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1
Yuan, Xiao Dong, Qun Li, Jin Hui i Bin Chen. "Research on the Existence of Genuine Inter-Harmonic Components Based on the Component Appearance Rate". Advanced Materials Research 875-877 (luty 2014): 1847–51. http://dx.doi.org/10.4028/www.scientific.net/amr.875-877.1847.
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The inter-harmonic spectrum of an electrical voltage or current from discrete Fourier transform can not only be caused by genuine inter-harmonic components, but can also be caused by other system disturbances. Therefore, the existence determination of genuine inter-harmonic s from the spectrum becomes the premise for further calculation of inter-harmonic parameters. From the theoretical perspective, this paper firstly analyzes and points out that the waveform difference among each cycle in the analysis window is the cause of the existence of inter-harmonic spectrum, and then presents a method to determine the existence of genuine inter-harmonic components, which is based on inter-harmonic time-frequency contour chart and the component appearance rate. The presented method firstly performs continuous discrete Fourier transform on the captured signal with certain duration and obtains the corresponding absolute time-frequency matrix, and then the genuine inter-harmonics can be distinguished based on the component appearance rate of the matrix and the criterion threshold. The method is easy to implement with clear principle, it can distinguish the genuine inter-harmonic s from the measured signal. The analysis on several data groups from real measurements verifies the effectiveness and the practicability of the method.
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Zhang, Run Han, Luo Quan Hu, Wei Fan i Xiao Lin Liu. "Application of Wavelet Transform with Tunable Q-Factor to Analysis of Non-Stationary Harmonics". Applied Mechanics and Materials 526 (luty 2014): 182–86. http://dx.doi.org/10.4028/www.scientific.net/amm.526.182.
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Harmonics of power system include steady and transient components, extraction and analysis of them can improve the power quality. Tunable Q-factor wavelet transform (TQWT), for which the Q-factor can be easily specified, is adopted to accomplish the extraction of non-stationary harmonic component from the noisy signal. The proposed method decomposes a signal into noise component and non-stationary harmonic component based on suitable Q-factor. Feasibility and effectiveness of the proposed method are verified by the simulation study.
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Mustafa, M. T. "Harmonic Morphisms Projecting Harmonic Functions to Harmonic Functions". Abstract and Applied Analysis 2012 (2012): 1–8. http://dx.doi.org/10.1155/2012/315757.
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For Riemannian manifoldsMandN, admitting a submersionϕwith compact fibres, we introduce the projection of a function via its decomposition into horizontal and vertical components. By comparing the Laplacians onMandN, we determine conditions under which a harmonic function onU=ϕ−1(V)⊂Mprojects down, via its horizontal component, to a harmonic function onV⊂N.
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He, Liyuan, Chuanwei Zhou i Lanjiang Wu. "Current Harmonic Control Method of Wind Turbine Based on PIR Controller". Journal of Physics: Conference Series 2480, nr 1 (1.04.2023): 012006. http://dx.doi.org/10.1088/1742-6596/2480/1/012006.
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Abstract Wind power equipment technology is the basis for the development of wind power generation. Aiming at the problem that the traditional PI controller is difficult to control the AC component of the current in the DQ axis, resulting in a large number of current harmonics in the process of power generation, which seriously affects the efficiency of power generation. This paper proposes a current harmonic control method for wind turbines based on a PIR controller. The mathematical model of wind power generation is constructed based on the synchronous rotating coordinate system. The current harmonic components are calculated according to the DQ rotor speed, shaft component, and other parameters. The PIR current harmonic controller is established by improving the ordinary PI controller to track and control the AC current signal. And finally, a current harmonic control target value is obtained according to different main control targets, and a specific harmonic component is eliminated. The experimental results show that the harmonic content is 3.12%, 2.06%, 1.17%, and 1. 02%, respectively, when the harmonic current order is 5, 7, 11, and 13. It is better than the comparison method. Therefore, this method can greatly reduce the harmonic content of the current in the process of different current orders, reduce the harmonic loss, and improve the generating efficiency of the unit.
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Sadiq, Muhammad Arslan, Dr Nusrat Husain, Fawad Shaukat, Ashraf Yahya, Zeeshan Ahmad Arfeen, Osama Mehboob i Huzaifa Altaf. "Prominence of Filtering Techniques for Harmonics Mitigation in Advanced Power Electronics Systems". Vol 4 Issue 2 4, nr 2 (27.06.2022): 512–25. http://dx.doi.org/10.33411/ijist/2022040220.
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With the advancement in technology, non-linear loads, continue to increase, and the enigma of harmonics is getting more and more serious. The huge addition of electronic loads in power systems has formed the problem of harmonic generation that has resulted in many associated drawbacks. This paper aims to analyze the harmonics in advanced power electronics-based systems and describes a solution to mitigate them through two distinguished filtering techniques. A rigorous analysis is done concerning the generation of harmonic distortion through different types of loads and harmonic mitigation by employing passive and active power filters. The active power (adaptive) filtering method mitigates all sorts of undesirable frequency components using artificial intelligence (AI) based algorithms by calculating the weight of the fundamental component and generating a harmonics replica to subtract it from the original periodic wave. The simulations that were done show that the indicated techniques can mitigate undesirable harmonics and can lower the total harmonic distortion (THD) effectively according to the statutory limit of the IEEE 519-2014 standard, thus lowering the associated drawbacks of harmonic generation in advanced power electronics systems.
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Su, Yu Xiang, Guo Ping Liu, Lin Li i Xiao Qun Shen. "Improved Hilbert-Huang Transform Applied in Power Quality Detection in Ship Power System". Applied Mechanics and Materials 88-89 (sierpień 2011): 365–72. http://dx.doi.org/10.4028/www.scientific.net/amm.88-89.365.
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In this paper, Hilbert-Huang Transform (HHT) and its improved method is introduced for detection and analysis of power quality in ship power system for the first time. This method is applied in detecting surge current and voltage interruption etc. of the ship power grid. Beginning-ending time, time-frequency, time-amplitude of the disturbance signal can be obtained accurately with HHT method. Mode mixing occurs when using empirical mode decomposition (EMD) to analyze harmonics, and consequently, all single harmonic components cannot be effectively decomposed. The improved HHT method based on Fourier transform is used to solve the problem in this paper. Complicated Harmonic can be decomposed into single harmonic component, and time-amplitude and time -frequency of harmonics can be obtained accurately by the improved method. In MATLAB/Simulink platform, harmonic source model of ship power system is established. Simulation results show that the improved method has better performance in Harmonics analysis than wavelet packet analysis.
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Fei, Zhenyan, Ming Lyu, Mariano Méndez, D. Altamirano, Guobao Zhang, G. C. Mancuso, Fu-Yuan Xiang i X. J. Yang. "The Harmonic Component of the Millihertz Quasi-periodic Oscillations in 4U 1636–53". Astrophysical Journal 922, nr 2 (25.11.2021): 119. http://dx.doi.org/10.3847/1538-4357/ac2501.
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Abstract We studied the harmonics of the millihertz quasi-periodic oscillations (mHz QPOs) in the neutron star low-mass X-ray binary 4U 1636–53 using the Rossi X-ray Timing Explorer observations. We detected the harmonics of the mHz QPOs in 73 data intervals, with most of them in the transitional spectra state. We found that the ratio between the rms amplitude of the harmonic and that of the fundamental remains constant in a wide range of the fundamental frequency. More importantly, we studied, for the first time, the rms amplitude of the harmonics versus energy in 4U 1636–53 in the 2–5 keV range. We found that the rms amplitude of both the harmonic and the fundamental shows a decreasing trend as the energy increases, which is different from the behaviors reported in QPOs in certain black hole systems. Furthermore, our results suggest that not all observations with mHz QPOs have the harmonic component, although the reason behind this is still unclear.
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Sasmoko, Priyo. "SIMULATOR GENERATOR HARMONIK". Gema Teknologi 16, nr 3 (6.02.2012): 146. http://dx.doi.org/10.14710/gt.v16i3.4713.
