A VOLTAGE-CONTROLLED DSTATCOM-BASED VOLTAGE …
Transcript of A VOLTAGE-CONTROLLED DSTATCOM-BASED VOLTAGE …
A VOLTAGE-CONTROLLED DSTATCOM-BASED VOLTAGE REGULATOR FOR ENHANCEMENT OF POWER QUALITY IN LOW VOLTAGE DISTRIBUTION GRIDS
1S. MADHURI 2Mr. V VISHNUVARDHAN YADAV 3G.RAVINDER REDDY
1Pg Scholar, Department of EEE (EPS), Holy Mary Institute of Technology& Science, Hyderabad, TS, India. 2Assistant Professor, Department of EEE, Holy Mary Institute of Technology& Science, Hyderabad, TS, India
3Assistant Professor, Department of EEE, Holy Mary Institute of Technology& Science, Hyderabad, TS, India
ABSTRACT
The main aim of this project is a voltage
controlled DSTATCOM based voltage regulator
for enhancement of power quality in low voltage
distribution grids. The time needed for
permanent solutions, like grid restructuring or
capacitor banks installation, to be operational
may exceed the deadlines. In the case of failure
to meet the deadlines, the power company has to
refund every customer in the distribution grid
during the time that the poor voltage regulation
persisted. Aiming to prevent refunds, a voltage
regulator can be utilized as a temporary solution.
The voltage regulator must have fast voltage
regulation, reduced weight and easy installation
.Using the proposed solution, the grid power
quality is re established and the PCC voltage is
restored in a short period of time. In the
meantime, the permanent solution can be
planned and installed in an appropriate time
frame. Once the definite solution is
implemented, the voltage regulator can be
disconnected from the grid and connected to
another grid with similar problems.
Key Words: DSTATCOM, Power quality,
PCC, Distribution grid
1. INTRODUCTION
The finish of low voltage dispersion
lattices may event poor voltage direction. As per
Brazilian framework code, control organizations
have compelled due dates (15 to 90 days) to
reestablish the voltage levels at the Purpose of
Regular Coupling (PCC) if the voltages are
outside the acceptable dimensions. The time
required for everlasting arrangements, similar to
lattice rebuilding or capacitor banks
establishment, to be operational may outperform
the due dates. On account of inability to gather
the due dates, the power organization needs to
discount each client in the dispersion matrix
amid the time that the poor voltage direction
persevered. Planning to keep away from
discounts, a voltage controller can be used as a
transitory arrangement. The voltage controller
must have quick voltage direction, condensed
weight and simple establishment. Utilizing the
proposed arrangement, the matrix Power quality
is restored and the PCC voltage is reestablished
in a brief timeframe. Meanwhile, the perpetual
arrangement can be arranged and introduced in
an appropriate time span. When the positive
answer is authorized, the voltage controller is
disengaged from the framework and associated
with an alternate matrix with comparable issues.
In genuine applications, poor voltage control
happens once the PCC is a long way from the
fundamental network transformer and the
separation between the PCC and the transformer
will basically be more distant than 100 meters.
Access to framework voltage data can be hard to
get. To take care of the voltage direction
demand, a voltage-controlled DSTATCOM-
based voltage controller is foreseen with shunt
association with PCC [2]– [9], as appeared in
Fig. 1. The shunt association maintains a
strategic distance from power supply intrusion
though the voltage controller is Putin or
detached. The anticipated DSTATCOM grants
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the power organization to postpone ventures and
upgrades the adaptability of network
administration.
Fig. 1. Low voltage distribution grid below analysis with
the voltage regulator
Voltage-controlled DSTATCOM will safeguard
the PCC voltages adjusted even beneath
framework or load unbalances. The PCC voltage
is specifically controlled by the DSTATCOM
and unexpected load varieties don't have
imperative effect in the PCC voltage waveforms.
Moreover, the voltage controlled. DSTATCOM
decouples the lattice and the heaps, filling in as a
low impedance way for consonant contortions
due the voltage source activities. Current
consonant contortions from the heaps have little
effect in the matrix and the other way around.
