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Response of Flicker Assessment Algorithms to Interharmonic Distortion Patterns
Abstract
An alternative algorithm for estimating flicker severity from voltage measurements was developed and published in literature and is currently under consideration by IEC SC77A WG2 for replacing the current standard flickermeter algorithm as described in IEC 61000-4-15. This paper compares the response of the two algorithms to voltage components and modulations with frequency above the fundamental.
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With two electrical analogs of the brightness system it is shown that at a low luminance level (<5 photons) and in the low-frequency region (<2 cps), when under the special visual conditions no attenuation in the system occurs and with a symmetrical luminance variation such as a sinusoidal modulation or a square-wave modulation with a 1:1 on-off ratio, half the crest-to-trough value of the percentage variation at flicker fusion equals the internal threshold value r0; but with an asymmetrical variation such as a square-wave modulation with a 1:3 on-off ratio, it is the crest value of the periodical percentage variation above the mean luminance level which at flicker fusion equals the internal threshold value r0. At high luminance levels an overshoot in the low-frequency region occurs with both forms of square-wave modulation in accordance with the shape of the attenuation characteristic (AC) of the system under the experimental circumstances. At the steep slope of the ACs for the whole luminance range in cone vision, half the crest-to-trough value of the Fourier fundamental percentage variation at the site of the threshold mechanism located anywhere in the system, equals the internal threshold value r0 at flicker fusion.
Voltage variation is one of lamps flickering main cause; thus evaluation of a disturbing light flicker is a part of volt-age quality classification. The instrument for flicker level measurement by means of voltage variation analysis is named flickermeter and is specified in standard EN 61000-4-15. The flickermeter is a specialized analyzer modeling response of a chain consisting of reference 60W incandes-cent lamp – eye – brain of an average observer. Hence, other lamp types like discharge are mainly used in illumina-tion systems at present, significant difference between flicker measurement using the standard flickermeter and observation can appear. In the paper, there is proposed a light flicker measurement method based on analysis of an irradiance (radiant flux) waveform, where the output flicker index is independent on the lamp type. With regard to ex-pected properties the proposed light-flickermeter can be called objective flickermeter. Nevertheless the range of application of the objective flickermeter is limited as it is also shown.
The amplitude and phase modulation effects of waveform distortion in power systems are analyzed. Recalls on Amplitude Modulation (AM) and Phase Modulation (PM) are given with particular reference to spectral components. Then, simple inverse formulas are obtained to demonstrate that summations of one or more small tones frequencies to a given tone of interest can always be interpreted in terms of AM and PM. The usefulness of AM and PM representation, in particular in the presence of interharmonic tones, is demonstrated with reference to simple case-studies and practical applications.
The aim of the paper is to describe procedures for systematical determination of immunity of lamps to supply voltage variations caused by interharmonics. The curve of lamp immunity is presented as an interharmonic magnitude versus interharmonic frequency curve and is called interharmonic-flicker curve. The interharmonic-flicker curves of lamps are determined by utilizing a modified concept for measurement of a lamp gain factor in frequency domain and by utilizing the published limits on voltage flicker. Another described method for establishing the interharmonic-flicker curves of lamps is the method based on measuring the luminous flux flicker curve which is defined by utilizing the published limits on voltage flicker as well. Further a complex measured data file of interharmonic-flicker curves in various combinations of discharge lamps (fluorescent lamps and high intensity discharge lamps) and ballasts are pointed. Measured and compared combinations include various types of discharge lamps, various wattages, modes of operation of the ballast and its specific designs and dimensioning of circuit elements etc. Finally, determined interharmonic-flicker curves of chosen lamps are used for proposal approach how to revise the compatibility level for interharmonic voltages relating to flicker.
Several changes and adaptions in the design of the current IEC flicker meter (IEC 61000-4-15) were proposed in literature. These changes relate mainly to Block 5 of the flicker meter, i.e., the calculation of the flicker severity index (Pst). This paper provides some background knowledge on the rationale behind the proposed changes and identifies and quantifies the differences between the two flicker meter implementations. The comparison is based on measurements in laboratory and field as well as experiments involving human observers. The aim is to contribute to the ongoing discussion in IEC SC77A WG2 about the suitability of the current and proposed implementations for voltage quality monitoring and its capability to reflect the irritation level of human observers for artificial lighting.
The paper reports on the experimental evaluation and classification of LED lamps for light flicker sensitivity. After the description of the experimental setup designed for tests, a classification based on the driving circuits is proposed. For each class, the circuit description and the Gain Factor (GF) curves versus interharmonic frequencies are reported. Finally, a comparison of the different GF curves is presented to show the Light Flicker sensitivity of the tested LED lamps.
As LEDs respond almost instantaneously to the driving current, they are susceptible to Temporal Light Artefacts (TLAs). We used the results of more than 10 perception studies to quantify the visibility of these TLAs. The developed and validated visibility measures can be used to design LED light sources with high lighting quality in various applications.