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Priyo Sasmoko, in this paper explain that the need of electric power recently progressively complex, not only the requirement of availability of electricity, but the quality of energy have become prime facie demand. Studies of electricity quality have been conducted by many experts, one of them is about harmonic. Harmonic represent waving current or tension which is tension distortion at electric power system mains so that can result unideal waveform. The study of harmonic required appliance or obyek which need to be checked. In this research Simulator Generator Harmonik is made a harmonic generator module which can deputize the appliance or obyek yielding harmonic with harmonic component and the THD which can be varried. This module works by dividing one cycle of mains become some slots so it can be got harmonic component as desired. To change the THD,a variation of linear load is used so that the ratio of non-linear load current can be varried. Keywords : Simulator, Harmonic component, THD
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Louossi, Theodore, Fabrice Kwefeu Mbakop, Abdouramani Dadje i Noel Djongyang. "Modeling of an Electrical Energy Switching System in Multisource Power Plants: The Case of Grid Connected Photovoltaic and Wind Power Systems". Journal of Renewable Energy 2022 (28.11.2022): 1–15. http://dx.doi.org/10.1155/2022/9972334.
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This paper proposes a multisource power plant management strategy for the proposed structure. This power plant consists of photovoltaic, wind, and grid. The principle of this management strategy is based on the reference currents and defines two components of the current namely a harmonic component related to the harmonics contained in the load current and current called fundamental related to the fundamental of the load current. This proposed strategy allows the different renewable sources to supply the load partially or totally. The harmonic component performs the power quality function while the fundamental component feeds the load and injects the surplus production into the grid. The power management is done according to the established scenarios and responds to the demand of the load. The simulations were carried out with Matlab software, and these results show the performance of this strategy for this structure studied to fulfill the following functions: power supply to the load, power factor (PF) correction, harmonic elimination, reactive energy compensation, and injection in the network of a current with a low rate of harmonic distortion lower than 1% in accordance with the IEEE Std 519-2014 standard.
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Alghamdi, Sultan, Hatem F. Sindi, Ahmed Al-Durra, Abdullah Ali Alhussainy, Muhyaddin Rawa, Hossam Kotb i Kareem M. AboRas. "Reduction in Voltage Harmonics of Parallel Inverters Based on Robust Droop Controller in Islanded Microgrid". Mathematics 11, nr 1 (29.12.2022): 172. http://dx.doi.org/10.3390/math11010172.
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In this article, a distributed control scheme to compensate for voltage harmonics in islanded microgrids is presented, where each distributed generation (DG) source has a primary control level and a secondary control level. In addition to the voltage and current control loops, the primary control level of DGs includes virtual impedance control loops in the main and harmonic components, which are responsible for dividing the power of the main component and the non-main component (harmonic) between the DGs of the microgrid, respectively. For coordinated operation between the inverters when facing the islanding phenomenon, it is very beneficial to use a droop controller structure. Here, the traditional droop controller is modified in such a way that the power is proportionally divided between the DGs, which causes accurate voltage regulation at the output of the DGs. By presenting a model for the inverter connected to the nonlinear load, a harmonic droop controller is designed. Through the droop controller related to each harmonic, the harmonic voltages are calculated and added to the reference voltage, which improves the quality of the output voltage. Then, the inverter voltage control loop is modified with resistive impedance in the presence of nonlinear loads in such a way that, when combined with the harmonic droop controller, the total harmonic distortion (THD) of the output voltage is significantly reduced. Lastly, the proposed method is implemented on the microgrid through MATLAB software, and the results show the ability of the proposed method to reduce voltage harmonics in the parallel operation of inverters.
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Nazir, Refdinal, Krismadinata Krismadinata i Rizka Amalia. "The Camparison of Harmonic Distortion Self-Excited Induction Generator with Isolated Synchronous Generator under Non-linear Loads". International Journal of Power Electronics and Drive Systems (IJPEDS) 6, nr 4 (1.12.2015): 759. http://dx.doi.org/10.11591/ijpeds.v6.i4.pp759-771.
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In this paper, the harmonic distortion for Self-Excited Induction Generator (SEIG) and an isolated synchronous generator (ISG) under non-linear load during steady state conditions are analyzed. The voltage and current harmonics distortion for both generators are calculated using the transfer function method in frequency domain for SEIG and phasor diagram method for ISG. This analysis is done independently one by one component for all harmonic components appear. The analysis results for both generators are verified to the laboratory test results. For loading with the same non-linear load to both generators, the harmonics distortion on the stator windings of SEIG was smaller than compare ISG. In addition, the harmonic distortion effects on other loads connected to PCC point of SEIG was lower than the other loads connected to ISG.
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Ghosh Moulic, S., i L. S. Yao. "Mixed Convection Along a Wavy Surface". Journal of Heat Transfer 111, nr 4 (1.11.1989): 974–79. http://dx.doi.org/10.1115/1.3250813.
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The results of a study of mixed-convection flow along a wavy surface are presented. The forced-convection component of the heat transfer contains two harmonics. The amplitude of the first harmonic is proportional to the amplitude of the wavy surface; the second harmonic is proportional to the square of this amplitude. Thus, for a slightly wavy surface, only the influence of the first harmonic can be detected. The natural-convection component is a second harmonic, with a frequency twice that of the wavy surface. Since natural convection has a cumulative effect, the second harmonic eventually becomes the dominant component far downstream from the leading edge where forced convection is the dominant heat transfer mode. The results also demonstrate that the total mixed-convection heat flux along a wavy surface is smaller than that of a flat surface.
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Zhao, Jinshuai, Honggeng Yang, Xiaoyang Ma i Fangwei Xu. "Evaluation of Harmonic Contributions for Multi Harmonic Sources System Based on Mixed Entropy Screening and an Improved Independent Component Analysis Method". Entropy 22, nr 3 (12.03.2020): 323. http://dx.doi.org/10.3390/e22030323.
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Evaluating the harmonic contributions of each nonlinear customer is important for harmonic mitigation in a power system with diverse and complex harmonic sources. The existing evaluation methods have two shortcomings: (1) the calculation accuracy is easily affected by background harmonics fluctuation; and (2) they rely on Global Positioning System (GPS) measurements, which is not economic when widely applied. In this paper, based on the properties of asynchronous measurements, we propose a model for evaluating harmonic contributions without GPS technology. In addition, based on the Gaussianity of the measured harmonic data, a mixed entropy screening mechanism is proposed to assess the fluctuation degree of the background harmonics for each data segment. Only the segments with relatively stable background harmonics are chosen for calculation, which reduces the impacts of the background harmonics in a certain degree. Additionally, complex independent component analysis, as a potential method to this field, is improved in this paper. During the calculation process, the sparseness of the mixed matrix in this method is used to reduce the optimization dimension and enhance the evaluation accuracy. The validity and the effectiveness of the proposed methods are verified through simulations and field case studies.
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Song, Peng Fei, Jian Sheng Zhang i Yong Hua Zhang. "Harmonic Detection Based on Genetic BP Neural Network". Applied Mechanics and Materials 427-429 (wrzesień 2013): 1892–95. http://dx.doi.org/10.4028/www.scientific.net/amm.427-429.1892.
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In view of the grid has a large number of harmonics, serious interference power quality, but the existing harmonic detection has many disadvantages, this paper uses genetic algorithm to optimize the BP neural network (GA-BP),Combined with fanaticism, independent component technique in the separation technology, achieve rapid separation and accurate fitting for harmonic reduction. The method to solve the problem of slow convergence speed of BP neural network and easier to fall into local optimal solution; Separation, independent component analysis in the signal could not accurate reduction the source signal. In this paper a signal containing harmonic component are simulated. Results show that GA-BP neural network optimization independent component analysis has convergence speed, high precision, compared with the single BP neural network and the independent component analysis of the superiority.
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Yao, Jianjun, Chenguang Xiao, Zhenshuai Wan, Shiqi Zhang i Xiaodong Zhang. "Acceleration Harmonics Identification for an Electro-Hydraulic Servo Shaking Table Based on a Nonlinear Adaptive Algorithm". Applied Sciences 8, nr 8 (9.08.2018): 1332. http://dx.doi.org/10.3390/app8081332.