The lattice current quality, accordingly, is
exclusively given by the framework voltage
quality. As indicated by [3], precise position
reference is required for the voltage controlled
DSTATCOM to work appropriately.
Before the DSTATCOM begins its task,
synchronization circuits produce the precise
position to the voltage controller. When the
activity starts, the voltage-controlled voltage
controller replaces the PCC voltage and the
framework voltage recurrence and edge are not
any more accessible. PCC voltage recurrence
and point are then dictated by the voltage
controller. For a genuine application, because of
the separation between the transformer and the
PCC, just the PCC voltage ought to be estimated
to make the voltage reference out of the
DSTATCOM. In past years, the PCC voltage
adequacy (VPCC) for responsive compensation
methodologies was ordinarily gotten as the
apparent system voltage, i.e. 1.00 p.u.
Regardless, Brazilian grid code chooses a most
outrageous (1.05 p.u.) and a base (0.92 p.u.)
voltage adequacy for low voltage apportionment
frameworks. The PCC can be viewed as a
dimension of chance and the readied power can
be diminished with a sensible control circle. In
this effort, [8] proposes another strategy to
choose the sensible PCC terminal voltage for
decline of the DSTATCOM control rating.
The procedure is figured by the pined for source
current, meaning to achieve the solidarity
control factor at the cross section. Regardless,
this technique requires information about the
source current, organize restriction and
reactance. In [9] the makers propose another
methodology to choose suitable VPCC using the
positive gathering sections of the store current to
figure the PCC voltage. In the two cases,
additional information is required, extending the
methodology multifaceted nature, number of
sensors and the expense of the course of action.
To keep up the straightforward foundation
feature and sensible costs, it is beneficial to set
the PCC voltage, in which the readied power is
inconsequential, without checking any load or
grid information and using simply inside
indications of the DSTATCOM, for instance, the
PCC voltages and DSTATCOM yield streams.
2. PROPOSED SYSTEM
A circulation static compensator is a voltage
source converter based power electronic
mechanical assembly. Consistently, this gadget
is continued by short residency vitality put away
in a dc capacitor. The DSTATCOM channels
stack current to such an extent that it amasses
the arrangements for utility association. The
DSTATCOM can achieve the accompanying
focuses.
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1. The result of poor load power factor such that
the current haggard from the supply has a close
to unity power factor.
2. The result of harmonic contents in loads
specified current haggard from the supply is
sinusoidal.
3. The result of unbalanced loads such that the
current drawn from the supply is balanced.
4. The dc offset in loads specified the current
pinched from the supply has no offset.
Fig. 2. Basic Circuit Diagram of the DSTATCOM
Framework.
One of the primary choices of DSTATCOM is
that age of the reference compensator flows. The
compensator, when it pursues these reference
flows, infuses three-stage flows inside the air
conditioner framework to wipe out unsettling
influences caused by the heap. Accordingly, the
age of reference flows from the estimations of
close factors has captivated wide thought [5].
These techniques pass on an inborn assumption
that the source is strong (i.e., the voltage at the
purpose of basic coupling is firmly managed and
can't be affected by the flows infused by the
shunt gadget). This anyway is certainly not a
legitimate supposition and the show of the
compensator will decrease widely with high
impedance air conditioning supplies.
The movement of VSI is upheld by a dc
stockpiling capacitor with fitting dc the transient
reaction of the voltage crosswise over it. The
transient reaction of the DSTATCOM is to a
great degree colossal while repaying air
conditioning and DC loads [15]. A static
synchronous compensator (STATCOM) is
emerge among the agent answers to coordinates
the line voltage. The STATCOM includes a
voltage source converter related in shunt with
the power framework and licenses to control a
main or slacking receptive power by strategies
for reviewing its air conditioning voltage. A
STATCOM for establishment on an
appropriation control framework called
DSTATCOM has been investigated clear
voltage changes and voltage gleams. A shunt
dynamic channel expected for establishment on
a power dissemination framework, with
emphasis on voltage control capacity.
