Power quality aspects of solar power

672
Power quality aspects of solar power
Working Group
JWG C4/C6.29
December 2016

Members
J. Smith, Convenor US
S. Ronnberg, Secretary SE
A. Blanco DE
M. Bollen SE
Z. Emin GB
D. Ilisiu RO
L. Koo GB
J. Meyer DE
D. Mushamalirwa FR
P. Ribeiro BR
N. Wilmot AU
JWG C4/C6.29
Copyright © 2016
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POWER QUALITY ASPECTS
OF SOLAR POWER
ISBN : 978-2-85873-375-0

Power Quality Aspects of Solar
Power
TABLE OF CONTENTS
EXECUTIVE SUMMARY................................................................................................................. 7
Background on the Working Group and Scope ............................................................................ 7
Technical Brochure Overview ....................................................................................................... 7
Key Findings.................................................................................................................................. 8
Harmonics................................................................................................................................... 8
Supraharmonics ......................................................................................................................... 9
Fast Voltage Variations ............................................................................................................ 10
Slow Voltage Variations............................................................................................................ 10
Overvoltage .............................................................................................................................. 11
Flicker 11
Voltage Unbalance ................................................................................................................... 11
Connection and Disconnection................................................................................................. 12
Industry Survey on Power Quality Experience Related to Solar PV Installations....................... 12
Further Work ............................................................................................................................... 13
INTRODUCTION ................................................................................................................... 14
1.1 Scope of the JWG............................................................................................................. 14
1.2 Overview of Disturbances................................................................................................. 15
1.2.1 Harmonics.................................................................................................................... 15
1.2.2 Supraharmonics .......................................................................................................... 15
1.2.3 Fast Voltage Variations ............................................................................................... 15
1.2.4 Slow Voltage Variations............................................................................................... 15
1.2.5 Flicker .......................................................................................................................... 15
1.2.6 Overvoltage ................................................................................................................. 15
1.2.7 Connect/Disconnect .................................................................................................... 16
1.2.8 Voltage unbalance....................................................................................................... 16
1.3 Terminology ...................................................................................................................... 16
1.4 Primary and Secondary Emissions................................................................................... 17
1.5 Overview of Impacts ......................................................................................................... 17
1.6 PV installation topology .................................................................................................... 19
1.7 Hosting Capacity Approach .............................................................................................. 19
1.8 References........................................................................................................................ 20
SURVEY ON UTILITY’S EXPERIENCES ............................................................................. 21
2.1 Survey participants ........................................................................................................... 21
2.2 General concerns ............................................................................................................. 23
2.3 Monitoring practice ........................................................................................................... 23
2.4 Impact on power quality levels ......................................................................................... 24
2.5 Interferences caused by PV installations.......................................................................... 24
2.6 Application of emission limits............................................................................................ 24

Power Quality Aspects of Solar Power
Page 4
2.7 Supporting Comments...................................................................................................... 25
2.8 Findings ............................................................................................................................ 25
2.9 Recommendations............................................................................................................ 25
2.10 Open Issues...................................................................................................................... 25
2.11 References........................................................................................................................ 25
HARMONICS......................................................................................................................... 27
3.1 Individual PV inverters (unit level) .................................................................................... 27
3.1.1 Small-sized PV inverters ............................................................................................. 28
3.1.2 Medium and large PV-inverters................................................................................... 32
3.2 Multiple PV inverters (plant level) ..................................................................................... 33
3.2.1 Small PV-inverters....................................................................................................... 34
3.2.2 Medium and large PV-inverters................................................................................... 36
3.3 Impact on the network (network level).............................................................................. 37
3.3.1 Impact on harmonic voltage distortion at the connection point ................................... 37
3.3.2 Impact of small PV plants at weak connection points ................................................. 38
3.3.3 Attenuation of harmonics by distribution transformer.................................................. 39
3.3.4 Impact of distributed PV inverters in low voltage networks ......................................... 41
3.3.5 Impact of harmonic impedance on stability ................................................................. 42
3.4 Emission assessment....................................................................................................... 43
3.4.1 Calculation of hosting capacity.................................................................................... 43
3.4.2 Emission limits............................................................................................................. 45
3.4.3 Emission assessment.................................................................................................. 45
3.5 Findings ............................................................................................................................ 46
3.7 Open Issues...................................................................................................................... 47
3.8 References........................................................................................................................ 47
SUPRAHARMONICS ............................................................................................................ 50
4.1 What are supraharmonics?............................................................................................... 50
4.2 Emission – primary and secondary .................................................................................. 50
4.3 Primary emission .............................................................................................................. 50
4.4 Variations in primary emission.......................................................................................... 52
4.5 Secondary emission ......................................................................................................... 54
4.6 Influence of harmonic distortion on supraharmonic emission of PV inverters.................. 54
4.7 Input impedance of PV inverters ...................................................................................... 55
4.8 Hosting Capacity Determinations ..................................................................................... 55
4.9 Findings ............................................................................................................................ 55
4.11 Open Issues...................................................................................................................... 56
4.12 References........................................................................................................................ 56
FAST VOLTAGE VARIATIONS............................................................................................ 58
5.1 Characterizing Changes in Active and Reactive Power ................................................... 58
5.1.1 Size and Layout of PV Plant........................................................................................ 58
5.1.2 Cloud Enhancement.................................................................................................... 59
5.1.3 Fixed-Axis vs Tracking ................................................................................................ 59
5.1.4 Climate Characteristics................................................................................................ 60
5.1.5 Reactive Power ........................................................................................................... 60
5.2 Single PV installation (Single Point of Connection).......................................................... 60
5.2.1 Quantifying PV Output Variability ................................................................................ 60
5.2.2 Small-Scale Distributed Systems ................................................................................ 61
5.2.3 Large-Scale Solar PV Systems ................................................................................... 62
5.3 Multiple PV Installations (Multiple Points of Connection) ................................................. 63

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5.4 Hosting Capacity............................................................................................................... 64
5.4.1 Single PV Systems...................................................................................................... 64
5.4.2 Multiple PV Systems.................................................................................................... 65
5.5 Findings ............................................................................................................................ 65
5.7 Open Issues...................................................................................................................... 65
5.8 References........................................................................................................................ 65
SLOW VOLTAGE VARIATIONS........................................................................................... 67
6.1 Impact of PV Installations on Slow Voltage Variations..................................................... 67
6.1.1 Daily Movement of the Sun ......................................................................................... 67
6.1.2 Weekly Variations........................................................................................................ 67
6.1.3 Annual Variations ........................................................................................................ 67
6.1.4 Changes in Amount of Cloud Cover............................................................................ 67
6.1.5 Shading due to Fixed Objects ..................................................................................... 68
6.1.6 Solar Eclipse................................................................................................................ 68
6.1.7 PV and Electricity Markets........................................................................................... 68
6.1.8 Existing Voltage Control .............................................................................................. 68
6.2 Findings ............................................................................................................................ 68
6.4 Open Issues...................................................................................................................... 69
OVERVOLTAGE ................................................................................................................... 70
7.1 Voltage Rise due to PV Production .................................................................................. 70
7.1.1 Overvoltage Protection of PV Installations .................................................................. 70
7.2 Consequences of the Increace in Voltage Magnitude...................................................... 71
7.3.1 Distributed generation in general ................................................................................ 71
7.3.2 Low-voltage feeders .................................................................................................... 72
7.3.3 PV installations ............................................................................................................ 73
7.3.4 Probability-based limits................................................................................................ 73
7.4 Findings ............................................................................................................................ 73
7.6 Open Issues...................................................................................................................... 73
FLICKER................................................................................................................................ 74
8.1 Large-Scale PV Systems.................................................................................................. 74
8.2 Small-Scale PV Installations............................................................................................. 75
8.3 Operational Considerations .............................................................................................. 77
8.5 Findings ............................................................................................................................ 78
8.7 Open Issues...................................................................................................................... 79
8.8 References........................................................................................................................ 79
VOLTAGE UNBALANCE...................................................................................................... 80
9.1 Individual units .................................................................................................................. 80
9.2 Multiple units at one location ............................................................................................ 80
9.3 Multiple units at multiple locations .................................................................................... 82
9.3.1 Deterministic approach................................................................................................ 82
9.3.2 Stochastic approach.................................................................................................... 84
9.4 Hosting capacity ............................................................................................................... 85
9.4.1 Individual units............................................................................................................. 85
9.4.2 Multiple units................................................................................................................ 86

