The research paper presents the results of the dynamic analysis of an existing bar dome subjected to wind loads. The calculation model of the structure was constructed using the finite element method. The dome was subjected to the standard wind pressure, assuming that it is operates in a harmonic manner. The numerical analyses were performed with the application of Autodesk Robot and MES3D. The analysis focused on the impact of selected factors such as the frequency of forcing, wind gustiness coefficient and structural damping on the behaviour of structures.

In this paper we introduce a self-tuning Kalman filter for fast time-domain amplitude estimation of noisy harmonic signals with non-stationary amplitude and harmonic distortion, which is the problem of a contactvoltage measurement to which we apply the proposed method. The research method is based on the self-tuning of the Kalman filter's dropping-off behavior. The optimal performance (in terms of accuracy and fast response) is achieved by detecting the jump of the amplitude based on statistical tests of the innovation vector of the Kalman filter and reacting to this jump by adjusting the values of the covariance matrix of the state vector. The method's optimal configuration of the parameters was chosen using a statistical power analysis. Experimental results show that the proposed method outperforms competing methods in terms of speed and accuracy of the jump detection and amplitude estimation.

The quality of the supplied power by electricity utilities is regulated and of concern to the end user. Power quality disturbances include interruptions, sags, swells, transients and harmonic distortion. The instruments used to measure these disturbances have to satisfy minimum requirements set by international standards. In this paper, an analysis of multi-harmonic least-squares fitting algorithms applied to total harmonic distortion (THD) estimation is presented. The results from the different least-squares algorithms are compared with the results from the discrete Fourier transform (DFT) algorithm. The algorithms are assessed in the different testing states required by the standards.

Expressing head-related transfer functions (HRTFs) in the spherical harmonic (SH) domain has been thoroughly studied as a method of obtaining continuity over space. However, HRTFs are functions not only of direction but also of frequency. This paper presents an extension of the SH-based method, utilizing hyperspherical harmonics (HSHs) to obtain an HRTF representation that is continuous over both space and frequency. The application of the HSH approximation results in a relatively small set of coefficients which can be decoded into HRTF values at any direction and frequency. The paper discusses results obtained by applying the method to magnitude spectra extracted from exemplary HRTF measurements. The HRTF representations based on SHs and HSHs exhibit similar reproduction accuracy, with the latter one featuring continuity over both space and frequency and requiring much lower number of coefficients. The developed HSH-based continuous functional model can serve multiple purposes, such as interpolation, compression or parametrization for machine-learning applications.

The impact of harmonic distortions on power grids is a major issue in contemporary power networks as a result of the extensive application of non-linear loads. The purpose of this article is to explore the problem of harmonic distortion in power grids and its impact on the elements of the power grid, such as cable lines and transformers. The Schaffner PQS software product was used in this study to model power grids. New techniques for modeling power grids and finding technical solutions that meet the IEEE 519-2014 standard were introduced. The study finds that harmonic distortion can lead to an additional heat load being placed on cable lines and reduces the power available to transformers, which can decrease their rated power. The application of modern software reduces the time and complexity of calculations, and the availability of software solutions for limiting harmonic distortion simplifies the creation of solutions that meet this standard. Using the methods presented in the study, engineering solutions can be improved, the reliability of electrical systems can be increased, and the loss of electrical energy can be reduced. This can enhance efficiency for design engineers and technical specialists involved in the operation of power grids.

The discrete Fourier transform (DFT) is the main method of electrical harmonic analysis since it’s easily realized in an embedded system. But there were some difficulties in performing synchronized sampling. The spectral leakage caused by asynchronous sampling affects the accuracy of harmonics analysis. Using window functions and interpolation algorithms can improve the accuracy of harmonics analysis. An approach for electrical harmonic analysis based on the interpolation DFT was proposed. A window function reduces DFT leakage and the interpolation algorithm modifies the calculation results of frequency, amplitude and the initial phase angle. The simulation results indicate that, by using the interpolation DFT electrical harmonic analysis method based on the Hanning window or the Blackman window, the error of calculating amplitudes and frequencies is not greater than 0.5%.

The paper presents abilities and advantages following from the use of the harmonicbalance method for analysis of steady state of a multiphase system with switching devices on example of a matrix converter. Switching elements are modelled as resistances with step-wise variable parameters, what allows to describe the converter by a linear infinite set of equations. The analysis in frequency domain is presented on example of the one-periodic control strategy. External systems were also added using the Thevenin method approach. The numerical calculation results of a linear equations set were verified by the variable structure method in a time domain and the numerical convergence was confirmed. Furthermore, the exemplary complex system was analysed using the cascade method and current waveforms were obtained.