Hypothetical examination and in addition PC
reproduction gives the dynamic execution of
symphonious damping and voltage control. In
this manner, symphonious damping has the
ability to improve the security of voltage
direction. In this way, adjustment of the input
picks up makes it likely to reduce
voltage vacillation in transient conditions, when
the dynamic channel has the undertaking of
joined consonant damping and voltage control.
The reproduction results are presented to
demonstrate the adequacy of the dynamic
channel fit for both consonant damping and
voltage direction. The matrix recurrence has
little frequencies deviations around the
ostensible regard and various burdens can work
under such deviations. In any case, voltage-
controlled DSTATCOM blends the PCC voltage
with a steady recurrence. Huge contrasts
between the framework and PCC frequencies,
related with long recurrence deviations, may
incite to separation of the DSTATCOM. A
conveyance static compensator (DSTATCOM)
is completed for controlling a disseminated
power producing framework using a proposed
composite eyewitness based control
methodology. The proposed control technique is
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used for the key parts extraction of twisted load
flows. These removed parts are used in the
estimation of reference source flows to make
gating signs of DSTATCOM. The proposed
control technique is executed for the easing of
Responsive power, contortion in term of music,
and load adjusting under straight/nonlinear
burdens. The execution of DSTATCOM is
viewed palatable for these buyer loads with
managed generator voltage at purpose of regular
coupling and self-upheld dc connection of
voltage-source converter of DSTATCOM..
3. CONTROL STRATEGY
The control strategy has three output voltage
loops, one total and one differential dc bus
voltage loop. The aforementioned controllers
were designed with the parameters presented in
Table II and evaluated for a range of the grid
impedance (0.1 to 10 of Rg and Lg) through
frequency response analysis. In this range the
designed controllers work properly.
Additionally, this paper includes two loops: a
loop responsible for the PCC voltage amplitude
and another one responsible for mitigating the
grid frequency effect on the voltage regulator.
Fig. 9 shows the complete control block diagram
with the amplitude and frequency loops.
I) Output Voltage Loop
The inputs of the output voltage loop are three
voltage references (vref). The voltage references
are composed of the dc bus controllers output,
the MPPT and the frequency loop, as
depicted in Fig. 9. To achieve adequate synthesis
of the voltage references, the output voltage loop
must have fast dynamic response. The output
controller is a PID controller. The simplified
output voltage loop block diagram can be seen
in Fig. 3. The output voltage loop has active
damping controllers to enhance the stability of
the voltage regulator against grid impedance
variations
Fig. 3. Output voltage loop block diagram
II). Grid Frequency Variation and the Total
dc Bus Controller
The DSTATCOM operation causes power losses
in the power converter as a result of
semiconductor switching. The losses diminish
the total dc bus voltage (vo). As seen in Section
II, the displacement angle θ determines the
active power flow at the PCC. Therefore, the
total dc bus loop compares vo to the reference
vo* and, through a PI plus pole controller, set a
suitable θ to drain active power from the grid
and reestablish the power balance between the
grid, the loads and the DSTATCOM. The
DSTATCOM is composed of three-phase four-
wire VSI and the voltage balance at the split
capacitors is required. The difference between
the split capacitor voltages (vd) is compared to
the reference (vd*) and a PI plus pole
contributes to the reference generator with a
small dc component (VPCC,dc).
4. MINIMUM POWER POINT TRACKER The voltage amplitude to be regulated at PCC
changes the power flow between the grid, load
and DSTATCOM, as demonstrated. Suitable
VPCC makes the processed apparent power be
minimal. When the VPCC is between the
desired voltage limits, the Mppt minimizes the
converter apparent power and no reactive power
at the grid frequency is processed. Apparent
power minimization means current
minimization, which lower the losses and
extends the equipment life cycle. For the MPPT
analysis, apparent power is chosen to be
minimized instead of reactive power due into: (i)
active power in DSTATCOMs is a small
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fraction of the apparent power; (ii) the harmonic
currents from the grid and load are also
processed; (iii) the converter power rating and
the losses are given by the apparent power; and
(iv) apparent power is easier to calculate in
comparison to extracting the reactive power at
the grid frequency from distorted current
waveforms.
