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HARMONIC ANALYSIS OF SELECTED DG DEVICES

Pradipta Kumar Tripathy, Durgesh P. Manjure, Dr. Elham B. Makram

CLEMSON UNIVERSITY ELECTRIC POWER RESEARCH ASSOCIATIONClemson University, Clemson, SC 29634

Power System 2002 Conference: Impact of Distributed GenerationMarch 13-15, 2002

Clemson, SC

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Introduction

Background

Modeling

Results

Conclusion & Future Work

OUTLINE

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INTRODUCTION

Objective

To study the effect of Distributed Generation on distribution systems with respect

to harmonic distortion.

Outline of Research

Literature review

Case studies on the impact of different types of DG in residential, commercial, and industrial systems to the distribution system

Methods Used

Time domain method for simulation

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Harmonic Sources in Power Systems

Saturable devices

Nonlinear loads

Power electronic devices

Harmonics in typical DG systems

Microturbines

Wind Turbines

Photovoltaics

BACKGROUND

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A TYPICAL RESIDENTIAL PV SYSTEM

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Circuit components used for modeling the PV system are

A constant voltage DC source

A single phase inverter

An isolating transformer

A single-tuned filter

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MODELING OF PV SYSTEM

Vpv

T1

T4 T2

D1 D3

D4 D2

T1

L

C

T3

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MODELING OF RESIDENTIAL SYSTEM

Residential system is modeled by considering four typical houses.

Loads considered in each house:

Linear Loads (assumed)

Incandescent light

Refrigerator load

Nonlinear Loads

Compact Fluorescent Light

Television Load

Heat pump

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Case 1:

Harmonic distortion in the presence of DG as a standalone unit

supplying residential loads

Case 2:

Harmonic distortion in the distribution system due to residential system loads alone

Case 3:Combined effect of residential loads and DG on distribution system harmonics

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CASES STUDIED

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TEST SYSTEM USED FOR CASE 1

Load current

Load voltage

Vpv

T1

T4 T2

D1 D3

D4 D2Isolation Transformer

L

C

T3

Filter

PV System

Residential loads

House1 House2 House3 House4

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RESULTS FOR CASE 1

4.82 4.84 4.86 4.88 4.9-150

-100

-50

0

50

100

150

Time(seconds)

Mag

nitu

de (

volt

s)

Load voltage

-60

-40

-20

0

20

40

60

Time(seconds)

Mag

nitu

de (

ampe

res)

Load current

0 5 10 15 20 25 300

5

10

15

20

25

30

Harmonic Order

Mag

nitu

de (

%)

Harmonic distortion in load voltage

0 5 10 15 20 25 300

5

10

15

20

25

Harmonic Order

Mag

nitu

de (

%)

Harmonic distortion in load current

4.83 4.85 4.87 4.89

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TEST SYSTEM USED FOR CASES 2 & 3

12.47 kV/4.16 kV 4.16 kV/0.208 kV

PV System

12.47 kV

Residential loads

Substation

Three phase loads

Single phase loads

House1 House2 House3 House4

Load current

Load voltage

Primary current

Primary voltage

Line reactor

Isolation transformer

12.47 kV/4.16 kV4.16 kV/0.208 kV

PV System

12.47 kV

Residential loads

Substation

Single phase loads

House1 House2 House3 House4

Load current

Load voltage

Primary current

Primary voltage

Line reactor

Isolation transformer

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RESULTS FOR CASES 2 & 3Comparison of load voltage

012345678910

Mag

nit

ud

e(%

)

3 5 7 9 11 13 15 17 19 21 23 25

Harmonic order

Load voltage without PVLoad voltage with PV

Comparison of load current

Harmonic order

05101520253035404550

Mag

nit

ud

e (%

)

3 5 7 9 11 13 15 17 19 21 23 25

Load current without PVLoad current with PV

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RESULTS FOR CASE 2 & 3Comparison of primary voltage

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

3 5 7 9 11 13 15 17 19 21 23 25Harmonic order

Primary Voltage without PVPrimary Voltage with PV

Mag

nit

ud

e (%

)

Primary current

Harmonic order

0

5

10

15

20

25

30

35

40

Mag

nit

ud

e (%

)

3 5 7 9 11 13 15 17 19 21 23 25

Primary current with PVPrimary current without PV

Comparison of primary current

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THD(%) Residential systemfed by distributionsystem

Residential systemfed by distributionsystem and PVsystem

Load current 49.3 44.14Load voltage 11.9 7.2Primary current 38.4 21.9Primary voltage 5.1 3.1

RESULTS FOR CASE 2 & 3

Comparison of THD

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CONCLUSIONS

Harmonics produced on the load side by the PV system were not significant compared to the high current distortion caused due to the household nonlinear loads.

Harmonic distortion injected to the distribution system decreased after connecting the PV system due to harmonic phasor cancellation.

Results presented are for the specific scenario discussed, and could change with varying nonlinear loads and/or varying DG types and sizes

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FUTURE WORK

Impact of varying levels of DG penetration on harmonic propagation, in the presence of nonlinear loads

Modeling of other types of DG

Effect of DG on harmonic distortion in case of commercial and industrial systems

Combined effect of PV and microturbine system

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