In this paper, a low kilo-volt-ampere rating zigzag connected autotransformer based 36-pulse rectifier system supplying vector controlled induction motor drives (VCIMD) is designed, modeled and simulated. Detailed design procedure and magnetic rating calculation of the proposed autotransformer and interphase reactor is studied. Moreover, the design process of the autotransformer is modified to make it suitable for retrofit applications. Simulation results confirm that the proposed 36-pulse rectifier system is able to suppress less than 35th harmonics in the utility line current. The influence of load variation and load character is also studied to demonstrate the performance and effectiveness of the proposed 36-pulse rectifiers. A set of power quality indices at AC mains and DC link are presented to compare the performance of 6-, 24- and 36-pulse AC-DC converters.

An analytical expression for the standard deviation of Total Harmonic Distortion (THD) estimation is derived. It applies to the case where the estimator uses sine fitting. It is shown that, in common circumstances, it is inversely proportional to the actual value of THD, the signal-to-noise ratio and the square root of the number of samples. The proposed expression is validated both with numerical simulations and an experimental setup using a Monte Carlo procedure.

To improve the power quality of a multi-pulse rectifier, a zigzag 18-pulse uncontrolled rectifier with an auxiliary circuit at the DC side is proposed. When the grid-side currents are sinusoidal waves, the required DC side injection currents to be compensated can be obtained by analyzing the AC-DC side relationship of diode bridge rectifiers. Then the 6 compensation currents generated by an active auxiliary circuit are injected into the DC side to eliminate the grid-side harmonics of the rectifier. The simulation results verifying the correctness of the theoretical analysis show that the proposed rectifier can mitigate the harmonic content, as the total harmonic distortion of the grid-side current is about 1.45%. In addition, the single-phase inverter used in the active auxiliary circuit has the characters of simple circuit structure and easy controllability.

The permanent magnet synchronous motor (PMSM) driven by an inverter is widely used in the industrial field, but the inverter has a significant impact on the operational stability of the PMSM. The torque ripple of the PMSM is directly affected by the coupling of multiple harmonic voltages in the motor windings. In order to analyze its influence, a water-cooled PMSM with 20 kW 2000 r/min is taken as an example to establish the finite element model of the prototype, and the correctness of the model is verified by experiments. Firstly, based on the finite element method, the electromagnetic field of the PMSM is numerically solved in different operating states, and the performance parameters of the PMSM are obtained. Based on these parameters, the influence of the harmonic voltage amplitude on the torque ripple is studied, and the influence law is obtained. Secondly, combined with the decoupling analysis method, the influence of harmonic voltage coupling on the torque ripple is compared and analyzed, and the variation law of harmonic voltage coupling on the torque ripple is obtained. In addition, the influence of different harmonic voltage coupling on the average torque of the PMSM is studied, and the influence degree of different harmonic voltage amplitude on the torque fluctuation is determined. The conclusion of this paper provides reliable theoretical guidance for improving motor performance.

The connection of renewable energy sources with significant nominal power (in the order of MW) to the medium-voltage distribution grid affects the operating conditions of that grid. Due to the increasing number of installed renewable energy sources and the limited transmission capacity of medium-voltage networks, the cooperation of these energy sources is becoming increasingly important. This article presents the results of a six-year study on a 2 MW wind power plant and a 1 MW photovoltaic power plant in the province of Warmia and Mazury, which are located a few kilometers away from each other. In this study, active energy, currents, voltages as well as active, reactive, and apparent power and higher harmonics of currents and voltages were measured. The obtained results show the parameters determining the power quality at different load levels. Long-term analysis of the operation of these power plants in terms of the generated electricity and active power transmitted to the power grid facilitated estimating the repeatability of active energy production and the active power generated in individual months of the year and times of day by a wind power plant and a photovoltaic power plant. It also allowed us to assess the options of cooperation between these energy sources. It is important, not only from a technical but also from an economic point of view, to determine the nominal power of individual power plants connected to the same connection point. Therefore, the cooperation of two such power plants with the same nominal power of 2 MW was analyzed and the economic losses caused by a reduction in electricity production resulting from connection capacity were estimated.