One interesting feature of the P&O method is its
independency of PV arrays parameters [14],
[18]. This feature makes the P&O not restricted
to PV systems. The P&O-based MPPT
algorithm presents the same features of the P&O
algorithm applied to MPPT, but is designed to
achieve the Minimum Power Point (MPP)
instead of MPP [6]. The MPPT can be derived
analyzing Fig. 4(a). The marker 1 represents an
increase of VPCC and the marker 4 represents a
decrease of VPCC which leads to reduction of
the Sinv. In these cases, the next perturbation will
conserve the perturbation signal (positive for
marker 1 and negative for marker 4) and the
MPPT will converge to the MPP. On the other
hand, the marker 2 represents a decrease of
VPCC and the marker 3 represents an increase
of VPCC diverging from MPP. Therefore, the
direction of the next perturbation must be
positive for marker 2 and negative for marker 3.
Fig. 4. (a) P&O-based MPPT derivation (b) Example of
the mPPT algorithm with voltage constraints
There are three different cases when voltage
constraints are present as depicted in Fig.4 (b).
In case 1, Smin requires a VPCC below the
minimum allowable PCC voltage (Vmin). The
MPPT goes toward the MPP, but VPCC cannot
be lower than Vmin. VPCC is kept at Vmin and the
voltage regulator supplies reactive power to
maintain the VPCC regulated. Therefore, the
MPP in case 1 will be at MPPL and the
processed power is represented by SminL. The
Case 3 shows a similar outcome to case 1 with
VPCC kept at the maximum allowable PCC
voltage (Vmax). The converter operates at MPPH
and process reactive power equal to SminH.
5. SIMULATION RESULTS
The block diagram for existing network is
shown below in figure .5 and corresponding
output waveforms shown figure 6, 7, 8 and 9.
Figure.5. Block diagram for power system network with
conventional control scheme.
A. Linear loads:
The linear loads are composed of 10.4KW three
phase resistive loads. Consider the PCC
magnitude of 212V with compensator. Without
DSTATCOM compensator output voltage is
unbalanced and harmonic ripple content is high
that observed in waveform figure.6. & it’s THD
value also high.
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Fig 6 output voltage DSTATCOM for linear loads.
The same load of 10.4 kW is operated. This load
is supplied by the source and with DSTATCOM
(compensator) so output voltage waveform as
shown in figure.7. And the harmonic content in
output waveform is also less compared to
without using DSTATCOM compensator
waveform Figure.3. Output voltages with
DSTATCOM for linear loads.
Fig 7.output voltages with DSTATCOM for linear
loads.
B. Non linear loads:
The non linear loads are composed of 12 KW
three phase resistive loads and diode networks.
Consider the PCC voltage magnitude of 212V
without compensator. Without compensator, and
presence of non linear loads output voltage is
more unbalanced and harmonic ripple content is
high. That is observed in waveform figure.8. &
it’s THD value also high.
Figure.8. output voltages DSTATCOM for non linear
loads.
The same load of 12 kW is operated. This load is
supplied by the source and with DSTATCOM
(compensator) so output voltage waveform as
shown in figure.9. And the harmonic content in
output waveform is also less compared
compensator waveform.
Fig 9.output voltages for non linear loads
CONCLUSION
This paper presents a three phase DSTATCOM
as a voltage regulator and its control approach,
composed of the predictable loops, output
voltage and dc bus regulation loops, as well as
the voltage amplitude and the frequency loops.