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Since the electro-hydraulic servo shaking table came into existence, many nonlinear elements, such as, dead zone, friction and backlash, as well as its acceleration response has higher harmonics which result in acceleration harmonic distortion, when the electro-hydraulic system is excited by sinusoidal signal. For suppressing the harmonic distortion and precisely identify harmonics, a combination of the adaptive linear neural network and least mean M-estimate (ADALINE-LMM), is proposed to identify the amplitude and phase of each harmonic component. Specifically, the Hampel’s three-part M-estimator is applied to provide thresholds for detecting and suppressing the impulse noise. Harmonic generators are used by this harmonic identification scheme to create input vectors and the value of the identified acceleration signal is subtracted from the true value of the system acceleration response to construct the criterion function. The weight vector of the ADALINE is updated iteratively by the LMM algorithm, and the amplitude and phase of each harmonic, even the results of harmonic components, can be computed directly online. The simulation and experiment are performed to validate the performance of the proposed algorithm. According to the experiment result, the above method of harmonic identification possesses great real-time performance and it has not only good convergence performance but also high identification precision.
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Elgammal, Adel, i Curtis Boodoo. "Optimal Hybrid Filtering Strategy Using Adaptive Genetic-Fuzzy Logic Control for Harmonics Reduction in a Standalone Micro Hydroelectric Power Plant Coordinated with a PV System". European Journal of Electrical Engineering and Computer Science 5, nr 4 (9.08.2021): 56–62. http://dx.doi.org/10.24018/ejece.2021.5.4.348.
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Micro Hydro Power Plants are a type of power production that uses the force of river flows or waterfalls to generate electricity. The generator generates current waves and harmonic voltage, which are distorted wave disturbances that cause fundamental frequency multiplication. The major goal of this work is to design a reliable, efficient, and innovative harmonic mitigation approach for a stand-alone micro hydroelectric system that is coordinated with a photovoltaic renewable energy system utilising an active power filter. We may pick the active filter highest harmonic to be suppressed using the magnitude information supplied for each harmonic component. A hybrid filtering approach to remove harmonics and a novel MOGA optimization technique are part of the suggested harmonics reduction solution. The goal of this article is to determine the optimum filter for decreasing harmonics in an induction generator. As the harmonic damper, two filters were chosen: a passive filter and an active power filter. The suggested MOGA control method is compared to GA and evaluated on simulated data. In tracking harmonic components and fundamental frequency, the suggested MOGA control system provides high convergence speed and accuracy. It's extremely adaptable, and it can predict changes in the phase angle, amplitude, and fundamental frequency of harmonic components. When compared to the Genetic Algorithm method, it performs better. Simulation results using the SIMULINK/MATLAB simulation tool are delivered to evaluate the efficacy of the suggested active filter system. The impact of harmonic currents on the magnetic flux density is investigated using the rated condition as a reference. It has been established that the time harmonic is a significant element influencing generator performance. At the same time, the impacts of harmonic currents on the generator's eddy current loss, average torque, and torque ripple are investigated, as well as the mechanism of eddy current loss fluctuation.
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Mujezinović, Adnan, Emir Turajlić, Ajdin Alihodžić, Maja Muftić Dedović i Nedis Dautbašić. "Calculation of Magnetic Flux Density Harmonics in the Vicinity of Overhead Lines". Electronics 11, nr 4 (9.02.2022): 512. http://dx.doi.org/10.3390/electronics11040512.
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This paper considers the method for the calculation of magnetic flux density in the vicinity of overhead distribution lines which takes into account the higher current harmonics. This method is based on the Biot–Savart law and the complex image method. The considered method calculates the values of the magnetic flux density for each harmonic component of the current separately at all points of interest (usually lateral profile). In this way, it is possible to determine the contributions of individual harmonic components of the current intensity to the total value of magnetic flux density. Based on the contributions of individual harmonic components, the total (resultant) value of the magnetic flux density at points of interest is determined. Validation of the computational method is carried out by comparison of the results obtained by the considered calculation method with measurement results. Furthermore, the application of the calculation method was demonstrated by calculating magnetic flux density harmonics in the vicinity of two overhead distribution lines of typical phase conductor arrangements.
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Gockel, Hedwig E., i Robert P. Carlyon. "On mistuning detection and beat perception for harmonic complex tones at low and very high frequencies". Journal of the Acoustical Society of America 152, nr 1 (lipiec 2022): 226–39. http://dx.doi.org/10.1121/10.0012351.
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This study assessed the detection of mistuning of a single harmonic in complex tones (CTs) containing either low-frequency harmonics or very high-frequency harmonics, for which phase locking to the temporal fine structure is weak or absent. CTs had F0s of either 280 or 1400 Hz and contained harmonics 6–10, the 8th of which could be mistuned. Harmonics were presented either diotically or dichotically (odd and even harmonics to different ears). In the diotic condition, mistuning-detection thresholds were very low for both F0s and consistent with detection of temporal interactions (beats) produced by peripheral interactions of components. In the dichotic condition, for which the components in each ear were more widely spaced and beats were not reported, the mistuned component was perceptually segregated from the complex for the low F0, but subjects reported no “popping out” for the high F0 and performance was close to chance. This is consistent with the idea that phase locking is required for perceptual segregation to occur. For diotic presentation, the perceived beat rate corresponded to the amount of mistuning (in Hz). It is argued that the beat percept cannot be explained solely by interactions between the mistuned component and its two closest harmonic neighbours.
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Vivert, Miguel, Rafael Diez, Marc Cousineau, Diego Bernal Cobaleda, Diego Patino i Philippe Ladoux. "Real-Time Adaptive Selective Harmonic Elimination for Cascaded Full-Bridge Multilevel Inverter". Energies 15, nr 9 (20.04.2022): 2995. http://dx.doi.org/10.3390/en15092995.
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Selective Harmonics Elimination is a high-efficiency modulation method for multilevel inverters that allows handling very high voltage applications. It eliminates the most significant harmonics and fixes the desired fundamental component. The main issue of these techniques is the complex process to obtain the appropriate switching-angles, being necessary to calculate them offline, meaning that if some disturbances occur, the system will not be compensated. This article proposes a real-time selective harmonic elimination for a single-phase cascaded multilevel inverter. The control strategy maintains constant the fundamental component of the output voltage while removing its third, fifth, and seventh order harmonics. The switching-angles are dynamically adapted to compensate for variations in the input voltage and the load. This is done by obtaining a virtual dynamic system using Groebner basis, an adaptation of the Newton-Raphson method, and implementing a digital PI controller into the virtual dynamical model. This adaptive modulation technique is validated experimentally in a 200 W, 9-levels Cascaded Full Bridge Inverter, canceling the harmonics and regulating the fundamental components in all the tests. The developed theory can be adapted or extended for any multilevel inverter modulated by selective harmonic elimination.
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Rastegar, J., L. Yuan i J. Zhang. "Smart Actuator Positioning and Displacement Transmissibility in Serial and Parallel Robot Manipulators for Performance Enhancement". Journal of Mechanical Design 127, nr 4 (14.09.2004): 589–95. http://dx.doi.org/10.1115/1.1898340.
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A method is presented for the evaluation of the transmissibility of displacement from smart (active) actuators integrated in the structure of robot manipulators to the manipulator joint and end-effector displacements. The method is based on studying the characteristics of the Jacobian of the mapping function between the two displacements for a given position of the robot manipulator. The developed method provides a tool for the determination of the positioning of smart actuators to provide maximum effectiveness in eliminating high harmonics of the joint or the end-effector motion. In robots with serial and parallel kinematics chains containing nonprismatic joints, due to the associated kinematics nonlinearity, if the joint motions were synthesized with low harmonic trajectories, the end-effector trajectory would still contain high harmonics of the joint motions. Alternatively, if the end-effector motion were synthesized with low harmonic components, due to the inverse kinematics nonlinearity, the actuated joint trajectories would contain a significant high harmonic component. As a result, the operating speed and tracking precision are degraded. By integrating smart materials based actuators in the structure of robot manipulators to provide small amplitude and high frequency motions, the high harmonic component of the actuated joint and/or the end-effector motions can be significantly reduced, thereby making it possible to achieve higher operating speed and tracking precision.
