J.J. Gutierrez

Flicker Measurement System for Wind Turbine Certification

There is currently a shortage of equipment specifically designed to measure and assess power quality in wind turbines in accordance with the IEC standard. This deficiency negatively affects the work of wind park installation companies facing the certification process. We have designed a system to measure and assess flicker in wind turbines in accordance with the standard. The system consists of two modules. The first is a signal register to store the established voltage and current series as a function of the wind speed; the second module processes these stored series in accordance with the standard specification to precisely obtain the required flicker parameters of the wind turbine. Our system facilitates the certification process and is sufficiently flexible to cope with changing standards.

A Review of Flicker Severity Assessment by the IEC Flickermeter

This paper presents an analysis of the flicker assessment by block 5 of the International Electrotechnical Commission (IEC) flickermeter. We compare the values provided by the IEC flickermeter from field measurements and the complaints from the customers. We also analyze the behavior of the IEC flickermeter when subject to signals containing nonuniform rectangular fluctuations. Finally, as it is not easy to find a consistent relationship between the true annoyance and the flicker severity, we describe some laboratory subjective tests with a small group of people, carried out to assign a true quantitative value of annoyance to a nonuniform light fluctuation from real situations. Block 5 of the IEC flickermeter derives its estimate of the annoyance accurately only for uniform fluctuations. In realistic conditions, when the voltage fluctuations are not uniform but have varying frequencies and amplitudes, the IEC flickermeter does not assess the true flicker annoyance precisely.

Linearity of the IEC Flickermeter Regarding Amplitude Variations of Rectangular Fluctuations

This paper studies the linearity of the IEC flickermeter as a function of the amplitude of rectangular voltage fluctuations DeltaV/V. The behavior of blocks 2, 3, 4, and 5 of the flickermeter is linear in DeltaV/V, the nonlinear behavior experimentally observed is due to block 1. The theoretical analysis presented provides a quantitative justification of this phenomenon

Distinction of ventricular fibrillation and ventricular tachycardia using cross correlation

The accurate discrimination of ventricular tachycardia (VT) from ventricular fibrillation (VF) is an important issue in automated external defibrillator (AED) and other cardiac monitoring systems. The correlation function of the ECG signal is an adequate tool for detecting irregularities or noise in signals. Therefore, methods for VF/VT discrimination based on the autocorrelation of the ECG signal and on the cross correlation of the ECG signal with different templates have been proposed. Our work is focused on the use of the cross correlation of the ECG signal with a segment of the same ECG signal, instead of using a given template. The developed algorithm has been tested on a database consisting of 179 human VF and 74 human VT records. The new algorithm classifies accurately 313 VF windows (90.2% sensitivity) and 179 VT windows (96.75% sensitivity). These results improve those obtained from other techniques, considered as a reference, for the same records database.

A simple effective filtering method for removing CPR caused artefacts from surface ECG signals

Cardiopulmonary Resuscitation (CPR) introduces strong interference on the surface ECG, corrupting any diagnosis of the cardiac rhythm. In this work a filtering method is proposed to remove the CPR artefact from Ventricular Fibrillation (VF) signals. It is a notch filter adapted to the fundamental frequency of the CPR artefact. It is designed using the mean time interval between compressions characteristic of each CPR artefact. The method has been tested with a set of 17 artefact signals and 191 VF signals, recorded in real out-of-hospital assistances. For the different corruption levels tested (i.e. SNR of -10, -6, -3, 0, 3 and 3 dB), the mean SNR values restored are: -3.16, 0.39, 2.77, 4.79 and 6.38 dB. The positive effect of the filtering on the rhythm classification algorithm of an AED has been evaluated. The sensitivities values after filtering are: 52.26%, 79.3%, 90.48%, 94.91% and 96.64% respectively

Influence of the Carrier Phase on Flicker Measurement for Rectangular Voltage Fluctuations

This paper presents an analysis of the influence of the phase relationship between the fundamental frequency and the rectangular voltage fluctuation on flicker measurements made by the International Electrotechnical Commission (IEC) flickermeter. We analytically studied the origin of the deviations for a set of significant fluctuation frequencies. We found that the nonlinear behavior of the squaring multiplier of the IEC flickermeter produces an additional dc component in instantaneous flicker sensation Pinst for several rectangular fluctuation frequencies. The value of this dc component depends on the phase relationship between the fundamental and the fluctuation frequency. The analysis of this paper has contributed to clarify the definition of some performance tests of the IEC flickermeter standard IEC 61000-4-15 ed.2. This will help develop calibration and verification methods for the flickermeters.

A Precise Analysis of the IEC Flickermeter When Subject to Rectangular Voltage Fluctuations

The Pst measured using the International Electrotechnical Commission (IEC) flickermeter for a rectangular fluctuation is discontinuous for certain values of the frequency of fluctuation. These discontinuities do not represent a real physiological perception of flicker, but they are a consequence of the nonlinear behavior of blocks 1, 4, and 5 of the IEC flickermeter. We have theoretically proved the origin of these discontinuities, and we have experimentally identified and quantified them. Although these discontinuities do not influence the Pst values recorded in the field, they are an intrinsic characteristic of the flickermeter model proposed in the IEC 61000-4-15 standard. This paper contributes to a better understanding of how the IEC flickermeter works when subject to rectangular fluctuations. Furthermore, the identification and quantification of these discontinuities can help to improve the design of the performance tests of the flickermeter.

Effect of the Sampling Rate on the Assessment of Flicker Severity Due to Phase Jumps

This paper presents an analysis of the effect of the sampling rate on the calculation by a digital flickermeter of the flicker severity caused by phase jumps. The new edition of the IEC 61000-4-15 standard includes an innovative test aimed at verifying that a flickermeter works properly during a phase jump event. Since phase jumps are rapid angle changes, it seems that a high sampling rate should be used by a digital instrument. This requirement could be too demanding, so we have studied this hypothesis by defining three analytical signal models. One is based on the characterization of ideal phase jump sequences and the other two are based on the definition of realistic band-limited signals containing phase jumps. We found that the minimum sampling rate necessary to pass that test is not as demanding as expected. Practical experiments made by an actual generation and acquisition system confirm this conclusion. A typical sampling rate of 3200 S/s, usually used in commercial flickermeters, becomes clearly sufficient to pass the test. However, we give notice that passing this test could not guarantee accurate results when the phase jumps are different from those specified by the standard.

A New Alternative for the Input-Voltage Adaptor of the IEC Flickermeter

In this paper, we present a study of the linearity of the International Electrotechnical Commission (IEC) 61000-4-15 flickermeter when subject to rectangular fluctuations of different amplitude. We show, both analytically and through simulation, how the scaling in block 1 causes the nonlinear response of the flickermeter. While the standard proposes scaling methods based on the rms value of the input voltage, we introduce an alternative method based on the mean value of the rectified input voltage. The measured Pst using the new scaling method has a linear relationship to the amplitude of the voltage fluctuations.

Singular Frequencies in Rectangular Fluctuations in the IEC Flickermeter

A detailed observation of the IEC flickermeter subject to rectangular voltage fluctuations indicates the presence of small discontinuities for a set of fluctuation frequencies. These discontinuities are not observed in the real lamp-eye-brain model. This work provides the theoretical framework for the analysis of this phenomenon, a consequence of the nonlinear variance estimator model used in block 4 of the flickermeter. This effect has a limited impact on the field performance of the flickermeter but should be avoided from a conceptual point of view