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9.5 Single-phase laterals ........................................................................................................ 87
9.6 Findings ............................................................................................................................ 87
9.8 Open issues...................................................................................................................... 88
9.9 References........................................................................................................................ 88
CONNECTION AND DISCONNECTION............................................................................ 89
10.1 Introduction ....................................................................................................................... 89
10.2 Occurrences for which solar PV are disconnected........................................................... 89
10.3 Switching of PV installations............................................................................................. 89
10.4 Transients Due to PV installation connection and disconnection..................................... 89
10.5 PV installatin energization sequence and inrush current ................................................. 90
10.6 Load rejection overvoltages.............................................................................................. 91
10.7 PV installation de-energization under short-circuit condition............................................ 92
10.8 Compensation shunt reactor............................................................................................. 93
10.9 Findings ............................................................................................................................ 93
10.11 Open issues...................................................................................................................... 94
10.12 References........................................................................................................................ 94
ANNEX A: QUESTIONNAIRE ON POWER QUALITY ISSUES RELATED TO PHOTOVOLTAIC
INSTALLATIONS .......................................................................................................................... 95
ANNEX B: CLIMATE REGIONS AND IMPACT ON SOLAR VARIABILITY..................... 98
12.1 References...................................................................................................................... 100
ANNEX C: PRIMARY AND SECONDARY EMISSIONS ................................................. 101
13.1 Single-phase diode rectifiers .......................................................................................... 101
13.2 Modern devices .............................................................................................................. 102
13.2.1 Active converters ....................................................................................................... 102
13.2.2 Supraharmonics ........................................................................................................ 102
13.2.3 Wind power plants ..................................................................................................... 102
13.2.4 Distinction between primary and secondary emission .............................................. 103
13.3 A general treatment ........................................................................................................ 103
13.3.1 Two sources and two impedances ............................................................................ 103
13.3.2 Contributions to the emission .................................................................................... 103
13.4 Proposed definitions ....................................................................................................... 104
13.4.1 Primary harmonic emission ....................................................................................... 104
13.4.2 Secondary harmonic emission .................................................................................. 104
13.4.3 Harmonic interaction.................................................................................................. 104
13.5 Some further discussion ................................................................................................. 105
13.5.1 Primary emission....................................................................................................... 105
13.5.2 Secondary emission .................................................................................................. 105
13.6 Harmonic finger prints..................................................................................................... 107
13.7 Conclusions .................................................................................................................... 108
13.8 References...................................................................................................................... 108

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EXECUTIVE SUMMARY
Background on the Working Group and Scope
The Working Group (WG) was formed in 2012 as a joint C4/C6 effort with the first official meeting taking place,
December 2012, following the 4th IRED Conference in Berlin, Germany.
This WG was formed to examine the power quality aspects of solar power in the form of photovoltaic installations
(PVIs), specifically addressing
 Characteristic harmonics (odd harmonics up to 2 kHz for single-phase installations; odd non-triple harmonics
for three-phase installations).
 Low-order non-characteristic harmonics (even harmonics and interharmonics up to 2 kHz, also odd triple
harmonics for three-phase installations)
 High-frequency distortion (frequency-components in the frequency range 2 to 150 kHz)
 Single rapid voltage changes, flicker and other voltage-magnitude variations at time scales below 10 minutes.
 Unbalance due to single-phase installations
 Supply voltage variations at time scales of 10 minutes and longer
Consideration was also given to two additional phenemona that distribution planners have found to be of high
concern:
 Overvoltage occurrences due to normal operation of solar power
 Sudden disconnection of PV installations and the impact of this disconnection on transient and temporary
overvoltages
Since the first meeting, the WG held eight physical meetings alongside various industry conferences (CIGRE, CIRED,
and IEEE PES) as well as multiple virtual meetings.
Technical Brochure Overview
The Technical Brochure (TB) resulting from the WG is divided into ten chapters and three annexes.
Chapter 1 provides a brief introduction to the work.
Chapter 2 provides a summary of an industry-wide survey of utility power quality experience with solar power.
Chapter 3 provides a summary of characteristic harmonics as well as low-order non-characteristic harmonics emitted
by PVIs.
Chapter 4 provides a summary of supraharmonics (any type of waveform distortion of voltage and current in the
frequency range between 2 and 150 kHz), emitted by PVIs.
Chapter 5 provides a summary of fast voltage variations (time scales less than 10 minutes) induced by variations in
solar active power production of PVIs.
Chapter 6 provides a brief summary of slow voltage variations (time scales of 10 minutes and longer) induced by
variations in production of PVIs.
Chapter 7 provides a brief summary of overvoltages induced by solar power production. While certainly not unique
to solar, this phenomenon is often one of the more critical aspects to consider today regarding grid performance due
to PVIs.
Chapter 8 summarizes the flicker performance from various PV installations according to IEC 61000-4-15 and IEEE
1453 standards.
Chapter 9 summarizes the potential for voltage unbalance due to single-phase connected solar PV installations.

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Chapter 10 summarizes the phenomena that can occur during sudden disconnection and reconnection of solar PV,
particularly transient overvoltages, temporary overvoltage, steady-state overvoltage and inrush currents.
Annex A provides a summary of the industry power quality survey that is referenced extensively throughout the TB.
Annex B provides a summary of climate regions in the US and how this impacts output variability of PV installations.
Annex C provides a brief summary of the differences between primary and secondary emission.
Key Findings
For each of the phenomena considered for PV installations (PVI1), a number of recommendations, key findings, and
open issues have been drawn by the WG, which are summarized below.
Harmonics
FINDINGS
The harmonic current characteristic of individual PV inverters largely varies between different models and
manufacturers. Magnitude and phase angle of the harmonic currents depend on many impact factors, like supply
voltage distortion, output power or harmonic network impedance. In most cases highest harmonic currents are
observed at 100% output power. Consequently, neither general models, nor simplified constant current source
approaches are sufficient for realistic simulation studies. This issue is also addressed by the CIGRE/CIRED working
group C4/B4.38 on network modelling for harmonic studies.
Harmonic magnitudes and phase angles (phasors) are important for realistic studies of cancellation effects between
PV inverters / PV installations and other installations. If larger PV plants are built using multiple individual PV inverters
of the same model, the harmonic currents of individual PV inverters add up arithmetically up to higher harmonic
orders. The standard summation exponents (e.g. according to IEC 61000-3-6) are not suitable in this case.
PV inverters can have a significant impact on harmonic network impedance. Particular in larger PV installations the
grid-side filter circuits can cause significant resonances at low frequencies. The resonant frequency decreases with
increasing number of inverters. Consequently, input impedances of PV inverters should be considered in harmonic
network impedance studies.
Under specific circumstances PV inverters can get unstable and trip. This has been observed along with high voltage
distortion due to network resonances, which are usually accompanied by high impedances at certain frequencies
around the resonance.
The analysis of network measurements has shown that particular harmonic voltages at orders higher than 25 are
significantly attenuated by the distribution transformers. In case of distributed PV-inverters in LV networks the impact
on the harmonic voltage in the network (decrease, increase or no impact) is usually different for each harmonic order.
It is determined by the existing potential of cancellation with other equipment and a possible filter effect of the grid-
side circuit of the PV inverters.
RECOMMENDATIONS
For realistic harmonic studies the dependency of harmonic currents of PV inverters on supply voltage distortion and
network impedance as well as the input impedance characteristic, which can cause resonances in the networks, has
to be considered.
In case of centrally located PV inverters (e.g. in large PV plants), particularly in case of similar inverter models,
harmonic currents should be added arithmetically independent of the harmonic order. For distributed PV inverters
(e.g. in residential areas) the aggregation with residential equipment should be taken into account.
1 A Photovoltaic installation (PVI) can be a single installation with one inverter, single installation with multiple
inverters, or multiple installations and inverters with multiple points of interconnect.

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Particularly in case of a high share of PV inverters in a network or in case of large PV plants the risk of high harmonic
voltages due to instabilities with multiple controllers should be considered.
With respect to standardization testing conditions and emission limits, especially for the small-sized PV inverters for
mass-market applications, should be revised. Setups using only sinusoidal test voltage and no reference impedance
(like in IEC 61000-3-2) do not reflect the real behavior of the inverter in the network and do not consider the different
sensitivities of the PV inverters to supply voltage distortion or network impedance at all. Even the specification of a
defined impedance characteristic for certain frequency ranges could be considered for future revisions of the
respective standards.
Measurements of PV inverters or PV plants in laboratory or field should include harmonic magnitudes and phase
angles. Knowledge about complex harmonic currents (phasors) can significantly improve e.g. studies of cancellation
effects or the separation between customer-side and network-side contributions to the harmonic emission levels.
OPEN ISSUES
More comprehensive knowledge about the harmonic current characteristic of medium-sized and large-sized PV
inverters is needed, particularly in order to improve the accuracy of respective harmonic studies.
Harmonic models for PV inverters require a lot of information from the manufactures, which is usually kept
confidential. Due to this lack of knowledge, suitable, manufacturer-specific harmonic models capable to be used for
studies of harmonic emission, harmonic instabilities or harmonic resonance are still missing. This includes also
aggregated harmonic models, e.g. for representing a PV plant consisting of multiple PV-inverters. Measurement-
based models seem to be a possible approach to improve the model accuracy compared to the simple models based
on constant current sources, however the superposition of the different impact factors, like supply voltage distortion,
network impedance, magnitude of supply voltage and output power of the PV-inverter is still not validated.
Comprehensive knowledge about the possible impact of PV inverters on the harmonic network impedance,
particularly their contribution to harmonic resonances in public LV grids, is still missing.
General and final conclusions about the impact of PV power on the harmonic levels are not known and might even
not be possible. It strongly depends on the situation, which is e.g. the size of PV installation, the harmonic impedance
at the connection point and the PV inverter models. However, a significant increase of harmonic levels on a large
scale cannot be observed yet.
Supraharmonics
FINDINGS
PVIs are a source of supraharmonics. Measurements show that the emissions from PVIs can be found at frequencies
up to 20 kHz. The emission from PVIs (as well as for other low voltage devices) is greatly affected by neighboring
devices; this has been shown for PVIs connected at the low voltage network in the following ways:
 The presence of neighboring supraharmonic sources can cause secondary emission at the PVI.
 Changes in source impedance due to connection and disconnection of neighboring devices will impact the
primary emission from a PVI.
 Voltage harmonics (3rd, 5th and 7th) have shown strong correlations with the supraharmonic emission from a
PVI.
RECOMMENDATIONS
More efforts from network operators as well as from the research community should be put towards harmonic studies
covering the whole frequency range up to 150 kHz. Small installations at LV (i.e. roof top installations) and larger
installations at higher voltage levels (i.e. solar plants) need to be treated differently with regards to supraharmonic
interaction. Solar plants are often connected to medium voltage with few other loads connected and any interaction
will likely take place within the plant between inverters. Roof top installations are connected at the customer site of
the meter and therewith close to other LV devices. Possible interaction between the inverter and other devices is
hence more likely to occur for small installations.

