1. EFFECT OF HARMONICS ON DISTRIBUTED GENERATION
Dr. Elham Makram
Department of Electrical and Computer Engineering
Clemson University
Clemson, South Carolina
Clemson University Electric Power Research Association
DG Conference, Clemson SC
March 14, 2002

2. DG Conference Clemson University March 13-15, 2002
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

3. DG Conference Clemson University March 13-15, 2002
Effect Of converter drive and arc furnace 2 4 6 8 10 12 14 16 18 20
Current Magnitude (%)
TRANS5_49
LINE3
LINE2
LINE1
Line Number
5th
7th
11th
13th
17th
19th
23rd
25th 2 4 6 8 10 12 14 16 18 20
Voltage Magnitude (%)
Bus 12
Bus 11
Bus Numbers 5 7 11 13 17 19 23 25
The presence of a 6-pulse converter on the power system causes harmonic currents to flow through the system. Voltage distortion is negligible
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.
DG Conference Clemson University March 13-15, 2002

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Effect Of Harmonics on Power Factor 1
A nonlinear load at a bus causes the power factor at that bus and at buses close to it to drop.
0.95
0.9
Power Factor
Linear Load
0.85
AF Load
0.8
0.75
Bus 12
Bus 11
Bus 8
Bus 4 1
Buses
0.9
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.
0.8
Power Factor
0.7
Without capacitor
With capacitor
0.6
0.5
0.4
Bus 12
Bus 11
Bus 8
Bus 4
Buses
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Effect of Capacitor placement on Harmonics
The presence of capacitor banks increases the current and voltage distortion at the nonlinear load bus and the buses close to it.
Before capacitor placement
After capacitor placement
Current
Voltage
Current
Voltage
200
2000
400
2000
100
1000
200
1000
-100
-1000
-200
-1000
-200
-2000
-400
-2000
0.02
0.04
0.06
0.08
0.02
0.04
0.06
0.08
Magnitude in Ampere
0.02
0.04
0.06
0.08
Magnitude in Volt
0.02
0.04
0.06
0.08
Magnitude in Ampere
Magnitude in Volt
Time (seconds)
Time (seconds)
Time (seconds)
Time (seconds)
250
400
1500
1500
200
300
1000
1000
150
200
100
500
100
500 50 5 10 15 20 25 5 10 15 20 25 5 10 15 20 25 5 10 15 20 25
Harmonic Order
Harmonic Order
Harmonic Order
Harmonic Order
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6. DG Conference Clemson University March 13-15, 2002
Impact of unbalance on harmonics
In addition to characteristic (6n1) harmonics, unbalance introduces uncharacteristic (triplen) harmonics
0.97
0.97
0.96
0.96
0.95
0.95
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
0.94
0.94
Power Factor
Power Factor
Nonlinear Model
Nonlinear Model
Linear Model
Linear Model
0.93
0.93
0.92
0.92
0.91
0.91
0.9
0.9 0% 0% 5% 5%
10%
10%
15%
15%
20%
20%
25%
25%
Degree of Unbalance
Degree of Unbalance
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7. DG Conference Clemson University March 13-15, 2002
Impact 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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Comparison of Time domain and Frequency domain methods 14 12
Frequency domain method of harmonic analysis gives pessimistic results, and is not equipped to accurately solve for certain types of harmonic analysis problems. 10 8
Current in line 3 (% magnitude)
Time 6
Frequency 4 2 5 7 11 13 17 19 23 25
Harmonic Number 25 20
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. 15
DC load
1/4 DC load
Current Magnitude (%)
1/8 DC load 10 5 5 7 11 13 17 19 23 25
Harmonic Number
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Performance analysis of models for nonlinear loads
Voltage-Current characteristics for the arc furnace
Using a Linear model
Using a Nonlinear model
400
200
300
150
200
100
100 50
Voltage (V)
Voltage (V)
-100
-50
-200
-100
-300
-150
-400
-150
-100
-50 50
100
150
-200
-150
-100
-50 50
100
150
Current (kA)
Current (kA)
Preserving the nonlinearity of the problem yields a more accurate solution.
DG Conference Clemson University March 13-15, 2002

10. DG Conference Clemson University March 13-15, 2002
Original Picture
Traditional
Distribution
System
NONLINEAR LOADS
Residential
Commercial
Industrial
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Change 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
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12. DG Conference Clemson University March 13-15, 2002
DG devices and corresponding systems to be considered
DG device
Interconnection
Type of system
Photovoltaics
Microturbines
Wind Energy
Inverters
Converter – Inverter pair
Induction generator – Converter - Inverter pair
Residential
Commercial
Industrial
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13. DG Conference Clemson University March 13-15, 2002
Preliminary results: Impact of a PV System
A Typical Residential PV System
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14. DG Conference Clemson University March 13-15, 2002
Modeling 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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Cases Studied
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
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Results for Case 1
Voltage and current at the load bus
4.82
4.84
4.86
4.88
4.9
-150
-100
-50 50
100
150
Time(seconds)
Magnitude (volts)
Load voltage waveform
4.83
4.85
4.87
4.89
-60
-40
-20 20 40 60
Magnitude (amperes)
Load current waveform 5 10 15 25 30
Harmonic Order
Magnitude (%)
Frequency Spectrum
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Results for Cases 2 & 3
COMPARISON OF LOAD VOLTAGE 1 2 3 4 5 6 7 8 9 10
Magnitude (%) 11 13 15 17 19 21 23 25
Harmonic order
Case 2
Case 3
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18. DG Conference Clemson University March 13-15, 2002
Results for Cases 2 & 3
COMPARISON OF LOAD CURRENT 50
Case 2
Case 3 45 40 35 30
Magnitude (%) 25 20 15 10 5 3 5 7 9 11 13 15 17 19 21 23 25
Harmonic order
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19. DG Conference Clemson University March 13-15, 2002
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 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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21. DG Conference Clemson University March 13-15, 2002
Future Power System
Transmission system
Load 2
Load 5
Load 1
Solar Energy
Fuel cell
Microturbine
Load 6
Load 3
Load 4
Wind energy
Distribution system
DG Conference Clemson University March 13-15, 2002