Showing papers on "Harmonic published in 2007"

High Performance Current Controller for Selective Harmonic Compensation in Active Power Filters

Abstract: A new current control scheme for selective harmonic compensation is proposed for shunt active power filters The method employs an array of resonant current controllers, one for the fundamental, and one for each harmonic, implemented in fundamental reference frame in order to reduce the overall computational effort The proposed controller design is based on the pole-zero cancellation technique, taking into account the load transfer function at each harmonic frequency Two design methods are provided, which give controller transfer functions with superior frequency response The complete current controller is realized as the superposition of all individual harmonic controllers The frequency response of the entire closed loop control is optimal with respect to filtering objectives, ie, the system provides good overall stability and excellent selectivity for interesting harmonics This conclusion is supported by experimental results on a 76-kVA laboratory filter, indicating a reduction in current THD factor from 34% to 2%, while the highest harmonic compensated is the 37th harmonic current

Detection is key - Harmonic detection methods for active power filter applications

Abstract: This article gives a survey of the commonly used methods for harmonic detection in active power filters (APFs). The work proposes a simulation setup that decouples the harmonic detection method from the active filter model and its controllers. In this way, the selected methods can be equally analyzed and compared with respect to their performance, which helps in anticipating possible implementation issues. A comparison is given that may be used to decide the future hardware setup implementation. The comparison shows that the choice of numerical filtering is a key factor for obtaining a good accuracy and dynamic performance of an active power filter.

Repetitive-Based Controller for a UPS Inverter to Compensate Unbalance and Harmonic Distortion

Abstract: This paper discusses a repetitive-based controller for an uninterruptible power supply (UPS) inverter. It is shown that a bank of resonant filters, used as a refinement term for harmonic compensation in earlier works, is equivalent to a repetitive scheme with a particular structure. The latter is implemented using a simple feedback array with a delay line, thus making the implementation relatively easy. More precisely, the repetitive scheme takes a negative feedback structure plus a feedforward path whenever the odd harmonics are considered for compensation only. The repetitive scheme, equivalent to the bank of resonant filters, acts as a refinement term to reject the harmonic distortion caused by the unbalanced and distorted load current, and thus, allowing the UPS inverter to deliver an almost pure sinusoidal balanced voltage. Experimental results in a 1.5 KVA three-phase inverter are included to show the performance of the proposed controller

Design of a New Cooperative Harmonic Filtering Strategy for Distributed Generation Interface Converters in an Islanding Network

Abstract: Increasing demand for premium electric power, in terms of both quality and reliability, and emerging new energy technologies have led to the development of distributed generation systems Due to rapid penetration of power electronics equipment, many of the loads within distributed generation systems are nonlinear in nature, and the resulting harmonics pollution needs to be addressed This paper proposes a new cooperative harmonic filtering strategy for the interface converters of distributed generation sources A droop control method based on the reactive volt-ampere consumption of harmonics of each interface converter is designed and implemented In this strategy, the overall harmonic filtering workload can be evenly shared without any communications The operation principle is explained in detail Computer simulations and laboratory test results validate the distributed harmonic damping capability of the proposed strategy

A Unified Artificial Neural Network Architecture for Active Power Filters

Abstract: In this paper, an efficient and reliable neural active power filter (APF) to estimate and compensate for harmonic distortions from an AC line is proposed. The proposed filter is completely based on Adaline neural networks which are organized in different independent blocks. We introduce a neural method based on Adalines for the online extraction of the voltage components to recover a balanced and equilibrated voltage system, and three different methods for harmonic filtering. These three methods efficiently separate the fundamental harmonic from the distortion harmonics of the measured currents. According to either the Instantaneous Power Theory or to the Fourier series analysis of the currents, each of these methods are based on a specific decomposition. The original decomposition of the currents or of the powers then allows defining the architecture and the inputs of Adaline neural networks. Different learning schemes are then used to control the inverter to inject elaborated reference currents in the power system. Results obtained by simulation and their real-time validation in experiments are presented to compare the compensation methods. By their learning capabilities, artificial neural networks are able to take into account time-varying parameters, and thus appreciably improve the performance of traditional compensating methods. The effectiveness of the algorithms is demonstrated in their application to harmonics compensation in power systems

