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

International Journal of Research

Volume 7, Issue XI, November/2018

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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



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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,



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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.



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