1 EFFECT OF HARMONICS ON DISTRIBUTED GENERATION Dr. Elham Makram Department of Electrical and...

1

EFFECT OF HARMONICS ON DISTRIBUTED GENERATION

Dr. Elham MakramDepartment of Electrical and Computer Engineering

Clemson UniversityClemson, South Carolina 29634-0915

Clemson University Electric Power Research AssociationDG Conference, Clemson SC

March 14, 2002

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Outline• Overview of the effect of nonlinear loads on Power System Harmonics

• Effect of converter drive and arc furnace

• Effect of harmonics on power factor

• Effect of capacitor placement on harmonics

• Impact of unbalance on harmonics

• Need for accurate modeling for harmonic analysis

• Comparison of Time domain and Frequency domain methods

• Performance analysis of models for nonlinear loads

• Change in the scenario due to addition of Distributed Generation

• DG devices and corresponding systems

DG Conference Clemson University March 13-15, 2002

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The presence of a 6-pulse converter on the power system causes harmonic currents to flow through the system. Voltage distortion is negligible

0

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Cu

rren

t M

agn

itu

de

(%)

TRANS5_49 LINE3 LINE2 LINE1

Line Number

5th

7th

11th

13th

17th

19th

23rd

25th

Arc furnace produces voltage distortion and current distortion; the distortion in voltage being much higher than that in current. As such the AF by itself is more harmful to other customer loads than the converter drive.

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Vol

tage

Mag

nit

ud

e (%

)

Bus 12 Bus 11

Bus Numbers

5

7

11

13

17

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23

25

Effect Of converter drive and arc furnace

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A nonlinear load at a bus causes the power factor at that bus and at buses close to it to drop.

Placement of power factor improvement capacitors at buses close to the nonlinear load bus worsens the power at the nonlinear load bus, and also at buses close to it.

0.75

0.8

0.85

0.9

0.95

1

Pow

er F

acto

r

Bus 12 Bus 11 Bus 8 Bus 4Buses

Linear LoadAF Load

0.4

0.5

0.6

0.7

0.8

0.9

1

Pow

er F

acto

r

Bus 12 Bus 11 Bus 8 Bus 4Buses

Without capacitorWith capacitor

Effect Of Harmonics on Power Factor


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The presence of capacitor banks increases the current and voltage distortion at the nonlinear load bus and the buses close to it.

Effect of Capacitor placement on Harmonics

0 0.02 0.04 0.06 0.08-200

-100

0

100

200

Mag

nitu

de in

Am

pere

Time (seconds)0 0.02 0.04 0.06 0.08

-2000

-1000

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Mag

nitu

de in

Vol

t

Time (seconds)

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200

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Harmonic Order0 5 10 15 20 25

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1500

Harmonic Order

Current Voltage

0 0.02 0.04 0.06 0.08-400

-200

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Mag

nitu

de in

Am

pere

Time (seconds)0 0.02 0.04 0.06 0.08

-2000

-1000

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Mag

nitu

de in

Vol

t

Time (seconds)

0 5 10 15 20 250

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Harmonic Order0 5 10 15 20 25

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Harmonic Order

Current Voltage

Before capacitor placement After capacitor placement


6Impact of unbalance on harmonics


0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08-400

-200

0

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400

Mag

nitu

de in

Am

pere

s

Time (seconds)

0 5 10 15 20 250

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10

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Harmonic Order

Mag

nitu

de in

per

cent

0.9

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0.94

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0.97

0% 5% 10% 15% 20% 25%Degree of Unbalance

Pow

er F

acto

r

Nonlinear ModelLinear Model

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0% 5% 10% 15% 20% 25%Degree of Unbalance

Pow

er F

acto

r

Nonlinear ModelLinear Model

In addition to characteristic (6n1) harmonics, unbalance introduces uncharacteristic (triplen) harmonics

Unbalance adversely affects the power factor. Comparison is shown between the results obtained using a linear model and those obtained using a nonlinear model for the arc furnace

7Impact of unbalance on harmonics


• Degree of unbalance affects harmonics differently, i.e. with an increase in the degree of unbalance, the non-characteristic harmonics increase, whereas the characteristic harmonics show a decrease.

• The symmetrical component decomposition of individual harmonics helps to give an insight into the behavior of harmonics under varying degrees of unbalance.

• Unbalance adversely affects the power factor, although if the unbalance is within practical limits, the drop in the power factor is not very significant.

• Unbalanced conditions render certain models for nonlinear loads, to be inadequate for use.

