Development and Implementation of Novel Techniques for the Control

of Shunt Active FilterBy

P.Rathika,

Asso.Prof, Cape Institute of Technology

Levengipuram, Kanyakumari.

Dr.D.Devaraj,Professor/EEE,

Arulmigu Kalasalingam College of Engineering,

Krishnankoil

Guided By

2

IntroductionI

II Shunt Active Filter

• Power Quality• Harmonics – an overview• Sources of harmonics• Mitigation Techniques for Harmonics

• Principle of operation• Reference Current Extraction• Voltage and Current control method Proposed Control StrategiesIII

Plan of Presentation

• Hysteresis Current Control Techniques• Fuzzy Logic based Current control strategies• Voltage Control Techniques• Time and Frequency domain based current extraction• Simulation Results• Hardware Implementation with Results

IV Conclusions

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Any deviation from a perfect sinusoidal waveform that can results in failure or mis-operation of customer equipment

Power Quality

Quality of the current and voltage provided to the customers Providing customers with a pure sinusoidal waveforms

at 50 Hz without any deviations. Providing power to allow sensitive electronic

equipment operate reliably.

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What are Harmonics

f(x) = sin(x)

f(x) = sin(5x)5

+

f(x) = sin(x) + sin(5x)5

=

In the resultant wave the

sinusoidal character is lost

HarmonicsA sinusoidal voltage or current having frequencies that are

integral multiples of the power frequency.

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Sources of Harmonics

Modern electronic equipments such as personal or notebook computers laser printers fax machines telephone systems, stereos, radios, TVs adjustable speed drives and variable frequency drives battery chargers, UPS, and any other equipment powered

by switched-mode power supply (SMPS) equipment

Non-linear load devices create harmonics when they convert ac to dc, dc to dc, dc to ac, and ac to ac

Non-linear loads: draw current only a part of the voltage cycle

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Harmonics

Total Harmonic Distortion (THD)

It is the ratio between the RMS value of the harmonic currents to the fundamental current.

(%)1001

...............

(%)1001

2

2

23

22

III

In nI

THD

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Harmonics Sources

Examples

Computer Rectifiers

THD = 80 to 140% THD = 20 to 60%

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Effects of Harmonics

Over heating of Transformer Excessive neutral current Damage of sensitive electronic equipments Tripping of Circuit Breakers Low system efficiency Poor power factor Skin Effect Interference in the nearby communication

systems

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Recommended limits - IEEE 519

The Institute of Electrical and Electronics Engineers (IEEE)has set recommended limits on both current and voltagedistortion in IEEE 519-1992.

Voltage Harmonic Distortion Limits

Bus Voltage at PCC Individual Voltage Distortion (%)

Total Voltage Distortion THD (%)

69 kV and below 3.0 5.0

69.001 kV through 161kV 1.5 2.5

161.001 kV and above 1.0 1.5

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Isc: Maximum short-circuit current at the Point of Common Coupling (PCC).IL: Maximum demand load current (fundamental) at the PCC.

Isc/IL h<11 11≤h<17 17≤h<23 23≤h<35 35≤h THD

(%)<20 4.0 2.0 1.5 0.6 0.3 5.0

20-50 7.0 3.5 2.5 1.0 0.5 8.0

50-100 10.0 4.5 4.0 1.5 0.7 12.0

100-1000 12.0 5.5 5.0 2.0 1.0 15.0

>1000 15.0 7.0 6.0 2.5 1.4 20.0

Harmonic Current Limits

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Harmonics Solution Techniques

1

Passive Filter

2 Active Filter shunt active filter

series active filter

hybrid shunt –

series active filter

3

Hybrid Filter

Filters: The harmonics filters are the solution to eliminate the harmonics.

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Basic Operation of Shunt Active Filter

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Heart of Shunt Active Filter

Heart of SAF

1

3 2

Reference Current Generator

DC Voltage Control Gating Signal Generator

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Block Diagram of SAF

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Research Objectives This research work focuses on developing suitable control techniques and reference current extraction method for the shunt active filter for three phase 3-wire and three phase 4-wire system. The objectives are To develop an effective and reliable control strategy for three

phase shunt active filter to suppress harmonic currents and compensate reactive power under ideal, non-ideal source voltage condition and also it should maintain a constant switching frequency.

To develop an effective reference current calculation method to extract the harmonics content present in the load current under ideal, non-ideal and noisy voltage source condition.

To develop a suitable voltage controller to maintain constant voltage across the DC bus capacitor.

