Download PV Cell Fed Unified Power Quality Conditioner for Voltage Sag

ISSN 2348–2370
Vol.07,Issue.08,
July-2015,
Pages:1298-1303
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PV Cell Fed Unified Power Quality Conditioner for Voltage Sag
Compensation
C. ANITHA1, G. VIJAYA LAKSHMI2
1
2
PG Scholar, Dept of EEE, Arjun College of Technology & Sciences, Ranga Reddy(Dt), Hyderabad, TS, India.
Assistant Professor, Dept of EEE, Arjun College of Technology & Sciences, Ranga Reddy(Dt), Hyderabad, TS, India.
Abstract: Power quality has become an important factor in
power systems, for consumer and household appliances
with proliferation of various electric and electronic
equipment and computer systems. The main causes of poor
power quality are harmonic currents, poor power factor,
supply voltage variations etc., A technique of achieving
both active current distortion compensation ,power factor
correction and also mitigating the supply voltage variations
at load side, is compensated by unique device UPQC
presented in this paper and this concept presents a multi
loop based controller to compensate power quality
problems through a three phase four wire unified power
quality conditioner(UPQC) under unbalanced and distorted
load conditions. The UPQC is constituted of two voltage
source converters (vsc) connected via power link. The
series compensator is connected to the line in series and
injects the voltage and thus compensates for voltage issues;
whereas the shunt compensator injects current thus
compensating for current issues, and is connected in shunt
to the line. The voltage injection to the line uses an
injecting transformer. The proposed concept has been
extended with RES for the dc link of the UPQC which
supplies the active power whenever the grid is at block out
conditions or else at peak power demands this extension
works also increases the power quality improvement
efficiently. The simulation results have to conform that the
proposed UPQC with RES for very efficient, very simple
continuous power generation to load as compared to the
contemporary ones.
Keywords: FACTS, Series-Shunt Controllers, Power
Quality, RES.
I. INTRODUCTION
The integration of renewable energy into existing power
system presents technical challenges and that requires
consideration of voltage regulation, stability, power quality
problems [13]. The power quality is an essential customer
focused measure and it’s greatly affected by the operation
of a distribution and transmission network. Nowadays,
generation of electricity from renewable sources has
improved very much. Since most renewable energy sources
are intermittent in nature, it is a challenging task to
integrate a significant portion of renewable energy
resources into the power grid infrastructure. Traditional
electricity grid was designed to transmit and distribute
electricity generated by large conventional power plants. The
electricity flow mainly takes place in one direction from the
centralized plants to consumers. In contrast to large power
plants, renewable energy plants have less capacity, and are
installed in a more distributed manner at different locations.
The integration of distributed renewable energy generators has
great impacts on the operation of the grid and calls for new
grid infrastructure. UPQC was widely studied by many
researchers as an eventual method to improve power quality in
distribution system. A small distributed generation (DG)
should be interconnected with the power system in order to
maintain the frequency and voltage.
Several studies proposed on the interconnection system for
distributed generation with the power system through the
inverter because the inverter gives versatile functions in
proving the ability of distributed generation. The attention to
distributed generating sources is increasing day by day. The
reason is their important roll they will likely play in the future
of power systems. Recently, several studies are accomplished
in the field of connecting DG to grid using power electronic
converters [9]. Here grid interface shunt inverters are
considered more where the reason is low sensitiveness of DG
to grid parameters and DG power transferring facility using
this approach. Although DG needs more controls to reduce the
problems like grid power quality and reliability. PV and
WECS distributed generation sources which provides a part of
human required energy now a day and will provide in the
future. The greatest share of this kind of energy in the future
will be its usage in interconnected system.