The paper is focused on power flow control in energy systems with grid-on renewable energy sources employing time-proportional controlled and phase angle controlled resistive loads (like boilers) to balance energy produced by the sources. The system operational properties are described and major mechanisms affecting power and voltage quality are identified. Contributions of the pulse-width regulated loads to voltage flicker, system harmonics and to high frequency conducted disturbances in audio range (2–250 kHz) are studied on a test system realized in a small laboratory measure. Finally, on the basis of experimental results, limiting power of regulated resistive loads from point of view of flicker and harmonic current emissions is estimated.
This paper presents a tunable flickermeter based on a generalized lamp model that is able to account for lamp technologies different from incandescent. The generalized lamp model is based on the use of only three input parameters derived from the type of the lamp and its electrical circuit. The flickermeter concept and scheme are described. Compliance with the Standard IEEE 1453 (IEC 61000-4-15:2010) is demonstrated and performances for different lamp technologies are demonstrated by means of numerical and laboratory experiments.
The IEC 61000-4-15 standard defines a flickermeter that is universally accepted as the meter used for the objective measurement of a disturbing light flicker. The accurate results provided by the IEC flickermeter under uniform fluctuations stand in contrast with its unpredictable behavior under real conditions when voltage fluctuations are not uniform over time. Under nonuniform fluctuations, the IEC flickermeter can indicate wrong values, and this could explain the absence of users’ complaints at sites where high flicker levels were measured. This work presents a new strategy for flicker measurement that overcomes the deficiencies presented in the IEC flickermeter, properly relating flicker severity values and temporal evolution of the fluctuation. The manuscript describes in detail the functional and design specifications of the new strategy, as well as the results obtained during the validation process in which the IEC flickermeter and the new strategy were subjected to input signals with different temporal fluctuation patterns. The manuscript also presents a comparison between the response of the two strategies to real voltage signals, which are complex and nonuniform in nature. The results confirm the differences between both strategies, despite both meet the same requirements established by the standard.
The flickermeter described in International Electrotechnical Commission (IEC) Standard 61000-4-15 is widely used to quantify the voltage flicker level in practical applications. The IEC flickermeter generally performs well for incandescent lamps. However, it fails to measure the flicker of non-incandescent lamps caused by some ranges of interharmonics. This paper suggests modifying the existing IEC flickermeter by adding a new block to it in order to enable accurate measurement of the flicker caused by high-frequency interharmonics. A digital implementation of the proposed modified flickermeter is tested, showing encouraging results. The error of the modified flickermeter is very low compared to the original one, even for the worst conditions. The changes implemented in the flickermeter do not affect its regular performance measuring incandescent lamp flicker due to amplitude modulation, making it a more generic flickermeter version. An arc furnace simulated by PSCAD/EMTDC is used to check the performance of this flickermeter.
1. The threshold intensities of various transient changes from a base line luminance in the mid‐photopic range have been measured.
2. Rectangular changes in luminance show no difference between increments and decrements, a threshold intensity decreasing inversely with durations up to 16 msec, a lesser reduction in threshold up to 64 msec and for longer durations a slight increase in threshold.
3. Two brief flashes separated by an interval show incomplete summation at 10 msec, almost no summation at 65 msec and a second reduction in threshold at 100 msec.
4. Two brief flashes in opposite directions negate each other at very small intervals but complement each other at longer intervals, maximally at 65 msec.
5. A model of the detector system is proposed that passes the stimulus wave form through a band‐pass filter and takes a running average of the variance of the filter output. Threshold is reached if this average attains a certain level.
6. The model satisfactorily accounts for the observations that any two wave forms occurring together and not exceeding a total of 100 msec in duration will interact so that the relationship between them at the combined threshold will be an ellipse; and that this ellipse will have no obliquity if one wave form is the differential of the other.
7. Measurements of the thresholds of two brief flashes separated by various intervals define the attenuation characteristics of the band‐pass filter invoked to explain the thresholds of repetitive stimuli.
8. The model reconciles the apparent disparity between the thresholds of single flashes of varying duration and pairs of flashes of varying interval.
9. The statistical efficiency of such a system is discussed.
Electromagnetic compatibility (EMC) -Part 4-15 Testing and measurement techniques -Flickermeter -Functional and design specifications
IEC, "IEC 61000-4-15:2010 Electromagnetic compatibility (EMC) -Part 4-15 Testing and measurement techniques -Flickermeter -Functional and design specifications," {IEC} Std. 61000-4-15, pp. 1-58,
2010.
Equipment for general lighting purposes -EMC immunity requirements -Part 1: An objective voltage fluctuation immunity test method
IEC, "IEC TR 61547-1:2015 Equipment for general lighting purposes -EMC immunity requirements -Part 1: An objective voltage fluctuation
immunity test method," {IEC} 61547, 2015.
Electromagnetic compatibility (EMC) -Part 2-2: Environment -Compatibility levels for low-frequency conducted disturbances and signalling in public low-voltage power supply systems
IEC, "IEC 61000-2-2:2002 Electromagnetic compatibility (EMC) -Part
2-2: Environment -Compatibility levels for low-frequency conducted
disturbances and signalling in public low-voltage power supply
systems," {IEC} 6100-2-2:2002, 2002.