Harmonic Components Research Articles

Decoupled Control of an Active Power Filter in a Vibrating Reference Frame

Abstract Active power filter (APF) control is a natural area of application for vibrating reference frame (VRF) transformation due to the intentional occurrence of higher harmonics in the active filter current compensating load current harmonics. Due to the vibrating frame transformation, the APF current can be represented by the DC values, and thus proportional-integral (PI) controllers are sufficient to control the converter current. However, in the typical approach, it may be impossible to combine harmonic filtration with reactive power compensation features, due to the transformation constraints. The solution to this issue is decoupling of the fundamental harmonic and high harmonic components and a separate control for each of them. This paper presents a decoupled control system of an APF, which uses VRF transformation for accurate control of high-current harmonics. Decoupling is a groundbreaking improvement of the VRF method. Moreover, different current limitation scenarios are proposed, considering both harmonics compensation and fundamental frequency reactive current compensation. Theoretical considerations are supported by simulation and experimental tests.

Method and software for processing daily EEG signals for detection of epileptic seizures in humans

A method, an algorithm and a software tool for processing daily EEG signals for computer electroencephalographic systems to detect the manifestation of epileptic seizures in humans have been developed. Mathematically, the daily EEG signal is presented as a random sequence of white Gaussian noise zones and additive mixtures of different-frequency harmonic components. Harmonic functions interpret the manifestations of epileptic seizures. The core of the method of processing daily EEG signals is a time-shifted window inter-covariance processing with multiple kernels in the form of different-frequency harmonic functions. Based on the method of window processing, an algorithm and a software tool for daily EEG signal processing with a graphical user interface using the MATLAB environment have been implemented. The developed software can be used as a component of computer EEG systems. The results of daily EEG signal processing using the software are displayed in the form of averaged products of covariance results (the value is measured in power units) within each processing window, which quantitatively reflect the time points of epileptic seizures in a person. Manifestations of epileptic seizures are reflected through the increase in the averaged values of the power of covariances in relation to observation intervals without corresponding manifestations of these seizures. To ensure the authorization of the process of determining the level of decision-making regarding the moments of epileptic seizures (exceeding the normal level), the threshold algorithm and the Neumann-Pearson statistical criterion were applied.

TMR Nonlinear Compensation Method Based on Odd Harmonic Components

TMR Nonlinear Compensation Method Based on Odd Harmonic Components

A Bibliometric and Comprehensive Review on Condition Monitoring of Metal Oxide Surge Arresters.

This paper presents a literature review on the subject of Condition-Based Maintenance of surge arresters. Both a bibliometric analysis and traditional comprehensive research are presented. The bibliometric analysis is useful for obtaining insights about the literature. It quantitatively highlights relationships between journals, authors and keywords (related to the monitoring methods) and reveals future trends for research based on the timeline of the keywords. The traditional comprehensive literature review is also presented. It summarizes the methods, their advantages and disadvantages and also points to some known measurement issues of the methods. Both online (leakage current, harmonic components, temperature, partial discharges, power loss and the counting of discharges) and offline (reference voltage, residual voltage, insulation resistance, polarization/depolarization, return voltage, microscopy, spectrometry, X-ray, RUS and the recent application of FRA) methods have been qualitatively analyzed.

Passive filters allocation in unbalanced distribution network with high penetration of distributed generation

The purpose of this paper is the allocation of passive filters in an unbalanced power network with high penetration of distributed generation to minimize the costs of power losses in the distribution lines, including power losses caused by harmonic components and neutral conductor power losses due to unbalanced loads. The harmonic components and the fundamental current generated by the distributed generation cause a voltage increase in the generation bus, and the voltages in the network above the limit allowed by standard are reduced by allocating passive filters without cutting the active power in the distributed generation. The unbalance and reactive power compensation is performed by the ideal compensation method applied to the distribution network. The tests are for the IEEE 34 bus network, with the fourth wire in the simulation being the isolated neutral. The scatter search metaheuristic applied in the simulation tends to minimize the costs of power losses in the lines and the costs of the passive filters allocated in the medium voltage distribution network, meeting the operational constraints of the network.

