faculty of electrical and computer engineering chair of...

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Faculty of Electrical and Computer Engineering Chair of Electrical Power Systems

Ana Maria Blanco, Jan Meyer,Sascha Müller, Anantaram Varatharajan08.08.2017

Some European experiences with renewable installations

Waveform distortion


1. Introduction

2. Distributed PV inverters (<10kW)

3. PV plant (1MW)

4. Wind-park (12MW)

5. Conclusions

Content

09.08.2017 European experiences with renewable installations

Slide 2

2


Terminology


Slide 3

a. DC componentb. Subharmonicsc. Harmonicsd. Interharmonics

a. Supraharmonics

− Supra = beyond− First mentioned at

IEEE PES GM 2013

Integer and non-integer multiples of power frequency

“Independent“of power frequency

Low frequency distortion(below 2 kHz)

Higher frequency distortion(2 kHz .. 150 kHz)


Distortion of self-commutating technologies vary depending on:

Network side− Supply voltage distortion− Supply voltage magnitude− Frequency-dependent network impedance− Supply voltage unbalance (3-phase PV-inverters only)

Installation side− Output power level− Implemented control algorithms and their time constants− Further parameter settings of inverter (e.g. volt-var-

control regime)

Scope


Slide 4

3


1. Introduction


3. PV plant (1MW)

4. Wind-park (12MW)

5. Conclusions

Content


Slide 5


Significant dependency of harmonic currents on voltage distortion

Harmonic emission


Slide 6

0 5 100

50

100

150

200

250

300

350

Vol

tage

in V

0

2

4

6

8

10

12

14

Cur

rent

in A

• Different sensitivity for different types of PVs• Current source model is not adequate

4


Sensitivity to harmonic voltages


Slide 7

PV 1

PV Inverter PV 1 PV 2 PV 3 PV 4 PV 5 PV 6Total Auto-Sensitivity 96,1 159,5 150,8 61,4 87,9 158,4Total Cross-Sensitivity 32,9 43,8 24,1 448,3 33,2 31,8

PV 4

Testing conditions with the IEC 61000-3-2 should be revised


• Capacitive behavior at several frequencies

• Different resonance frequency

Input impedance


Slide 8

PV 1 PV 3

PVs can have a high impact on the network stability

5


Impact of harmonic impedance on stability


Slide 9

Current controllerswing

• High oscillations caused by the current controllers produce the trip-off of the PVs

Measurements by University of Applied Science Biel, Switzerland

within the research project “Swinging Grids”


HF emission of small PV inverters


Slide 10

• Laboratory measurements of 3 different single-phase PV inverters

• Significant differences in magnitude and switching frequency of HF emission

We wish to thank the Technical University of Dortmund / Chair of Energy Efficiency for their support of the measurements.

Cur

rent

in

A

6


• Propagation to the device responsible for the decrease in impedance (the EV in this case) and not towards the grid

HF propagation


Slide 11

0.52 V 0.32 A

0.35 V 0.26 A

EV

Propagation of the 16 kHz component in a LV network

Supraharmonics usually do not propagate too far in the network


Disturbance of communication

8/9/2017 European experiences with renewable installations

Slide 12

• Significant damping of PLC signal during the day (impedance reduction by PV inverters input impedances)

Impact of PV inverters on PLC signal level

Night:PV-Inv

OFF

Day:PV-Inv

ON

18:00 20:00 22:00 04:00 06:00 08:0010

50

100

150

f /

kHz

00:00 02:00t / h

Day: PV-Inv

ONLowlevel

Low level

High signaling level

7


1. Introduction


3. PV plant (1MW)

4. Wind-park (12MW)

5. Conclusions

Content


Slide 13


Solar campus layout


Slide 14

• 9 big PVs each of 100 kW (same type, 3-phase)

• 15 small PVs (total approx. 50 kW, different types, 1-phase)

• Measurement duration 1 day− Normal operation of installation− Coordinated switching of

inverters 0 1 2 3 4 5 6 7 8 9

-250

-200

-150

-100

-50

0

50

Time in Mins

Pow

er in

kW

L1L2L3

Active power per phase

8


5th harmonic of individual large inverters


Slide 15

Impact of cosϕ(P)-control on magnitude and phase angleImpact of voltage distortion on current harmonic