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OPEN ISSUES
The lack of a good method to distinguish between primary and secondary emission2 is a serious barrier when studying
emission from PV installations and other modern types of devices or installations.
It is unclear if the impact from neighbouring devices shown for PVIs connected at the low voltage network will be the
same within large solar plants. The large variation of input impedance of different PVIs indicates that this will be the
case.
Fast Voltage Variations
FINDINGS
Statistics of PV ramping characteristics are provided for various sizes and configurations.
Geographic size and layout have the greatest impact on PVI output variability. The larger PVIs (in terms of capacity
and geographic footprint) exhibit slower ramping compared to their smaller-sized counterparts.
Relating the PVI ramping characteristics to voltage fluctuations is dependent on the grid-connection point of the PVI
and the associated grid impedance (especially the resistance). Simple calculation methods for determining impact
from PVIs connected at a single point of interconnect are provided. Distributed PVI across a network requires more
detailed network modeling.
RECOMMENDATIONS
When examining voltage impacts due to output variability of a PVI, appropriately sized (kVA) PVI data should be
used based upon the PVI under study. For example, utilizing measurement data from a 1 kW system and scaling the
output to a much larger 1 MW system will result in overestimation of PV ramping impacts
The output distribution characteristics provided for various sized PVIs in the report can be used as guidance for
examining the impact of sudden changes in PV output on voltage.
OPEN ISSUES
There are no general aggregation rules for multiple PV systems connected to the same distribution grid.
Slow Voltage Variations
FINDINGS
The presence of PV installations in distribution networks will result in additional contribution to the variations of voltage
magnitude at time scales of 10 minutes and longer. The average voltage magnitude will increase, but the voltage
magnitude will also show more variations. This includes daily variations, annual variations and intra-hour variations
due to passing clouds. Also rare but predictable solar eclipses will result in additional variations in voltage magnitude.
The presence of PV may also lead to an increase or decrease in operations of mechanically-switched regulation
equipment (OLTC, regulators, switched capacitor banks) depending upon coincidence of solar production and load.
When solar and load profiles are non-coincident increased operations are expected. However, when the solar and
load profiles are coincident decreased operations are possible.
RECOMMENDATIONS
Studies are needed to quantify the consequences of coincident and non-coincident solar production and load profiles
on voltage-magnitude variations. A good starting point will be the gathering of long-term data on voltage-magnitude
variations at locations with and without solar power, as well as the analysis of historical data.
2 See Annex C of the TB for further information regarding primary and secondary emissions

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OPEN ISSUES
The net impact of solar and load coincidence or non-coincidence on voltage regulation equipment is not understood
in a quantitative way yet.
Overvoltage
FINDINGS
The presence of PV installations in distribution networks will increase the probability of overvoltages. The setting of
the overvoltage protection, as part of the anti-islanding protection, has played an important role in preventing
sustained overvoltages which could lead to damaged equipment. In many countries, the required settings require
that the PV inverters trip before the regulatory overvoltage limits are exceeded. However, use of anti-islanding
protection for voltage control could lead to nuisance tripping of PV generation.
RECOMMENDATIONS
The overvoltage settings as part of the anti-islanding protection should consider the impact this has on the operation
of the PV installations during periods with high production and low consumption. Network planning methodologies
for control of voltage levels that consider hosting capacity for PV generation based on relative voltage margins as
well as advanced voltage control from inverters which reduce output before overvoltage occur should be considered.
OPEN ISSUES
Should the regulatory limits be based on 100% values or are there arguments to allow the overvoltage limits to be
exceeded during a certain percentage of the time?
Flicker
FINDINGS
Results indicate that low levels of flicker can be contributed to the active power production from PV installations.
While this increase in flicker is measurable it is not expected to reach levels that are considered unacceptable.
RECOMMENDATIONS
While unacceptable flicker levels are not found to be contributable to the changes in active power from PV
installations, the results have shown that some PV installations can in fact cause unacceptable changes in voltage if
the capacity of the PV installation exceeds the local hosting capacity of the grid. This change in voltage is slower by
nature due to the slow-response time of PV installations relative to frequencies of concern relative to flicker. This
phenomenon is appropriately identified in this report as slow and fast voltage variations.
OPEN ISSUES
Flicker contribution from changes in reactive power has been observed in some PV installations. Analysis should be
performed using measurements from additional PV installations to determine the extent of this phenomena.
Voltage Unbalance
FINDINGS
The hosting capacity for voltage unbalance is only relevant for single-phase PVIs. Large individual PVIs and large
numbers of small PVIs should be treated differently. For large individual units the hosting capacity is obtained from
the source impedance at the point of connection (point of common coupling), the existing (pre-connection) unbalance,
and the acceptable voltage unbalance.
For small units, calculation of the hosting capacity requires knowledge on their spread over the phase and over the
locations. A simple relation has been obtained between voltage unbalance and number of units.
Voltage unbalance is only possibly an issue when single-phase units are used. For three-phase units, unbalance
should not be an issue. However, it has been mentioned that certain older types of three-phase inverters also exhibit
a large unbalance in current. No further information on this has been obtained.

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RECOMMENDATIONS
To be able to estimate the hosting capacity, it is important to obtain background measurements of voltage unbalance
at many locations including information on the phase angle of the voltage unbalance.
OPEN ISSUES
Some countries have put requirements on inverters, requiring them to be three-phase above a certain size. Other
countries even consider this requirement to cover all inverter sizes. It remains unclear to which extent such
requirements are needed.
Single-phase inverters can be connected to the phase in which they give the smallest increase in voltage unbalance.
It may even be possible to use PV inverters to compensate the background unbalance. It is however unclear to which
extend this is practically possible.
Connection and Disconnection
FINDINGS
Transient overvoltages and currents due to sudden PVI connection and disconnection have been documented.
Energization of the PVI MV/LV transformer can result in inrush currents up to 8-10 times rated current.
Laboratory tests have been performed to assess the duration and magnitude of transient over-voltages created PV
inverters during load-rejection conditions. While these tests are not all encompassing by addressing all potential grid
and PV conditions, these tests have shown that the measured maximum load rejection over-voltage did not exceed
2 PU of nominal peak voltage.
Laboratory tests have also been performed in order to assess the inverter behaviour during the presence of ground
faults once the breaker is opened. Ground fault overvoltages up to 1.6 pu have been observed.
RECOMMENDATIONS
The test results available at this time are based upon single and three-phase inverters of relatively small size (20kW
and below). Additional testing of larger sized inverters is recommended to determine the full extent of load rejection
and ground fault overvoltages.
Additional testing is also recommended to consider additional fault conditions, inverter vendor technologies, load
levels, and load compositions (e.g, motor loads).
OPEN ISSUES
Although different tests on PV inverters are performed by laboratories there is an absence of acceptance criteria to
characterize load rejection and ground faults overvoltages. The tests themselves are not yet standardized.
Industry Survey on Power Quality Experience Related to Solar PV
Installations
In addition to addressing specific power quality phenomena, the WG conducted an international survey of utility
personnel to gauge their experience as it relates to PV-induced power quality phenomena. This industry survey
consolidates international results from 32 responses from 18 countries.
The survey shows that still a significant lack of information exists in the utilities with respect to the possible impact of
PV installations on power quality in their networks. Most utilities do not have consistent monitoring programs and
they cannot reliably identify the impact on the different power quality disturbance phenomena. Until now, most utilities
have a relatively low installed PV capacity in their networks and therefore they do not consider the impact of PVIs as
a major concern.
However, with the expected increase of PV installations in the coming years, it is recommended that the utilities put
more attention on monitoring and understanding the impact of PV installations on power quality.

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Responses have been received by only 6 out of the 10 countries from the top 10 ranking list of cumulative installed
PV capacity. Unfortunately, only few or no responses were received from countries with the major cumulative PV
installed capacity. This refers e.g. to China, Japan, Italy, Spain and France. This fact should be considered when
interpreting the outcome of the survey.
Further Work
Additional work is needed as it relates to establishing and/or recommending methods for establishing hosting capacity
limits for each of the power quality phenomena addressed herein.