Model of the turboprop engine reduction gear tooth harmonic spectral component

The width of spectral components in rotary machines is determined by the frequency modulation of the carrier from the rotor speed deviation in the stationary operation mode. It was shown that, for the tooth spectral component, it is not enough to take into account this factor only. The analysis of publications and the studies performed show that it is also determined by the effect of many other factors: process-related ones (errors in manufacturing and assembly of gear wheels), operation mode parameters (rpm, temperature, transmitted load); design-related factors (flexibility of drive parts; modification of the tooth face), as well as uneven wear of tooth flanks. Using the planetary gearbox of a turboprop engine as an example, the structure of the tooth spectral component width in function of the analyzed influencing factors was considered. Based on the vibration statistics for eighteen gearboxes in overhauled engines, the choice of a ratio for the spectral component width of a frequency modulated process was justified. This choice showed readings closest to the corresponding experimental data. For the vibration of ten gearboxes with different degrees of tooth flank wear, the corresponding dependence of the width on the wear is presented. A mathematical model for the tooth spectral component width in overhauled and newly manufactured gearboxes as the product of the constant coefficient with the deviation dispersion sum from the considered factors was proposed. The same dependence was also given for gearboxes with wear when adding the dispersion from wear to the dispersion sum. It was demonstrated that, for the presented case of the maximum wear, its fraction in the total width was about 50%, whereas the fraction of the frequency modulation from the operating system of adjusting relative rotor speed constancy in the stationary engine operation mode was equal to half of all the other factors.

Study and Quantitative Analysis of Mode Localization in Wind Turbine Blades

The study of damage mechanisms for wind turbine blades is important. Generally, modal localization tends to accelerate structural damage. This is a new approach to studying these damage mechanisms for wind turbine blades through modal localization theory. Therefore, this paper investigates whether modal localization phenomena exist in wind turbine blades, as well as the impact of different forms of detuning on modal localization. Based on perturbation theory, a mechanism for mode localization is described quantitatively using the degree of detuning, the degree of mode density, and the mode assurance criterion. A finite element model for wind turbine blades was established using ANSYS software (R15.0), and three detuning cases were simulated by changing the density, elastic modulus, and installation angles of the blades. Moreover, an improved mode localization factor is proposed to quantitatively evaluate the degree of mode localization in wind turbine blades. The numerical results indicate that the degree of modal localization increases with an increasing degree of detuning, but the increase in modal localization gradually slows. Finally, the detuning modal shape composition, which includes harmonic components, is analyzed. The results show that the closer the composition of the detuning modes is, the stronger the degree of mode localization.

Nonlinear signal conversion in gold nanoparticle random array for physical reservoir applications

We present nonlinear electrical characteristics of a random array of gold nanoparticles (GNPs). We fabricated a GNP random array with six electrodes by using dielectrophoresis. The Coulomb blockade appeared on current–voltage characteristics at 4.2 K. Input–output characteristics of the GNP random array were also measured for a configuration with one-input and three-output terminals. For a sinusoidal voltage input of 100 Hz, distorted output voltage waveforms were acquired at the three output terminals. Higher harmonic components were confirmed on the FFT spectra of the outputs. Wave reconstruction tasks for a triangle and a cosine waveform were performed via an echo-state-network model with ridge regression, which demonstrated that nonlinear signal conversion in a GNP random array had potential for a physical reservoir device.

NEURAL NETWORK PROCESSING OF ELECTROMAGNETIC ACOUSTIC SIGNALS TO IDENTIFY THE STRESS-STRAIN STATE AND DAMAGE OF POWER EQUIPMENT

The purpose of the study is to develop and train an artificial neural network to identify the stress-strain state and damage to the metal of power equipment based on the values of the parameters of the harmonic components of the electromagnetic-acoustic transducer signal.
 
 Materials and methods. Experimental study of the relationship between the parameters of the harmonic components of the signal of an electromagnetic-acoustic transducer with the stress-strain state and damage to the structure of standard metal samples, development of an artificial neural network and methods for its training to identify the stress-strain state and damage to the structure of the metal according to the loading diagram.
 
