analysis of statcom performance with single phase and
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Vol.07,Issue.20,
December-2015,
Pages:4064-4072
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Analysis of STATCOM Performance with Single Phase and Three Phase
Balanced and Un-Balanced Loads KATCHALA Y. N. VENUGOPAL
1, B. KRISHNA
2, V. KAMARAJU
3
1PG Scholar, Dept of EEE, Sanketika Vidya Parishad Engineering College, Visakhapatnam (Dt), AP, India, E-mail:
[email protected]. 2Assistant Professor, Dept of EEE, Sanketika Vidya Parishad Engineering College, Visakhapatnam (Dt), AP, India,
E-mail: [email protected]. 3Assistant Professor, Dept of EEE, Sanketika Vidya Parishad Engineering College, Visakhapatnam (Dt), AP, India.
Abstract: this paper presents an analysis of the three-phase
self excited induction generator (SEIG) with static
compensator (STATCOM) as a voltage regulator. Current
controlled voltage source inverter (CC-VSI) is used as
STATCOM, which provides fast dynamic response to
maintain constant voltage at SEIG terminals during severe
load perturbations and acts as a source and sink of reactive
power. The performance equations are derived sing d-q
variable in stationary reference frame to develop a
mathematical model of SEIG-STATCOM system feeding
unbalanced loads. Transient analysis of the SEIG
STATCOM system is carried out for voltage build-up
switching in STATCOM, application and removal of
balanced/unbalanced resistive/reactive loads. The
STATCOM regulates the SEIG terminal voltage through
reactive power compensation and also suppresses the
harmonics injected by consumer loads. A single-phase
synchronous D-Q frame theory-based control algorithm is
used to generate gating pulses to the three-phase
STATCOM. In this proposed scheme Static Compensator
(STATCOM) is connected at a point of common coupling
with a battery energy storage system (BESS) to
photovoltaic system mitigate the power quality issues. By
using MATLAB/SIMULINK software.
Keywords: Self-Excited Induction Generator (SEIG),
Single Phase Synchronous D-Q Frame Theory, Static
Synchronous Compensator (STATCOM).
I. INTRODUCTION
The proliferation of the power electronics-based
equipment, nonlinear and unbalanced loads, has aggravated
the power quality (PQ) problems in the power distribution
network. They cause excessive neutral currents, over
heating of electrical apparatus, poor power factor, voltage
distortion, and high levels of neutral –to ground voltage,
and inference with communication systems. The literature
records the evolution of different custom power devices to
mitigate the power-quality problems by injecting the
voltages/currents or both in to the system. Power
distribution systems, ideally, should provide their
customers with an uninterrupted flow of energy at smooth
sinusoidal voltage at the contracted magnitude level and
frequency [1]. However, in practice, power systems,
especially the distribution systems, have numerous
nonlinear loads, which significantly affect the quality of
power supplies. As a result of the nonlinear loads, the
purity of the waveform of supplies is lost. This ends up
producing many power quality problems. Apart from
nonlinear loads, some system events, both usual (e.g.
capacitor switching, motor starting) and unusual (e.g.
faults) could also inflict power quality problems [2].Power
quality phenomenon or power quality disturbance can be
defined as the deviation of the voltage and the current from
its ideal waveform.
Many efforts have been taken by utilities to fulfill
consumer requirement, some consumers require a level of
PQ higher than the level provided by modern networks of
electricity. It shows that some measures must be taken in
order to achieve higher levels of Power Quality. The
FACTS devices and Custom power devices are introduced
to electrical system to improve the power quality of the
electrical power. DVR, STATCOM/DSTATCOM, Active
Filters, UPFC, UPQC etc are some of the devices used to
improve the power quality of the current and voltage. By
the help of these devices we are able to reduce the
problems related to power quality. The unbalanced loads
would pose additional problem on the design of controller
that should not only provide needed VAR but also
maintain the generator output voltage and current under
balance in spite of unbalanced load. This paper addresses
this issue and suggests a viable STATCOM based
controller. Here the total system comprising SEIG;
STATCOM and a general balanced/unbalanced load is
modeled and analyzed for transients/dynamic performance
under realistic load conditions for both resistive and
partially reactive load. The simulated results demonstrate
that the use of STATCOM with SEIG has applicability for
three-phase power generation under all types of
balanced/unbalanced loads.
KATCHALA Y. N. VENUGOPAL, B. KRISHNA, V. KAMARAJU
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.20, December-2015, Pages: 4064-4072
Fig.1. Schematic Diagram of the SEIG–STATCOM
System Feeding Single-Phase Loads.