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INTRODUCTION
1.1 Scope of the JWG
There has recently been a massive increase in the amount of PV installations (PVIs) connected to the grid, and this
trend is expected to continue and even grow during the coming years.
Figure 1-1: Global Installed Solar PV from 2005-2015 (Source : www.ren21.net [1])
Not only are the number of PV installations increasing but also the sizes of the installations as well. PV installations
can be from a few MWs to tens of MWs. With large numbers of PV solar plants under construction and being planned
in many countries, their impact on power quality in the network is becoming of concern to grid operators.
A concern with the connection of PV installations is their potential impact on the voltage and current quality in the
grid. The creation of this working group should in no way be seen as a confirmation of any negative impact of PV
installations on the grid. Instead, the principal aim of this working group is a mapping and quantification of that impact
where it concerns power quality disturbances. A decision about possible negative impacts can only be made, most
likely on a case by case basis, after the completion of the working-group activities.
The following power-quality disturbances have been covered by this working group:
 Characteristic harmonics (odd harmonics up to 2 kHz for single-phase installations; odd non-triple harmonics
for three-phase installations).
 Low-order non-characteristic harmonics (even harmonics and interharmonics up to 2 kHz, also odd triple
harmonics for three-phase installations)
 High-frequency distortion (frequency-components in the frequency range 2 to 150 kHz)
 Single rapid voltage changes, flicker and other voltage-magnitude variations at time scales below 10 minutes.
 Unbalance due to single-phase installations
 Supply voltage variations at time scales of 10 minutes and longer
 Connection and disconnection transients induced by PVIs
For supply voltage variations at time scales of 10 minutes and longer, there exist already well documented work from
several sources, therefore only a brief description of the basics and of the state-of-the-art has been given.
For each of the other listed disturbances, the emission by PV installations will be mapped based on detailed
measurements. As much as possible, measurements from actual installations have been used. Information from
relevant literature has been used as well.
The impact on voltage quality has been studied, especially where this differs from the impact of emission by other
equipment. This part of the work covers a combination of measurements, simulation studies and information from
relevant literature.

Page 15
Power frequency variations, overloading and increased losses due to reverse power flow, voltage dips, and other
impacts or disturbances not mentioned above have been beyond the scope of this working group.
A number of factors are not addressed in this TB, including:
1. Grounding practices: While grounding practices have an impact on various power quality phenomena (e.g.
harmonics and temporary overvoltage during sudden disconnection), specific grounding practices are not
addressed in the TB.
2. Mitigation of PV impacts on grid performance
1.2 Overview of Disturbances
This technical brochure will only cover a limited set of power quality disturbances in relation to PVIs. A brief
description of those disturbances is given below. The fact that other disturbances are not treated here does not
necessarily mean that they are not affected by the introduction of solar power or that their impact can be neglected.
1.2.1 Harmonics
The term harmonics is used to describe a quasi-stationary distortion of the voltage or current waveform. The term is
here used for components up to order 40 (2 kHz in a 50 Hz system).
1.2.2 Supraharmonics
The term “supraharmonics” is used to refer to any type of waveform distortion of voltage and current in the frequency
range between 2 kHz and 150 kHz. This is not an official definition adopted by any organisation, nor is there general
agreement about the term. Also it should be noted that there is no abrupt change in phenomena at 2 kHz or at
150 kHz, so that the boundaries can be seen as being arbitrary.
The term “supraharmonics” will be used here, in absence of a better term.
1.2.3 Fast Voltage Variations
The term fast voltage variations will be used for variations in the rms voltage at times scales of less than 10 minutes.
1.2.4 Slow Voltage Variations
The term slow voltage variations will be used for variations in the rms voltage at times scales of 10 minutes and
longer. Slow voltage variations are only briefly treated in this report.
1.2.5 Flicker
The term flicker will be used for variations in the rms voltage at times scales of less than 1 second. Voltage-induced
light flicker is caused by voltage variations on these time scales.
1.2.6 Overvoltage
Two types of overvoltage should be distinguished when considered the impact of PVI:
 Overvoltages that exceeds limits
 The 10-minute rms voltage being above a defined limit;
 The rms voltage is above a certain limit during a period less than 10 minutes
 Overvoltages that cause damage
 The rms voltage or the peak voltage is such that leads to damage or significant loss of life of end-
user equipment
The term “overvoltage limit” typically refers to the first or the second of the above limits. Overvoltages are only briefly
treated in this TB.

Page 16
1.2.7 Connect/Disconnect
Connection and disconnection refers to the power quality impact from scheduled operation or sudden un-scheduled
disconnection of a PV installation.
1.2.8 Voltage unbalance
Voltage unbalance refers to a power quality phenomenon in a three phase system in which the rms value of the
voltages or the phase angle between consecutive phases is not equal.
1.3 Terminology
Table 1-1 provides a brief comparison of IEEE, Cenelec and IEC definitions for power quality phenomena and the
terms that are used in this report.
Table 1-1: Comparison IEEE, Cenelec, and IEC Terminologies Used in this Report
Term used in
this report
General description of
the phenomenon
IEEE 1250 EN 50160: 2010 IEC 61000-2-2:
2002
Voltage dip Short duration
reduction on voltage
magnitude
Voltage sag
(dip or sag are
accepted as
synonyms)
Voltage dip Voltage dip
Voltage swell Short-duration
increase in voltage
magnitude
Not mentioned Voltage swell Not mentioned
Harmonics Quasi-stationary
distortion of the
voltage or current
waveform
Voltage
distortion
Harmonics and
interharmonics
Harmonics and
interharmonics
Supraharmonics waveform distortion of
voltage and current in
the frequency range
between 2 and 150
kHz
Not mentioned Frequency range 2 to 150
kHz is described in annex B
(informative) of application
guide and as part of Mains
signalling voltages
Voltage distortion
at higher
frequencies; mains
signalling
Slow voltage
variations
Slow variations in
voltage magnitude at
time scales over 10
min
Voltage
regulation
Supply voltage variations Not mentioned
Fast voltage
variations
Fast individual
variations in voltage
magnitude at time
scales less than 10
min
Not specifically
mentioned
Single rapid voltage changes Voltage fluctuation
Flicker Fast, quasi-stationary,
variations in voltage
magnitude at time
scales less than one
second
Voltage
fluctuations
Flicker severity (the term
“rapid voltage changes”
covers “flicker severity” and
“single rapid voltage
changes”
Voltage
fluctuations and
flicker
Transient
overvoltage
Sub-cycle changes in
voltage or currents
Transients Transient overvoltages Transient
overvoltages

Page 17
Voltage
unbalance
rms values of the
phase voltages or the
phase angles between
consecutive phases
are not all equal
Voltage
imbalance
Supply voltage unbalance Voltage unbalance
Overvoltage rms value of the
voltage exceeds a
defined value
Overvoltage Temporary power frequency
overvoltage
Not mentioned
Primary
emission
part of the total
emission that is driven
by the internal
emission of the device
itself
Not mentioned Not mentioned Not mentioned
Secondary
emission
part of the total
emission that is driven
by emission of a
device connected
elsewhere in the grid
Not mentioned Not mentioned Not mentioned
1.4 Primary and Secondary Emissions
The harmonic or supraharmonic current at the terminals of a device or installation can be considered to consist of
two distinctively different components, referred to as primary emission and secondary emission. The primary
emission is the part of the harmonic or supraharmonic current driven by power electronic or other sources inside of
the device or installation (driven by 𝐽1 in Figure 1-2). The secondary emission is the part driven by sources outside
of the device or installation (driven by 𝐸2 in Figure 1-2).
Figure 1-2: Model for the connection of a device or installation to the rest of the power system; the rest of the power
system is to the right of the location at which the voltage U is obtained
More details on primary and secondary emission can be found in Annex C with this TB.
1.5 Overview of Impacts
Table 1-2 gives an overview of the impacts of the PV inverter technology on different power quality disturbances.

Page 18
Table 1-2 : PV Technolgy Characteristics and Power Quality Disturbances
Power
electronic
switching
Power
electronic
control
DC side
capacitor
size
Transformer
connection
Cable
length
between PV
and
transformer
Single-Phase vs
Three-Phase
Harmonics Strong
impact,
but
harmonics
are small
for PV
inverters.
Likely no
impact.
Strong
impact.
Certain
connections
block triplen
harmonics.
Two
transformers
with different
connections
could cancel
harmonics 5
and 7.
Impacts
resonance
frequencies,
but when no
capacitor
bank at MV
or LV,
resonance
frequency is
typically
beyond
harmonic
range.
No triplen for
three-phase
Supraharmonics Strong
impact.
No
impact.
Unknown Unknown Impacts
resonance
frequencies
Unknown
Fast voltage
variations
None The
reactive
power
variations
and the
maximum
power
point
tracker
could
have
impact.
None None The longer
and thinner
the cable,
the bigger
the impact.
Impact depends
upon capacity of
PVI relative to
the grid
impedance.
Slow voltage
variations
None Reactive-
power
control
impacts
the
voltage
None None The longer
and thinner
the cable,
the bigger
the impact.
Impact depends
upon capacity of
PVI relative to
the grid
impedance.
Unbalance None None None Not relevant Not relevant Relevant impact
for single-phase
Connect/Disconnect Unknown Unknown Unknown None Impacts
resonance
frequency
None