Intelligent Neural Network-Based Fast Power System Harmonic Detection

Abstract: Nowadays, harmonic distortion in power systems is attracting significant attention. Traditional technical tools for harmonic distortion analysis using either fast Fourier transform or discrete Fourier transform are, however, susceptible to the presence of noise in the distorted signals. Harmonic detection by using Fourier transformation also requires input data for more than one cycle of the current waveform and requires time for the analysis in the next coming cycle. In this paper, an alternative method using neural network algorithm has achieved satisfactory results for fast and precise harmonic detection in noisy environments by providing only 1/2 cycle sampled values of distorted waveforms to neural network. Sensitivity considerations are conducted to determine the key factors affecting the performance efficiency of the proposed model to reach the lowest errors of testing patterns

A Flexible Selective Harmonic Mitigation Technique to Meet Grid Codes in Three-Level PWM Converters

Abstract: Due to the development of new grid codes, power converters' output signal harmonic control is currently becoming extremely important in medium- and high-power applications. By taking this new scenario into account, a new method to generate switching three-level pulsewidth-modulation (PWM) patterns to meet specific grid codes is presented. The proposed method, which is named selective harmonic mitigation PWM , generates switching three-level PWM patterns with high quality from the point of view of harmonic content, avoiding the elimination of some specific harmonics and studying all harmonics and the total harmonic distortion as a global problem by using a general-purpose random-search heuristic algorithm. This fact leads to a drastic reduction or even avoidance of the bulky and costly grid connection tuned filters of power systems. Any harmonic shaping can be considered due to the flexibility of the method. Power devices switching constraints are considered to obtain directly applicable results. As a practical example, limits from one actual grid code have been used to get the experimental results by means of a 150-kVA three-level diode-clamped converter test bench. Comparisons between the proposed technique, optimized PWM and Selective Harmonic Elimination methods have been carried out. The results obtained with this new method greatly improve previous ones.

Experimental characterization of material nonlinearity using Lamb waves

Abstract: The objective of this research is to develop an accurate and reliable procedure to measure the second order harmonic of a Lamb wave propagating in a metallic plate. There are two associated complications in measuring these nonlinear Lamb waves, namely, their inherent dispersive and multimode natures. To overcome these, this research combines a time-frequency representation with a hybrid wedge generation and laser interferometric detection system. The effectiveness of the proposed procedure is demonstrated by characterizing the inherent material nonlinearity of two different aluminum plates whose absolute nonlinearity parameters are known from longitudinal wave measurements.

The p-q theory in three-phase systems under non-sinusoidal conditions

Abstract: The conventional theory of active and reactive power in single-phase or three-phase systems is based on an average value concept, thus making it impossible to define instantaneous active and reactive power in a real sense. On the basis of an instantaneous value concept, the authors have already proposed a new definition of instantaneous active and reactive power in three-phase circuits for arbitrary voltage and current waveforms without any restriction. This is called the instantaneous reactive power theory or the p-q theory, which is considered a basic theory of active power line conditioners such as reactive power compensators and active power filters for harmonic compensation

Strong-coupling theory of periodically driven two-level systems

Abstract: We present a simple but highly efficient iterating approach for strong-coupling periodically driven two-level systems. The obtained explicit approximating analytical solution reproduces accurately the exact numerical solution in the strong-coupling regime for a wide frequency range including resonance, far-off resonance, harmonic, and subharmonic cases. Our theory is suitable for singe- and multiperiod periodic driving and for the periodic driving with a few-cycle pulse as well, and it gives a general formula for calculating the strong-field ac Stark effect in such diverse situations.