II. SYSTEM CONFIGURATION AND PRINCIPLE
OF OPERATION
Fig.1 shows the schematic diagram of the STATCOM
compensated three-phase SEIG feeding single-phase loads.
The system consists of an SEIG driven by renewable
energy-based prime mover. The single-phase consumer
loads are connected across ―a‖ and ―c‖ phases of the SEIG.
A two-level, three-leg insulated-gate bipolar transistor
(IGBT)-based VSI with a self sustaining dc-bus capacitor
is used as a STATCOM. The STATCOM is connected at
point of common coupling (PCC) through filter inductors
as shown in Fig.1. The STATCOM regulates the system
voltage by maintaining equilibrium among the reactive
power circulations within the system. Moreover, the
STATCOM suppresses harmonics injected by nonlinear
loads and provides load balancing while feeding single-
phase loads. The unbalanced load currents in a three-phase
system can be divided into two sets of balanced currents
known as positive sequence components and negative
sequence components.
A. Unit Vector
The control diagram of grid- interfacing inverter for a 3-
phase system is shown in Fig. 2. The main aim of proposed
approach is to regulate the power at PCC during: While
performing the power management operation, the inverter
is actively controlled in such a way that it always draws/
supplies fundamental active power from/ to the grid. If the
load connected to the PCC is non-linear or unbalanced or
the combination of both, the given control approach also
compensates the harmonics, unbalance, and neutral
current. The duty ratio of inverter switches are varied in a
power cycle such that the combination of load and inverter
injected power appears as balanced resistive load to the
grid.
Fig.2. Block diagram representation of grid-interfacing
inverter control.
The regulation of dc-link voltage carries the information
regarding the exchange of active power in between
renewable source and grid. Thus the output of dc-link
voltage regulator results in an active current (Im). The
multiplication of active current component (Im). With
unity grid voltage vector templates (Ua,Ub, and Uc)
generates the reference grid currents . The reference grid
neutral current (I*n) is set to zero, being the instantaneous
sum of balanced grid currents. The grid synchronizing
angle (θ) obtained from phase locked loop (PLL) is used to
generate unity vector template as [9]–[11]
(1)
(2)
(3)
The actual dc-link voltage (Vdc) is sensed and passed
through a first-order low pass filter (LPF) to eliminate the
presence of switching ripples on the dc-link voltage and in
the generated reference current signals. The difference of
this filtered dc-link voltage and reference dc-link voltage
(V*dc) is given to a discrete- PI regulator to maintain a
constant dc-link voltage under varying generation and load
conditions. The dc-link voltage error Vdceer(n) at nth
sampling instant is given as:
(4)
The output of discrete-PI regulator at th sampling
instant is expressed as
(5)
Where KPVdc = 10 and KIVdc = 0.05 are proportional and
integral gains of dc-voltage regulator. The instantaneous
values of reference three phase grid currents are computed
as
(6)
Analysis of STATCOM Performance with Single Phase and Three Phase Balanced and Un-Balanced Loads
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.20, December-2015, Pages: 4064-4072
(7)
(8)
The reference grid currents (I*a, I
*b, I
*c) are compared
with actual grid currents (Ia, Ib, Ic) to compute the current
errors as
(9)
(10)
(11)
(12)
These current errors are given to hysteresis current
controller. The hysteresis controller then generates the
switching pulses (P1 to P8) for the gate drives of grid-
interfacing inverter. The average model of 4-leg inverter
can be obtained by the following state space equations
(13)
(14)
(15)
(16)
(17)
Where VInva, VInvb, VInvc and VInvn are the three-phase ac
switching voltages generated on the output terminal of
inverter.
These inverter output voltages can be modeled in terms
of instantaneous dc bus voltage and switching pulses of the
inverter as
(18)
(19)
(20)
(21)
Similarly the charging currents VInvad, VInvbd, VInvcd and
Vinvnd on dc bus due to the each leg of inverter can be
expressed as
(22)
(23)
(24)
(25)
The switching pattern of each IGBT inside inverter can
be formulated on the basis of error between actual and
reference current of inverter, which can be explained as:
If IInva < (I*Inva-hb), then upper switch S1will be OFF
(P1 =0) and lower switch S4 will be ON (P4=1) in the
phase ―a‖ leg of inverter.
If IInva > (I*Inva-hb), then upper switch S1 will be ON
(P1 =1) and lower switch S4 will be OFF (P4=0) in the
phase ―a‖ leg of inverter Where hb is the width of
hysteresis band. On the same principle, the switching
pulses for the other remaining three legs can be
derived.