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Frequency domain method of harmonic analysis gives pessimistic results, and is not equipped to accurately solve for certain types of harmonic analysis problems.

The DC side load also determines the amount of harmonics injected into the system. There is no provision in the frequency domain method to model this.

Comparison of Time domain and Frequency domain methods

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t in

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e 3

(% m

agn

itu

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Harmonic Number

Time

Frequency

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Cu

rren

t M

agn

itu

de

(%)

5 7 11 13 17 19 23 25Harmonic Number

DC load1/4 DC load1/8 DC load


9Performance analysis of models for nonlinear loads

400

-150 -100 -50 0 50 100 150-400

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Current (kA)

Vol

tage

(V

)

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-100

-50

0

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150

200

Current (kA) V

olta

ge (

V)

Using a Linear model

Voltage-Current characteristics for the arc furnace

Using a Nonlinear model


Preserving the nonlinearity of the problem yields a more accurate solution.

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Traditional Distribution

System

NONLINEAR LOADS

Residential

Commercial

Industrial

Original Picture


11Change in the scenario due to addition of Distributed Generation

• System would no longer be radial

• DG devices would have power conditioning sub-systems, which would inject harmonics into the distribution system as well

• This situation would be different from the case of multiple nonlinear loads



System

NONLINEAR LOADS

Residential

Commercial

Industrial

DISTRIBUTED GENERATION

SOURCES

INTERCONNECTION DEVICES


System

NONLINEAR LOADS

Residential

Commercial

Industrial

DISTRIBUTED GENERATION

SOURCES

INTERCONNECTION DEVICES

12DG devices and corresponding systems to be considered

Photovoltaics

Microturbines

Wind Energy

Inverters

Converter – Inverter pair

Induction generator – Converter - Inverter pair

Residential

Commercial

Industrial

DG device Interconnection Type of system


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A Typical Residential PV System


Preliminary results: Impact of a PV System

14Modeling of Residential System

Residential system is modeled by considering four typical houses. Loads considered in each house are:

Linear Loads (assumed):

Incandescent light

Refrigerator load

Nonlinear Loads:

Compact Fluorescent Lights

Television Set

Heat pump


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Case 1:

DG as a standalone unit supplying residential loads

Case 2:

Residential system loads fed by the distribution system only

Case 3:Residential loads fed by PV and the distribution system

Cases Studied


16Results for Case 1


4.82 4.84 4.86 4.88 4.9-150

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-50

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50

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150

Time(seconds)

Mag

nitu

de (

volt

s)Load voltage waveform

4.83 4.85 4.87 4.89-60

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-20

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40

60

Time(seconds)

Mag

nitu

de (

ampe

res)

Load current waveform

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10

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20

25

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Harmonic Order

Mag

nitu

de (

%)

Frequency Spectrum

0 5 10 15 20 250

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10

15

20

25

Harmonic Order

Mag

nitu

de (

%)

Frequency Spectrum

Voltage and current at the load bus

17Results for Cases 2 & 3

HOUSE1 HOUSE2 HOUSE4HOUSE3

12.47/4.16 4.16/0.208

1- LOADS

DG

SUBSTATION

3- LOADS

RESIDENTIAL LOADSTRANSFORMER

LINE REACTOR

COMPARISON OF LOAD VOLTAGE

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Mag

nitu

de (

%)

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Harmonic order

Case 2Case 3


18Results for Cases 2 & 3

HOUSE1 HOUSE2 HOUSE4HOUSE3

12.47/4.16 4.16/0.208

1- LOADS

DG

SUBSTATION

3- LOADS

RESIDENTIAL LOADSTRANSFORMER

LINE REACTOR

COMPARISON OF LOAD CURRENT

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Mag

nitu

de (

%)

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Harmonic order

Case 2Case 3


19Conclusions

• 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 into the distribution system decreased after connecting the PV system

• The harmonics picture may change than the way it appears now when number of PV systems connected to the distribution system increase.


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Work In Progress

• Modeling of other types of DG – Micro turbines, Wind Energy

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

• Impact of varying degrees of penetration of DG

• Combined effect of different combinations of DG devices


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Transmission system

Solar Energy

Wind energy

Microturbine

Load 1

Load 2

Load 3 Load 4

Load 5

Load 6

Distribution system

Fuel cell


Future Power System

1 EFFECT OF HARMONICS ON DISTRIBUTED GENERATION Dr. Elham Makram Department of Electrical and...

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