Page 19
1.6 PV installation topology
There are different connecting topologies of PV plants. The two main inverter connection modes are String Inverter
and Central Inverter as depicted in Figure 1-3 below. Each connection mode has advantages and drawbacks which
are beyond the scope of this document.
Figure 1-3 : PV Installation Inverter Connection Modes
1.7 Hosting Capacity Approach
The maximum amount of distributed generation that can be connected to a certain location, without resulting in an
unacceptable quality or reliability for other customers, is the so called hosting capacity [2] [3]. The hosting capacity
varies significantly between different locations in the grid. At some locations, the grid can accept almost no distributed
generation without additional investments, whereas it can accept large amounts at other locations.
To know how much distributed generation can be connected it is important to define appropriate performance
indicators. In a simplified way, the hosting capacity approach proceeds as follows:
 Choose a phenomenon and one or more performance indices;
 Determine a suitable limit or limits;
 Calculate the performance index or indices as a function of the amount of generation;
 Obtain the hosting capacity;
The hosting capacity approach is based on this procedure. The choice of index and limit will have a big influence on
the amount of distributed generation that can be accepted. Where applicable, a recommended approach for
assessing hosting capacity based upon the power quality phenomena addressed throughout this TB is provided.
PV
PV
PV
PV
PV
PV
PV
PV
PV
PV
PV
PV
Central
Inverter
To the Grid
PV
PV
PV
PV
PV
PV
PV
PV
PV
PV
PV
PV
To the Grid To the Grid
To the Grid
String
Inverter

Page 20
1.8 References3
[1] Renewables Global Status Report, 2016, ISBN 978-3-9818107-0-7, www.ren21.net
[2] M. Bollen and F. Hassan, Integrating distributed generation in the power system, Wiley – IEEE Press, 2011.
[3] Distribution Feeder Hosting Capacity: What Matters When Planning for DER?. EPRI, Palo Alto, CA: 2015.
3002004777
3 The reader should note that the referenced publications throughout the report reflect only a limited selection of the
available papers on PV power and Power Quality

Page 21
SURVEY ON UTILITY’S EXPERIENCES
A survey with five multiple choice questions was conducted to obtain an indication regarding the experiences and
current practices of utilities from around the world regarding power quality related to the connection of PV
installations. The survey addresses the following aspects:
1. General concerns:
Various concerns that utilities may have as a result of their own experience or due to information acquired
from conferences, research papers, technical recommendations, etc.
2. Monitoring practices:
Present strategies of utilities for monitoring possible impact of PV installations on power quality levels in the
networks.
3. Observed impact of PV installations on power quality:
During the connection and operation of PV installations in the distribution systems, utilities may have
experienced a change on the level of different power quality phenomena in their networks.
4. Observed interferences caused by PV installations:
During the connection and operation of PVs in the distribution systems, utilities may have experienced
interferences produced by the PV installations.
5. Application of emission limits:
Present framework of guidelines for calculating and assessing emission limits for PV installations that has
to be applied by utilities.
The questionnaire relates to the following power quality phenomena:
Voltage fluctuations:
 flicker
 rapid voltage changes,
 sags, swells, transients
Voltage unbalance
Waveform distortion
 in the frequency range below 2 kHz (harmonics, interharmonics)
 in the frequency range between 2 kHz and 150 kHz (supraharmonics)
Moreover, some statistical data about the network, the total load and total amount of connected PV installations were
also acquired in order to assess the relative “importance” attributed by the utility to PV installations. Besides, the
utilities could also add commentaries at the end of each question in order to explain some of their answers or indicate
other issues that were not addressed by the survey.
2.1 Survey participants
The survey was conducted between April 2015 and May 2016. In total 32 responses from 18 different countries have
been received. Table 2-1 lists the participating countries and the number of responding utilities. Based on the
available information about the distribution of solar power in the world [1-3], responses have been received from
countries with high as well as low cumulative installed PV capacity. According to the rank of countries with highest
cumulative installed PV capacity in the world [3], six out of the ten countries from the top ten ranking list are included
in the survey. Consequently, the survey likely mixes the opinion of countries with different levels of experience with
PV.
In order to have a rough estimation of the relevance of installed PV power penetration in each utility, the following
index is calculated based on the statistical data provided by 30 of the 32 utilities:

Page 22
𝐿𝑒𝑣𝑒𝑙 𝑜𝑓 𝑃𝑉 𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 𝑜𝑓 𝑖𝑛𝑠𝑡𝑎𝑙𝑙𝑒𝑑 𝑃𝑉 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑀𝑊
𝑇𝑜𝑡𝑎𝑙 𝑝𝑒𝑎𝑘 𝑙𝑜𝑎𝑑 𝑖𝑛 𝑀𝑊
∗ 100
Table 2-1 Nationalities of survey answers
Country
Cumulative installed
PV capacity (MW) [3]
Rank of countries for
cumulative installed capacity
Responses
Germany 38200 1 3
China 28199 2 1
USA 18280 5 5
Spain 5358 7 1
United Kingdom 5104 8 2
Australia 4136 9 5
Czech Republic 2134 14 1
Canada 1710 15 1
Romania 1219 17 1
Netherlands 1123 18 1
Switzerland 1076 19 1
South Africa 922 21 1
Austria 766 22 2
Mexico 176 29 1
Sweden 79 31 1
Turkey 58 32 3
Uruguay NA* NA* 1
Bosnia and Herzegovina NA* NA* 1
Total 32
(*) NA: Information not available
This index was calculated for each utility and all utilities were classified in five categories as shown in Table 2-2. Half
of the participating utilities have a relatively low level of PV penetration with less than 5% of their peak load. The total
installed PV generation of most utilities is less than 500 MW, as shown in Table 2-3.
Table 2-2 : Level of PV penetration
Level of PV
penetration
Percentage of
utilities
0-5% 50.0 %
5-10% 16.7 %
10-25% 23.3 %
25-50% 3.3 %
>50% 6.7 %
Table 2-3 : Installed PV generation
Total installed PV
generation (MW)
Number of
utilities
<50 10
50-500 10
500-1500 5
1500 - 3500 4
>3500 1
The distribution of the most common size of PV installations, which to a certain extend is linked to governmental
incentive schemes, is shown in Table 2-4. PV installations of less than 30 kW in size are the most common equating
to almost 70% of all installations.
Table 2-4 Size of the PVs
Most common size of PV
installations
Percentage
of utilities
P < 5kW 32.6 %
5kW ≤ P < 30kW 37.0 %
30kW ≤ P <500kW 13.0 %
500kW ≤ P < 10MW 8.7 %
P > 10MW 8.7 %

Page 23
2.2 General concerns
Figure 2-1 shows the results for the question “Do you consider the increase of PV installations as a concern in terms
of the following power quality parameters?”. The major concern for the utilities is a possible increase of unbalance
levels due to the connection of small-sized PV installations. An increase of harmonics seems to be a concern for
most utilities as well. For the other power quality phenomena a specific tendency cannot be established. All voltage
fluctuation phenomena seem not to be a concern for most of the utilities. Up to 40% of the utilities do not have an
opinion with regards to interharmonics and supraharmonics. Consequently, dissemination of more information and
education is needed with respect to these phenomena.
Figure 2-1 : Results of the question “Do you consider the increase of PV installations as a concern in terms of the
following power quality parameters?”
2.3 Monitoring practice
The question “Do you monitor power quality levels and/or emissions of (small and large) PV installations?” is aimed
at establishing monitoring practice among utilities with respect to installed PV installations. The results in Figure 2-2
show that most of the utilities perform only measurements at a few of the PV installations and only for short durations.
A significant number does not perform any measurements at all, particular for the small-size PV installations. Just
few utilities set up continuous measurements. Again, least attention is given to supraharmonics and interharmonics,
which might be due to the fact that information on these parameters, particular supraharmonics, are often not
provided by the commonly used PQ instruments.
Figure 2-2 : Results of the question: “Do you monitor power quality levels and/or emissions of (small and large) PV
installations?”
0,0%
10,0%
20,0%
30,0%
40,0%
50,0%
60,0%
70,0%
80,0%
90,0%
100,0%
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
Flicker Rapid Voltage
Charge
Unbalance Sags, Swells,
Transients
Harmonics Interharmonics Supra-
harmonics
"Regarding which issues do you consider PV installations a concern?"
not sure major issues minor issues no issues
0
5
10
15
20
25
30
35
40
45
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
Charge
Transients
harmonics
numberofanswers
"How do you monitor Power Quality levels and/or emissions
of PV installations?"
not at all during commissioning few during commissioning many
temporary in operation few temporary in operation many permanent in operation few
permanent in operation many

Page 24
2.4 Impact on power quality levels
Figure 2-3 shows the analysis of responses to the question “Do you observe significant changes in the levels of the
following power quality parameters, which can be clearly dedicated to PV installations?”. According to the results,
most of the utilities have not experienced significant changes on various power quality levels in the networks.
However, as shown before, utilities do not monitor continuously the PV installations, making it difficult to understand
the real impact of the PVs on the networks.
Figure 2-3 : Results of the question: “Do you observe significant changes in the levels of the following power quality
parameters, which can be clearly dedicated to PV installations?”
2.5 Interferences caused by PV installations
Figure 2-4 shows the responses of the question “Do you experience any interference caused by PV installations?”.
Most of the utilities have not found major interferences caused by PV installations or they are very rare. Only
unbalance in connection with PV installations less than 30 kW seems to occur more frequent. However, it is not clear
whether this means “true” interferences (malfunction of other equipment) or only an exceedance of respective voltage
unbalance limits, which seems to be more likely.
Figure 2-4 : Results of the question: “Do you experience any interference caused by PV installations?”
2.6 Application of emission limits
Figure 2-5 shows the analysis of responses to the question “Do you apply emissions limits for PV installations?”.
Most utilities have to follow external rules, which can be established either on national or international level and most
0,0%
10,0%
20,0%
30,0%
40,0%
50,0%
60,0%
70,0%
80,0%
90,0%
100,0%
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
Charge
Transients
harmonics
"Do you observe any significant changes which can be dedicated to PV?"
not sure often decreasing rarely decreasing no rarely increasing often increasing
0,0%
10,0%
20,0%
30,0%
40,0%
50,0%
60,0%
70,0%
80,0%
90,0%
100,0%
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
Charge
Transients
harmonics
"Do you experience any interferences caused by PV installations?"
No Rare Few Frequently

