a strategic wind form integration method to polluted distibuted system with shunt capacitor 2-3

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –

6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME

147

A STRATEGIC WIND FORM INTEGRATION METHOD TO

POLLUTED DISTIBUTED SYSTEM WITH SHUNT CAPACITOR

NagaRaju. Annam,

Senior Asst professor, H.O.D, Department of E.E.E,

Aryabhata Inst of Technology and Sciences,

Dr. J. Bhagwan Reddy

Professor, Department of E.E.E, Astra, Hyd

Dr. Sardar Ali

Professor, H.O.D, Department of E.E.E,

Royal Institute of Technology and Science

ABSTRAC

Renewable energy is reliable and plentiful and will potentially be very cheap once technology

and infrastructure improve. It includes solar, wind, geothermal, hydropower and tidal energy, plus

biofuels that are grown and harvested without fossil fuels. Nonrenewable energy, such as coal and

petroleum, require costly explorations and potentially dangerous mining and drilling, and they will

become more expensive as supplies dwindle and demand increases. Renewable energy produces only

minute levels of carbon emissions and therefore helps combat climate change caused by fossil fuel

usage. Now Distributed Generation plays a vital role to face the issues such as increased fossil fuel

costs, various technical and environmental problems, system reliability and energy security. The DG

supply local and distributed loads and reduces the amount of energy lost in transmitting electricity

because the electricity is generated very near where it is used. The number of DG units is increasing

rapidly in present distributed generation grids. Integration of newer DG units in to the distribution grid

leads to planning as well as operational challenges. Due to the presence of non linear loads the system

becomes highly polluted which leads to complicated integration. This paper discusses the important

issue which deals with the problems and difficulties when integrating wind power plants in to the

electrical power system. In this paper shunt compensator is implemented to achieve reliable, efficient

and unity power factor operation at point of connection when wind form is integrated to polluted

distributed system and simulation results are presented.

Index Terms: Wind Form Integration, Polluted Distributed System, Distributed Generation (DG),

Current Harmonics, Shunt Compensator

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN

ENGINEERING AND TECHNOLOGY (IJARET)

ISSN 0976 - 6480 (Print) ISSN 0976 - 6499 (Online) Volume 4, Issue 3, April 2013, pp. 147-157 © IAEME: www.iaeme.com/ijaret.asp Journal Impact Factor (2013): 5.8376 (Calculated by GISI) www.jifactor.com

IJARET

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148

I. INTRODUCTION

The need for alternative energy sources is getting urgent, hence the development of renewable

energy is moving fast. Nationally and internationally various individuals and research companies are

creating new and exciting energy systems. Some of these apparatus are great works and need improving

for massive use. The first problem is that the fossil fuels are depleting in a rapid rate and are harder to

retrieve. The consequence is that we can be facing an energy crisis in the future is we are not careful

today. The energy prices will sky rocket and not be available for many individuals or countries. To

avoid this doom scenario we need to find alternatives and used them to their full potential. Luckily this

is already happening.At present Distributed Generation has become the only alternative for global

energy sector to face the challenges such as continuously increasing costs of fossil fuels , many

technical and environmental issues,power system reliability and future energy security increase.

Distributed Generation, (DG), is a term to describe in most cases small, renewable fuel(s)

generators intergrated into the nationwide electrical distribution grid Distributed Generation. DG refers

to the power generation at the point of consumption. Generating power onsite rather than centrally,

eliminates the cost, complexicity, interdependencies, and inefficiencies associated with transmission

and distribution.

Fig. 1Integrated Renewable distributed generation system

Out of the renewable energy resources like Wind, Biomass, Solar PV, Geothermal etc., wind is one of

the most renewable resources found in nature available free of cost with zero hazardous effects.

Harnessing power from wind through wind farms is given greater attention around the globe as it is one

of the most mature technologies among all the renewable resources [1].By the end of 2011, of the total

renewable power capacity, 238 GW, across the world 61.1% of the renewable power is through Wind

energy [2], [3]. Wind energy is a major source of power in over 70 countries across the world Fig. 1

shows the increasing trend of the installed capacity of Global wind power cumulative capacity from

1996 to 2011.

Fig. 2 Wind power total world capacity 1996-2011



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During 2011, an estimated 40 GW of wind power capacity was put into operation, more than any other

renewable technology, increasing global wind capacity by 20% to approximately 238 GW. Around 50

countries added capacity during 2011; at least 68 countries have more than 10 MW of reported capacity,

with 22 of these passing the 1 GW level; and the top 10 countries account for nearly 87% of total

capacity. Over the period from end-2006 to end-2011, annual growth rates of cumulative wind power

capacity averaged 26%.