 Results. Analysis of changes in the microstructure and frequency models of standard steel samples used in power engineering confirmed the possibility of identifying the stress-strain state and damage to the structure of metals based on the values of the parameters of the harmonic components of the electromagnetic-acoustic transducer signal. To solve this problem, an artificial neural network has been developed and trained. After training, the effectiveness of the network in identifying the stress-strain state and damage to the structure of metals reached 92.16%, which is acceptable for the tasks of recognizing the technical condition of metal structural elements of electrical installation equipment.
 
 Conclusions. The use of an artificial neural network to identify the stress-strain state and damage to metal structures based on the harmonic parameters of the electromagnetic-acoustic transducer signal enables to identify areas of concentration of mechanical stress and damage to the metal structure at the early stage of development, thereby increasing reliability and safety operation of electrical equipment.

АНАЛІЗ АКУСТИЧНИХ СИГНАЛІВ ЗАСОБІВ ПОВІТРЯНОГО НАПАДУ

This paper analyzes the acoustic signals of aerodynamic aerial attack weapons used by the Russian Federation during a full-scale invasion. These include strike unmanned aerial vehicles, cruise missiles, jet and turboprop aircraft, and helicopters. It has been established that the time for observing an acoustic signal is limited by the speed of the vehicle. For high-speed targets (cruise missiles, airplanes), it averages 10 s, and for slower targets, 40-50 s. The Welch periodogram method was used to extract the spectral characteristics of acoustic signals. It is shown that the acoustic signal of propeller-driven vehicles is the sum of harmonic and noise-like broadband components, and that of turbojet-powered vehicles has a predominantly noise-like structure with several narrowband components. It was found that at the moment of maximum convergence, the signal spectrum has the greatest width. The characteristic change in the frequency of harmonic components associated with the Doppler effect is investigated. It can be used to estimate the parameters of motion and identify the vehicle. By correlation analysis of acoustic signals, it was found that broadband components have a noise-like structure. An acoustic signal for the case of simultaneous over flight of different types of vehicles was formed by adding records of different acoustic signals. It is shown that the characteristic spectral characteristics of all objects are preserved on the frequency-time plane. The results of the analysis can be used to build mathematical models of acoustic signals and to develop methods for processing signals of aerial attack weapons in an acoustic airspace monitoring system. Keywords: aerial attack weapons; acoustic signal; spectrogram; acoustic monitoring system; harmonic component.

Close accord on partial discharge diagnosis during voltage harmonics in electric motors fed by variable frequency drives

AbstractPartial discharge (PD) diagnostics test is a reliable solution for estimating insulation health conditions in power system components. During laboratory PD diagnostics, the effect of harmonic components in the voltage waveform generated by variable frequency drives (VFD) fed electric motors (EMs) is often overlooked. As VFD‐fed EMs operate at low speeds, the harmonic concentration in the voltage increases. It has been found that PD activity in VFD‐fed EM is significantly affected by the addition of harmonic components in the voltage, thus making it necessary to consider their impact when performing true PD diagnostics. This paper investigates the influence of voltage harmonic distortion produced in VFD‐fed EM on PD severity and the subsequent insulation degradation. Eight VFD‐fed EM are used to study the PD behaviour under different levels of harmonic pollution. The PD characteristics, such as inception voltage, pulse repetition rate, accumulated apparent charge, average discharge current, discharge power, and quadratic rate, are determined. Using probability distribution functions, PD activity and severity at various voltage harmonic levels are estimated. The proposed technique can be used to plan the maintenance activities that ensure the reliability for industrial applications dealing with the voltage harmonic distortion.

Measurement of High-Frequency Sub-Noise Temperature Signal and RMS Current Using a Single-Detector High-Speed IR System

NETD (Noise Equivalent Temperature Difference) parameter of infrared systems is the important parameter that allows determining the limit of temperature measurement of tested objects. Currently, the commercially available devices have the NETD < 20 mK. The infrared (IR) detectors and accompanying electronic circuits generate noise. In consequence, it is difficult to achieve the high level of signal-to-noise ratio (SNR) while measuring temperature. This paper presents a method of measuring the root mean square (RMS) value of alternating current, using a single-detector high-speed IR system for detecting 100 Hz harmonic spectral component of temperature, whose value is certainly below NETD limit.

