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This paper deals with the use of least mean squares (LMS, NLMS) and recursive least squares (RLS) algorithms for total harmonic distortion (THD) reduction using shunt active power filter (SAPF) control. The article presents a pilot study necessary for the construction of our own controlled adaptive modular inverter. The objective of the study is to find an optimal algorithm for the implementation. The introduction contains a survey of the literature and summarizes contemporary methods. According to this research, only adaptive filtration fulfills our requirements (adaptability, real-time processing, etc.). The primary benefit of the paper is the study of the efficiency of two basic approaches to adaptation ((N)LMS and RLS) in the application area of SAPF control. The study examines the impact of parameter settings (filter length, convergence constant, forgetting factor) on THD, signal-to-noise ratio (SNR), root mean square error (RMSE), percentage root mean square difference (PRD), speed, and stability. The experiments are realized with real current and voltage recordings (consumer electronics such as PC source without power factor correction (PFC), HI-FI amplifier, etc.), which contain fast dynamic transient phenomena. The realized model takes into account a delay caused by digital signal processing (DSP) (the implementation of algorithms on field programmable gate array (FPGA), approximately 1–5 μs) and a delay caused by the reaction time of the proper inverter (approximately 100 μs). The pilot study clearly showed that the RLS algorithm is the most suitable for the implementation of an adaptive modular inverter because it achieved the best results for all analyzed parameters.

The article presents a solution to the problem of optimizing the structure of filter-compensating devices (FCD) when installed in high-voltage mine networks with powerful nonlinear electrical receivers. The urgency of the problem of choosing a rational structure of the FCD. The problem of choosing the design and installation location of the FCD is presented. The main technical means of compensation of higher harmonics of currents and voltages in high-voltage networks with powerful nonlinear electrical receivers are considered. Analysis of different types of passive filters (PF) and their frequency properties showed that the choice of specific types of PF refers to the multi-criteria optimization problem. The main methods of optimization of FCD design are considered. The variant of FCD construction based on the solution of multi-criteria optimization problem with the use of fuzzy sets is proposed and justified. To this end, the calculation of PF parameters and frequency characteristics of equivalent systems of the \"filter-external network\" type for four possible combinations of PF is performed. The optimal is a FCD with two resonant PF tuned to the 11th and 13th harmonics, and a second-order broadband PF tuned to compensate harmonics starting from the 23rd and above. The analysis of simulation results showed effective compensation of higher harmonic currents and voltages.

The usage of multiphase electrical drives expands the operation possibilities of electrical machines and opens new directions of research on inverter-fed electrical machines. With an increasing number of phases, the standard approach of the electromagnetic design of machines has to be generalized to m-phase systems, which is not usually respected in the literature focused on electric machine design, and it is rarely published. This paper summarizes the specific problems linked with the design of machines with different numbers of phases, focusing on the winding design and the calculation of equivalent circuit parameters. In addition to the direct effect of different numbers of phases, the impact of injecting higher order time harmonic components on the electromagnetic design of electric machines is analyzed. The obtained analytical results are verified by the measurement of a nine-phase experimental induction motor.

Plasma optics enables the manipulation of highly intense laser beams. Now, plasma holograms, involving the creation of a modulated plasma surface on a solid target, are reported — for example, plasma hologram fork gratings produce optical vortices. The manipulation of ultraintense laser beams gets increasingly challenging with growing laser peak power, as the breakdown of conventional optics imposes ever larger beam diameters. Using compact plasma-based optical elements to control or even generate such beams 1 , 2 , 3 , 4 is a promising approach, since plasmas can sustain considerable light intensities. We introduce a new type of plasma optics, called plasma holograms, by initiating plasma expansion on a flat solid target with a holographic prepulse beam focus. A modulated plasma surface then grows out of the target after ionization, which can be used for several picoseconds to diffract and spatially shape ultraintense laser beams. On the basis of this concept, we demonstrate the generation of fork plasma gratings, which we use to induce optical vortices on a femtosecond laser beam as well as its high-order harmonics, at intensities exceeding 10 19  W cm −2 . These plasma holograms open up a whole new range of possibilities for the manipulation of ultraintense lasers and the generation of structured coherent short-wavelength sources.

This paper presents a constraint-aware and systematic methodology for the design of LCL filters in grid-connected electric vehicle (EV) fast chargers. The proposed step-by-step process provides analytical sizing equations for the passive components L1, L2, and C while explicitly accounting for key design trade-offs such as voltage drop, reactive power draw, resonance frequency, and harmonic attenuation. Unlike conventional practice, which often relies on oversized inductors, the proposed approach selects inductance values near the permissible lower bound, resulting in a more compact and cost-effective filter solution. A 100 kVA bidirectional converter model was used to validate the design through time-domain simulations. Results show that the proposed filter maintains a grid current total harmonic distortion of less than 2% and limits individual high-order harmonics to below 0.3%, fully complying with IEEE Std. 519 taken as reference among other power quality standards. By selecting the minimum inductance that satisfies these limits, the required inductor mass is reduced by approximately 67% compared with a conservative design, translating into substantial savings in size and cost. The methodology is scalable to other power ratings by updating the base parameters, providing a practical design tool for EV charger manufacturers and utilities to achieve higher efficiency, lower cost, and reliable grid-code compliance.