Simulation results convey the voltage regulation
capability, supplying three balanced voltages at
the PCC, even under nonlinear loads. The
projected amplitude loop was able to reduce the
voltage regulator procedure apparent power
about 51 % with nonlinear load and even more
with linear load (80%). The MPPT algorithm
tracked the minimum power point inside the
allowable voltage range when reactive power
compensation isn’t necessary. With grid voltage
sag and swell, the amplitude loop meets the grid
code. The Mppt may be realized in current-
controlled DSTATCOMs, achieving similar
results. The frequency loop kept the
compensation angle inside the analog limits,
increasing the autonomy of the voltage
regulator, and the dc bus voltage regulated at
nominal value, therefore minimizing the dc bus
voltage steady state error. Simultaneous
operation of the MPPT and in the frequency
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loop was verified. The anticipated voltage
regulator may be a shunt connected solution,
that is connected to low voltage distribution
grids without any power interruption to the
loads, without any grid voltage and impedance
information, and afford balanced and low-THD
voltages to the customers.
REFERENCES
[1] ANEEL National Electric Power Distribution
System Procedures – PRODIST, Module 8:
Energy Quality. Revision 07, 2014.
[2] M. Mishra, A. Ghosh and A. Joshi,
“Operation of a DSTATCOM in voltage control
mode,” IEEE Trans. Power Del., vol.18, no. 1,
pp. 258-264, Jan. 2003.
[3] G. Ledwich and A. Ghosh, “A flexible
DSTATCOM operating in voltage or current
control mode,” IEE Proc.-Gener., Transmiss.
Distrib., vol. 149, n. 2, pp. 215-224, Mar. 2002.
[4] T. P. Enderle, G. da Silva, C. Fischer, R. C.
Beltrame, L. Schuch, V. F. Montagner and C.
Rech, “D-STATCOM applied to single-phase
distribution networks: Modeling and control,” in
Proc. IEEE Ind. Electron. Soc. Annu. Conf., Oct.
2012, pp. 321 - 326.
[5] C. Kumar and M. Mishra, “Energy
conservation and power quality improvement
with voltage controlled DSTATCOM,” in Proc.
Annu. IEEE India Conf., Dec. 2013 pp. 1-6.
[6] R. T. Hock, Y. R. De Novaes and A. L.
Batschauer, “A voltage regulator based in a
voltage-controlled DSTATCOM with minimum
power point tracker,” in Proc. IEEE Energy
Convers. Congr. Expo. Sep. 2014, pp.3694-
3701.
[7] B. Singh, R. Saha, A. Chandra and K. Al-
Haddad, “Static synchronous compensators
(STATCOM): a review,” IET Power Electron.,
vol. 2, no. 4, pp. 297-324, Jul. 2009.
[8] C. Kumar and M. Mishra, “A
Multifunctional DSTATCOM Operating Under
Stiff Source,” IEEE Trans. Ind. Electron., vol.
61, no. 7, pp. 3131-3136, Jul. 2014.
[9] C. Kumar and M. Mishra, “A Voltage-
Controlled DSTATCOM for Power-Quality
Improvement,” IEEE Trans. Power Del., vol.29,
no. 3, pp. 1499-1507, Jun. 2014.
Author’s Profiles
1S. MADHURI is the student of Post Graduation
M.Tech (EPS) in Holy Mary Institute of Technology
and Science, Hyderabad, Telangana. She Completed
her B.Tech EEE from ANU, Guntur. Her area of
interest is Power Systems, Power electronics and
FACTS etc.
2Mr. V VISHNUVARDHAN YADAV is born in
Anantapur, Andhra Pradesh, India on 13th July,
1990. He is working as an assistant professor in EEE
department of Holy Mary Institute of Technology and
Science, Hyderabad. He has exposure in industry and
teaching. He received B.Tech from JNTU Anantapur
in 2011 and M.Tech from JNTU Anantapur, Andhra
Pradesh in 2014 in the specialization on Electrical
Power System. His research areas of interest are
electrical machines and power systems, smart grid
technologies and HVDC and HVAC transmission
lines etc.
3G.RAVINDER REDDY received Master of
Engineering from Osmania University with a
specialization of Power systems & Power
Electronics, Bachelor of Technology in EEE from
JNTU Hyderabad. Presently working as Assistant
Professor in EEE Department, H.I.T.S. Hyderabad.
