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