In oscillating mechanical systems, nonlinearity is responsible for the departure from proportionality between the forces that sustain their motion and the resulting vibration amplitude. Such effect may have both beneficial and harmful effects in a broad class of technological applications, ranging from microelectromechanical devices to edifice structures. The dependence of the oscillation frequency on the amplitude, in particular, jeopardizes the use of nonlinear oscillators in the design of time-keeping electronic components. Nonlinearity, however, can itself counteract this adverse response by triggering a resonant interaction between different oscillation modes, which transfers the excess of energy in the main oscillation to higher harmonics, and thus stabilizes its frequency. In this paper, we examine a model for internal resonance in a vibrating elastic beam clamped at its two ends. In this case, nonlinearity occurs in the form of a restoring force proportional to the cube of the oscillation amplitude, which induces resonance between modes whose frequencies are in a ratio close to 1:3. The model is based on a representation of the resonant modes as two Duffing oscillators, coupled through cubic interactions. Our focus is put on illustrating the diversity of behavior that internal resonance brings about in the dynamical response of the system, depending on the detailed form of the coupling forces. The mathematical treatment of the model is developed at several approximation levels. A qualitative comparison of our results with previous experiments and numerical calculations on elastic beams is outlined.

We present a numerical model for the in-situ generation and focusing of extreme-ultraviolet (XUV) high harmonics via a Fresnel zone plate etched into a dielectric (MgO) surface. Our simulations show that propagation of the intense infrared field driving high-harmonic emission through the etched surface rings introduces well-controlled amplitude and phase modulations of the XUV field emitted from the surface itself that enhance the focusing efficiency up to 25%, beyond that of both conventional amplitude-modulated transmission XUV zone plates as well as ideal phase-only zone plates. Rings with a width comparable to the wavelength of the infrared driver exhibit strongest XUV emission with a larger phase modulation due to enhancement of the infrared field. On the contrary, a smooth phase modulation is achieved in the outskirts of the zone plates, where the width of the rings is much smaller than the infrared driving wavelength. These findings highlight the potential of sub-wavelength metasurface design in optimizing nanostructured optical elements for XUV nano-spectroscopy and on-chip XUV beam shaping.

This article deals with problems related to electromagnetic compatibility, which is a very important issue due to the fact of ensuring the proper coexistence of devices and systems in a given electromagnetic environment. The devices manufactured today can, on the one hand, be a source of electromagnetic disturbance emissions and, on the other hand, be susceptible to disturbance signals from the environment. A large group of receivers in which electronic specialised circuits are used are LED lamps. The operation of an RGB LED lamp due to higher harmonic current emissions has been analysed in this paper. Lamp tests were carried out in several stages. In each of them, the values of the generated higher harmonics were analysed and related to the parameters of the current flowing through the lamp. It was shown how the parameters of the current pulse affect the generated harmonics when the value of the luminous flux was changed, its colour was changed, or the built-in function was turned on. It is also shown how, for example, changing the value of an electronic component in the lamp’s power supply changes the parameters of the current and thus the value of the generated higher harmonics.

Discrete unstable modes of hypersonic laminar boundary layers, obtained from an eigenvalue analysis, provide insight into key transition scenarios. The character of such modes near the leading edge is often identified with the corresponding asymptotic free-stream behaviour of acoustic, vortical or entropic (thermal) content, which we designate fluid-thermodynamic (FT) components. In downstream regions, however, this direct one-to-one correspondence between discrete modes and FT components does not hold, since FT components interact in well-defined ways with the basic state and with each other (even under linear scenarios). In the present work, we perform an FT decomposition of discrete modes using momentum potential theory, to yield a physics-based analysis that complements linear stability theory in the linear regime, and seamlessly extends to the nonlinear domain where direct numerical simulations are appropriate. Linear and nonlinear saturated disturbance effects, different forcing types and wall thermal conditions are considered, with emphasis on phenomena occurring near stability-mode synchronization locations. The results show that, in the linear regime, each discrete mode contains all FT components, whose relative amplitudes vary with streamwise distance. Vortical components are always the largest, followed by thermal and acoustic components. These latter two show distinct fore and aft signatures near mode synchronization. The vortical component displays a series of rope-shaped recirculation-cell patterns across the generalized inflection point. However, both acoustic and thermal components display ‘trapped’ structures. The former contains an alternating monopole array between the wall and the critical layer, while the latter is confined to an undulating region between the wall and a wavy locus straddling the generalized inflection point. Nonlinear saturation in the region of Mack-mode growth further strengthens the rope-shaped structures in the vortical component and higher harmonics appear, whose form and location depend on the specific component. Wall cooling modifies the eigenfunctions such that the acoustic component accounts for more of its composition, consistent with its destabilization. Analysis of energy interactions among the FT components indicates that, even though the vorticity component is the largest, the thermal component induces the most significant source term for the growth of acoustic perturbations, possibly due to the trapped nature of both.

The beating of cilia and flagella is essential to perform many important biological functions, including generating fluid flows on the cell surface or propulsion of micro-organisms. In this work, we analyze the motion of isolated and demembranated flagella from green algae Chlamydomonas reinhardtii , which act as ATP-driven micro-swimmers. The beating flagella of Chlamydomonas exhibit an asymmetric waveform that is known to involve the superposition of a static component, corresponding to a fixed, intrinsic curvature, and a dynamic wave component traveling from base-to-tip at the fundamental beat frequency, plus higher harmonics. Here, we analyse free, hinged and clamped axonemes using principal component analysis. The axonemal motion is described with a high degree of accuracy, taking into account only the first four dominant eigenmodes. Our analysis suggests that the wave motion can be alternatively described with Fourier modes, with a wavelength λ , larger than the length of the filament L ( λ / L ≈ 1.3). Within this representation, we demonstrate that the main base-to-tip traveling wave component coexists with standing waves. Finally, we report the effect of calcium on the constituting wave components and find that the static mode is the most sensitive component to the calcium ion concentration.