His area of interest is FACTS.
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GRID SYNCHRONIZATION METHOD FOR THREE-PHASE THREE-WIRE
NETWORKS UNDER GRID FAULT CONDITIONS
DR.SIVAGANESAN SIVANANTHAM1 BANDA SHIREESHA2
1 Professor, Department of EEE, Holy Mary Institute of Technology& Science, Hyderabad, TS, India
2Pg Scholar, Department of EEE(EPS), Holy Mary Institute of Technology& Science, Hyderabad, TS, India.
ABSTRACT:
Grid synchronization algorithms are of great importance in the control of grid-connected power converters, as fast and accurate detection of the grid voltage parameters is crucial in order to implement stable control strategies under generic grid conditions. This paper presents a new grid synchronization method for three-phase three-wire networks, namely three-phase enhanced PLL The enhanced phase-locked loop (EPLL) is a synchronization system that has proven to provide good results in single phase synchronization systems. An EPLL is essentially an adaptive band pass filter, which is able to adjust the cutoff frequency as a function of the input signal. Its structure was later adapted for the three-phase case, in order to detect the positive-sequence vector of three-phase signals, This paper analyses the performance of the proposed synchronization method including different design issues. Moreover, the behavior of the method for synchronizing with highly unbalanced grid is proven by means of simulation demonstrating its excellent performance.
Key words: Grid, Power converters, EPLL
1. INTRODUCTION
Nowadays, the use of power electronics and information and communication technology (ICT) applications are key issues in the development of future electrical networks. The high penetration of renewable energy sources such as wind power and photovoltaic, experienced in the last decades is a good example, as both generation systems are connected to the grid by means of power electronics- based power processors, that should not only control the power delivered to the network, but also contribute to the grid stability, supporting the grid services voltage/frequency under generic conditions, even under grid faults. One of the most important issues in the connection of power converters to the grid is the synchronization with the grid voltage at the point of common coupling (PCC) .Although the grid voltage waveforms are sinusoidal and balanced
under regular operating conditions, they can easily become unbalanced and distorted due to the effect of grid faults and nonlinear loads. Under these conditions, grid-connected converters should be properly synchronized with the grid in order to stay actively connected, supporting the grid services and keeping the generation up and running .Actually, these are currently former requirements in all grid codes (GCs) for the connection of distributed generation systems to the network, where the criteria for the injection of active and reactive power during either balanced or unbalanced grid fault conditions are also provided. Despite the fact that the dynamics of grid synchronization are not established in the GC, requirements are needed in order to achieve a certain dynamical response in the synchronization. Algorithms based on the implementation of phase locked loops (PLL) have traditionally been used for synchronizing the control system of power converters with the grid voltage. In Fig. 1, the layout of a generic control structure for a three phase power converter connected to the grid is shown. As depicted in Fig. 1, the grid synchronization block is responsible for estimating the magnitude frequency and phase angle of the positive- and the negative- sequence components of the grid voltage, v±, ω, and θ ±, respectively. These estimated values are later used at the current controller block, which settles finally the voltage waveform to be modulated v∗ c as well as at the reference generator, responsible of determining the current reference to be tracked. This last block will vary if the power converter is acting as an active filter, a STATCOM, or a power processor belonging to a power generation plant. In three-phase systems, a PLL based on a synchronous reference frame (SRF-PLL) has become a conventional grid synchronization technique.
