Fig. 2.2 Examples of small electronic devices containing power electronics (plus an incandescent
lamp). Note the difference in vertical scale between the different waveforms.
DOCTORAL THESIS
On High-Frequency Distortion in Low-Voltage Power Systems -Anders Larsson- Luleå University of Technology Department of Engineering Sciences and Mathematics Division of Energy Engineering
Abstract
Power quality is a subject that has received a lot of attention during the last 10 to 20
years, both in industry and in academia. Power quality concerns interaction between the
power grid and its customers and between the power grid and equipment connected to it,
reflected in voltages and currents. Research and other developments in this area have to a
great extent concentrated on relatively slow and low-frequency phenomena, with the main
emphasis being on voltage dips (reductions in voltage magnitude with duration between
about 50 ms and several seconds) and low-frequency harmonics (waveform distortion by
frequency components up to about 2 kHz). These phenomena are reasonably well
understood and several standards cover the area.
For higher-frequency phenomena, above 2 kHz, there is no such general understanding,
nor is there anything close to a complete set of standards covering this area. Modern energy
efficient equipment connected to the grid, like fluorescent lamps but also solar panels,
often uses switching technology, with switching frequencies that can range from a couple of
kHz up to several hundreds of kHz. The grid is also used for communication of e.g. meter
readings, system controls etc. This so-called power-line communication is using the same
frequency range.
The main frequency range of interest for this thesis has been the range from 2 to 150
kHz. There are two completely different measurement methods covering this frequency
range: time-domain based and frequency-domain based. Time domain based measurements
are used throughout the thesis. This gives an opportunity to choose between different
analysing tools where among others the joint time-frequency domain has shown to be a
useful tool for describing waveform distortion in our frequency range of interest.
The majority of the measurements presented in this thesis have been directed towards
fluorescent light powered by high frequency ballasts. This type of load has been, due to
stringent harmonic limits, one of the first to use a more advanced switching technology
called active power factor correction. This technique is also getting more frequently used in
other small-power equipment, like computers. Installations of lights in stores etc. normally
contain a large number of ballast connected together and the interaction is of importance,
for example for setting emission and immunity standards.
The measurements on ballasts presented in this work have shown that distortion in the
frequency rage 2-150 kHz comes in three types: narrowband distortion; wideband
distortion; and recurrent oscillations. The recurrent oscillations are a new type of powerquality
disturbance that had not been recognized as such before. The measurements
further have shown that the three types of distortion spread in a completely different way
from the individual devices to the grid. This knowledge is essential for the setting of
emission requirements on energy-efficient equipment.
LINK ORIGINAL:
http://pure.ltu.se/portal/files/32571608/Anders_Larsson.pdf