Page 25
utilities have regulations for harmonics, while least rules exist for supraharmonics and interharmonics. This reflects
the presently existing gap in the standardization related to these aspects of power quality.
Figure 2-5 : Results of the question: “Do you apply emissions limits for PV installations?”
2.7 Supporting Comments
Most of the comments from the utilities are related to the monitoring practices. Several utilities indicated that the
monitoring is only carried out shortly before and after the connection of PV installations or in case of complaints by
the users. Therefore, continuous monitoring programs are not usually conducted and the utilities cannot give a
confident opinion about the impact of PV installations on the networks. Some utilities also state their concern about
the impact of PV installations and the urgent need to make more measurements to study this issue.
Moreover, some utilities also indicated that they do not have the capability to measure supraharmonics, and therefore
they cannot give a certain answer about the increase or decrease of the supraharmonic levels in the network. One
utility mentions that the inverters are “affecting the ripple control signal”, which could be a result of additional signal
damping due to the capacitive input impedance characteristic or a possible disturbing impact of the supraharmonic
emission of PV inverters.
2.8 Findings
The survey shows that there still is a significant lack of knowledge within the utilities with respect to the possible
impact of PV installations on power quality in their networks. Most utilities do not have consistent monitoring programs
and they cannot reliably identify the impact on the different power quality disturbance phenomena. Until now, most
utilities have a relatively low installed PV capacity in the networks and therefore they do not consider their effect as
a major concern.
2.9 Recommendations
However, with the expected increase of PV installations in the coming years, it is recommended that the utilities put
more attention on monitoring and understanding the impact of PV installations on power quality. Long term
measurements before and after the installation is needed for this.
2.10 Open Issues
Responses have been received by only 6 out of the 10 countries from the top 10 ranking list of cumulative installed
PV capacity. Unfortunately, only few or no responses were received from countries with the major cumulative PV
installed capacity. This refers e.g. to China, Japan, Italy, Spain and France. This fact should be considered when
interpreting the outcome of the survey.
2.11 References
[1] Renewables Global Status Report, 2016, ISBN 978-3-9818107-0-7, www.ren21.net
0,0%
20,0%
40,0%
60,0%
80,0%
100,0%
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
<
30kW
>
30kW
Charge
Transients
harmonics
"Do you apply emission limits for PV installations?"
no internal rules external rules

Page 26
[2] Solar Power Europe. Global Market Outlook for Solar Power 2015 – 2019. http://www.solarpowereurope.org
[3] International Energy Agency. 2014 Snapshot of Global PV Markets. Report IEA PVPS T1-26:2015. http://www.iea-
pvps.org

Page 27
HARMONICS
PV inverters, which are available on the market today, utilize power electronics based on self-commutating
techniques at high switching frequencies (supraharmonics). Consequently, the harmonic emission at frequencies
below 2 kHz is usually low compared to other equipment using line-commutating circuit topologies. However, many
measurements have shown that harmonic emission is still a significant issue for individual inverters and PV
installations.
Based on the rated current ranges used within the IEC 61000 series, different sizes of individual PV-inverters can be
broadly distinguished:
 Small size : Ir  16 A (Ppk  3.7 kVA single-phase or 11 kVA three-phase)
 Medium size : 16 A < Ir  75 A (11 kVA < Ppk < 52 kVA)
 Large size :Ir > 75 A (Ppk > 52 kVA)
According to a survey among grid operators (cf. Chapter 2), small-sized, single-phase PV installations with Ppk  5
kVA are the most common devices used in low voltage networks. Many studies are focused on that group of PV
inverters. It is not yet known, if and how the size impacts the harmonic emission characteristic of PV installations.
However, field measurements indicate a certain level of qualitative difference. Particularly the impact of network
impedance is more likely to be of concern for larger PV inverters (lower short circuit ratio). Small-sized PV inverters
are also easier to study in the laboratory and more detailed knowledge is available about their behavior.
Consequently, this chapter emphasizes on results of small-sized PV inverters.
In order to comprehensively analyze the interaction between multiple PV inverters, between PV inverters and other
equipment or the impact of PV inverters emission on the voltage distortion in the network, it is essential to consider
both magnitude and phase angle of the individual harmonics. More information, in particular with regard to the
measurement and analysis of harmonic phasors, can be found in [1].
The harmonic emission of PV inverters usually consists of two parts, namely primary emission and secondary
emission (cf. Annex C ) [2]. While the primary emission is mainly determined by the control algorithms implemented
in the PV inverter and their time constants, the secondary emission is mainly caused by the grid-side filter circuits of
the PV inverter. Usually the total harmonic emission consists of both primary and secondary emission, which are
furthermore variable and almost impossible to separate.
The first two sections of this chapter discuss the potential impact on harmonics for individual PV inverters as well as
the operation of multiple inverters within a single installation. Section 3.3 describes potential impacts at network level.
An overview about commonly applied methods for calculation and assessment of emission limits and hosting capacity
is provided in section 3.4. Finally, findings, recommendations and open issues are summarized. Harmonic
measurements carried out in laboratory enviroment as well as in the field are used to illustrate the different aspects.
The field measurements discussed in these sections were obtained from standalone PV plants as well as from
installations in residential areas and were provided by several countries.
3.1 Individual PV inverters (unit level)
Many studies have shown that the harmonic emission of PV inverters can vary considerably depending on a complex
set of impact factors including:
 Supply voltage distortion
 Supply voltage magnitude
 Harmonic network impedance
 Output power level
 Supply voltage unbalance (3-phase PV-inverters only)
 Implemented control algorithms and their time constants
 Further parameter settings of inverter (e.g. volt-var-control regime)
Selected influences are briefly discussed in the next sections based on the results of laboratory and field
measurements.

Page 28
3.1.1 Small-sized PV inverters
3.1.1.1 REFERENCE CONDITIONS
Figure 3-1 compares the magnitudes of the harmonic currents emitted by six small-sized PV inverters from different
manufacturers (Error! Reference source not found.).
Table 3-1 Overview of analyzed PV inverters measured at Technische Universitaet Dresden, Germany.
The measurements were obtained under laboratory conditions using a sinusoidal supply voltage waveform and no
network impedance. Additionally, the PV inverters were operated at rated power. In general, the harmonic emissions
are very low, but significant differences between the manufacturers are prevalent. These are mainly determined by
the different circuit design and control algorithms.
Figure 3-1 Current harmonic magnitudes of six different PV inverters under sinusoidal grid voltage
3.1.1.2 IMPACT OF SUPPLY VOLTAGE DISTORTION
Figure 3-2 a compares the magnitude of the harmonic currents emitted by the six PV inverters in Table 3-1 between
sinusoidal (light colored bars) and distorted (dark colored bars) supply voltage (no impedance, rated output power).
The voltage distortion was set to a flat-top waveform as this is most common for public LV networks with a dominating
share of single phase connected electronic equipment. All PV-inverters increase their third harmonic emission
magnitude, but by different levels. PV inverter 3 is with almost seven times the most sensitive amongst them. For the
other harmonic orders the behavior is not consistent. While e.g. PV inverter 2 reduces its 5th harmonic current
emission, PV inverter 3 increases it.
In addition to the magnitudes the harmonic phase angles are affected by the voltage distortion as well. Figure 3-2b
and Figure 3-2c show the 3rd and 5th harmonic emission of the six PV inverters in the polar plane. The circle and
square markers indicate the measurements with sinusoidal and flat-top voltage, respectively. In most of the cases
the variation of the phase angles is less than 10°, except for the 5th harmonic of PV inverter 3, where the phase angle
shifts almost 180°. Extensive measurements of different PV inverters under different distorted voltages are e.g.
presented in [3] and [4] and indicate that each PV inverter has a specific response characteristic to changes in the
supply voltage distortion.
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
0
0.05
0.1
0.15
0.2
0.25
Harmonic Order h 
I
(h)
inA
PV 1
PV 2
PV 3
PV 4
PV 5
PV 6
PV Inverter PV 1 PV 2 PV 3 PV 4 PV 5 PV 6
Connection
type single-phase single-phase three-phase three-phase three-phase three-phase
Rated
power 4,6 kW 4,6 kW 10 kW 7,5 kW 4,0 kW 10 kW
Circuit
design transformerless
LF
transformer
HF
transformer transformerless transformerless transformerless