II. SYSTEM DESCRIPTION
A. Basic System with Injection Transformer
The circuit diagram of the UPQC system with injection
transformer is shown in Fig. 1. The series and shunt VSC are
in full bridge configuration and are interconnected via a DC
link. DC link is constituted of a single capacitor alone. The
UPQC module is constituted of the VSCs in full bridge
configuration and a DC link. Out of the two bridged VSCs,
one acts as the series VSC and other as Parallel VSC. This
conventional UPQC works when there is disturbance in the
line. The control signals/gating signals are obtained from the
control strategy used. This control signal activates the VSCs.
Copyright @ 2015 IJATIR. All rights reserved.
C. ANITHA, G. VIJAYA LAKSHMI
The VSC acting as series VSC compensates for the
The circuit diagram of UPQC with the injection capacitor
voltage. Hence, when an over-voltage occurs, the system
shows the filter inductances in both sides of the VSCs through
balances itself by injecting a voltage which in effect
which the VSCs are connected to the transmission line. The
reduces the line voltage and maintains the desired voltage
controller for series VSC produces a proportional signal
level. But whenever there is a voltage sag/dip, an
according to the signal obtained from the comparison of the
additional voltage will be added to the line with the help of
desired/reference voltage with the actual voltage measured
the injecting transformer. The shunt VSC compensates for
from the system. This error voltage is used for PWM
the reactive component and thus conditions the current and
generation. This PWM signals generated is used for switching
reduces the harmonics. Thus the UPQC conditions power
of the IGBT switches which constitutes the series VSC. The
totally.
shunt VSC of the UPQC module is the responsible for the
compensation of the current and elimination of the unwanted
frequencies in the system. The PWM signal switches the VSC
according to the changes in the system by producing a PWM
signal accordingly so that the output of the VSC injected to
the line conditions the power flow through t he line. The
switching frequency of the IGBT switches used for the
comparative study is taken as 5 kHz.
Fig .1.Circuit diagram of UPQC with injection
transformer.
B. Basic System with Injection Capacitor
The major difference between the conventional system
and the proposed system are listed:
 Replacement of the injection transformer with a
capacitor. The voltage across the capacitor is adjusted
so that voltage compensation is obtained in the
system.
 DC link between the VSCs is constituted of two
capacitance- split capacitance.
 The split capacitance provides one terminal for the
injection capacitor.
III. CONTROL STRATEGY
The control strategy used here is a multi-loop based
controller which is based on the feedbacks obtained from the
systems. The control strategies for the series and shunt
controllers are discussed below:
A. Control Strategy for the Series VSC
The flowchart for the series control strategy is shown in
Fig 3. The control signals obtained from the PWM generator
is used for switching the switches of the series VSC. The
feedbacks from the systems is taken and compared with
various parameters. The reference voltage generation is done
by extracting the positive sequence component and its phase
from the system voltage. The Phase Locked Loops (PLL)
along with the positive extraction is used to generate the
positive sequence component. The following equation (1)
represents the reference capacitor voltage.
The single line diagram of the device is shown. Both the
VSCs are connected to the transmission line via a filter
circuit. Here a filter inductance is used in both sides which
is shown in the circuit diagrams for the both proposed
system (Fig 2) & conventional system (Fig 1).
Fig.3.Flowchart for Series VSC Controller.
(1)
Fig.2.Circuit
capacitor.
diagram
of
UPQC
with
injection
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.08, July-2015, Pages: 1298-1303
(2)
PV Cell Fed Unified Power Quality Conditioner for Voltage Sag Compensation
Vl* is the peak value of the line voltage. This is set by user.
θp is the phase angle of the positive sequence component.
(3)
The equation (2) shows the reference source voltage used
to obtain the required capacitor reference voltage. The
Where, the voltages Vα, Vβ are given as below
voltages Vsp and Vsn are the peak voltages of positive
sequence component and negative sequence component
respectively. θn is the phase angle of the negative sequence
(4)
component of the line voltage. Thus the generated voltage
Vsd is the positive sequence component of supply. The
is compared is with actual voltage and as per the algorithm
reference current generated in α-β reference frame is
gating signals are obtained the generated signal controls the
converted to abc reference frame. And we obtain the reference
switching of the switches of the series VSC.
frame currents – I*a, I*b& I*c.