Scaffolding is equipment usually used at construction sites. A scaffolding structure is lightweight and made of elements used many times. The characteristics of scaffolding make it susceptible to dynamic actions present at the structure or occurring nearby. A scaffolding structure of medium size was subjected to analysis in this paper. The structure FEM model was loaded with single force harmonic excitation with various frequencies ranging from 1 Hz to 12 Hz applied in one of many selected points on the scaffolding façade. In the first step, natural frequencies and mode shapes of the analyzed structure were calculated. Then the full dynamic analysis was carried out to obtain maximum displacements of selected control points. The relation of excitation force frequency and location to the amplitudes of generated displacement was observed. It was found that low excitation frequencies close to the natural frequencies of the structure produced vibrations ranging to large areas of the scaffolding surface. Higher excitation frequencies are usually less propagated at the scaffolding but still may produce some discomfort to the structure users in the vicinity of the excitation force location. Scaffolding is equipment usually used at construction sites. A scaffolding structure is lightweight and made of elements used many times. The characteristics of scaffolding make it susceptible to dynamic actions present at the structure or occurring nearby. A scaffolding structure of medium size was subjected to analysis in this paper. The structure FEM model was loaded with single force harmonic excitation with various frequencies ranging from 1 Hz to 12 Hz applied in one of many selected points on the scaffolding façade. In the first step, natural frequencies and mode shapes of the analyzed structure were calculated. Then the full dynamic analysis was carried out to obtain maximum displacements of selected control points. The relation of excitation force frequency and location to the amplitudes of generated displacement was observed. It was found that low excitation frequencies close to the natural frequencies of the structure produced vibrations ranging to large areas of the scaffolding surface. Higher excitation frequencies are usually less propagated at the scaffolding but still may produce some discomfort to the structure users in the vicinity of the excitation force location.

Periodic inventory and check surveys of the surfaces in engineering structures using terrestrial laser scanning require performing scans from many locations. The survey should be planned so as to obtain full coverage of the measured surface with a point cloud of appropriate density. Due to a variety of terrain obstacles in the close vicinity of the surveyed structure, structural and technical elements, as well as machinery and construction equipment (whose removal is impossible e.g. because of their role in the building and protection of the structure), it is often necessary to combine scans acquired from locations having different measurement geometry of the scene and performed in different lighting conditions. This makes it necessary to fill in blank spots with data of different spectral and geometric quality. This paper presents selected aspects of data harmonization in terrestrial laser scanning. The laser beam incidence angle and the scanning distance are assumed as parameters affecting the quality of the data. Based on the assumed minimum parameters for spectral data, an example of a harmonizing function for the concrete surface of a slurry wall was determined, and the methodology for determining its parameters was described. The presented solution for spectral data harmonization is based on the selection of reference fields representative of a given surface, and their classification with respect to selected geometric parameters of the registered point cloud. For geometric data, possible solutions to the harmonization problem have been analyzed, and criteria for point cloud reduction have been defined in order to obtain qualitatively consistent data. The presented results show that harmonization of point clouds obtained from different stations is necessary before their registration, in order to increase the reliability of analyses performed on the basis of check survey results in the assessment of the technical condition of a surface, its deformation, cracks and scratches.

The paper presents the propagation assessment and power quality parameters improvement system in power distribution grid. In this work main functionalities of the system are described focusing on the individual assessment module. The module is using CIRED/CIGRE C4.109 method which is based on the 10-minutes aggregated data. Three cases of individual emission assessment using real measurement data in the distribution system operator environment ware analyzed. The obtained results confirmed the legitimacy of using 10-minute data to assess the emissions of harmonics.

Electrified railways are an example of AC single phase distribution networks. A non-negligible amount of active and nonactive power may be related to harmonics, especially for distorted highly-loaded systems. The paper considers the relevance of the harmonic power terms in order to identify distortion sources in a single-point perspective, in line with the approach of EN 50463 for the quantification of the power and energy consumption. Some single-point Harmonic Producer Indicators (HPI) based on harmonic active power direction and nonactive distortion power terms are reviewed and evaluated using pantograph voltage and current measured during several hours of runs in two European AC railways (operated at 16.7 and 50 Hz). The HPI based on active power shows to be consistent and provides detailed information of rolling stock characteristic components under variable operating conditions; those based on nonactive distortion power are global indexes and hardly can operate with complex harmonic patterns in variable operating conditions.

The article presents selected static characteristics of a parallel active filter with voltage control in the supply line (VPAPF – Voltage-controlled Active Power Filter) as a function of parameters of the supply network. The tests were done on the basis of a simulation model of the supply network and an appropriate compensator. The test results showed that VPAPFs are most suitable for operation in weak networks, maintaining an almost constant level of voltage distortion, regardless of the value of the network impedance. In addition, the influence of the parameter G corresponding to the conductance value suppressing higher harmonics of the network voltage on the operation of the active power filter was determined.

This work presents a simulation of the response of packets of microbubbles in an ultrasonic pulse-echo scan line. Rayleigh-Plesset equation has been used to predict the echo from numerically obtained radial dynamics of microbubbles. Varying the number of scattering microbubbles on the pulse wave form has been discussed. To improve microbubble-specific imaging at high frequencies, the subharmonic and second harmonic signals from individual microbubbles as well as microbubbles packets were simulated as a function of size and pressure. Two different modes of harmonic generation have been distinguished. The strength and bandwidth of the subharmonic component in the scattering spectrum of microbubbles is greater than that of the second harmonic. The pressure spectra provide quantitative and detailed information on the dynamic behaviour of ultrasound contrast agent microbubbles packet.