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NORCIA, ANTHONY M., WOLFGANG WESEMANN i RUTH E. MANNY. "Electrophysiological correlates of vernier and relative motion mechanisms in human visual cortex". Visual Neuroscience 16, nr 6 (listopad 1999): 1123–31. http://dx.doi.org/10.1017/s0952523899166124.
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Vernier onset/offset thresholds were measured both psychophysically and with the steady-state VEP by introducing a series of horizontal breaks in a vertical square-wave luminance grating. Several diagnostic tests indicated that the first harmonic component of the evoked response generated by periodic modulation of offset gratings taps mechanisms that encode the relative position of spatial features. In the first test, a first harmonic component was only found with targets that contained transitions between collinear and noncollinear states. VEP vernier onset/offset thresholds obtained with foveal viewing were in the range of 15–22 arc sec. Control experiments with transitions between symmetrical, noncollinear patterns (relative motion) did not produce first harmonic components, nor did full-field motion of a collinear grating. A second series of experiments showed that VEP thresholds based on the first harmonic component of the vernier onset/offset response had an eccentricity dependence that was very similar to that found in a psychophysical discrimination task that required a left/right position judgment (vernier acuity). Other recordings showed that the first harmonic of the vernier onset/offset VEP was degraded by the introduction of a gap between stimulus elements, as is the displacement threshold. The vernier onset/offset target also produced a second harmonic component that was virtually identical to the one produced by a relative motion stimulus. Displacement thresholds based on these second harmonic components showed a more gradual decline with retinal eccentricity than did the first harmonic component elicited by vernier offsets. The second harmonic of the vernier onset/offset VEP was relatively unaffected by the introduction of gaps between the stimulus elements. The first and second harmonic components of the vernier onset/offset VEP thus tap different mechanisms, both of which support displacement thresholds that are finer than the resolution limits set by the spacing of the photoreceptors (hyperacuity).
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Li, Po, Xiang Li, Jinghui Li, Yimin You i Zhongqing Sang. "A Real-Time Harmonic Extraction Approach for Distorted Grid". Mathematics 9, nr 18 (12.09.2021): 2245. http://dx.doi.org/10.3390/math9182245.
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Harmonic interference is a major hazard in the current power system that affects power quality. How to extract harmonics quickly and accurately is the premise to ensure the sustainable operation of power system, which is particularly important in the field of new energy power generation. In this paper, a harmonic extraction method based on a time-varying observer is proposed. Firstly, a frequency estimation algorithm is used to estimate the power grid current frequency, which can estimate the frequency in real time. Then, applying the zero-crossing detection method to convert the frequency into a phase variable. Finally, using the phase variable and integral current signal as input, a observer is modeled to extract each order harmonic component. The proposed method is evaluated on a FGPA test platform, which shows that the method can extract the harmonic components of the grid current and converge within 80 ms even in the presence of grid distortions. In the verification case, the relative errors of the 1st, 5th, 7th and 11th harmonics are 0.005%, −0.003%, 0.251% and 0.620%, respectively, which are sufficiently small.
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Junesco, Devan, Shahad Al-Youif, Mohannad Jabbar Mnati i Mohammad Ali Tofigh. "Various Passive Filter Designs Proposed for Harmonic Extenuation in Industrial Distribution Systems". International Journal of Engineering & Technology 7, nr 4.11 (2.10.2018): 75. http://dx.doi.org/10.14419/ijet.v7i4.11.20691.
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This paper discusses various passive filter designs to reduce the harmonic in the industrial distributions system. The passive filter used is a single and double tuned harmonic filter. In the designing of this filter, analyzing filter properties of passive component of the filter. The study was conducted to examine the efficacy of using single and double tuned filters in reducing harmonic as well as determining the best location to install the filters. Different system effects and load limits on harmonic distortion and performance of filters are also being examined. The output of the simulation indicated that a superior performance in extenuating harmonics by the double tuned filter is more effective in reducing harmonics when it is placed near the harmonic generating loads.
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Xu, Maoguang, Zhongqing Sang, Xiang Li, Yimin You i Dongyun Dai. "An Observer-Based Harmonic Extraction Method with Front SOGI". Machines 10, nr 2 (26.01.2022): 95. http://dx.doi.org/10.3390/machines10020095.
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With the further development of harmonic pollution in the power system, scientists have carried out research on harmonics. Among them, harmonic detection is the first step in harmonic research. In this paper, a harmonic detection method based on an observer is proposed. This method first uses the cascaded Second-Order Generalized Integration (SOGI) algorithm, which can filter the Direct Current (DC) component of the input signal to extract the fundamental frequency, and then uses a time-varying observer to extract the harmonics. This can be used to extract harmonics from a distorted online grid signal. The effectiveness of the proposed method was evaluated on the Speedgoat Rapid Control Prototype (RCP) platform. The results show that it can complete the convergence within 0.05 s, and the standard deviation after stability will not exceed 1%.
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Kostinskiy, S. S. "Review and results of studies of the harmonic composition of the current consumed by low-power frequency converters, as well as methods and devices to reduce their negative impact on power supply systems". Power engineering: research, equipment, technology 22, nr 2 (15.05.2020): 27–42. http://dx.doi.org/10.30724/1998-9903-2020-22-2-27-42.
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The ACS150 frequency Converter was chosen as the object for experimental research. On the basis of the measurements it is concluded that in the spectral composition of current drawn by the frequency Converter, in addition to currents the main harmonic component is dominated by currents 5, 7, 11, 13, and 17th harmonics, i.e. harmonic components of odd non-multiple of three. Currents 3, 9 and 15 th harmonic components are also present in the spectral composition, but their value is much smaller. Also, based on the data obtained, it can be argued that with a decrease in the frequency of motor speed control and the load value of the frequency Converter, the number of pulsations on the current waveform increases, as a result, there is an increase in the values of the higher harmonic components and an increase in the value of the total harmonic components of the current. The main contribution to the increase in the index of the total harmonic components of the amperage with a decrease in the load of the frequency Converter and the output frequency of the motor speed control is made by odd harmonic components of the amperage multiple of three, at the same time harmonic components of the amperage non-multiple of three, namely the 5th and 7th order, are not subject to change. A brief review of technical solutions aimed at improving the electromagnetic compatibility of asynchronous frequency-controlled drive is given. In particular, such solutions as increasing the number of semiconductor switches used in inverters, improving control modes, the use of special separation transformers, passive (resonant) and active filters are noted.
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Chang, Gary W., Yu-Luh Lin, Yu-Jen Liu, Gary H. Sun i Johnson T. Yu. "A Hybrid Approach for Time-Varying Harmonic and Interharmonic Detection Using Synchrosqueezing Wavelet Transform". Applied Sciences 11, nr 2 (14.01.2021): 752. http://dx.doi.org/10.3390/app11020752.
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With widespread non-linear loads and the increasing penetration of distributed generations in the power system, harmonic pollution has become a great concern. The causes of harmonic pollution not only include the integer harmonics, but also interharmonics, which exacerbate the complexity of harmonic analysis. In addition, the output variability of highly non-linear loads and renewables such as electric arc furnaces and photovoltaic solar or wind generation may lead to weakly time-varying harmonics and interharmonics in both frequency and magnitude. These features present challenges for accurate assessment of associated power-quality (PQ) disturbances. To tackle such increasing time-varying PQ problems, a hybrid detection method using synchrosqueezing wavelet transform (SSWT) is proposed. The proposed method first obtains the proper parameter values for the mother wavelet according to numerical computations. The wavelet transform-based synchrosqueezing and a clustering method are applied to determine each frequency component of the waveform under assessment. The time-domain waveform and the associated magnitude of each frequency component is then reconstructed by the inverse SSWT operation. The novelty of the proposed method is that it can decompose the measured waveform containing both harmonics and interharmonics into intrinsic mode functions without the need for fundamental frequency detection. Compared to other time–frequency analysis methods, SSWT has better anti-noise and higher resolution of time–frequency curves; even the measured signal has close frequency components. Simulation results and actual measurement validations show that the proposed method is effective and relatively accurate in time-varying harmonic and interharmonic detection and is suitable for applications in power networks and microgrids that have high penetration of renewables or non-linear loads causing time-varying voltage or current waveforms.