Nevertheless, the response of the SRF-PLL is unacceptably deficient when the grid voltage is unbalanced due to the appearance of a negative-sequence component that the SRF-PLL is unable to process properly. In order to solve this problem, different advanced grid synchronization systems have recently been proposed. This is the case of the
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decoupled double SRF PLL (DDSRFPLL), an extension of the SRF- PLL, which uses two SRFs and a decoupling network to isolate the effects of the positive and the negative- sequence voltage components. Another interesting synchronization technique was presented in, where three single-phase enhanced PLLs are combined with a positive sequence calculator to synchronize with unbalanced and distorted three-phase networks without using any SRF. Considering the same structure, other single-phase PLL approaches, like those presented in, can be used to provide the input signals to the positive-sequence calculation algorithm. Likewise, other synchronization structures have been proposed for three-phase systems based on PLL, as those published in. However, the dynamical response of these algorithms is very sensitive to phase angle jumps in the voltage at the PCC due the fact that the PLL is synchronizing with this variable. This is a serious drawback, as sudden phase angle changes are prone to happen when a fault occurs, due to the change in the network impedance. In this paper, a new approach using frequency locking instead of conventional phase locking will be presented as an effective solution for grid synchronization under adverse grid conditions
2. PROBLEM IDENTIFIED
DES technologies have very different issues compared with traditional centralized power sources. For example, they are applied to the mains or the loads with voltage of 480 volts or less; and require power converters and different strategies of control and dispatch. All of these energy technologies provide a DC output which requires power electronic interfaces with the distribution power networks and its loads. In most cases the conversion is performed by using a voltage source inverter (VSI) with a possibility of pulse width modulation (PWM) that provides fast regulation for voltage magnitude. Power electronic interfaces introduce new control issues, but at the same time, new possibilities. For example, a system which consists of micro-generators and storage devices could be designed to operate in bothan autonomous mode and connected to the power grid. One large class of problems is related to the fact that the power sources such as micro turbines and fuel cell have slow response and their inertia is much less. It must be remembered that the current power systems have storage in generators’ inertia, and this may result in a slight reduction in system frequency. As these generators become more compact, the need to link them to lower network voltage is significantly increasing. However, without any medium voltage networks adaptation, this fast expansion can affect
the quality of supply as well as the public and equipment safety because distribution networks have not been designed to connect a significant amount of generation. Therefore, a new voltage control system to facilitate the connection of distributed generation resources to distribution networks should be developed. In many cases there are also major technical barriers to operating independently in a standalone AC system, or to connecting small generation systems to the electrical distribution network with lower voltage, and the recent research issues includes: 1. Control strategy to facilitate the connection of distributed generation resources to distribution networks. 2. Efficient battery control. 3. Inverter control based on only local information. 4. Synchronization with the utility mains. 5. Compensation of the reactive power and higher harmonic components. 6. Power Factor Correction. 7. System protection. 8. Load sharing. 9. Reliability of communication. 10. Requirements of the customer. DES offers significant research and engineering challenges in solving these problems. Moreover, the electrical and economic relationships between customers and the distribution utility and among customers may take forms quite distinct from those we know today. For example, rather than devices being individually interconnected in parallel with the grid, they may be grouped with loads in a semi- autonomous neighborhood that could be termed a micro grid is a cluster of small sources, storage systems, and loads which presents itself to the grid as a legitimate single entity. Hence, future research work will focus on solving the above issues so that DES with more advantages compared with tradition large power plants can thrive in electric power industry.
3. PROBLEM DESCRIPTION
These new distributed generations interconnected to the low grid voltage or low load voltage cause new problems which require innovative approaches to managing and operating the distributed resources. In the fields of Power Electronics, the recent papers have focused on applications of a standby generation, a standalone AC system, a combined heat and power (cogeneration) system, and interconnection with the grid of distribution generations on the distribution network, and have suggested technical solutions which would permit to connect more generators on the network in good conditions and to perform a good voltage regulation. Depending on the load, generation level, and local connection conditions, each generator can cause the problems described in the previous chapter. The main goals which should be achieved will thus be: to increase the network connection
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capacity by allowing more consumers and producer customers connection without creating new reinforcement costs, to enhance the reliability of the systems by the protections, to improve the overall quality of supply with a best voltage control.
Fig. 1. Generation of grid voltage sags in the experimental setup. (a) Generation of a Type “A” voltage sag. (b) Generation of a Type “B” voltage sag. (c) Generation of a Type “C” voltage sag. (d)
Generation of a Type “D” voltage sag
4. SOLUTION TO THE PROBLEM
Facts controllers are the best of solution to that problems. Here we have to control the facts devices by considering different types of PLLS. In this project we develop following EPLL Structure
3phEPLL Discretization
The block diagram of the EPLL implemented in this paper is presented in Fig
Fig. 2. Quadrature signal generator based on an EPLL structure.