Coherent superposition of laser-driven soft-X-ray harmonics from successive sources

Abstract: High-order harmonic generation from atoms ionized by femtosecond laser pulses has been a promising approach for the development of coherent short-wavelength sources. However, the realization of a powerful harmonic X-ray source has been hampered by a phase velocity mismatch between the driving wave and its harmonics, limiting their coherent build-up to a short propagation length and thereby compromising the efficiency of a single source. Here, we report coherent superposition of laser-driven soft-X-ray (SXR) harmonics, at wavelengths of 2–5 nm, generated in two successive sources by one and the same laser pulse. Observation of constructive and destructive interference suggests the feasibility of quasi-phase-matched SXR harmonic generation by a focused laser beam in a gas medium of modulated density. Our proof-of-concept study opens the prospect of enhancing the photon flux of SXR harmonic sources to levels enabling researchers to tackle a range of applications in physical as well as life sciences.

Neural Network-Based Selective Compensation of Current Quality Problems in Distribution System

Abstract: Active power filters (APFs) have been used to compensate harmonics, reactive current, and negative sequence fundamental frequency current drawn by nonlinear loads. The control of APF is the core issue for their proper operation. The flexibility of selective compensation embedded in the control scheme makes APF versatile for compensation of reactive power, harmonic currents, and unbalance in source currents and their combinations, depending upon the limited rating of voltage source inverter employed as APF. The proposed scheme utilizes neural network-based decomposition of the load current into positive and negative sequence fundamental frequency component, reactive component and harmonic components. The adaline-based current decomposer estimates the reference currents through tracking of unit vectors together with tuning of the weights. The implementation of the control scheme facilitates selective compensation which respects the limited rating of the APF. The simulated results using developed MATLAB model are presented and are validated by experimental results to depict the effectiveness of the proposed control method of APF

Structures with Semiactive Variable Stiffness Single/Multiple Tuned Mass Dampers

Abstract: This paper proposes application of single and multiple semiactive variable stiffness tuned mass dampers (STMD/SMTMD) for response control of multistory structures under several types of excitation A new semiactive control algorithm is developed based on real-time frequency tracking of excitation signal by short time Fourier transform A parametric study is performed in the frequency domain to investigate the dynamic characteristics and effectiveness of STMDs Time history responses of single-degree-of-freedom and five-degree-of-freedom structures equipped with STMDs at the roof level, subjected to harmonic, stationary, and nonstationary excitations are presented STMD/SMTMD are most effective when they have low damping ratios and the excitation frequency can be tracked They are superior than their passive counterparts in reducing the response of the main structure both under force and base excitations In case the fundamental frequency changes due to damage or deterioration of the main structure then th

THE FIRST EXPERIMENT OF A THz GYROTRON WITH A PULSE MAGNET

Abstract: A THz gyrotron with a pulse magnet has been designed, constructed and operated in FIR FU It is developed as one of high frequency gyrotrons included in Gyrotron FU Series The gyrotron has already achieved the first experimental result for high frequency operations whose radiation frequency exceeds 1 THz In this paper, the design detail and the operation test results for sub-terahertz to terahertz range are described The second harmonic operation is confirmed experimentally at the expected frequency of 1005 THz due to TE6,11 cavity mode at the magnetic field intensity of 190 T

An Adaptive Control for UPS to Compensate Unbalance and Harmonic Distortion Using a Combined Capacitor/Load Current Sensing

Abstract: This paper investigates the control of an uninterruptible power supply (UPS) using a combined measurement of capacitor and load currents in the same current sensor arrangement. The purpose of this combined measurement is, on one hand, to reach a similar performance as that obtained in the inductor current controller with load current feedforward and, on the other hand, to easily obtain an estimate of the inductor current for overcurrent protection capability. Based on this combined current measurement, a voltage controller based on resonant harmonic filters is investigated in order to compensate for unbalance and harmonic distortion on the load. Adaptation is included to cope with uncertainties in the system parameters. It is shown that after transformations the proposed controller gets a simple and practical form that includes a bank of resonant filters, which is in agreement with the internal model principle and corresponds to similar approaches proposed recently. The controller is based on a frequency-domain description of the periodic disturbances, which include both symmetric components, namely, the negative and positive sequence. Experimental results on the output stage of a three-phase three-wire UPS are presented to assess the performance of the proposed algorithm