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Guo, Yufu, Hang Xu i Aobing Chi. "Broadband Dynamic Phasor Measurement Method for Harmonic Detection". Electronics 11, nr 11 (24.05.2022): 1667. http://dx.doi.org/10.3390/electronics11111667.
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A large number of nonlinear loads and distributed energy sources are connected to the power system, leading to the generation of broadband dynamic signals including inter-harmonics and decaying DC (DDC) components. This causes deterioration of power quality and errors during power measurement. Therefore, effective phasor estimation methods are needed for accurate monitoring and effective analysis of harmonics and interharmonic phasors. For this purpose, an algorithm is proposed in this paper that is implemented in two parts. The first part is based on the least square method in order to obtain accurate DDC component. In the second part, a Taylor–Fourier model of broadband dynamic harmonic phasor is established. The regularization optimization problem of the sparse acquisition model is solved by harmonic vector estimation method. Finally, the piecewise Split-Bregman Iterative (SBI) framework is used to obtain the estimated value of the harmonic phasor measurement and to realize the reconstruction of the original signal. Through simulation and performance test, the proposed algorithm significantly improves the accuracy of the phasor measurement and estimation, and can provide a reliable theoretical basis for the PMU measurement.
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Liu, Shaojie, Yingying Zhao, Yue Tian, Yubo Fan i Jifang Ye. "Research on Supraharmonics Suppression Strategy of Distribution Network based on Dynamic Cooperative Control of Multiple Harmonic Sources". Journal of Physics: Conference Series 2488, nr 1 (1.05.2023): 012047. http://dx.doi.org/10.1088/1742-6596/2488/1/012047.
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Abstract In view of the increasing number of supraharmonic sources in distribution network and the increasing distortion of power grid waveform, a strategy of supraharmonic suppression in distribution network based on dynamic coordinated control of multi-harmonic sources is proposed. The characteristic harmonic current components related to carrier frequency in the output current of each supraharmonic source are shifted by several angles through carrier phase shifting, so that the total current harmonics of all supraharmonic sources merged into point of common coupling (PCC) are obviously reduced to meet the requirements of PCC supraharmonic control. This strategy dynamically adjusts the phase-shift angle according to the running number of supraharmonic sources to avoid the problem that the harmonics of the remaining supraharmonic sources cannot be cancelled after some supraharmonic sources exit the system. The simulation results show that the supraharmonic suppression strategy based on dynamic cooperative control of multi-harmonic sources in distribution network can significantly suppress the supraharmonic current component and voltage distortion rate of a certain number of parallel points.
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Zhao, W., H. A. Wolgamot, P. H. Taylor i R. Eatock Taylor. "Gap resonance and higher harmonics driven by focused transient wave groups". Journal of Fluid Mechanics 812 (9.01.2017): 905–39. http://dx.doi.org/10.1017/jfm.2016.824.
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The first and higher harmonic components of the resonant fluid response in the gap between two identical fixed rectangular boxes are experimentally investigated in a wave basin. Gap response is excited by transient wave groups (being based on scaled versions of the autocorrelation function of sea-state spectra, representing NewWaves, the average shape of large waves in a sea state). Several different wave groups with different maximum surface elevations, spectral peak frequencies and bandwidths are used, while the bilge shape of the boxes and approach angle of the waves are also varied. Unlike a simple regular wave, it is complicated to separate the harmonic components for a transient wave group due to nonlinear wave–wave and wave–structure interactions. A four-phase combination methodology is used to separate the first four harmonic components, and this also allows higher harmonic components to be isolated with simple digital frequency filtering. Harmonic components up to 14th order in the incident wave amplitude have been extracted. It is shown that for an incident group with appropriate frequency content, the linear gap response may be substantially smaller than the second harmonic component, which is strongly driven via quadratic coupling of the linear terms from the incident wave and occurs in the gap resonant modes. Double frequency excitation may have important practical implications for offshore operations. Fourth and zeroth (long-wave) harmonics in the gap are further driven via quadratic coupling of the second harmonic itself. Linear damping coefficients for the first few modes of the gap resonant response are derived from measured time series using a numerical fit and shown to be higher than those from linear diffraction calculations.
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Solekhan, Solekhan, Yoyon K. Suprapto i Wirawan Wirawan. "Impulsive spike enhancement on gamelan audio using harmonic percussive separation". International Journal of Electrical and Computer Engineering (IJECE) 9, nr 3 (1.06.2019): 1700. http://dx.doi.org/10.11591/ijece.v9i3.pp1700-1710.
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Impulsive spikes often occur in audio recording of gamelan where most existing methods reduce it. This research offers new method to enhance audio impulsive spike in gamelan music that is able to reduce, eliminate and even strengthen spikes. The process separates audio components into harmonics and percussive components. Percussion component is set to rise or lowered, and the results of the process combined with harmonic components again. This study proposes a new method that allows reducing, eliminating and even amplifying the spike. From the similarity test using the Cosine Distance method, it is seen that spike enhancement through Harmonic Percussive Source Separation (HPSS) has an average Cosine Distance value of 0.0004 or similar to its original, while Mean Square Error (MSE) has an average value of 0.0004 that is very small in average error and also very similar. From the Perceptual Evaluation of Audio Quality (PEAQ) testing with Harmonic Percussive Source Separation (HPSS), it has a better quality with an average Objective Difference Grade (ODG) of -0.24 or Imperceptible.
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Bezzubm, Maksim, Oleksiy Bialobrzheskyi i Oleg Todorov. "The power harmonic components distribution study in the power circuit of a dynamic voltage restorer". Electrical Engineering and Power Engineering, nr 1 (30.06.2023): 19–29. http://dx.doi.org/10.15588/1607-6761-2023-1-2.
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Purpose. Investigation of the distribution of harmonic power components in the power circuit of a dynamic voltage restorer. Methodology. On the basis of the differential equations of the power circuit of a dynamic restorer, a search for the relationship between the mode parameters and the parameters of the circuit elements is performed. On the basis of the obtained expressions, a model of a dynamic voltage regulator was created using the methods of mathematical modeling in the visual programming environment.. Findings. The equations that reflect the relationship between the mode parameters of a dynamic voltage restorer and the parameters of circuit elements are obtained. As a result of modeling the mode with different harmonic composition of current and voltage, the following features of the distribution of instantaneous power components are revealed. Originality. It has been established that the presence of different current and voltage harmonics acting in the transformer of a dynamic restorer causes additional power harmonics that are transformed in the windings. It is noted that the low-frequency power harmonics of the LC filter dominate on the capacitor, which is connected in parallel to the transformer winding, while the level of high-frequency components caused by PWM modulation for the capacitor and the filter choke differ slightly. The zero-frequency power component of the storage capacitor corresponds to a tripled zero-time power component at the output of the converter, which is due to its operation in three phases. This cannot be extended to the second and third harmonics of the powers of the converter and the capacitor; these components are absent in the latter, which is due to energy exchange processes between the phases of the converter. Practical value. Using the obtained expressions, the principle of determining the parameters of the elements of the power circuit of a dynamic voltage restorer, in particular, the storage elements, is formulated.
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Mehta, Anahita H., i Andrew J. Oxenham. "Role of perceptual integration in pitch discrimination at high frequencies". JASA Express Letters 2, nr 8 (sierpień 2022): 084402. http://dx.doi.org/10.1121/10.0013429.
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At very high frequencies, fundamental-frequency difference limens (F0DLs) for five-component harmonic complex tones can be better than predicted by optimal integration of information, assuming performance is limited by noise at the peripheral level, but are in line with predictions based on more central sources of noise. This study investigates whether there is a minimum number of harmonic components needed for such super-optimal integration effects and if harmonic range or inharmonicity affects this super-optimal integration. Results show super-optimal integration, even with two harmonic components and for most combinations of consecutive harmonic, but not inharmonic, components.