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Shunt Active Filter with Fixed Hysteresis Band

Technique

17

Hysteresis current controller

When the current through the inductor exceeds the upper hysteresis limit a negative voltage is applied by the inverter to the inductor. This causes the current in the inductor to decrease. Once the current reaches the lower hysteresis limit a positive voltage is applied by the inverter to the inductor and this causes the current to increase and the cycle repeats.

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Current Extraction Techniques

Methods Time domain Techniques Frequency Domain Techniques - Large number of calculation is involved hence it is less

practical.

Time Domain Technique Harmonics extraction methods in the time domain are

based on instantaneous derivation of compensating signals in the form of either voltage or current signals from distorted and harmonic polluted voltage or current signals.

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Reference Current Extraction Clarke Transformation

c

b

a

VVV

VV

23

230

21

211

32

c

b

a

III

II

23

230

21

211

32

Current

…..Contd

Voltage

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Contd…..

II

VV

VV

qp

qp

VV

VV

i

i

c

c~

*

*

Instantaneous Real and Reactive Power

Reference compensation currents in α-β coordinates

Reference compensation currents in a-b-c coordinates

*

*

*

*

*

23

21

23

21

01

c

c

cc

cb

ca

i

i

i

i

i

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PI – DC Bus Voltage Control

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Vc ref – Reference DC Voltage

Vc - Actual DC Voltage

Simulation Results

23

Test System

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Circuit Diagram of Shunt Active Filter

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Distorted three phase line current

Without Filter

Harmonic Spectrum of the distorted line current

THD=26.34%

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Three phase line current with filter

Harmonic Spectrum of the line current with filter

Results with AF

THD=4.1%

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Switching Frequency

• The switching frequency is varying between 19kHz to 20kHz

• The switching loss gets increases

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Constant Frequency Hysteresis Band Control

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Constant Frequency Hysteresis Current Control

generates switching pulses based on the prediction of current error and its slope and the past switching ON/OFF time of the switches in the inverter. In this technique, the hysteresis bandwidth need not be specified in the entire control algorithm.

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Calculation of Switching Time

1

,1*

1,

1)]()(([

2

ONfafaf

dcOFF ttitiL

Vt

1

,33*,

1)]()(([

2

OFFfafaf

dcON ttitiL

Vt

2,,Ttt ONOFF

2,,Ttt ONOFF

The switching time is calculated from the system parameters

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Distorted three phase line current

Without Filter

Harmonic Spectrum of the distorted line current

THD=26.34%

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Results with Filter

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Harmonic Contents -supply current and voltageHarmonic

OrderIndividual Harmonic Content (% of fundamental)

Without Filter Filter with FHBCC Filter with CFHCC

Current Voltage Current Voltage Current

3 0 0.01 0.5 0 0.03

5 23 0.12 1.5 0.11 1.27

7 12 0.12 1.52 0.13 1.03

9 0 0.01 0.12 0.01 0.07

11 9 0.3 1.61 0.28 1.34

13 7 0.23 1.45 0.23 1.1

15 0 0.02 0.26 0.01 0.15

17 5 0.39 1.33 0.39 1.0

19 4 0.25 0.9 0.25 0.2

THD(%) 26.34 3.3 4.1 2.91 3.89

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Source voltage and Current

Real and Reactive power supplied by the source to the Load

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Average Switching Frequency of the Inverters

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DRAWBACKS

The performance is poor under non-ideal source voltage condition- Not suitable for unbalance system

The switching frequency is high

Switching loss is high

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Fuzzy Adaptive Hysteresis Band Current Control

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Adaptive Hysteresis Current Control

Band width

CurrentferenceFilteri

VoltageSupplytv

dtditvfHB

fa

s

fasj

Re

)(

)),((

*

*

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Fuzzy Membership function

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Fuzzy Rule Base

dtdi fa

*

)(tvs

NL NM EZ PM PL

NL PS PM PM PM PS

NM PS PM PL PM PS

EZ PVS PM PVL PM PVL

PM PS PM PL PM PS

PL PS PM PM PM PS

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Simulation Results

42

Test System

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Four wire System with APF

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Distorted Phase and Neutral current

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Ideal supply voltage conditions

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Ideal supply voltage conditions (Contd..)