B. Control Strategy for the Shunt VSC
The algorithm for the generation of control signals for
the shunt VSC is shown in fig.4. The feedbacks obtained
from the system are compared and then used generate the
PWM signals used for switching the switches of the shunt
VSC.
IV. PHOTOVOLTAIC MODULE
Here we are taking photovoltaic cells are the renewable
energy sources. In the crystalline silicon PV module, the
complex physics of the PV cell can be represented by the
equivalent electrical circuit shown in Fig.5. For that
equivalent circuit, a set of equations have been derived, based
on standard theory, which allows the operation of a single
solar cell to be simulated using data from manufacturers or
field experiments.
Fig 4 .Flowchart for Shunt VSC Controller.
Fig.5. Equivalent electrical circuit of a PV module.
The series resistance RS represents the internal losses due
to the current flow. Shunt resistance Rsh, in parallel with
diode, this corresponds to the leakage current to the ground.
The single exponential equation which models a PV cell is
extracted from the physics of the PN junction and is widely
agreed as echoing the behaviour of the PV cell
Fig.5.Reference current generation.
The reference current generation for the shunt VSC
controller is obtained using power balance theory. The
reference currents generated are in α-β reference frame.
This is transformed to abc reference frame and used as the
reference current for the PWM generation. The generation
of the reference current in abc frame is depicted in fig.4
The Cpq-1 is a transformation matrix and is given by the
following equations,
(5)
The number of PV modules connected in parallel and series
in PV array are used in expression. The Vt is also
Defined in terms of the ideality factor of PN junction (n),
Boltzmann’s constant (KB), temperature of photovoltaic array
(T), and the electron charge (q). applied a dynamical electrical
array reconfiguration (EAR) strategy on the photovoltaic
(PV) generator of a grid-connected PV system based on a
plant-oriented configuration, in order to improve its energy
production when the operating conditions of the solar panels
are different. The EAR strategy is carried out by inserting a
controllable switching matrix between the PV generator and
the central inverter, which allows the electrical reconnection
of the available PV modules.
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.08, July-2015, Pages: 1298-1303
C. ANITHA, G. VIJAYA LAKSHMI
V. MATLAB/SIMULINK RESULTS
Simulation results of this paper is shown in bellow Figs.6
to 15.
Fig.6. Simulink circuit for without UPQC.
Fig.10.Simulation results for load voltage and load
current.
Fig.7. Simulation results for source voltage without
UPQC.
Fig.11.FFT analysis for load voltage.
Fig.8. Simulation results for source current without
UPQC.
Fig.9. Simulink circuit with injecting transformer.
Fig.12. Simulink circuit for with UPQC having ultra
capacitance.
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.08, July-2015, Pages: 1298-1303
PV Cell Fed Unified Power Quality Conditioner for Voltage Sag Compensation
VI. CONCLUSION
The major power quality problems were minimized with
the implementation of the UPQC in the system. The UPQC
with three types of injecting devices were compared here to
find out the efficiency and effectiveness of the UPQC with the
change in the injecting devices. Thus the proposed injecting
device (injecting capacitor) was found effective for
minimizing the power quality issues over the conventional
injecting device (injecting transformer).And by using
renewable energy sources the injection capability is increases.
Fig.13. Simulation results for load voltage and load
current.
Fig.14. FFT analysis for load voltage.
VII. REFERENCES
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Fig.15. Simulation results for upqc having photovoltaic
cell.
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.08, July-2015, Pages: 1298-1303
C. ANITHA, G. VIJAYA LAKSHMI
[12] Singh, B.N., Chandra, H., Al-Haddad, K., Singh, B.:
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International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.08, July-2015, Pages: 1298-1303