voltage error and its derivation.
The numerical values of the variables are converted into
3.3.2. Series Inverter Control Quantities
The injected voltage as follows:
linguistic variables in the fuzzification stage. For every
vinj = vs – v1
(5)
input and output variable seven linguistic variables are
The magnitude of the injected voltage is expressed
assigned they are NB(negative big), NM(negative
as:
medium), NS(negative small), ZE(zero), PS(positive
vinj = |vinj|
small), PM(positive medium), and PB(positive
(6)
big).
While, the phase of injected voltage is given as:
For fuzzy implementation normalized values are
δinj = tan (Re[vpq]/Im[vpq])
used. As there are seven variables
(7)
for input and
For the compensating the harmonics in load voltage,
output, 49 possibilities can be obtained (i.e., 7*7=49)
the given inequalities are followed:
as tabulated in table1.
a)
vinj<vinjmax magnitude control;
b)
0 <δinj< 360° phase control;
The reference values of the injected voltages are
given as:
vla* = √2vinjsin(wt+δinj)
vlb* = √2vinjsin(wt+2π/3+δinj)
vlc* = √2vinjsin(wt-2π/3+δinj)
(8)
The series inverter’s three phase reference currents
Fig.2. dc voltage control using f uzzy logic
(iref) are computed as follows:
A membership function value between zero and one
isea* = vla*/zse ;
will be assigned to each of the numerical values in
iseb* = vlb*/zse ;
the membership function graph. In this(9)chapter, we
isec* = vlc*/zse ;
applied max-min inference method to get implied
Secondary windingsare maintaining the currents in
fuzzy set of the turning Rules.
ideal, the insertion transformer in order to inject
Table.1. Fuzzy set rules of inference for the dc voltage
CE
E
NL
NM
NS
EZ
PM
PS
PL
NL
NM
NS
EZ
PM
PS
PL
NL
NL
NL
NL
NM
NS
EZ
NL
NL
NL
NM
NS
EZ
PS
NL
NL
NM
NS
EZ
PS
PM
NL
NM
NS
EZ
PS
PM
PL
NM
NS
EZ
PS
PM
PL
PL
NS
EZ
PS
PM
PL
PL
PL
EZ
PS
PM
PL
PL
PL
PL
Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/1293-1300
S. Arulkumar et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
4. SIMULATION RESULT
4.1. PI CONTROLLER
Fig. 3.Simulation diagram for PI controller
The figure 4, 5 and 6 shows the source side and load side voltage, current, real and reactive power performance
by using PI controller with Non-linear load connect the time period of 0.1sec to 0.15 sec.
Fig. 4.Load side voltage and current
Fig. 5.Source side voltage and current
Fig. 6.Real and Reactive power
Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/1293-1300
S. Arulkumar et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
4.2. IUPQC CONTROLLER
The figure 8, 9 and 10 shows the source side and load
side voltage, current, real and reactive power
performance by using IUPQC controller. Non-linear
load connect the time period of 0.15sec to 0.25 sec.
In that period some amount of voltage is reduce, that
voltage is compensated by using IUPQC controller to
regulate the back to back DC capacitor. After 0.25
sec the normal voltage is maintain at constant level
and also current, real and reactive power improved.
Compare to PI controller it gives better results.
Fig. 7.Simulation diagram for IUPQC controller
Fig. 8.Load side voltage and current
Fig. 9.Source side voltage and current
Fig. 10.Real and Reactive power
Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/1293-1300
S. Arulkumar et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
4.3.
FUZZY CONTROLLER
Fig. 11.Simulation diagram for FUZZY controller
The figure 12, 13 and 14 shows the source side and
regulate the back to back connected DC capacitor.
load side voltage, current, real and reactive power
After 0.2 sec the normal voltage is maintain at
performance by using Fuzzy controller. Non-linear
constant level and also current, real and reactive
load connect the time period of 0.1sec to 0.2 sec. In
power improved. Compare to other two controllers it
that period some amount of voltage is reduce, that
gives better results.
voltage is to compensate by using Fuzzy controller to
Fig. 12.Load side voltage and current
Fig. 13.Source side voltage and current
Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/1293-1300
S. Arulkumar et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
Fig. 14.Real and Reactive power for source side and load side
Fig. 15.Control Surface of the Fuzzy controller
(a)
(b)
(c)
Fig.16. Membership functions for input and output variables (a), (b) and (c)
Figure16 shows the membership functions of input and output and triangle shaped membership function has the
advantages of simplicity and easier implementation and is chosen in this application.
5. RESULT COMPARISON
Fig. 17.Total Harmonic Distortion level of 1.47%
Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/1293-1300
S. Arulkumar et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
Fig. 18.Total Harmonic Distortion level of 0.88%
Fig.19.Total Harmonic Distortion level of 0.16%
Table.2. RESULT COMPARISON (FFT ANALYSIS THD LEVEL)
CONTROLLER
PI CONTROLLER
IUPQC
CONTROLLER
FUZZY LOGIC
CONTROLLER
1.47%
0.88%
0.16%
DEVICE
UPQC
CONCLUSION
The simulation results show that UPQC can be used
for effectively improving the power quality of an
electrical power system. The shunt APF has been
used for compensating the source current harmonics
and it reduces the source current. The series APF has
been used for compensating the load voltage
harmonics and it reduces the load Voltage. The
performance of UPQC with PI controller (1.47%) ,
IUPQC controller (0.88%) and Fuzzy controller
(0.16%) by using the FFT analysis to get the reduced
Total Harmonic Distortion (THD) level, voltage sag
compensation, real and reactive power of the system.
The fuzzy logic controller provide quickand better
results than the PI controller and IUPQC controller.
Hence it is proved that fuzzy logic controller is
superior when compare to other controllers.
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