Analysis of power grid operation modes considering the influence of tooth harmonics

A harmonic analysis of the magnetic field of an asynchronous motor was carried out, taking into account bilateral gearing and magnetic asymmetry of the air gap. The spectrum is obtained in the form of infinite series of spatio-temporal harmonic components. Magnetic asymmetry of an asynchronous motor takes into account static and dynamic eccentricity, magnetic asymmetry of steel. 27 different spatial harmonics of the field in the air gap of the induction motor were obtained. The considered spectrum of harmonics of the magnetic field will be induced in the stator windings by the electromotive force with the corresponding frequencies. The fields with γр ± κ pairs of poles rotate asynchronously with the rotor and are damped by the fields created by the currents of the rotor cage. Thus, the magnetic asymmetry affects the spatial harmonics of the magnetic field, changing the angular velocities of their rotation in the air gap. The appearance of magnetic asymmetry causes a redistribution of the spatio-temporal distribution of the harmonics of the magnetic field of the tooth frequency, which leads to a change in the amplitude and phase relationships between the quantities. This leads to the appearance of an asymmetric system of electromotive force of tooth frequency in the stator windings, and, therefore, to a different effect of the asymmetry of the air gap at the level of symmetrical components. In the general case, at the level of symmetric components, the electromotive force of the gear frequency is influenced by two groups of factors that determine asymmetric or different from the nominal operating modes of an asynchronous motor of the same size. An increase in the magnetic asymmetry of the air gap causes a nonlinear, close to parabolic character of the growth of the existing symmetrical components. Symmetric components of the electromotive force of the toothed frequency cause currents of the corresponding components to flow through the closed circuits of the stator windings of the asynchronous motor and the entire power supply system. The calculation scheme for replacing a three-phase network for toothed harmonics of electromotive force is given. The phase resistances of the windings of rotating electric machines for asymmetric three-phase networks are not the same for different sequences. The main method of calculating the considered network is the method of symmetrical components. The calculation is made for one main phase according to the substitution schemes, which corresponds to the symmetrical components of the electromotive force of the tooth frequency. As a result of theoretical studies, functional dependences of the influence of magnetic asymmetry on the level and distribution of phase currents of the toothed frequency were obtained. The nature of the influence at the level of symmetric components is close to parabolic, and the most sensitive to changes in magnetic asymmetry is the minor symmetric component of the zero sequence. The method of calculating the currents and voltages of the toothed frequencies of asynchronous motors in the conditions of power consumption has been developed. Theoretical propositions are confirmed by experimental studies. It has been established that the levels of toothed harmonics in power supply systems, as a rule, do not exceed 10–15 % of the level of the fundamental frequency. This leads to a decrease in the reliability of the operation of electrical networks and a shortening of the service life of the main energy equipment at the enterprise. However, frequency-amplitude resonance at tooth frequencies causes the greatest threat to the power plants of industrial enterprises. This is due to the specific nature of gear harmonics of asynchronous motors (parity, dependence on load and various technological factors). The biggest threat arises when using the same type of asynchronous motors with similar operating modes. Oscillograms of experimental studies are given.

Low-Engine-Order Forced Response Analysis of a Turbine Stage with Damaged Stator Vane.

A damaged stator vane can disrupt the circumferential symmetry of the design flow for turbine assemblies, which can lead to a low-engine-order (LEO) forced response of rotor blades. To help engineers be able to better address sudden vane damage failures, this paper conducts a mechanism analysis of the LEO forced response of rotor blades induced by a single damaged vane using an in-house computational fluid dynamic code (Hybrid Grid Aeroelasticity Environment). Firstly, it is found that the damaged vane introduces a family of LEO aerodynamic excitations with high amplitudes by full-annulus unsteady aeroelastic simulations of a single-stage turbine. In particular, the LEO forced response of the rotor blades excited by 3EO is 2.01 times higher than the resonance response excited by vane passing frequency, and the LEO resonance risk of the rotor blades is greatly increased. Then, by analyzing the flow characteristics of the wake and potential field of the stator row with a damaged vane, the localized high transient pressure in the notch cavity and the radial redistribution of the secondary vortex at the stator exit are the main sources of the low-order harmonic components in the flow field. Importantly, the interaction mechanisms in two regions with high LEO excitation amplitude on the rotor blade surface are revealed separately. Finally, an evaluation and comparison of a single damaged vane in terms of aerodynamic performance and LEO forced response was carried out. The results of this paper provide a good theoretical basis for engineers to effectively control the resonance response of rotor blades caused by a damaged stator vane in turbine design.