Fig. 3 Average annual growth rates of renewable energy

Capacity and Bio fuels production 2006-2011

Large percentage of wind energy conversion systems around the world is employing Squirrel

Cage Induction Generators (SCIG). The operation of SCIG demands reactive power, usually provided

from the grid and/or by shunt operated capacitor banks. Wind generation based DG units can operate

individually or in a micro-grid which is formed by the cluster of DG units connected to a Distribution

Network to serve local and distributed loads.This strengthens the Distribution system and improves the

service reliability.

II. HARMONICS

The advancements and ease of control of Power Electronic Devices made extensive usage of

semiconductor technology in power industry [4]. This has led to deterioration of Power Quality in both

Transmission and Distribution systems.The presence of non linear loads injects harmonics into the

power system and is becoming a serious concern not only to the consumers but also to the utility

causing problems such as overheating and destruction of electrical equipment, voltage quality

degradation, mall functioning of meters etc.,[5].The distribution system feeds different kinds of linear

and non linear loads. The non linear loads draw non-sinusoidal currents from ac mains and cause

reactive power burden and excessive neutral currents and are also responsible for lower efficiency and

interfere with neighboring communication networks [6] - [9].

The power factor and efficiency can be improved by using capacitors and synchronous

condensers but they cannot eliminate harmonics. Passive Filters provided to be the solution for

harmonic suppression, greater efficiency and power factor improvement in distribution systems.

However, they have their own potentialities (more economical, maintenance free, zero short circuit

currents compared to synchronous condensers) [10] and limitations (not suitable for changing system

conditions, mistuning, fixed compensation, large size instability and they may create new system

resonance) [5], [10].

To overcome these problems, many authors have proposed many alternatives but Attractive

Power Filters (APFs) proved to be a very effective alternative for suppression of harmonics.



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Shunt Active Power Filter (ShAPF) proves to be an attractive solution for reactive power compensation

and suppression of current harmonics [5] and Series Active Power Filter (SeAPF) for suppression of

voltage harmonics [6].

This paper emphasizes on suppression of current harmonics using shunt compensator. Shunt

Compensator supplies harmonic current of same magnitude but opposite in phase of the current

harmonics due to non-linear load. The main task in this compensator is the computation of reference

current signal and generation of gate signals for Voltage Source

Inverter (VSI). So many methods have been proposed by various authors for harmonic elimination [11]

- [14]. But, the mathematical model and the control scheme given in [15] are

simple and easy to implement. The control schemes used for the generation of gate signals for PWM

inverter are compared and reported in [15], [16] and the Fuzzy Logic controller is found superior

compared to the conventional PI controller.

The Fuzzy Logic (FL) is closer in spirit to human thinking and natural language than

conventional logical systems. This provides a means of converting a linguistic control strategy based on

expert knowledge into an automatic control strategy. The ability of fuzzy logic to handle imprecise and

inconsistent real-world data made it suitable for a wide variety of applications [17]. In particular, the

methodology of the fuzzy logic controller (FLC) appears very useful when processes are too complex

for analysis or when the available sources of information are interpreted qualitatively, inexactly or with

certain uncertainty. Thus FLC may be viewed as a step towards a rapprochement between conventional

precise mathematical control and human-like decision making.

III. SYSTEM MODELING

The single line diagram of the power system under consideration is shown in Fig. 4

The network consists of a 33KV, 50 Hz, grid supply point, feeding a 33KV distribution system.There

are four load centers in the system L1, L2, L3 and L4. The four load centers comprise of Linear and

Non-Linear loads. The Wind farm comprises of 4 wind turbines using squirrel cage induction

generators each rated 1.5MW, 690V, 50Hz. Each generator is provided 170 KVAr fixed reactive power

compensation through a bank of capacitors to give necessary reactive power support at the time of

starting. The total wind farm capacity 6MW is connected to the 33KV distribution system at MV7,

Point of Common Coupling (PCC), through a 690V/33KV transformer. In this study a mean wind speed

of 12 m/s is considered. The Squirrel Cage Induction Generator model available in Matlab / Simulink

SimPowerSystem libraries is used.

Fig. 4 one-line diagram of distribution system with wind farm integrated at PCC

IV.PROPOSED COMPENSATION SCHEME

In many cases, the power system design criterion is based on the current and its waveform.

Hence, it is necessary that the rms value of the total current (current harmonics) be reduced as much as

possible. This not only reduces the losses but also reduces the distortion in voltage at the point of

connection. Fig. 5 shows the basic compensation scheme of compensator to make the source current



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free from harmonics and in phase with source voltage by drawing or supplying a filter current ic from or

to the utility at point of connection.

