Harmonics Issues that Limit Solar Photovoltaic Generation on
Distribution Circuits
Ketut Dartawan
Ricardo Austria, Le Hui and Mark Suehiro*
Pterra Consulting
Maui Electric Company*
May 17th, 2012 Denver, CO
WREF 2012 Paper # 0482
2
I. Harmonic is Distortion of “Ideal” Waveform
Fundamental
-2.0
-1.0
0.0
1.0
2.0
0 90 180 270 360 450 540 630 720
Angle (degree)
Vo
lta
ge
Ma
gn
itu
de
Fundamental + Harmonic Voltages Versus Angles
-2.0
-1.0
0.0
1.0
2.0
0 90 180 270 360 450 540 630 720
Angle (degree)
Vo
lta
ge
Ma
gn
itu
de
Ideal Distorted
Fundamental + Harmonic Voltages Versus Angles
-2.0
-1.0
0.0
1.0
2.0
0 90 180 270 360 450 540 630 720
Angle (degree)
Vo
lta
ge
Ma
gn
itu
de
3
Distortion Caused by Harmonic Source
Ideal Waveform
60 Hz
Distorted Waveform
3rd Harmonic Source
180 Hz – 3 x 60 Hz
+
Fundamental + Harmonic Voltages Versus Angles
-2.0
-1.0
0.0
1.0
2.0
0 90 180 270 360 450 540 630 720
Angle (degree)
Vo
lta
ge
Ma
gn
itu
de
4
Distortion Caused by Harmonic Sources
Ideal Waveform
60 Hz
Distorted Waveform
Multiple Harmonic
Sources
3rd,5th,7th,9th
+
5
Power Plant Transmission Lines
Distribution Substation
DC AC
Photovoltaic Panels Power Inverters
Harmonics
Harmonics from renewable resources
6
Harmonics are risky/hazardous to power systems • overheating equipment
• over-voltages
• interferences with communication systems
• mis-operation of sensitive loads
• etc
7
IEEE standards
• IEEE standard 519: IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, 1992
• IEEE standard 1547: IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems, 2003
8
Total harmonics distortion (THD)
1
22
4
2
3
2
2
I
IIIII
n
THD
1
22
4
2
3
2
2
V
VVVVV
n
THD
9
Criteria - IEEE Std 519 1992
Harmonic Voltage Distortion in % at PCC
2.3 - 69 kV 69 - 161 kV > 161 kV
Maximum for Individual Harmonic 3.0 1.5 1.0
Total Harmonic Distortion (THD) 5.0 2.5 1.5
ID*
Maximum Harmonic Current Distortion in % of Load Demand Current Voltages 0.12-69-kV
ISC/IL Harmonic Order (Odd Harmonics)
THD <11 11<h<17 17<h<23 23<h<35 35<h
A1 <20* 4 2 1.5 0.6 0.3 5
A2 20<50 7 3.5 2.5 1 0.5 8
*: only portions are shown here IEEE Std 1547
10
Even Harmonic Was not a controlling factor back when the standard was created
• IEEE Std 519 & 1547
Even harmonics Odd harmonics = 25% ×
• Authors recommendation (Even = Odd)
Even harmonics Odd harmonics = 100% ×
• PV has even harmonics that comparable to the odd harmonic
11
II. Modeling and simulation
Circuit model:
• 2Mile 12.47 kV CKT
• 10 MVA substation transformer
• 4 MVAR Cap Bank • 500 kW PV units (total: 2 ~ 5 MW)
12.47 kV Bus
Substation Transformer
69/12.47 kV
PV unit#1
PV unit#2
PV unit#3
PV unit#4
480 V Bus
Load
2 mile
500 MCM
Cable
Utility69 kV Bus
Additional
PV units
Harmonic
source
10 mile 336 Al
Overhead Line
Lumped Load: 3
MVA, 0.9 p.f.
...
4 MVAR
Cap BankFilter
Sunlight
DCAC
Background
Harmonics
12
TYPE-I, THD = 3% TYPE-II, THD = 6%
Harmonics from renewable Energies - below 9th harmonic order
- both even and odd harmonics
Background harmonics: - from TV, computer, fluorescent lamps, etc
- harmonic orders: 1, 3, 5, 7, 9
13
Study Cases
System Loading Time Profile
• Heavy load • Capacitor on • PV on/off
Light Load and
Capacitors off
Light
LoadHeavy Load and Capacitors on
Photovoltaic Power
Case 2
Case 4
12 4 8 12 4 8 12
AM PM AM
Case 1 Case 3 Case 1
14
III. Analysis, results and discussions
Research approach:
Resonance Point
THDCompare
PVPenetration
level
1 3 5 7 9 11 13 15
Harmonic order
standards
Harmonic LimitDecide
15
Capacitor and Resonance Point
Impedance Scan at the 12.47 kV Bus
0
100
200
300
400
500
600
700
0 5 10 15 20 25 30 35 40 45 50
Harmonic Order
2 M
VA
R
1 M
VA
R
4 M
VA
R
0 M
VA
R
Bu
s S
can
Im
ped
an
ce M
ag
nit
ud
e
(pu
)
16
Voltage Distortion Percentage
at 12.47 kV Bus with 4 MVAR Capacitor in Service Voltage Distortion
at the 12.47 kV Bus 4 MVAR Capacitor
0
1
2
3
4
5
1 2 3 4 5 6
PV (MW)
Vo
ltag
e D
isto
rtio
n (
%)
TYPE-I THDTYPE-II THD
IEEE criteria
Limit: 1.2 MW – TYPE II
Limit: 5 MW – TYPE I
17
Current Distortion Percentage (Type-II harmonics)
at 480 V Cable with 4 MVAR Capacitor in Service 0.0
2.0
4.0
6.0
8.0
10.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Harmonics
Cu
rren
t D
isto
rtio
n (
%)
1.0 MW
1.2 MW
1.4 MW
IEEE-519 modified
IEEE-519
Violations
0.0
2.0
4.0
6.0
8.0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Harmonics
Cu
rren
t D
isto
rtio
n (
%)
1.6 MW
1.8 MW
2.0 MWIEEE-519 modified
IEEE-519
Violations
IEEE-1547 modified
IEEE-1547 modified
18
PV penetration limit summary
Type-I Harmonics Type-II Harmonics
w/o background harmonics
w/ background harmonics
w/o background harmonics
w/ background harmonics
12.47 kV Bus 5.0 MW 3.0 MW 1.2 MW 0.8 MW
480 V Cable
IEEE-519 > 5.0 MW > 5.0 MW 0.6 MW 0.6 MW
IEEE-519 modified > 5.0 MW > 5.0 MW 1.6 MW > 2.0 MW
IEEE-1547 modified > 5.0 MW > 5.0 MW 1.0 MW 1.0 MW
19
Mitigation: Harmonic filters
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35 40 45 50
Bu
s S
ca
n I
mp
ed
an
ce M
ag
nit
ud
e
(pu
)
Harmonic Order
without
filters
With
filters
12.47 kV Bus
To Distribution Circuit
4 MVAR Capacitor
bank. Operation
mode: 1, 2, and 4
MVAR
Notch Filter
Tune at the 5th
Order
Harmonics
High-Pass
Filter Tune at
the 7th Order
Harmonics
Utility
69 kV BusSubstation
Transformer
FILTER
Dirty Water
Dirty power
Clean Water
Clean power
20
IV. Conclusions
• The maximum PV penetration can be significantly influenced by: ▫ criteria adopted
▫ capacitor operating modes
▫ harmonics injected from PV units
• Harmonic filters could be used to increase PV penetration