Page 29
a) harmonic magnitudes b) third harmonic c) fifth harmonic
Figure 3-2 Harmonic emission of six different PV inverters under sinusoidal and flat-top voltages
The level of dependency between harmonic currents and harmonic voltages is closely linked to the input impedance
characteristic and the design of the internal control algorithms of a PV inverter. It can be determined by e.g. a
Fingerprint analysis [5], where each harmonic voltage is varied in magnitude and phase angle and the response of
harmonic currents is measured. An individual harmonic voltage of order h results usually in harmonic currents of
multiple orders. The ratio of the complex difference of a harmonic current of order k and a harmonic voltage of order
h provides a complex admittance, which can also be interpreted as sensitivity.
( ) ( )
( )
( ) ( )
10 00

 

k k
test refhk
h h
test ref
I I
S
V V
(3.1)
The relation between harmonic currents and voltages of the same order can be considered as auto-sensitivities,
while the relation between harmonic currents and voltages of different order can be considered as cross-sensitivities.
The individual sensitivities can be presented in plots like in Figure 3-3, where Figure 3-3a presents a more robust PV
inverter in comparison to the one in Figure 3-3b. This is indicated by the less number of darker squares in Figure
3-3a. In both figures the horizontal axis presents the applied voltage harmonic orders and the y-axis presents the
current harmonic orders. E.g. applying a 5th harmonic voltage means for the PV inverter in Figure 3-3a a significant
response of 3rd, 5th and 7th harmonic current, while the less robust PV inverter in Figure 3b shows a significant
response at 2nd, 4th, 5th 7th and 8th harmonic current.
a) PV 1 b) PV 4
Figure 3-3 Graphical representation of sensitivity against voltage harmonics
Figure 3-4 presents the auto-sensitivity (diagonal elements in Figure 3-3) of the six PV-inverters in Table 3-1, which
is similar to the magnitude of frequency-dependent input admittance and shows variations by a factor of more than
3 5 7 9 11 13
0
0.2
0.4
0.6
0.8
1
I
(h)
inA
PV 1
PV 2
PV 3
PV 4
PV 5
PV 6
0.2
0.4
0.6
0.8
1
30
210
60
240
90
270
120
300
150
330
180 0
0.2
0.4
0.6
0.8
1
30
210
60
240
90
270
120
300
150
330
180 0
0
5
10
15
>20
dark
bright Sinusoidal
Flat top

Page 30
10. Auto-sensitivity is usually significantly higher than cross-sensitivity, which indicates a dominating impact of the
input impedance (secondary emission) on the emission. Existing cross-couplings represent an “active” behavior of
the PV inverter and are mainly determined by the internal control algorithms as well as possible modulations between
the DC-side and the AC-side.
Figure 3-4 Auto sensitivities of PV-inverters in Table 1
Similar to the THD auto- and cross-sensitivities can be aggregated in order to quantify the total sensitivity of a PV
inverter by a single value.
 
2( )1
  hh
auto
h
S S
n
(3.2)
2( )
( )
1
100% , h k
 
   
 

hk
cross hh
hk
S
S
n S
(3.3)
Table 3-2 presents the total auto- and cross-sensitivity indices for the six PV inverters in Table 3-1. When assessing
the ratio between both indices, again the behavior of each PV inverter is different. Particularly, the very high total
cross-sensitivity of PV inverter 4 indicates a high sensitivity of the internal control algorithms. Additional information
on some of the inverters can be found in [4].
Table 3-2 Overview of total senstivities for PV inverters in Table 3-1
PV Inverter PV 1 PV 2 PV 3 PV 4 PV 5 PV 6
Total Auto-
Sensitivity
Sauto in mA/V 96,1 159,5 150,8 61,4 87,9 158,4
Total Cross-
Sensitivity
Scross in % 32,9 43,8 24,1 448,3 33,2 31,8
3.1.1.3 IMPACT OF OUTPUT POWER LEVEL
Figure 3-5 presents the laboratory measurements (sinusoidal supply voltage, no impedance) of the six PV inverters
in Table 3-1 at three different output power levels, i.e. 10, 50 and 100% of the rated power of the respective PV
inverter.
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
0
50
100
150
200
250
300
350
400
S
(hh)
inmS
PV 1
PV 2
PV 3
PV 4
PV 5
PV 6

Page 31
Figure 3-5 Harmonic Emission of PV inverters in Table 1 at different DC power levels
Highest harmonic current levels are in most cases (except for PV 5 and 6) observed at rated power. It should be
noted that some of the PV inverters get unstable and trip if the output power falls below 10 % of the rated power (cf.
also [6]).
Figure 3-6 shows field measurements of the third harmonic magnitude and phase angle of two PV inverters during
one week of operation [7]. The response of each PV inverter is different and a general behavior cannot be defined.
The small PV inverter of 1.5 kW seems to produce more harmonics during low power generation which agrees with
the conclusions of [6, 8, 9], but the other PV inverter behaves different. Moreover, the variation for the other harmonic
orders is also different from that of the 3rd harmonic. The significant change of the harmonic phase angle in Figure
3-6 can have a significant influence on the cancellation of harmonic currents between PV inverters and other
equipment connected to the same grid. This will be discussed further in Section 3.2.
a) 1,5 KW single phase PV inverter b) 2,5 kW single phase PV inverter
Figure 3-6 Third harmonic current (magnitude and phase angle) of two different PV plants [3]
3.1.1.4 IMPACT OF HARMONIC NETWORK IMPEDANCE
Figure 3-7 shows the laboratory measurements (sinusoidal supply voltage, rated output power) of the six PV inverters
in Table 3-1 under different impedance conditions. The used impedance corresponds to the reference impedance
according to IEC 60725, which consists of a series R-L representation and represents a short-circuit power of 570
kVA.
3 5 7 9 11 13
0
0.05
0.1
0.15
0.2
0.25
I
(h)
inA PV 1
PV 2
PV 3
PV 4
PV 5
PV 6
medium
bright 10 % Pr
50 % Pr
dark 100 % Pr

Page 32
Figure 3-7 Harmonic emission of PV inverters in Table 1 with and without network impedance (acc. to IEC/TR 60725)
In most cases the harmonic current emission increases in presence of the impedance. The main reason is that
harmonic currents emitted by the PV inverters result in harmonic voltage drops at the impedance and consequently,
in a voltage distortion at the supply terminals. This in turn further increases the harmonic currents. However, some
PV inverters show for some harmonic orders almost no change or even a decrease of harmonic current magnitudes.
The reason for this behavior has still to be researched.
3.1.1.5 SUPPLY VOLTAGE MAGNITUDE
The magnitude of the supply voltage also affects the harmonic emission of the PV inverters. Figure 3-7 shows the
variation of the third, fifth and seventh current harmonics emitted by the six PV inverters in Table 3-1 when the supply
voltage (sinusoidal waveform) has a magnitude of 207 V, 230 V (nominal) and 253 V. The measurements were
carried out under laboratory conditions with no impedance and PV inverters operated at rated power.
Again the response of each PV inverter is significantly different from each other, which is linked to the different design.
In most of the cases the PV inverters increase their harmonic currents when the magnitude of supply voltage is
decreased. Inverters PV 4 and PV 6 are the most sensitive ones with variations of the harmonic current magnitudes
of more than 10 % of their rated values (at 230 V), while PV 5 seems to be the most robust.
Figure 3-8 Harmonic emission of PV inverters in Table 3-1 at different supply voltage magntiudes
3.1.2 Medium and large PV-inverters
No systematic laboratory studies on the influence of the different impact factors on the harmonic current emission of
medium and large scale PV inverters are publicly available at the time of this brochure.
In [10] the results of extensive measurements performed in a PV installation with nine large inverters with rated power
of Pr = 100 kW each and a number of small inverters are presented. Each individual current of the large inverters
3 5 7 9 11 13
0
0.05
0.1
0.15
0.2
0.25
0.3
I
(h)
inA
PV 1
PV 2
PV 3
PV 4
PV 5
PV 6
00
0.05
0.1
0.15
0.2
0.25
0.3
0.35
CurrentmagnitudeinA
PV1 PV2 PV3
3rd
harmonic
PV4 PV5 PV6 PV1 PV2 PV3 PV4 PV5 PV6 PV1 PV2 PV3 PV4 PV5 PV6
5th
harmonic 7th
harmonic
Sinus 230V
Sinus 207 V
Sinus 253 V
dark
bright No Imp
Full Imp