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Ichsari, Lintang Fauzia, Gentur Handoyo, Heryoso Setiyono, Aris Ismanto, Jarot Marwoto, Muh Yusuf i Azis Rifai. "Studi Komparasi Hasil Pengolahan Pasang Surut Dengan 3 Metode (Admiralty, Least Square Dan Fast Fourier Transform) Di Pelabuhan Malahayati, Banda Aceh". Indonesian Journal of Oceanography 2, nr 2 (9.06.2020): 121–28. http://dx.doi.org/10.14710/ijoce.v2i2.7985.
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Pelabuhan Malahayati menjadi alur lintas serta tempat sandar bagi peti kemas domestik. Untuk menjalankan aktifitas pelabuhan secara optimal serta merencanakan pembangunan pelabuhan, pengetahuan mengenai tipe dan karakteristik pasang surut sangat penting. Pengolahan data pasang surut dengan berbagai metode dapat memberikan hasil yang berbeda-beda. Tujuan penelitian ini adalah untuk mengetahui karakteristik pasang surut dan komponen harmonik pembangkit pada lokasi penelitian, mengetahui perbandingan hasil pengolahan pasang surut dengan metode admiralty, least square dan fast fourier transform. Serta melakukan prediksi elevasi pasang surut dengan metode least square pada waktu setelah penelitian. Validasi hasil pengolahan pasang surut dilakukan dengan menghitung nilai RMSE hasil pengolahan metode least square terhadap data lapangan. Ketiga metode menghasilkan tipe pasang surut Pelabuhan Malahayati yaitu tipe pasang surut harian ganda. Metode admiralty menghasilkan 9 komponen utama pasang surut, sedangkan metode least square menhasilkan sejumlah 68 komponen. Sementara metode FFT digunakan untuk mengidentifikasi 21 komponen harmonik pasang surut Pelabuhan Malahayati. Didapatkan dominasi komponen harmonik pasang surut pada Pelabuhan Malahayati, yaitu komponen semidiurnal (M2 dan S2). Didapatkan nilai RMSE pada hasil pengolahan sebesar 32 cm, sedangkan RMSE hasil prediksi sebesar 64 cm. Perbedaan nilai formzhal kurang dari 0.02 sedangkan perbedaan nilai amplitudo masing-masing komponen pasang surut kurang dari 0.1 meter. Malahayati Port serves as crossing lane and transit for domestic container ships. To carry out port activities optimally and design port development, knowledge of the types and characteristics of the tides in the location is very important. This study was to determine the tidal characteristics and harmonic components of the Malahayati Port, to compare the results of tidal processing using 3 methods (admiralty, least square and fast fourier transform) and to predict the elevation of tides after this study using the least square method. Validation on this study was done by calculating the RMSE between least square result and field data. All of the 3 methods resulted the Malahayati Port tidal type which was semi diurnal tide. The admiralty method produced 9 major components, while the least square produced 68 of tidal harmonic components. And the FFT is used to identify 21 harmonic components of the Malahayati Port. Obtained that the dominance of the tidal harmonic component at the Malahayati Port was semidiurnal component M2 and S2. Noted that the RMSE value between least square result and field data is 32 cm, while the prediction RMSE is 64 cm. Using 3 methods the Formzhal difference is less than 0.02 while the difference in the amplitude of tidal component is less than 0.1 meters.
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Ismail, Baharuddin, Syed Idris Syed Hassan, Rizalafande Che Ismail i Azralmukmin Azmi. "Elimination of Lower Order Harmonics in Seven-Level Cascaded Inverters". Applied Mechanics and Materials 793 (wrzesień 2015): 206–10. http://dx.doi.org/10.4028/www.scientific.net/amm.793.206.
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This paper deals with an elimination of lower order harmonics in the seven - level cascaded inverters. The main objective of selective harmonic elimination pulse width modulation strategy is eliminating lower order harmonic by solving nonlinear equations, while the fundamental component is satisfied. In this paper, the Particle Swarm Optimization (PSO) is applied to a seven-level inverter for solving the nonlinear equation. With the proposed approach, the required switching angles are computed efficiently by PSO algorithm. Lower order harmonics up to the 7th are eliminated. Simulation results verify the proposed method.
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Hörlein, R., S. Steinke, A. Henig, S. G. Rykovanov, M. Schnürer, T. Sokollik, D. Kiefer i in. "Dynamics of nanometer-scale foil targets irradiated with relativistically intense laser pulses". Laser and Particle Beams 29, nr 4 (4.10.2011): 383–88. http://dx.doi.org/10.1017/s0263034611000462.
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AbstractIn this paper we report on an experimental study of high harmonic radiation generated in nanometer-scale foil targets irradiated under normal incidence. The experiments constitute the first unambiguous observation of odd-numbered relativistic harmonics generated by the v × B component of the Lorentz force verifying a long predicted property of solid target harmonics. Simultaneously the observed harmonic spectra allow in-situ extraction of the target density in an experimental scenario which is of utmost interest for applications such as ion acceleration by the radiation pressure of an ultraintense laser.
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Zhang, Xian, Tao Tao, Gedong Jiang, Xuesong Mei i Chuang Zou. "A Refined Dynamic Model of Harmonic Drive and Its Dynamic Response Analysis". Shock and Vibration 2020 (29.06.2020): 1–13. http://dx.doi.org/10.1155/2020/1841724.
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To highlight the key factors which influence the dynamic performance of the harmonic drive, a refined harmonic drive model considering nonlinear stiffness, kinematic error, and friction of the critical components is established. A dedicated experimental apparatus based on double motor twisting is constructed to measure the characteristics of harmonic drive, and the attribute parameters of the proposed model are identified. A series of experiments on the dynamic transmission error at different driving velocities are carried out to verify the proposed model. Based on the proposed model, the influence of different component stiffness on the velocity step response of the harmonic drive is analyzed. The results show that the influence of the component stiffness on the system dynamic response is more significant at high driving velocity, the increase of the stiffness of each component will decrease the dynamic transmission accuracy of harmonic drive, and the bearing radial stiffness is the most sensitive parameter to system’s dynamic response among all the stiffness factors.
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Aalami, H. A., i R. Salehi. "Extended Modulation Index with more Eliminated Low Order Harmonics at Cascaded Multilevel Inverters". Applied Mechanics and Materials 492 (styczeń 2014): 123–27. http://dx.doi.org/10.4028/www.scientific.net/amm.492.123.
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Principle aim in standard Selective Harmonic Elimination pulse wide modulation (SHE-PWM) is elimination of low-order harmonics as well as production of desired fundamental component. To accomplish this objective, a set of N switching angles should be determined. In fact, N-1 angles are hired to remove N-1 harmonics from voltage waveform and one angle is allotted to produce the fundamental. This paper presents a solution in order to remove low order harmonics as much as possible. It suggests eliminating next harmonic instead of highest order harmonic in infeasible points. A genetic algorithm is employed to solve the new transcendental equation for finding the switching angles. The proposed method is experimentally applied to a seven-level cascaded H-bridge inverter. The results confirm the validity and effectiveness of the proposed method in extending modulation index range.
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Cooper, Bonnie, Barry B. Lee i Dingcai Cao. "Macaque retinal ganglion cell responses to visual patterns: harmonic composition, noise, and psychophysical detectability". Journal of Neurophysiology 115, nr 6 (1.06.2016): 2976–88. http://dx.doi.org/10.1152/jn.00411.2015.
