Flicker Components Research Articles

Dynamic Mode Decomposition Based Approach for Accurate Measurement of Voltage Flicker Components

In this work, an accurate estimation of the amplitudes and frequencies of the flicker components has been proposed using dynamic mode decomposition. The proposed method consists of Hilbert transform for envelope extraction, dynamic mode decomposition (DMD) for spectral analysis, and finally, the assessment of flicker severity index (Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> ) based on the eye-brain model. The DMD method constructs a shifted-stack matrix of the voltage signal, and thereby it is processed through singular value decomposition for extracting the dominant signal parameters. To verify the effectiveness of the proposed technique, voltage flickers are considered with single flicker and multiple flicker components. It is also investigated in presence of sensitive conditions such as harmonic disturbance, power frequency deviation, noisy environment, phase jumps, and transients. The simulation results are compared with the existing techniques in terms of the relative errors of flicker parameters. Finally, a hardware prototype is developed for practical flicker measurement and the proposed algorithm has been implemented on the Raspberry pi board. The experimental results are presented and compared with simulation findings of the proposed technique to prove its applicability.

Analytic Mode Decomposition and Windowed Three-Point Interpolated Chirp-Z Transform for Voltage Flicker Components Detection

The extensive development and applications of new energy and power electronics technologies have a significant impact on grid voltage fluctuations and flicker. This paper proposes an accurate method based on analytic mode decomposition (AMD) and windowed three-point interpolated Chirp-Z transform (WICZT) to detect voltage flicker components. The voltage flicker envelope signal is extracted by AMD through the multiplicative result of voltage flicker signal and synchronizing voltage signal to avoid spectrum aliasing, without the analog filter. Then, WICZT based on six-term cosine window is presented to obtain the voltage flicker parameters, which can enhance the frequency resolution and effectively reduce the error caused by the spectral leakage due to the non-synchronous sampling and constraints of fence effect. Based on the proposed method a voltage flicker parameter detection system is developed and implemented in a PXI platform, using LabVIEW. The simulation and experimental results show that the proposed algorithm can effectively provide accurate detection and analysis in cases of single frequency modulation, multi-frequency modulation, harmonic contamination, fundamental frequency deviation and noise interference.

Analysis of Timing Accuracy and Sensitivity in a RF Correlation-Based Impulse Radio Receiver With Phase Interpolation for Data Synchronization

This paper presents an analytical method for the performance evaluation of the correlation-based impulse radio (IR) receivers, which detect the data based on synchronizing the received signal with a locally generated template pulse. In this paper, a phase interpolation technique is employed to preserve synchronization accuracy with low power consumption. The analytical method computes the spectral density of jitter at the phase interpolator output, resulting from both flicker and thermal noise components. The analysis considers the aliasing phenomenon due to the sampling of the noise to predict the induced jitter accurately. Bit error rate (BER) of the receiver is also statistically estimated in terms of the induced jitter on the template pulse, the noise effect of the receiver chain, and the template signal level. The proposed estimation procedure is validated by comparing its results with transient noise simulations. It is shown that increasing the template signal range in the correlator and improving the linearity of the phase interpolation transfer curve, at a given power consumption, enhances the receiver sensitivity by 2 and 3.5 dB, respectively. The BER estimation results also reveal that the effect of the template signal jitter on the sensitivity of the correlation-based IR receivers becomes dominant with the increasing input signal level.

Power system frequency estimation based on an orthogonal decomposition method

In recent years, several frequency estimation techniques have been proposed by which to estimate the frequency variations in power systems. In order to properly identify power quality issues under asynchronously-sampled signals that are contaminated with noise, flicker, and harmonic and inter-harmonic components, a good frequency estimator that is able to estimate the frequency as well as the rate of frequency changes precisely is needed. However, accurately estimating the fundamental frequency becomes a very difficult task without a priori information about the sampling frequency. In this paper, a better frequency evaluation scheme for power systems is proposed. This method employs a reconstruction technique in combination with orthogonal filters, which may maintain the required frequency characteristics of the orthogonal filters and improve the overall efficiency of power system monitoring through two-stage sliding discrete Fourier transforms. The results showed that this method can accurately estimate the power system frequency under different conditions, including asynchronously sampled signals contaminated by noise, flicker, and harmonic and inter-harmonic components. The proposed approach also provides high computational efficiency.