Experimental Study on No-Load Loss Characteristics of an Alternating Current Excitation Motor

An AC excitation power supply will produce a series of harmonic currents in motors compared to the conventional power supply, increase the time harmonic component, and then generate a harmonic magnetic field; harmonics will cause motor vibrations and noise in the motor and will produce a corresponding additional loss, increasing the motor temperature rise; these key technical problems need to be solved in domestic pumped storage AC excitation motor engineering applications. Herein, the no-load loss characteristic test of a 3 MW alternating current excited motor was mainly carried out using a test prototype of the 3 MW alternating current excitation motor. Further, with the aid of the finite element method, the numerical study of the no-load loss characteristics of a 3 MW alternating current excited motor was performed. The relationship between the key factors such as the no-load characteristics, no-load loss characteristics, and constant loss and voltage per unit value is analyzed, and the variation law of the no-load core loss of motors under different loads is explored. The results demonstrate that, under no-load conditions, when the applied voltage was less than the rated voltage, the voltage was proportional to the current. When the applied voltage was more significant than the rated voltage, the current increased as the voltage increased, but the relationship between the two was no longer proportional. The constant loss of the motor maintained a linear relationship with the square of the unit value of the voltage scale. When the square of the unit value of the voltage scale was zero, the loss was equivalent to the wind friction loss under no load. The core loss increased with the increase in load, and the greater the load, the faster the increase rate of the motor iron loss. The comparison deviation between the test and simulation results was less than 10%. The simulation and experimental results verified the effectiveness of finite element modeling and the finite element calculation method.

Показатели качества потребления энергии в коллекторном и асинхронном тяговых приводах электровозов переменного тока

Purpose: To conduct an experimental study of the indicators of electrical energy consumption quality for serially produced freight electric locomotives of alternating current 2(3)ES5K with a collector traction drive and electric locomotives 2(3)ES5S with an asynchronous traction drive, to provide their comparison and comparative analysis. Methods: The main technical characteristics of the collector traction electric drive (TED) NB-514E and asynchronous TED DTA-1100 are presented. A measurement scheme for voltage and current on the power winding of the transformer is proposed. The monitoring of parameters has been carried out directly on electric locomotives using specialized metrological equipment. The processing of experimental data is based on decomposing the original signal into harmonic components using Fast Fourier Transform (FFT). Results: Parameters of voltage and current harmonics, phase shifts, as well as the values of active and reactive power of the corresponding harmonics have been obtained. An analysis of the spectral composition of voltage and current has been performed. Comparative analysis of the results obtained for electric locomotives with collector and asynchronous traction drives in traction mode has shown that the power factor is 0.65 and 0.99, respectively; and the coefficient of non-linear current distortions is 0.53 and 0.15. A conclusion has been drawn regarding significantly higher quality of electrical energy consumption in the asynchronous traction drive. Practical significance: Based on the specific values of the indicators of electrical energy consumption quality in collector and asynchronous traction drives in traction mode, it is possible to proceed to obtaining economic assessments for the transition of the locomotive fleet of Russian Railways (JSCo “RZD”) to nextgeneration electric locomotives of the 2(3)ES5S series.