III. PHOTOVOLTAIC (PV) SYSTEM
In the crystalline silicon PV module, the complex physics
of the PV cell can be represented by the equivalent
electrical circuit shown in Fig.3. 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.3. 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 behavior of the PV cell
(26)
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.
IV. MATLAB/SIMULINK RESULTS
Simulation results of this paper is as shown in bellow
Figs. 4 to 30.
Case I: For Linear Load
KATCHALA Y. N. VENUGOPAL, B. KRISHNA, V. KAMARAJU
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.20, December-2015, Pages: 4064-4072
Fig.4.Simulink Circuit for Linear Load.
Fig.5. Source Voltage and Current.
Fig.6 Source Voltage and Load Current.
Fig.7.Simulation Results For Active Power At Source
Side And Load Side.
Fig.4. shows the Matlab/Simulink model of linear load,
fig.5. Shows the Source voltage and current, fig.6. Shows
the three phase Source voltage and load current,
fig.7.shows the active power at source side and load side.
Case II: For Single Phase Non Linear Load
Fig.8.Simulink Circuit for Single Phase Non Linear
Load.
Fig.9.Simulation Results for Source Voltage And
Source Currents.
Fig.10. Simulation Results for Source Voltage, Dc Link
Current, RMS Voltage and Load Current.
Analysis of STATCOM Performance with Single Phase and Three Phase Balanced and Un-Balanced Loads
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.20, December-2015, Pages: 4064-4072
Fig.11.Source Voltage and Compensation Currents.
Fig.12.Simulated Results for Input Power Factor.
Fig.13.THD Analysis for Source Voltage.
Case.III. Dynamic Performance of the SEIG–
STATCOM System Feeding Single-Phase Nonlinear
Loads
Fig.14.Simulink Model of Dynamic Performance of the
SEIG–STATCOM System Feeding Single-Phase
Nonlinear Loads.
(a)
( b)
(c)
Fig.15. Dynamic performance of the SEIG–STATCOM
during load removal. (a) vab, icomc, igc and il. (b) vab,
icom a, icomb and icomc. (c) vab, Vdc, icomc and il.
KATCHALA Y. N. VENUGOPAL, B. KRISHNA, V. KAMARAJU
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.20, December-2015, Pages: 4064-4072
(a)
(b)
(c)
Fig.16. Dynamic performance of the SEIG–STATCOM
during load application. (a) vab , icomc , igc and il . (b)
Vab, icom a, icomb and icom c. (c) Vab, Vdc, icomc and
il.
Case IV: Three Phase Balanced Linear And Non
Linear Load
Fig.17.Simulink circuit for three phase balanced linear
load.
Fig.18.simulation of Source Voltage Three phase
Source Current(ia,ib,ic) for linear load.
Fig.19.Single-phase linear loads Vab, Vdc and VtRMS
and three phase Load Current.
Analysis of STATCOM Performance with Single Phase and Three Phase Balanced and Un-Balanced Loads
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.20, December-2015, Pages: 4064-4072
Fig.20.Simulation of Source Voltage Three phase Load
Current(ia,ib,ic) for linear load.
Fig.21.Simulink Circuit for Three Phase Balanced Non-
Linear Load.
Fig.22.Simulation of Source Voltage And Three Phase
Source Current(Ia,Ib,Ic).
Fig.23.Simulation Results for Single Source Voltage
and Three Phase Source Current And Load Current At
Non Linear Load.
Fig.24.Simulation Results for Source Voltage, DC Link
Current, RMS Voltage and Load Current.
Fig.25. Source Voltage and Compensation Currents.
KATCHALA Y. N. VENUGOPAL, B. KRISHNA, V. KAMARAJU
International Journal of Advanced Technology and Innovative Research
Volume.07, IssueNo.20, December-2015, Pages: 4064-4072
Case V: Three Phase Unbalanced Linear And Non-
Linear Load
Fig.26.Simulink Circuit for Three Phase Unbalanced
Linear Load.
Fig.27.Single-Phase Linear Loads Vab , Vdc And Vtrms
And Three Phase Load Current.
Fig.28.Simulink Circuit for Three Phase Unbalanced
Non-Linear Load.
Fig.29.Single-Phase Linear Loads Vab , Vdc And Vtrms
And Three Phase Load Current.
Fig.30. Source Voltage and Compensation Currents.
V. CONCLUSION
The proposed method of feeding single-phase loads from
a three-phase SEIG and STATCOM combination has been
tested, and it has been proved that the SEIG is able to feed
single phase loads up to its rated capacity. A single-phase
synchronous D-Q frame theory-based control of a three-
phase STATCOM has been proposed, discussed, and
implemented for current balancing of the SEIG system and
different loading conditions.
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