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The goal of these experiments was to test how well cell responses to visual patterns can be predicted from the sinewave tuning curve. Magnocellular (MC) and parvocellular (PC) ganglion cell responses to different spatial waveforms (sinewave, squarewave, and ramp waveforms) were measured across a range of spatial frequencies. Sinewave spatial tuning curves were fit with standard Gaussian models. From these fits, waveforms and spatial tuning of a cell's responses to the other waveforms were predicted for different harmonics by scaling in amplitude for the power in the waveform's Fourier expansion series over spatial frequency. Since higher spatial harmonics move at a higher temporal frequency, an additional scaling for each harmonic by the MC (bandpass) or PC (lowpass) temporal response was included, together with response phase. Finally, the model included a rectifying nonlinearity. This provided a largely satisfactory estimation of MC and PC cell responses to complex waveforms. As a consequence of their transient responses, MC responses to complex waveforms were found to have significantly more energy in higher spatial harmonic components than PC responses. Response variance (noise) was also quantified as a function of harmonic component. Noise increased to some degree for the higher harmonics. The data are relevant for psychophysical detection or discrimination of visual patterns, and we discuss the results in this context.
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Siregar, Yulianta, Waleed Khalid Al-Azzawi, Zulkarnaen Pane, Unedo E Parhusip i Suherman Suherman. "Study of harmonic distortion from variable speed drive and energy saving lamps". Indonesian Journal of Electrical Engineering and Computer Science 27, nr 2 (1.08.2022): 667. http://dx.doi.org/10.11591/ijeecs.v27.i2.pp667-677.
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The power <span>electronic component has been widely used in the current industrial era. It has been considered more efficient than the previous devices as it saves more space and uses less power. One example of power electronic components is the variable speed drive for speed regulation of electric motors in the industrial world. Another application of power electronic components is to be used in energy-saving lamps. The use of power electronic components in these two loads generates harmonic distortion and reduces network power quality. In this paper, the authors analyzed the harmonics in both loads. As a result, the total harmonic distortion (THD) current for four energy-saving lamps is 88.3%. Meanwhile, the THD current at the 50 Hz, 5 A, and variable speed drive is 46.2%. After mixing the two loads, the THD current decreases by around 35%.</span>
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Zhukovsky, K. V. "Analytical account for off-axis effects in X-ray radiation of free electron lasers". Izvestiya vysshikh uchebnykh zavedenii. Fizika 64, nr 1 (2021): 21–28. http://dx.doi.org/10.17223/00213411/64/1/21.
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We give analytical description of generation of harmonics of the undulator radiation (UR) with account for the finite electron beam size, emittance, off-axis beam deviation and electron energy spread, as well as for the constant magnetic components and field harmonics effects. We give exact analytical expressions for the generalized Bessel and Airy functions, which describe the spectrum line shape and intensities in the two-frequency bi-harmonic undulator with account for the above factors. The obtained analytical formulae distinguish contributions of each field component and every undulator and beam parameter on the harmonic radiation in free electron lasers (FEL). The effect of the field on the harmonic radiation is analyzed with account for the beam finite size and its off-axis deviation. The phenomenological model is employed for the FEL modeling; with its help we study the harmonic generation, including even ones, in the experiments LCLS and LEUTL. We demonstrate analytically that strong second FEL harmonic in X-ray FEL at the wavelengths λ = 0.75nm in the LCLS experiment is caused by the deviation of the electron trajectories off the axis in 15 μm on the gain length 1.6 m, which is comparable with the beam size; the strong second FEL harmonic in the LEUTL experiment at the wavelength λ = 192nm can be attributed to interaction of the electrons in wide, ~ 0.2 mm, beam with the photon radiation at the gain length 0.87 m. The modeling results fully agree with the measurements. The developed formalism allows the analysis of projected and built FELs and their radiation, helps minimizing losses and correcting magnetic fields; it also shows physical background and reasons for each harmonic radiated power in the FEL.
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Liu, Jieng-Jang, i Yee-Pien Yang. "Disk Wobble Control in Optical Disk Drives". Journal of Dynamic Systems, Measurement, and Control 127, nr 3 (13.09.2004): 508–14. http://dx.doi.org/10.1115/1.1988339.
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Focusing errors in optical disk drives comprise significant periodic components and an eventful dc content. The dc component is not explicitly taken into account in many periodic compensation methods. This paper investigates the design of adaptive feedforward cancellation (AFC) and frequency adaptive control technique (FACT) algorithms for periodic components as well as dc disturbance compensation. Both algorithms are applied as a plug-in module to an optical disk drive for demonstrating their facility in the reduction of focusing errors. By making good use of frequency sampling filter (FSF), the real-time harmonic identification can be fulfilled in FACT method for various playing speeds. Analysis and experimental results show that FACT has better properties than AFC in terms of dc cancellation and harmonic independence. It is also shown that AFC fails when both the dc content and harmonics are compensated simultaneously.
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McKeefry, D. J., M. H. A. Russell, I. J. Murray i J. J. Kulikowski. "Amplitude and phase variations of harmonic components in human achromatic and chromatic visual evoked potentials". Visual Neuroscience 13, nr 4 (lipiec 1996): 639–53. http://dx.doi.org/10.1017/s0952523800008543.
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AbstractOccipital visual evoked potentials (VEPs) were recorded in response to low-contrast, low spatial-frequency chromatic, and achromatic gratings. Fast Fourier Transform (FFT) and time-domain analysis were used to reveal differences in harmonic content and amplitude of chromatic and achromatic response components over a wide range of temporal frequencies. The chromatic ON/OFF VHP is dominated by the fundamental component indicating that onset and offset responses are different. This type of response is typical of neurons with sustained type response characteristics. Conversely, the achromatic onset VEP contains a predominant second harmonic component in addition to the fundamental. This similarity between onset and offset responses suggests that transient mechanisms are responsible for the generation of achromatic components. Frequency analysis of VEPs elicited by phase-reversing stimuli reveals that all of the response energy is concentrated at the second harmonic of the stimulating frequency. The magnitude of the second harmonic component is maximal for achromatic stimuli and undergoes a distinct minimum for isoluminant, chromatic stimuli. This behavior indicates that under the stimulus conditions used, magnocellular neurons with transient characteristics dominate the reversal VEP.
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Aboadla, Ezzidin Hassan, Sheroz Khan, Mohamed H. Habaebi, Teddy Surya Gunawan, Belal A. Hamida, Mashkuri Bin Yaacob i Ali Aboadla. "A novel optimization harmonic elimination technique for cascaded multilevel inverter". Bulletin of Electrical Engineering and Informatics 8, nr 2 (1.06.2019): 405–13. http://dx.doi.org/10.11591/eei.v8i2.1500.
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The main goal of utilizing Selective Harmonic Elimination (SHE) techniques in Multilevel Inverters (MLI) is to produce a high-quality output voltage signal with a minimum Total Harmonic Distortion (THD). By calculating N switching angles, SHE technique can eliminate (N-1) low order odd harmonics of the output voltage waveform. To optimized and obtained these switching angles, N of nonlinear equations should be solved using a numerical method. Modulation index (m) and duty cycle play a big role in selective harmonic elimination technique to obtain a minimum harmonic distortion and desired fundamental component voltage. In this paper, a novel Optimization Harmonic Elimination Technique (OHET) based on SHE scheme is proposed to re-mitigate Total Harmonic Distortion. The performance of seven-level H-bridge cascade inverter is evaluated using PSIM and validated experimentally by developing a purposely built microcontroller-based printed circuit board.
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HU, Z. D., Z. M. SHENG, W. J. DING, W. M. WANG, Q. L. DONG i J. ZHANG. "Electromagnetic emission from laser wakefields in underdense magnetized plasmas". Journal of Plasma Physics 78, nr 4 (15.03.2012): 421–27. http://dx.doi.org/10.1017/s002237781200027x.
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AbstractThe laser wakefield structure in a magnetized underdense plasma is studied analytically and numerically. Because of the DC magnetic field perpendicular to the laser propagation direction, an electromagnetic component appears in addition to the normal electrostatic component. This electromagnetic component can transmit partially into vacuum at the plasma–vacuum boundary as shown by particle-in-cell simulation. It is found that the emission has components both at the fundamental plasma frequency and its harmonics if the wakefield is driven at a high amplitude. Comparing with the emission at the plasma frequency, the harmonic emission depends weakly upon the density profile at plasma–vacuum boundary and it can pass through the boundary almost without energy loss, providing a new method for the diagnostic of wakefields.