The parametric anti-resonance phenomenon as an active damping tool for suppression of externally excited resonant vibration is numerically studied herein. It is well known fact that the anti-resonance phenomenon, i.e. the stiffness periodic variation by subtractive, combination resonance frequency, brings stabilization and cancelling into self-excited vibrations. But this paper aims at a new possibility of its application, namely a damping of externally excited resonant vibration. For estimation of its effect we come both from a characteristic exponent of the analytical solution and numerical solution of forced vibration of 2DOF linear system with additional parametric excitation. The amplitude suppression owing to the parametric anti-resonance is studied on several parameters of the system: a depth of parametric excitation, mass ratio, damping coefficient and small frequency deviations from the parametric anti-resonance.

The paper investigates a significant influence of transients on steady states in a matrix converter with the one-periodic control strategy. Proposed controller can be used as an interconnection device within a power system for a power flow control. However, the presence of inductances in external systems has the significant influence on steady state of a matrix converter operation. The special current injection method has been developed to ensure a proper operation of a matrix converter. Presented analysis of steady states is carried out in a frequency domain using the harmonic balance method. Obtained numerical results, which are confirmed by a time domain analysis, prove the effectiveness of the proposed method.

This study presents the dependence of the level and harmonic structure of the cogging torque in permanent magnet synchronous motors (PMSM) to imperfections of permanent magnet (PM) dimensions and positions, which can not be avoided in massproduction. Slightly diverse dimensions and misplacements of PMs are introducing asymmetries in magnetic field distribution which cause additional harmonic components. A finite element method (FEM) and Fast Fourier transform (FFT) were used to calculate cogging torque harmonic components with regard to several combinations of PM assembly imperfections. It has been established and proved that unequal PMs cause magnetic asymmetries which give rise to additional cogging torque harmonic components and consequently increase the total cogging torque. It is also shown that in some particular combinations the influence of an individual PM imprecision could compensate with others due to different phase shifts which can result even in the decrease of cogging torque. Considering presented results it is possible to foresee which additional harmonic components will comprise the cogging torque of mass-produced PMSMs due to PM imperfections. In this way the designers are able to predetermine required manufacturing tolerances to keep the level of cogging torque in a admissible level. Simulation results were verified and confirmed by laboratory tests.

Along with the increase in the use of nonlinear electronic devices, e.g. personal computers, power tools and other electrical appliances, the requirements for uninterruptible power supplies are constantly growing. This paper proposes a method and deep analysis of results viable for checking how single-phase uninterruptible power supplies (UPSs) cope with nonlinear circuits under varying power loads in terms of electric energy quality.Various classes of single-phase UPS systems with different topologies were tested, for instance line-interactive and double conversion (online) single-phase UPS devices. Furthermore, measurements were carried out in view of a power source – loads were supplied both from a power grid and UPS built-in battery. Juxtaposition of the obtained results such as a THDU, THDI (Total Harmonic Distortion) percentage ratio of input/output voltage and current, a power factor and crest factor volume etc. of the tested UPS systems indicated major differences in their performance during laboratory tests.

A limited ability to discriminate between different materials is the fundamental problem with all conventional eddy-current-based metal detectors. This paper presents the use, evaluation and classification of nontraditional excitation signals for eddy-current metal detectors to improve their detection and discrimination ability. The presented multi-frequency excitation signals are as follows: a step sweep sine wave, a linear frequency sweep and sin(x)/x signals. All signals are evaluated in the frequency domain. Amplitude and phase spectra and polar graphs of the detector output signal are used for classification and discrimination of the tested objects. Four different classifiers are presented. The classification results obtained with the use of poly-harmonic signals are compared with those obtained with a classical single-tone method. Multifrequency signals provide more detailed information, due to the response function – the frequency characteristic of a detected object, than standard single-tone methods. Based on the measurements and analysis, a metal object can be better distinguished than when using a single-tone method.

This paper presents a new modification of the least-squares Prony’s method with reduced sampling, which allows for a significant reduction in the number of the analysed signal samples collected per unit time. The specific combination of non-uniform sampling with Prony’s method enables sampling of the analysed signals at virtually any average frequency, regardless of the Nyquist frequency, maintaining high accuracy in parameter estimation of sinusoidal signal components. This property allows using the method in measuring devices, such as for electric power quality testing equipped with low power signal processors, which in turn contributes to reducing complexity of these devices. This paper presents research on a method for selecting a sampling frequency and an analysis window length for the presented method, which provide maximum estimation accuracy for Prony’s model component parameters. This paper presents simulation tests performed in terms of the proposed method application for analysis of harmonics and interharmonics in electric power signals. Furthermore, the paper provides sensitivity analysis of the method, in terms of common interferences occurring in the actual measurement systems.