Fig. 5 Shunt Compensator basic compensation scheme

IV.A. Mathematical Formulation

The peak value of reference source current is calculated by regulating voltage across capacitor

of the VSI. Source supplies two current components i. active and ii. loss (to meet losses in the VSI). The

controller used in the VSI is supposed to generate the gating signals to maintain the required value of

active current component by maintaining the DC voltage constant.

The source voltage and source current are given by

vs (t ) � Vsm sin ωt (1)

is (t ) � Ism sin ωt (2)

Where Vsm and Ism peak values of source voltage and current respectively

As per Fig. 5, the load, source and compensator currents are related as

is (t ) � iL (t ) - iC (t ) (3)

∞

iL (t ) � ∑I n sin(nωt φn )

n �1

∞

� I1 sin(ωt φf ) ∑I n sin(nωt φn )

n �2

� iLf (t ) iLh (t ) (4)

Where iLf and iLh are the fundamental and harmonic components of load current. I1 and I n are

the peak values of fundamental and nth harmonic component of load currents respectively. Assuming

the voltage at load as vs (t ) , the instantaneous load power can be expressed as

P Load (t ) � vs (t ) * iL (t ) � Vsm I1 sin 2 ωt * cosφ f Vsm I1 sin ωt * cosωt * sin φ f

∞

Vsm sin ωt * ∑I n sin(nωt φn )

n �2 � p L (t ) � q L (t ) � p Lh (t ) (5)

where p L (t ) , q L (t ) and p Lh (t ) are active, reactive and harmonic power of load. Out of these powers



152

p L (t ) will be supplied by the source i.e.,

p L (t ) � Vsm ( I1 sin 2 ωt ) ( cosφ f )

= (Vsm sin ωt ).(I1 cosφ f ) sin ωt

� Vs (t ) * is (t ) (6)

From (2) and (6), the peak value of source current is given by I sm � I1 cos φ f There are also some switching losses in the PWM converter and, hence, the utility must supply a small

overhead for the capacitor leakage and converter switching losses in addition to the real power to the

load. The total peak current to be supplied by the source is therefore

I*

sm

� I

sm I sl (7)

The peak value of reference current I sm can be estimated by capacitor voltage. The ideal compensation

requires the source current to be sinusoidal and in-phase with the source voltage irrespective of the

nature of load current. The desired source currents after compensation can be given as

i*sa � I

*sm sin ωt, (8)

i*

sb � I*

sm sin(ωt − 120), (9)

i*sc � I

*sm sin(ωt − 240) (10)

Hence, the magnitude of the source currents needs to be determined by controlling the dc side capacitor

voltage.

IV.B. Dc side Capacitor Whenever the load changes not only a real power imbalance gets established between source

and load but also a reactive power and harmonic real power imbalance between active filter and the

load. The real power imbalance has to be compensated by the DC capacitor. This drives the DC

capacitor voltage away from the reference value. For satisfactory operation of the compensator, the

peak value of the reference current must be regulated to change in proportion to the real power drawn

from the source. This real power charged or discharged by the capacitor compensates for the real power

consumed by the load. Whenever the capacitor recovers from its transient state to its reference voltage,

the real power imbalance gets vanished. Also the reactive power required at the point of connection will

be compensated by the compensator.

Thus the role of the DC side capacitor is (i) to absorb / supply real power demand of the load

during transient period and (ii) maintain DC voltage in the steady state. The design of the DC side

capacitor is based on the maximum possible variation in load and the required reduction in voltage

ripple [11].

ANFIS ARCHITECTURE

System modeling based on conventional mathematical tools is not well suited for dealing with

ill-defined and uncertain systems. By contrast, a fuzzy inference system employing fuzzy ‘if-then’ rules

can model the qualitative aspects of human knowledge and reasoning processes without employing

precise quantitative analysis. However, even today, no standard methods exist for transforming human

knowledge or experience into the rule base and database of a fuzzy inference system. There is a need for

effective methods for tuning the membership functions so as to minimize the output error measure.

Recently, ANFIS architecture has proved to be an effective tool for tuning the membership functions.



153

Fig. 7 Sample ANFIS Architecture

ANFIS can serve as basis for constructing a set of fuzzy ‘if-then’ rules with appropriate

membership functions to generate the stipulated input-output pairs. An initial fuzzy inference system is

taken from PI controller and is tuned with back propagation algorithm based on the collection of

input-output data. The proposed control scheme is shown in Fig. 8. The system considered is a balanced

three-phase system with a wind farm integrated to the system at MV6 and compensator is connected at

MV1 as shown in Fig. 2. The scheme of generation of reference currents for the generation of gating

signals of PWM inverter is also illustrated in Fig. 5. The shunt compensator employs a diode clamped

PWM inverter.