Application of a Hybrid Method for Power System Frequency Estimation with a 0.2-second Sampled Period

The signal processing technique is one of the principal tools for diagnosing power quality (PQ) issues in electrical power systems. The Discrete Fourier Transform (DFT) is a frequency analysis technique used to process power system signals and identify PQ problems. However, the DFT algorithm may lead to spectral leakage and picket-fence effect problems for asynchronously sampled signals that contain harmonic, inter-harmonic, and flicker components. To resolve this shortcoming, a hybrid method for frequency estimation based on a second-level DFT approach and a frequency-domain interpolation algorithm to obtain the accurate fundamental frequency of a power system is proposed in this paper. This method uses a second-level DFT to compute the cosine and sine parts for the fundamental frequency components of the acquired signals. Then, a frequency-domain interpolation approach is adopted to determine the amplitude ratio for the cosine and sine parts of the system’s fundamental frequency. A set of mixed signals with harmonic, inter-harmonic, and flicker components with the fundamental frequency deviation is used. The evaluation results demonstrate the superiority of the new method over other approaches for assessing asynchronously sampled signals contaminated with noise, harmonic, inter-harmonic, and flicker components.

Noise parameters of defects of the emitting surface of thermionic cathodes

A noise model in which fluctuation noise of output current is determined by weakly emitting fragments of thermionic cathode working in the saturation regime (defects on the emitting surface) is proposed. The measured noise characteristics of the shot and flicker components of noise can be used to determine distribution of defects with respect to emission current densities and the noise parameters of defects. The relation of noise parameters and the degree of degradation of cathode is analyzed using the pulsed emission current at relatively long working times of dispenser cathodes with the W–Re sponge and Os coating. Preliminary results show that that proposed noise parameters can be used for the development of working methods for estimation of cathode quality.

Improved Teager Energy Operator and Improved Chirp-Z Transform for Parameter Estimation of Voltage Flicker

Effective estimation of voltage flicker components plays an important role in distribution systems for either flicker meters or flicker compensators. A novel approach has been presented in this paper to accurately estimate voltage flicker components by using the improved Teager energy operator (ITEO) and the improved chirp-Z transform (ICZT). The error correction factor $K$ of the Teager energy operator is presented and ITEO is established to reduce the extraction errors of voltage flicker waveform. ICZT is used to extract the frequency and magnitude of the voltage envelope which is corrected by the $K$ factor of ITEO. The effects of signal sampling rate, sampling number, spectrum subdivision points of ICZT, voltage harmonics and interharmonics, frequency fluctuation, and white noise are investigated. The implementation of the proposed approach in the digital-signal-processor platform is also introduced. Multiple simulation and experimental test application results validate the accuracy and efficiency of the proposed approach.

An Accurate Solution Procedure for Calculation of Voltage Flicker Components

Voltage flicker is one of many serious power quality disturbances, which would deteriorate the stability and operation efficiency of a power system. Effective evaluation of flicker severity plays an important role in the monitoring and control of developing advanced metering infrastructure. Since the evaluation process for voltage flicker is complicated, some inaccurate intermediate results may give rise to the propagation of estimation errors. Therefore, an accurate solution procedure for the calculation of voltage flicker components is proposed in this paper. With the extraction technique for envelope signal and high-frequency resolution mechanism for flicker spectral analysis, the superior performance to achieve the instantaneous flicker severity evaluation can be obtained.

Effective Voltage Flicker Calculation Based on Multiresolution S-Transform

This paper introduces a new method for calculating the voltage flicker characteristics. A voltage waveform envelope, which captures the main flicker characteristics, is obtained by calculating rms values instantaneously using a moving window approach. The S-transform (ST) is then used to extract the voltage flicker components for each frequency. The multiresolution characteristic of the ST provides timing data which presents a “Magnitude-Time” and “Frequency-Time” contour for tracking flicker. The effects of signal sampling rate, voltage harmonics, and frequency variation on the calculation results are considered. The results show that the proposed method can identify the frequency and magnitude of flicker components in a short time and with very good precision. This method is independent of calculating the fundamental frequency of the system, which has been used for flicker index calculation. Finally, the method is tested on a real voltage flicker signal sampled from the voltage signal of an electric arc furnace. The results are quite promising.

Improvement in Computation of Δ V10Flicker Severity Index Using Intelligent Methods

The <TEX>${\Delta}\;V_{10}$</TEX> or 10-Hz flicker index, as a common method of measurement of voltage flicker severity in power systems, requires a high computational cost and a large amount of memory. In this paper, for measuring the <TEX>${\Delta}\;V_{10}$</TEX> index, a new method based on the Adaline (adaptive linear neuron) system, the FFT (fast Fourier transform), and the PSO (particle swarm optimization) algorithm is proposed. In this method, for reducing the sampling frequency, calculations are carried out on the envelope of a power system voltage that contains a flicker component. Extracting the envelope of the voltage is implemented by the Adaline system. In addition, in order to increase the accuracy in computing the flicker components, the PSO algorithm is used for reducing the spectral leakage error in the FFT calculations. Therefore, the proposed method has a lower computational cost in FFT computation due to the use of a smaller sampling window. It also requires less memory since it uses the envelope of the power system voltage. Moreover, it shows more accuracy because the PSO algorithm is used in the determination of the flicker frequency and the corresponding amplitude. The sensitivity of the proposed method with respect to the main frequency drift is very low. The proposed algorithm is evaluated by simulations. The validity of the simulations is proven by the implementation of the algorithm with an ARM microcontroller-based digital system. Finally, its function is evaluated with real-time measurements.