Page 33
and the sum of all small inverters has been measured while the inverters have been switched OFF one after each
other. The results for the 5th harmonic are shown in Figure 3-9.
a) 5th harmonic current
(colors indicate individual inverters;
a: large inverters/cos(P) control ON
b: large inverters/cos(P) control OFF
c: sum of small inverters)
b) 5th harmonic voltage at
the busbar
c) Time characteristic of an
individual inverter (voltage and
current)
Figure 3-9 5th harmonic current and voltage during consecutive disconnection of nine large PV inverters
(100 kW each)
The harmonic emission, particularly the 5th and 7th harmonic current of large PV inverters can be significantly higher
than that of small PV inverters (cf. difference between groups a/b and c in Figure 3-9a). A clear dependency between
harmonic currents and harmonic voltages has been identified. This is presented by the “paths” in the complex plane
(Figure 3-9a) for all inverters and in Figure 3-10c as time characteristic for the large PV inverter that has been
switched OFF at last. Consequently, the behavior of large PV inverters equals that of the small inverters with respect
to supply voltage distortion. The difference between group a and b in Figure 3-9a indicates that for this particular PV
inverter type also the setting of cos(P) control has a significant impact on the harmonic current emission, which is
about 50% higher if the control is active. This behavior is most likely caused by a change in the internal control
algorithms.
Further measurement results for a medium-sized inverter can be found in [11].
3.2 Multiple PV inverters (plant level)
In order to analyze the harmonic emission of multiple PV inverters in a single installation, two different aspects have
to be considered: summation of harmonics of multiple PV inverters connected at the same point and the possible
impact on the harmonic network impedance (i.e. harmonic resonances). Both aspects are briefly introduced below
and are discussed with respect to small and medium/large sized PV inverters in two subsections.
Summation of harmonics:
Particularly, the presence of different devices with different topologies at one connection point can cause a diversity
of current harmonic phase angles and subsequently may lead to a lower magnitude of the phasor sum compared to
the arithmetical sum of the harmonic currents. This is known as diversity effect (or cancellation effect) and has a high
influence on the total harmonic current emitted by larger groups of non-linear devices [1].
Two different indices are commonly used for the quantification of the diversity effect: prevailing ratio PR(h) and
summation exponent (h). The prevailing ratio (also known as diversity factor) for an individual harmonic h requires
knowledge about harmonic magnitudes and phase angles and is calculated by:
2
4
6
30
60
240
90
270
120
300
330
0
Fifth Harmonic Currents in A
CurrentinA
Inv 1
Inv 2
Inv 3
Inv 4
Inv 5
Inv 6
Inv 7
Inv 8
Inv 9
Sum Small Inv
1
2
3
4
5
30
210
60
240
90
270
120
300
150
330
180 0
VoltageinV
0 1 2 3 4 5 6 7 8 9
2
3
4
5
6
Time in Mins
VoltageinV
Fifth Voltage and Current of Inverter 9
0 1 2 3 4 5 6 7 8 9
0
2
4
6
8
10
CurrentinA
Fifth Voltage
Fifth Current
ON
OF
FON
OF
F
c
b
a

Page 34
1
1


  


( )
( )
( )
( )
( )
n
h
ih
ih PHA
h n
hARI
i
i
I
IPhasor sum
PR
Arithmetic sum I
I
(3.4)
where
)(h
iI
represents the harmonic current phasor at order h of an individual device i, n is the number of devices
and h the order of the harmonic. The prevailing ratio varies between 0 (perfect cancellation, no prevalence) and 1
(no cancellation, high prevalence). The summation exponent ( )
 h
requires only knowledge of harmonic magnitudes
and is determined by solving the following non-linear equation iteratively:
 1
 ( ) ( )
n
h h
PHA i
i
I I

 (3.5)
A summation exponent ( )
 h
= 1 correspond to
( )h
PR = 1 and represents the arithmetic sum of the harmonic currents
(no cancellation). If ( )
 h
= 2, the phasor sum is equal to the root of sum of squares of the current harmonic
magnitudes. The higher the value of ( )
 h
, the better is the cancellation between the harmonic currents. In case of
perfect cancellation the summation exponent would become infinite. The relation between ( )
 h
and the level of
cancellation is not linear and under some conditions the equation may not have a solution.
Impact on harmonic network impedance:
PV inverters usually include a grid-side filter circuit in order to reduce the supraharmonic emission at switching
frequency and its multiples to the network. This filter circuit utilizes shunt capacitances, which can cause in connection
with the inductance of the network impedance harmonic resonances. The resonance frequency is expected to
decrease with increasing number of connected PV inverters. Such a resonance can lead to an unwanted amplification
of harmonics around the resonance frequency, but might also result in a reduction of harmonic voltages at higher
frequencies (PV inverters act as harmonic filters). The resonant frequency is mainly determined by the short circuit
impedance of the grid and the size of the PV plant, which determines the size of capacitance.
3.2.1 Small PV-inverters
3.2.1.1 SUMMATION OF MULTIPLE UNITS
Similar PV inverters connected to the same supply voltage are expected to have similar harmonic emission
(magnitude and phase angle) and will most likely add up arithmetically. In order to validate this assumption, field
measurements have been performed in a PV plant with a total installed power of 110 kW. It consists of 16 single-
phase inverters of similar type and with rated power of Sr = 7 kW. The results for summation exponent and prevailing
ratio of the odd harmonics until 17th order are shown in Table 3-3 and Table 3-4, respectively. In case no value is
provided in a cell, the harmonic current measurements are below the accuracy threshold and no analysis was
possible.
Table 3-3 Summation Exponents for a 110-kVA-PV-plant
h 3 5 7 9 11 13 15 17
L1 1.003 1.002 1.003 1.005 1.005 1.015 1.037 1.025
L2 1.002 1.002 1.003 1.006 1.011 1.022 1.087 1.039
L3 1.002 1.002 1.005 - 1.010 - - -
Table 3-4 Prevailing ratioS for a 110-kVA-PV-plant
h 3 5 7 9 11 13 15 17
L1 0.998 1.0 0.998 0.994 0.994 0.979 0.946 0.964
L2 0.999 1.0 0.997 0.993 0.986 0.968 0.882 0.943
L3 0.999 0.999 0.995 0.987

Page 35
For this PV plant the results confirm that virtually no cancellation exists between PV inverters of the same type even
at higher orders. This should be taken into account if the harmonic emission of a PV plant is calculated based on
current spectra available for an individual inverter.
3.2.1.2 IMPACT ON HARMONIC NETWORK IMPEDANCE
During the field measurements in the 110 kW PV plant discussed earlier in this section, the harmonic network
impedance was measured while the PV inverters have been switched OFF one after each other. The system used
to measure the impedance as well as the accuracy of the measurements are described in [12]. The results are shown
in Figure 3-10 examplarily for phase L1. Five out of the 16 single-phase PV inverters are connected to phase L1 and
consequently 6 individual curves are shown in the figure.
Figure 3-10 Magnitude of harmonic network impedance during stepwise disconnection of PV inverters (M6 – all PV
inverters connected; M1 – all PV inverters disconnected)
The PV inverters cause a significant resonance in the frequency range between 1.5 kHz and 3 kHz, depending on
the number of connected PV inverters. Without any PV inverter connected (M1) the resonance does not exist. It has
its lowest resonant frequency of about 1.75 kHz if all PV inverters are connected (M6) with a resonance rise of up to
a factor of 2 compared to the impedance without PV inverters connected. Due to the small size of the PV plant and
a high short circuit power at the connection point, the resonance is located at relatively high frequencies. Above
3 kHz the impedance reduction compared to the case without PV inverters will result in a certain amount of damping
of harmonic voltages (act as a filter).
This behavior is caused by the input impedance characteristic of the PV-inverters, which is in most cases capacitive
in a wide range. This is illustrated in Figure 3-11 for the small-sized PV-inverters already discussed in Section 3.1.1
and is also confirmed by studies in [13] and [14].
a) Magnitude characteristic b) Phase angle characteristic
Figure 3-11 Input impedances of PV-inverters in Table 1
With respect to harmonic network impedance studies either a simplified shunt capacitance as found e.g. in [14] or a
more accurate model consisting of a CLC network including series resistances in the shunt branches (capacitors)
seem to be suitable. Neglecting the described input impedance characteristic will usually not lead to useful results.
Anzahl
PV
Anzahl
PV
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
0
10
20
30
40
50
60
70
80
90
100
|Z|in
PV 1
PV 2
PV 3
PV 4
PV 5
PV 6
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
-120
-60
0
60
120
Zin
PV 1
PV 2
PV 3
PV 4
PV 5
PV 6
Number of PVIs

Page 36
3.2.2 Medium and large PV-inverters
3.2.2.1 SUMMATION OF MULTIPLE UNITS
As for the summation of small PV inverters also for the summation of large PV-inverters no significant cancellation is
expected in case of similar inverter type connected to the same supply voltage. This has also been confirmed for one
case by field measurements in a 1 MW PV plant consisting of nine large PV inverters with rated power of Pr = 100 kW.
The distribution of summation exponents and prevailing ratio of selected low odd order harmonics have been
calculated based on 150-cycle-measurments for about 2 hour of operation of all PV inverters and is shown in Figure
3-12.
a) Summation exponent b) Prevailing ratio
Figure 3-12 Summation of nine large PV inverters of the same type
Summation exponents and prevailing ratios are both close to one, which confirms that the current emission of the PV
inverters adds up virtually arithmetical without any considerable cancellation. Even the difference in harmonic
emission caused by different cos(P) control regimes (cf. Figure 3-9a in section 3.1.2) does not impact the
cancellation behavior as harmonic phase angles are almost the same with/without activated cos(P) control (groups
a and b in Figure 3-9a).
3.2.2.2 IMPACT ON HARMONIC NETWORK IMPEDANCE
Field measurements in a larger PV installation (Figure 3-13) confirm the findings from Section 3.2.1 (Figure 3-10).
The connection of 39 PV inverters (rated power Sr = 15 kW) causes a significant resonance at 400 Hz, while it
reduces the impedance considerable between 500 Hz and 2 kHz.
Figure 3-13 Harmonic network impedance at the connection point of a PV plant consisting of 39 PV inverters
(Measurements by University of Applied Science Biel, Switzerland within the research project “Swinging Grids”)
5 7 9 11 13
1
1.005
1.01
1.015
1.02
1.025
1.03
1.035
1.04
Harmonic Order
SummationExponent
5 7 9 11 13
0.91
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
Harmonic Order
DiversityFactor

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