Improvement of grid injected currents in single-phase inverters rejecting DC link voltage oscillations based on multi-resonant filtering

The operation of grid-tied single-phase inverters generates oscillations in its DC link voltage. If only active/reactive power is controlled by the inverter, this oscillation is at twice the grid frequency. In situations where the inverter output current and/or the grid voltage also has harmonic components, the DC link voltage becomes also polluted by oscillating components at even multiple frequencies of the grid voltage. Such oscillations are propagated through the DC link voltage control loop, increasing the THD index of grid current reference signal. To solve this drawback, this article proposes the insertion of a multi-resonant filter into the DC link voltage control loop, ensuring a harmonic free grid current reference signal. With the proposed filter and without any increase in the power circuit, the use of smaller capacitances in the DC link is allowed, since the DC link voltage oscillation does not interfere in the power quality indexes of the controlled current. A filter tuning methodology is presented to ensure that the design of each filter and of the DC link voltage controller is independent, relating the filter settling time and the system stability. At the same time, the use of the proposed filter allows the voltage controller to be tuned at higher frequencies, improving the DC link voltage dynamic response. The proposal is experimentally validated through a single-phase grid-tied double-stage photovoltaic (PV) system, that can also operate only as a parallel active power filter (PAPF) or, simultaneously as a multifunctional PAPF + PV system.

Optimal Frequency-domain Analysis for Spacecraft Time Series: Introducing the Missing-data Multitaper Power Spectrum Estimator

While the Lomb–Scargle periodogram is foundational to astronomy, it has a significant shortcoming: the variance in the estimated power spectrum does not decrease as more data are acquired. Statisticians have a 60 yr history of developing variance-suppressing power spectrum estimators, but most are not used in astronomy because they are formulated for time series with uniform observing cadence and without seasonal or daily gaps. Here we demonstrate how to apply the missing-data multitaper power spectrum estimator to spacecraft data with uniform time intervals between observations but missing data during thruster fires or momentum dumps. The F-test for harmonic components may be applied to multitaper power spectrum estimates to identify statistically significant oscillations that would not rise above a white noise–based false alarm probability. Multitapering improves the dynamic range of the power spectrum estimate and suppresses spectral window artifacts. We show that the multitaper–F-test combination applied to Kepler observations of KIC 6102338 detects differential rotation without requiring iterative sinusoid fitting and subtraction. Significant signals reside at harmonics of both fundamental rotation frequencies and suggest an antisolar rotation profile. Next we use the missing-data multitaper power spectrum estimator to identify the oscillation modes responsible for the complex “scallop-shell” shape of the K2 light curve of EPIC 203354381. We argue that multitaper power spectrum estimators should be used for all time series with regular observing cadence.

High dynamic range 3D measurement based on the Butterworth low-pass filter and Hilbert transform

Due to the limited dynamic range of the camera, a measured object with non-Lambert reflection saturates the fringe pattern, which will lead to three-dimensional (3D) measurement error. In this paper, we propose a novel, to our knowledge, high dynamic range 3D measurement technique based on the Butterworth low-pass filter (BLPF) and Hilbert transform (HT), which is called BLPFHT for short. First, we analyze the Fourier transform (FT) spectrum of saturated fringe pattern. Then, we use the Butterworth low-pass filter to filter out the higher harmonic components introduced by fringe intensity saturation. BLPF leads to a non-sinusoidal fringe pattern in the saturated region, which introduces periodic phase error. Therefore, we establish a phase error model and use HT to correct the phase error. Experimental comparison confirms that the proposed BLPFHT can efficiently and accurately reconstruct the 3D shape of non-Lambert reflective surfaces without additional image or hardware assistance.

Time-frequency feature extraction based on multivariable synchronization index for training-free SSVEP-based BCI.

Multivariate synchronization index (MSI), as an effective recognition algorithm for steady-state visual evoked potential (SSVEP) brain-computer interface (BCI), can accurately decode target frequencies without training. To further consider temporal features or extract harmonic components, extended MSI (EMSI), temporally local MSI (TMSI), and filter bank MSI (FBMSI) have been proposed. However, the promotion effects of the above three strategies on MSI have not been compared in detail. In this paper, the performance of EMSI, TMSI, and FBMSI under different time windows was analyzed with the same dataset. The results indicated that the improvement effect of the temporally local method on MSI was better than that of the other two methods under the short time window, and the effect of the filter bank method was better when the time window was greater than 0.8s. Based on the idea of simultaneously extracting time-frequency features, FBEMSI and FBTMSI were proposed by integrating time delay embedding and temporally local method into FBMSI respectively. The two improved methods, which has no significant difference, can improve the recognition effect of FBMSI. But the computing time of FBEMSI was shorter, which can be a potential method for SSVEP-BCI.