Fig. 8 Shunt Compensator control scheme

The parameters for the ANFIS network used for the system under study are as detailed in Table 1.

Table 1 Parameters used for ANFIS controller

The rule base used for the TS-Fuzzy and ANFIS controller is shown in Table 2.



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Table 2 Rule base for Fuzzy & ANFIS controllers

V. RESULTS & OBSERVATIONS

The power system with wind farm integrated to it at MV6 along with the shunt compensator is

illustrated in Fig. 4. Simulations are carried out using Matlab/Simulink to study the impact of the

compensator on the operation of the system. The total simulation time considered is 0.5 Sec.

Simulations are carried out to show that the filter eliminates the harmonics and also improves the power

factor at the point of connection. The simulation was conducted with the following chronology:

• at t = 0.0 sec, the simulation starts with shunt compensator not connected to the system

• at t = 0.1 sec, the filter is turned ON

• at t = 0.2 sec, the load is increased from 155 amps to 185 amps

• at t = 0.3 sec, the load is decreased from 185 amps to 170 amps

• at t = 0.4 sec, the load is increased from 170 amps to 185 amps

Fig. 9 Load current in phase-a

Fig. 9 depicts the non-sinusoidal nature of current due to non-linear loads. These non-linear currents

have serious impact as detailed in section I.A, on the operation of electrical equipment being operated.

As a result of this harmonic current the performance and life span of the induction generators being

operated in wind farm integrated to distribution system beyond MV1 at the Point of Common Coupling

(PCC), MV7, gets deteriorated.

To protect the wind farm from the adverse effects due to harmonics, the shunt compensator is

turned ON at t = 0.1 sec. The instant the filter is switched ON, the current becomes sinusoidal. Fig. 10

illustrates the significance of compensator in making the current sinusoidal

Fig. 10 Current in phase-a at source (MV1)

Comparison of Fig. 9 and Fig. 10 indicates that the current at MV1 continues to be sinusoidal after t =

0.1 sec for any load condition. The harmonic content in current and power factor at different load



155

conditions is listed in Table 3. The Total Harmonic Distortion (THD) in current without the

compensator is found as 31% and the power factor 0.7. Both are objectionable from the industry

standards point of view.

The Distortion Power Factor (DPF) is calculated at five different instants and tabulated in Table

3. The Distortion Power Factor describes how the harmonic distortion of load current decreases the

average power transferred to the load. DPF is given by

DPF= 1

√1+THD2

Table 3 THD and power factor for different load conditions

Fig. 11 shows that the power factor at MV1 oscillates due to the starting of induction generators in wind

farm and stabilizes finally to 0.7 at 0.015 sec. The power factor is low due to the reactive power drawn

by the induction generators in the wind farm. The power factor 0.7 is a low value as per the IEEE-519

[22] and IEC-61000 standards.

Fig. 11 Power factor at MV1

The compensator when turned ON not only generates harmonic power in such a way that it

cancels the harmonic content in the current but also generates the reactive power needed at MV1. The

reactive power needed for wind farm operation is met from the compensator. Thus the power factor is

maintained unity by the compensator. For any load condition, the current is found to be sinusoidal and

the power factor is unity. The steady state and dynamic performance of the shunt compensator is found

satisfactory. The compensator current increases with the increase in load and is illustrated in Fig. 12.

The current will be in opposition to the harmonic current to make the source current sinusoidal and

unity power factor operation at the point of connection.



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Fig. 12 Compensator current

The instant compensator is switched ON the current becomes sinusoidal i.e., free from

harmonics and the power factor becomes unity. The improvement in the power factor from 0.7 to unity

means that the filter supplies the required reactive power for the operation of induction generators in the

wind farm. The performance of the proposed shunt compensator is much better in terms of THD and

DPF.

VI. CONCLUSION

The role of shunt compensator for harmonic minimization and reactive power support for the

wind farm is presented in this paper. The proposed compensator is found satisfactory for harmonics

mitigation meeting the IEEE-519 standards. The average power transferred to load is increased. The

mitigation of harmonics reduces the unnecessary heating and increase the life span of induction

generators used in wind farm. Compensator is able to provide reactive power for the operation of

induction generators in the wind farm, thus reducing the burden on the grid. The simulation results show

that the Shunt Compensator can be used for satisfactory integration of wind farm to the distribution

system.

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a strategic wind form integration method to polluted distibuted system with shunt capacitor 2-3

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