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Yang, Jianfeng, i Ningning Meng. "Active Disturbance Rejection Control of Three-Phase LCL Grid-Connected Inverter under Unbalanced Grid Voltage". Mathematical Problems in Engineering 2022 (14.02.2022): 1–10. http://dx.doi.org/10.1155/2022/3702607.
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When the three-phase LCL grid-connected inverter operates under the condition of unbalanced grid voltage, the influence of the negative sequence component in the grid voltage will cause the grid-connected inverter system to produce active and reactive dual-frequency interference. This will cause the grid-side current to have many low-order harmonics, mainly the third harmonic, which does not conform the IEEE-Std. 929–2000 standard. In order to solve this problem, this paper designs a current auto-disturbance-rejection controller, which speeds up the tracking response speed of the system and reduces the harmonic content of the grid-side current under unbalanced conditions. At the same time, optimize the phase-locked loop structure and introduce a notch filter in the modulation link to eliminate the third low-frequency harmonic components and further improve the quality of the grid-side current waveform. Finally, the correctness of the control strategy suggested in this paper is verified by MATLAB/Simulink simulation.
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Selvajyothi, K., i P. A. Janakiraman. "FPGA-Based Software Implementation of Series Harmonic Compensation for Single Phase Inverters". VLSI Design 2010 (24.01.2010): 1–14. http://dx.doi.org/10.1155/2010/512312.
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This paper presents a single chip FPGA (Altera Cyclone II) controlled single phase inverter, programmed for the reduction of harmonics in the output voltage. Separate composite digital observers have been designed for extracting the fundamental and harmonic components of the voltage and the highly distorted current signals, particularly when the inverter supplies nonlinear loads. These observers have been embedded into the FPGA along with the controllers and I/O interfaces. The multiple observers yield very pure in-phase and quadrature voltage signals for use in the outer loop and similar signals for stabilizing the inner current loop. The Inverter could be modeled as a feed back control system with the fundamental component of the voltage as the desired output while the voltage harmonics take the role of noise creeping into the output. To obtain a very low total harmonic distortion in the voltage waveform, the well-known control strategy of using a very large feed back around the noise signal has been employed.
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Meliga, P. "Harmonics generation and the mechanics of saturation in flow over an open cavity: a second-order self-consistent description". Journal of Fluid Mechanics 826 (4.08.2017): 503–21. http://dx.doi.org/10.1017/jfm.2017.439.
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The flow over an open cavity is an example of supercritical Hopf bifurcation leading to periodic limit-cycle oscillations. One of its distinctive features is the existence of strong higher harmonics, which results in the time-averaged mean flow being strongly linearly unstable. For this class of flows, a simplified formalism capable of unravelling how exactly the instability grows and saturates is lacking. This study builds on previous work by Mantič-Lugo et al. (Phys. Rev. Lett., vol. 113, 2014, 084501) to fill in the gap using a parametrized approximation of an instantaneous, phase-averaged mean flow, coupled in a quasi-static manner to multiple linear harmonic disturbances interacting nonlinearly with one another and feeding back on the mean flow via their Reynolds stresses. This provides a self-consistent modelling of the mean flow–fluctuation interaction, in the sense that all perturbation structures are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations. The first harmonic is sought as the superposition of two components, a linear component generated by the instability and aligned along the leading eigenmode of the mean flow, and a nonlinear orthogonal component generated by the higher harmonics, which progressively distorts the linear growth rate and eigenfrequency of the eigenmode. Saturation occurs when the growth rate of the first harmonic is zero, at which point the stabilizing effect of the second harmonic balances exactly the linear instability of the eigenmode. The model does not require any input from numerical or experimental data, and accurately predicts the transient development and the saturation of the instability, as established from comparison to time and phase averages of direct numerical simulation data.
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Choi, Min Joo, Gwan Suk Kang, Dong Guk Paeng, Sung Min Rhim, Moo Ho Bae, Bajarm Zeqiri i Andrew Coleman. "Characterization of the Harmonic Generation from Cavitating Bubbles Interacted with a Diagnostic Ultrasound in the Focal Region of High Intensity Focused Ultrasound". Key Engineering Materials 321-323 (październik 2006): 1123–28. http://dx.doi.org/10.4028/www.scientific.net/kem.321-323.1123.
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Harmonic image (HI) has been proposed to be promising for visualizing lesions produced by therapeutic high intensity focused ultrasound (HIFU). The study characterizes harmonics generated from the bubble cavitating at the focal region of a therapeutic HIFU field in response to a typical diagnostic ultrasound. Based on Gilmore model, it was simulated the nonlinear dynamics of the bubble being resonated at 1 MHz of the therapeutic ultrasound and driven by a typical 3.5 MHz diagnostic pulse. It was shown that harmonic generation increased with MI in a sigmoid pattern where the rapid and transient changes occurred between 0.5 and 2 in MI. For whole ranges of MI (less than 8), the sub-harmonic was the predominant in magnitudes over other harmonic bands. This reveals that, if HI is considered for improving the detection of focal legion highly cavitating caused by a HIFU field, the sub-harmonic component would be a preferred parameter rather than the 2nd harmonic which has been commonly used in current harmonic imaging.
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Cai, Guowei, Lixin Wang, Deyou Yang, Zhenglong Sun i Bo Wang. "Harmonic Detection for Power Grids Using Adaptive Variational Mode Decomposition". Energies 12, nr 2 (13.01.2019): 232. http://dx.doi.org/10.3390/en12020232.
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The harmonic pollution problem in power grids has become increasingly prominent with the large-scale application of power electronic equipment, nonlinear loads, and renewable energy. This study proposes a method based on adaptive variational mode decomposition (AVMD) and Hilbert transform (HT) that is applicable to harmonic detection in power system. The AVMD method constructs and solves the constrained variational model. Then, a single-frequency harmonic component with stable features can be obtained. The proposed method can effectively avoid the recursive process in empirical mode decomposition (EMD). In this study, the variational mode decomposition algorithm is used to obtain the periodic harmonic components concurrently. Subsequently, the characteristic parameters of each harmonic component are extracted via HT. Simulation analysis and measured data verify the validity and feasibility of the proposed algorithm. Compared with the detection results obtained using the EMD algorithm, the proposed method is proven to exhibit stronger applicability to harmonic detection in power system.
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Chen, L. F., J. Zang, P. H. Taylor, L. Sun, G. C. J. Morgan, J. Grice, J. Orszaghova i M. Tello Ruiz. "An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics". Journal of Fluid Mechanics 848 (1.06.2018): 42–77. http://dx.doi.org/10.1017/jfm.2018.339.
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Wave loading on marine structures is the major external force to be considered in the design of such structures. The accurate prediction of the nonlinear high-order components of the wave loading has been an unresolved challenging problem. In this paper, the nonlinear harmonic components of hydrodynamic forces on a bottom-mounted vertical cylinder are investigated experimentally. A large number of experiments were conducted in the Danish Hydraulic Institute shallow water wave basin on the cylinder, both on a flat bed and a sloping bed, as part of a European collaborative research project. High-quality data sets for focused wave groups have been collected for a wide range of wave conditions. The high-order harmonic force components are separated by applying the ‘phase-inversion’ method to the measured force time histories for a crest focused wave group and the same wave group inverted. This separation method is found to work well even for locally violent nearly-breaking waves formed from bidirectional wave pairs. It is also found that the $n$th-harmonic force scales with the $n$th power of the envelope of both the linear undisturbed free-surface elevation and the linear force component in both time variation and amplitude. This allows estimation of the higher-order harmonic shapes and time histories from knowledge of the linear component alone. The experiments also show that the harmonic structure of the wave loading on the cylinder is virtually unaltered by the introduction of a sloping bed, depending only on the local wave properties at the cylinder. Furthermore, our new experimental results reveal that for certain wave cases the linear loading is actually less than 40 % of the total wave loading and the high-order harmonics contribute more than 60 % of the loading. The significance of this striking new result is that it reveals the importance of high-order nonlinear wave loading on offshore structures and means that such loading should be considered in their design.