Lp norm approaches for estimating voltage flicker

It is important to accurately estimate instantaneous voltage flicker magnitudes and frequencies in order to correctly evaluate voltage fluctuations. Voltage flicker is a problem in electric power quality. Different approaches used to determine the magnitude of the voltage flicker have been presented: measurement methods generally use a flickermeter device. Simulation methods require a computer model of the disturbing load and the flickermeter. Calculation methods necessitate a simplified empirical formula. Estimation algorithms are based on the estimation of the voltage flicker components. In this paper, two models of voltage flicker are discussed: L p estimation algorithms utilizing L 1, L 2 and L ∞ norms are used to estimate the voltage magnitudes of the flicker signals as well as the fundamental voltage magnitude. The main result is that it is possible to design an L p estimator to identify flicker frequency and amplitude from time series measurements.

A Novel Algorithm for Precise Voltage Flicker Calculation by Using Instantaneous Voltage Vector

A novel approach has been presented in this paper to calculate voltage flicker components precisely by using instantaneous voltage vectors. After the voltage waveform of a phase is recorded, the smart discrete Fourier transform can be used to obtain the system frequency and magnitude. Then, the other two phases are assumed perfectly sinusoidal to construct a virtual three-phase system. The instantaneous voltage vectors are calculated from the virtual three-phase voltages. Finally, the fast Fourier transform is used to obtain the voltage flicker components from instantaneous voltage vectors. The flicker components of the other two phases can be calculated by repeating the procedure. The flicker values of three phases are calculated individually and separately. The effects of jump-sampling, harmonics, power frequency shifting, and sampling rates are investigated. The calculation ability of this approach is compared with the traditional indirect demodulation method. Some given waveforms and field measured waveforms of arc furnace loads with voltage flicker disturbances are used to show the goodness of this approach. From the results, this approach could calculate flicker components accurately with short calculation time by using small size data. It also avoids the frequency leakage effect.

Voltage flicker estimation based on linearization and L/sub p/ norms

This paper presents an approach to estimate voltage flicker components magnitudes and frequencies. The approach is based on L/sub p/ norms (p = 1, 2 and /spl infin/) and Taylor series linearization. Effects of sampling frequency, number of samples, time interval, and noise are introduced. The main result is that it is possible to design an L/sub p/ estimator to identify flicker frequency and amplitude from time series measurements.

Effective voltage flicker calculation algorithm using indirect demodulation method

The voltage flicker is one of the major power quality disturbances in a weak power system. Better measurement and limitation techniques are always desired. An effective and accurate calculation method is presented to obtain the voltage flicker components and the 10 Hz equivalent value. By using the indirect demodulation method, the RMS values of a voltage waveform are calculated cycle by cycle to obtain the envelope. Then the fast Fourier transform (FFT) is used to obtain the flicker components. This method can increase the computing speed and reduce the hardware requirement in a power quality instrument when the FFT is used. The effects of sampling rate, harmonics, and system frequency shifting are investigated. The latter two are common disturbances in addition to the voltage flicker when arc furnace loads are connected in a weak power system. A calibration procedure is used to improve the frequency leakage effect and increase the calculation accuracy. The calculation results from given voltage flicker waveforms and field measured waveforms reveal the effectiveness of the proposed method. It can be used in both 50 and 60 Hz systems.

Decoding visual information from a population of retinal ganglion cells.

Decoding visual information from a population of retinal ganglion cells. J. Neurophysiol. 78: 2336-2350, 1997. This work investigates how a time-dependent visual stimulus is encoded by the collective activity of many retinal ganglion cells. Multiple ganglion cell spike trains were recorded simultaneously from the isolated retina of the tiger salamander using a multielectrode array. The stimulus consisted of photopic, spatially uniform, temporally broadband flicker. From the recorded spike trains, an estimate was obtained of the stimulus intensity as a function of time. This was compared with the actual stimulus to assess the quality and quantity of visual information conveyed by the ganglion cell population. Two algorithms were used to decode the spike trains: an optimized linear filter in which each action potential made an additive contribution to the stimulus estimate and an artificial neural network trained by back-propagation to match spike trains with stimuli. The two methods performed indistinguishably, suggesting that most of the information about this stimulus can be extracted by linear operations on the spike trains. Individual ganglion cells conveyed information at a rate of 3.2 +/- 1.7 bits/s (mean +/- SD), with an average information content per spike of 1.6 bits. The maximal possible rate of information transmission compatible with the measured spiking statistics was 13.9 +/- 6.3 bits/s. On average, ganglion cells used 22% of this capacity to encode visual information. When a decoder received two spike trains of the same response type, the reconstruction improved only marginally over that obtained from a single cell. However, a decoder using an ON and an OFF cell extracted as much information as the sum of that obtained from each cell alone.Thus cells of opposite response type encode different and nonoverlapping features of the stimulus. As more spike trains were provided to the decoder, the total information rate rapidly saturated, with 79% of the maximal value obtained from a local cluster of just four neurons of different functional types. The decoding filter applied to a given neuron's spikes within such a multiunit decoder differed substantially from the filter applied to that same neuron in a single-unit decoder. This shows that the optimal interpretation of a ganglion cell's action potential depends strongly on the simultaneous activity of other nearby cells. The quality of the stimulus reconstruction varied greatly with frequency: flicker components below 1 Hz and above 10 Hz were reconstructed poorly, and the performance was optimal near 2.5 Hz. Further analysis suggests that temporal encoding by ganglion cell spike trains is limited by slow phototransduction in the cone photoreceptors and a corrupting noise source proximal to the cones.