5th current harmonic (L1)during switching OFF interval

5th voltage harmonic (L1) during switching OFF interval

2

4

6

270

300

330

0

Curr

ent i

n A

Inv 1Inv 2Inv 3Inv 4Inv 5Inv 6Inv 7Inv 8Inv 9Sum Small Inv

1

2

3

4

5

30

210

60

240

90

270

120

300

150

330

180 0

Vol

tage

in V

All ON

All OFF

cosϕ(P)-controlOFF / ON


Summation exponent and diversity factor


Slide 16

• Analysis of the interval when all inverters are switched ON

Summation exponent Phase angle diversity factor

5 7 9 11 130.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

Harmonic Order

Div

ersi

ty F

acto

r

( )( )

1( )( )

( )

1

nh

ihih VEC

p h nhARI

ii

II

kI I

=

=

= =

5 7 9 11 131

1.005

1.01

1.015

1.02

1.025

1.03

1.035

1.04

Harmonic Order

Sum

mat

ion

Expo

nent

( )( ) ( )( )

1

hh

nhh

VEC ii

I Iα

α

=

=

Virtual arithmetic summation without any considerable cancellation effect

9


HF emission in a larger PV plant


Slide 17

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 15040

60

80

100

120

140

Frequenz / kHz →

Spa

nnun

g /d

BµV

→

• large inverters of Sr=100kW(switching frequencies below 10 kHz)

• small inverters below 10kW (switching frequencies around 15-20 kHz)

• Narrow-band PLC application for meter communication (35 kHz – 95 kHz, 8 channels)

Voltage spectrum

Frequency in kHz

Volta

ge in

The higher the rated power, the lower the switching frequency

80 dBµV≈10 mV100 dBµV≈ 100 mV120dBµV ≈ 1 V1 V ≈ 0,44% at 230 V fund. frequency.


1. Introduction


3. PV plant (1MW)

4. Wind-park (12MW)

5. Conclusions

Content


Slide 18

10


• Six type 4 turbines (full converter), wind park: 12 MW rated power

Measurements:

• Passive test (1 month): Normal operation

• Active test (few hours): Test of different operating conditions

• Harmonics (H), interharmonics (IH) and supraharmonics (SH)

Wind-park layout


Slide 19

Transient recorder

110kV/20kV substation

23.5 km

PQ analyzer

DE02DE01

PQ analyzer

PQ analyzer PQ analyzer

PQ analyzer

PQ analyzer


• Similar behavior of all turbines• Significant variations due to

− network conditions: harmonic impedance, supply voltage distortion, ...

− wind-park conditions: Type of Q-setting, Output power, ...• Supraharmonics (2 kHz – 9 kHz) are smaller than 2A

Harmonic and interharmonic currents


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

0

5

10

15

20

I(h)

in A

Slide 20

Phase L1Phase L2Phase L3

0.51% Ir

3 5 7 9 11 13 15 17 19 21Interharmonic order

0

2

4

6

8

10

I i(h)

inA0.34% Ir

0.17% Ir

0.27% Ir

0.14% Ir

11


• Influence of voltage distortion and harmonic impedance

Comparison with certificates


Slide 21

Harmonics Supraharmonics

Dots: real measurementsBars: values provided in manufacturer certificate (IEC 61400-21)

Calculations based on certificate values are uncertain


• Not consistent behavior for all harmonics

• Clear secondary cancellation for the 7th harmonic

Influence of output power


Slide 22

PActive test: increasing P mantaining Q=0

• Consistently increase of current and voltage interharmonics with active output power

• Level of increase is partly linked to the network impedance

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1. Introduction


3. PV plant (1MW)

4. Wind-park (12MW)

5. Conclusions

Content


Slide 23


Conclusions


Slide 24

• Significant dependency of current harmonic emission from voltage distortion and frequency-dependent network impedance

Testing with sinusoidal voltage suitable?

• Virtually no cancellation for harmonics up to 13th order in case of identical units

• Significant interaction between inverters and PLC in the frequency range 2-150 kHz

Recommended summation exponents has to be individually adapted to the situation.

Additional stress for other equipment?Impact of high share of PV inverters on mains signaling?

13


Thank you for your attention!


Slide 25

M.Eng. Ana Maria BlancoTechnische Universität DresdenInstitute of Power Systems and High Voltage EngineeringEmail: [email protected]

faculty of electrical and computer engineering chair of...

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