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Unbalanced and Distorted Condition

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Result-After filtering

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Results Summary

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Voltage

ControlCurrent Control

THD (%)

Phase A Phase B Phase C

Without Filter 18.74 25.74 50.42

PI Fixed Hysteresis 3.4 4.3 4.5

PIFuzzy-Adaptive

Hysteresis2.72 3.6 3.6

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Average Switching Frequency

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S.No Control TechniqueAverage Switching

Frequency (KHz)

Real Power Supplied from

Source (Kw)

1 Fixed HBCC 19 4500

2 CFHCC 16 4000

3 Fuzzy-Adaptive HBCC 10 3400

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Average Switching loss

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Fuzzy Logic based PWM Current Control

53

Block Diagram of SAF

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Fuzzy Logic Controller

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Membership Function

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Rule Base

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e

deNL NM EZ PM PL

NL PB PM PM PM PB

NM PB PM PL PM PB

EZ PVB PM PVL PM PVL

PM PB PM PL PM PB

PL PB PM PM PM PB

57

Fuzzy Based DC bus Voltage Control

The input to the fuzzy logic controller are

I. DC voltage error e (t) II. Rate of Change in error de(t)/dt

Block diagram of the DC voltage control using a Fuzzy controller

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Membership Function

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Fuzzy Rule Basee

de

NL NM NS ZE PS PM PL

NL NL NL NL NL NM NS ZE

NM NL NL NL NM NS ZE PS

NS NL NL NM NS ZE PS PM

ZE NL NM NS ZE PS PM PL

PS NM NS ZE PS PM PL PL

PM NS ZE PS PM PL PL PL

PL NL NM NS ZE PS PM PL

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Simulation Results

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Test System

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Load

I

Load

II

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Distorted three phase line current

Without Filter

Harmonic Spectrum of the distorted line current

THD=26.34%

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Harmonic compensation with Fuzzy-Controller

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Result – Unbalanced Condition

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Result with Filter

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Under Varying load condition

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Performance comparison of PI and Fuzzy controller

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Wavelet Transform based Current Extraction

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Block Diagram of SAF

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Wavelet Decomposition

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Wavelet Reconstruction

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Fundamental Current Extraction

Fundamental current Extraction using Wavelet Transform Technique

Estimated phase A harmonic current using db8

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Simulation Results

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Test System

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Source Current and Spectrum-Before Filtering

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Fundamental Current Extraction

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Result –After Filtering

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Source current –After Filtering with p-q theory

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Result-Summary

Phase

THD (%)

Without Filter

With Filter

p-q method Wavelet Method

Phase A 30.66 16.0 10.0

Phase B 29.58 16.3 10.34

Phase C 30.02 16.7 10.34

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Performance Summary

Detection Parameter Performance Comparison

Source Voltage Condition Ideal Noisy

THD of Source voltage (%) 0 16

Current Detection Method p-q WT p-q WT

Transient time (cycle) 1 <1/4 1 <1/4

Fundamental Extraction good good bad good

Response Time high low high low

Selective harmonic Elimination Not suitable suitable Not suitable Suitable

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Hardware Implementation

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Overall Block Diagram

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Power circuit

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Distorted Source Current

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Source Current and Frequency Spectrum

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Source Current after Filtering

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Source Current

FFT Spectrum

THD = 4.5 %

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Hardware setup

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ConclusionThis research work has focused on the development and implementation of novel techniques for the control of Shunt Active Filter to suppress harmonics and compensate reactive power. A suitable reference current extraction method is also developed which performs well under noisy condition.

The constant frequency hysteresis current controller proposed to overcome the drawback of the conventional hysteresis control, namely variable switching frequency.

The fuzzy logic based adaptive hysteresis current control technique proposed for the three phase four-wire system can effectively cancel the neutral current produced due to the unbalanced load. Also, the proposed controller maintains constant switching frequency with reduced switching loss.

The fuzzy logic based PWM current control technique proposed to eliminate harmonics under varying load conditions. the proposed fuzzy-logic based DC voltage control keeps constant voltage across the capacitor. The proposed controller maintains the reference voltage without any deviations.

The wavelet transform based approach proposed for current extraction method can effectively calculate the reference compensation current under noisy source voltage condition compared with the conventional p-q theory.

The simulation results obtained using fuzzy logic based hysteresis current control techniques are validated by implementing the proposed technique using DSP processor.

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Journal Publications

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1. P.Rathika, D. Devaraj, “Fuzzy Logic – Based Approach for Adaptive Hysteresis Band and DC Voltage Control in Shunt Active Filter” International Journal of Computer and Electrical Engineering, vol.2, No.3, June 2010, pp 1793-8163.

