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Title:
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Estimation of the potential to pollute the electricity network with harmonics due to the use of small micro generators with inverters; Measurements of the Complex Conductance, an additional test method for inverters
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Author(s):
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Heskes, P.J.M.; Rooij, P.M.; Cobben, J.F.G.; Oldenkamp, H.E.
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Published by:
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Publication date:
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ECN
Energy in the Built Environment
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1-8-2004
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ECN report number:
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Document type:
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ECN-C--04-087
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ECN publication
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Number of pages:
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Full text:
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31
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Download PDF
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Abstract:
Currently the total power of PV-generators in the built environmentis small compared to the power of the distribution transformer. With
the steady growth of PV installations, the penetration of PV-generators
in the built environment will grow as well. This will lead to new phenomena,
which may eventually result in grid instabilities [3]. In order to be
able to predict whether these phenomena will occur, a simple though
accurate harmonics model for the grid, the cables the loads and the
inverters is presented, as well as a measuring method to determine the
necessary frequency dependent parameters of inverters and loads in general.
In a previous project [4] a preliminary harmonic interaction test method
for inverters was proposed, this result was an important input for this
project.
This project focuses on harmonic pollution of the grid voltage at large-scale
implementation of small grid connected micro generators with inverters,
like photovoltaics. The goal of this project is to lay down a test method
to qualify inverters on this subject. The upper lying target is to contribute
to a new standard on inverter testing, NTA 8494 [1] (Netherlands Technical
Agreement), a guideline for inverter testing.
In the first part of this report the 'Complex Conductance Measurement
Method' has been critically reviewed both theoretically and practically.
In the second part of this report the 'Complex Conductance Measurement
Method' has been adapted to situations in practice. With the latter
method a few measurement examples are presented and discussed.
The measuring method described in this report can be used to determine
the frequency dependent parameters of inverters and loads. The results
depend strongly on the inverter topology. Negative values for the normalized
conductance appear to be possible for some types of inverters. As this
may result in grid instabilities, inverters with negative conductance
should only be used in projects with large-scale implementation of PV
when sufficient compensation is available.
Results of the mentioned Measurement Method can easily be used in a
more complex simulation to predict the level of harmonic distortion
and the possibility of resonance-effects.
From the experiments can be remarked that a further research on the
behaviour of different kinds of loads in relation to harmonics is needed
to get familiar with test results.
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