A Flicker and Harmonic Compensator Using a Series Active Filter.

A specially designed twelve-pulse thyristor rectifier of 5-8MVA is required as a low-voltage high-current dc power supply for super-conductive material tests. It is, however, too susceptible to low frequency variation of the utility voltage, or to the so-called “flicker” to generate a strong magnetic field with high stability.This paper presents a flicker and harmonic compensator based on the combined system of a small-rated series active filter and a conventional shunt passive filter. The main purpose of the compensator is to remove susceptibility to the flicker from the thyristor rectifier. The series active filter, which is connected in series with the utility, can compensate for flicker components present at the utility grid, the frequency range of which is from 1Hz to 20Hz. In addition, it helps almost all harmonic currents produced by the thyristor rectifier to flow into the shunt passive filter installed in parallel with the harmonic-producing load, i.e. the thyristor rectifier.

Low-frequency noise in Schottky-gate field-effect transistors

A three-section analytic model of a Schottky-gate field-effect transistor is used to calculate the drain-current modulation sensitivity to low-frequency fluctuations in various regions of the active layer. The examined noise sources in the conducting channel and in the gate depletion region are fluctuations of the carrier and bound-charge concentrations, whose spectra can include generation-recombination and flicker components. The theoretical results are compared with measurements of low-frequency current noise.

Amplitude and phase of responses of macaque retinal ganglion cells to flickering stimuli.

1. We have measured responses of macaque retinal ganglion cells to a uniform flickering field, with variation in luminance, chromaticity or both (heterochromatic flicker). 2. With heterochromatic flicker, as the luminance ratio of the flicker components was varied, phasic ganglion cell activity went through a minimum and an abrupt phase change close to equal luminance. Tonic ganglion cell responses underwent a gradual phase change without any minimum close to equal luminance. For red on-centre cells, when wavelengths above 570 nm were altered with white, a progressive phase advance occurred as luminance ratio (L lambda/LW) was increased. With wavelengths below 570 nm a progressive phase lag occurred. For green on-centre cells, the opposite pattern was found. For all tonic cells, the higher the temporal frequency, the more rapidly did such phase changes occur. A simple model incorporating a centre-surround delay of 3-8 ms could quantitatively account for these changes. 3. With luminance flicker of different dominant wavelengths, amplitudes and phase of responses of phasic ganglion cells were independent of wavelength at all frequencies. The amplitude and phase of the responses of tonic ganglion cells was very dependent on wavelength, as well as on flicker frequency. Their characteristics hardly ever resembled results from phasic cells. 4. For achromatic flicker, response phase of tonic cells at or above 10 Hz was variable, probably due to the centre-surround delay. Such variability was not seen among phasic cells. 5. An interesting implication of these results is that the ability of tonic ganglion cells to unambiguously signal rapid chromatic or spatial change is limited.

Suppression and Measurement of Arc Furnace Flicker with a Large Static Var Compensator

This paper describes the system outline, the features of component equipments and the operating results of 120 MVA Static VAR Compensator (SVC). The SVC was installed for suppressing flicker caused by two 100 ton arc furnaces and has been in operation since April of 1978. In addition, an exclusive monitor panel was installed to monitor the flicker, harmonic currents and other components at critical bus. Special emphasis is placed on the analysis of flicker compensating effect with new measuring method, 33 kV thyristor switch hardware and outline of the monitor panel.

Evoked Brain Potential Correlates of Psychophysical Responses: Heterochromatic Flicker Photometry

The relation between the amplitude of evoked brain potentials in man and the relative luminance of two flicker components of different color was determined. The function, which is U-shaped, has a minimum which occurs near the point of equal luminance as judged by the psychophysical method of flicker photometry.