2. P.Rathika, D. Devaraj, “Fuzzy Logic Based Three-Phase Four-Wire and Four-Leg Shunt Active Power Filter for Harmonics, Reactive and Neutral Current Compensation”, International journal of Electrical Engineering, 2011.

3. P.Rathika, D. Devaraj, “Fuzzy Logic Based D.C Voltage and Current Control Technique for Shunt Active Filter Design”, Asian journal of Power electronics Applications (Accepted for Publication)

4. P.Rathika, D. Devaraj, “Fuzzy-Adaptive Hysteresis Based Current Control based VSI for Active Power Filter to Reduce Switching Frequency” International journal of Electronics, Taylor and Francis publications (Revised and submitted)

5. P.Rathika, D. Devaraj,” Artificial Intelligent Controller Based Three- Phase Shunt Active Filter for Harmonic Reduction and Reactive Power Compensation” International journal of Lecture notes in Engineering and Computer Science, 2010.

6. P.Rathika, D. Devaraj, “Wavelet Transform Based Reference Current Computation and Fuzzy adaptive Hysteresis Band Current Control for Shunt Active Power Filter”, International journal on Electrical Engineering, Springer Publication. (Under Review)

7. P.Rathika, D. Devaraj, “Fuzzy Logic-Based Adaptive Hysteresis Current Control Technique for Shunt Active Filter”, International Journal on Adaptive and Innovative Systems, Inderscience Publication. (Under Review)

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International Conference Publications

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1. P.Rathika, D. Devaraj, ” Artificial Intelligent Controller Based Three- Phase Shunt Active Filter For Harmonic Reduction And Reactive Power Compensation” International Multi Conference of Engineers and Computer Scientists 2010 Hotel Royal Garden, Hong Kong , March 2010, pp 1170-1175 .

2. P.Rathika, D. Devaraj, “Discrimination of Power Quality Disturbances using Combined Mathematical Transforms and Artificial Neural Network”, IEEE International Conference on Sustainable Energy Technologies (IEEE-ICSET’08), SMU Conference Centre, Singapore, Nov 2008, pp 1265-1270.

3. P.Rathika, D. Devaraj, “Power Quality Monitoring using wavelet transform and Artificial Neural Networks”, India International Conference on Power Electronics (IICPE ’06), Hotel Le Royal Meridien, Chennai, Dec 2006, pp 425-430.

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National Conference Publication

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1. P.Rathika, D. Devaraj,” Implementation of Shunt Active Filter using DSP”, INCOS’10 Kalasalingam University, Krishnanakoil, Apr 2010, pp 63-68.

2. P.Rathika, D. Devaraj,” Design of D-STATCOM using DSP Controller for Voltage sag/swell Mitigation”, INCOS’10 Kalasalingam University, Krishnanakoil, Apr 2010, pp 52-56.

3. P.Rathika, D. Devaraj,” Shunt Active Filter with Fuzzy Logic Control of DC Bus Voltage”, Power and Energy Systems (NPES’09) Kalasalingam University, Krishnanakoil, March 2009, pp 183-186.

4. P.Rathika, D. Devaraj,” Power Quality Monitoring by evaluation of Energy curves using wavelet Transform”, Recent Trends and Emerging technologies in Electrical Systems (ELCON’06), National Engineering College, Kovilpatti, Nov 2006, pp 198-207.

5. P.Rathika, D.Devaraj, ”Shunt Active Power Filter for Power Quality Improvement”, Recent Trends and Emerging technologies in Electrical Systems (ELCON’06), National Engineering College, Kovilpatti, Nov 2006, pp 81-88.

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REFERENCES9. Edson, H. Watanabe, Mauriclo Aredes and Hirofumi Akagi, “The p-q theory for Active filter

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10. Firouzjah, K.G., Sheikholeslami, A., Karami-Mollaei, M.R. and Khateghi, M. “A new Harmonic Detection Method for Shunt Active Filter Based on Wavelet Transform”, Journal of Applied Science Research, Vol. 4, No. 11, pp.1561-1568, 2008.

11. Herrera, R.S., Salmeron, P. and Hyosung Kim, “Insantaneous Reactive Power Theory Applied to Active Power Filter Compensation: Different Approaches, Assessment and Experimental Results”, IEEE Transactions Industrial Electronics, Vol. 55, No. 1, pp.184-196, 2008.

12. Hui Liu, Guohai Liu and Yue Shen, “A Novel Harmonics Detection Method based on Wavelet Algorithm for Active Power Filter”, Proceedings of the 6 th World Congress on Intelligent Control and Automation, pp. 21-23, 2006.

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Thank You !