According to this diagram, the state space representation of the EPLL in the continuous domain can be written as shown in
The discrete state space variable representation was described in [44] using a forward Euler approximation to reach satisfactory results; therefore, the same method has been implemented here
Finally, after the state variables are calculated, the EPLL output can be obtained by (13), generating the two quadrature signals
This type of discretization method needs a more accurate tuning, due to the fact that the stable regions of the s-plane and z-plane are different . However, its major simplicity, compared to the Tustin or backward integration, benefits from the computational speed of this block
5.MATLAB/SIMULATION RESULTS:
Fig.3 MATLB/SIMULINK diagram of proposed system
single phase sag
International Journal of Research
Volume 7, Issue XI, November/2018
ISSN NO:2236-6124
Page No:2053
Fig.4 controller Subsystem
Fig.5 Discrete phase PLL
SINGLE PHASE SAG
Fig.6 bus 2 voltage
Fig.7 bus 3 voltage
Fig.8 injected voltage
THREE PHASE SAG
Fig.9 bus 2 voltage
Fig.10 injected voltage
CONCLUSION
In the process of synchronization of DG generated power with the utility, phase tracking is very essential for proper grid synchronization. A PLL can be used to obtain magnitude, frequency and phase information for estimation of fundamental positive-sequence component of grid voltage. Accurate and fast estimation of these quantities can be used for control and protection of the system. Overall the grid synchronization system based on positive-sequence estimation is able to handle non ideal conditions well. The positive-sequence phase angle is tracked within acceptable margins and therefore the PLL system as given with the positive sequence estimation could indeed operate in a real life application
REFERENCES
[1] A. Zervos and C. Kjaer, Pure Power: Wind Energy Scenarios for 2030. Brussels, Belgium: European Wind Energy Association (EWEA), Apr. 2008. [2] e-on, “Grid code—High and extra high voltage,” Bayreuth, Germany. Apr. 2006. [Online]. Available: http://www.pvupscale.org/IMG/pdf/ D4_2_DE_annex_A 3_EON_HV_grid__connection_requirements_ ENENARHS2006de.pdf [3] PO-12.3 Requisitos de Respuesta Frente a Huecos de Tension de las Instalaciones Eolicas, Comisión Nacional de Energía, Madrid, Spain, Oct. 2006. [4] IEEE Standard for Interconnecting Distributed Resources With Electric Power Systems, IEEE Std. 1547-2003, 2003. [5] The Grid Code: Revision 31, National Grid Electricity Transmission,Warwick, U.K., Oct. 2008,
International Journal of Research
Volume 7, Issue XI, November/2018
ISSN NO:2236-6124
Page No:2054
no. 3. [Online]. Available: http://www2. nationalgrid.com/uk/industry information/electricity-codes/grid-code/ the-grid-code/
AUTHORS PROFILE
Dr.Sivaganesan Sivanantham received the B.E. in Electrical and Electronics Engineering from University of Madras, TN in2003and M.Tech.in Power Electronics & Drives from SASTRA University, TN in 2006and the Ph.D. degree in Electrical Engineering from Vels University, Tamilnadu in 2017. He is currently an Professor of Dept. of Electrical & Electronics Engineering at Holy Mary Institute of Technology and Science, Hyderabad. His research interests include photovoltaic systems, renewable energy systems, power electronics, and control of power electronics interfaces.
Banda Shireesha received in B.tech degree in Electrical and Electronics Engineering from Avanthi institute of engineering And technology.And M.tech from Holy Mary Institute of Technology and Science, Hyderabad. Her research interests include renewable energy systems, power electronics.
International Journal of Research
Volume 7, Issue XI, November/2018
ISSN NO:2236-6124
Page No:2055