Moderate cochlear hearing loss leads to a reduced ability to use temporal fine structure information

Abstract: The ability of normally hearing and hearing-impaired subjects to use temporal fine structure information in complex tones was measured. Subjects were required to discriminate a harmonic complex tone from a tone in which all components were shifted upwards by the same amount in Hz, in a three-alternative, forced-choice task. The tones either contained five equal-amplitude components (non-shaped stimuli) or contained many components, but were passed through a fixed bandpass filter to reduce excitation pattern changes (shaped stimuli). Components were centered at nominal harmonic numbers (N) 7, 11, and 18. For the shaped stimuli, hearing-impaired subjects performed much more poorly than normally hearing subjects, with most of the former scoring no better than chance when N=11 or 18, suggesting that they could not access the temporal fine structure information. Performance for the hearing-impaired subjects was significantly improved for the non-shaped stimuli, presumably because they could benefit from spectral cues. It is proposed that normal-hearing subjects can use temporal fine structure information provided the spacing between fine structure peaks is not too small relative to the envelope period, but subjects with moderate cochlear hearing loss make little use of temporal fine structure information for unresolved components.

An Investigation of the Harmonic Emissions of Wind Turbines

Abstract: Harmonic emissions of variable speed wind turbines (WTs) are a well-known issue, but little information that is based on field measurements on actual machines has been published on the subject. In this paper, the harmonic behavior of modern WTs using extensive measurements performed on commercially available machines is discussed. Specific issues addressed include the shape and the frequency range of the harmonic current spectrum, the variation of the harmonics with the WT operating point, the statistical characteristics of their magnitude and phase angle, the effect of grouping and time-averaging, as well as their symmetrical component characteristics. The objective of the paper is to outline important general characteristics of the harmonic behavior of WTs, rather than to analyze specific machines or compare alternative WT designs

Ultrasonic diagnostic imaging with blended tissue harmonic signals

Abstract: An ultrasonic diagnostic imaging system and method are described which produce tissue harmonic images containing both fundamental and harmonic frequency components. Such a blended image takes advantage of the performance possible with the two types of ultrasonic echo information and can advantageously reduce near field clutter while improving signal to noise performance in the far field of the image.

Electromechanical energy conversion systems

Abstract: An exemplary power system may include an electric machine with multiple sets of stator windings, each set of windings being coupled through a separate switch matrix to a common voltage bus, and each of which may be spatially arranged in full pitch around the stator such that stator flux harmonics are substantially reduced. The reduced stator flux harmonics may be associated with phase current harmonic content. In an example application, such power systems may operate in a generating mode to transfer mechanical energy to electrical energy on a DC voltage bus. In some illustrative embodiments, the power system may provide both high-power and high-speed (e.g., 1MW at 8000 rpm or above) motoring and/or generating capability suitable, for example, for on-board (e.g., marine, aviation, traction) power systems.

High-order harmonic generation in a laser plasma: a review of recent achievements

Abstract: A review of studies of high-order harmonic generation in plasma plumes is presented. The generation of high-order harmonics (up to the 101st order, λ = 7.9 nm) of Ti:sapphire laser radiation during the propagation of short laser pulses through a low-excited, low-ionized plasma produced on the surfaces of different targets is analysed. The observation of considerable resonance-induced enhancement of a single harmonic (λ = 61.2 nm) at the plateau region with 10−4 conversion efficiency in the case of an In plume can offer some expectations that analogous processes can be realized in other plasma samples in the shorter wavelength range. Recent achievements of single-harmonic enhancement at mid- and end-plateau regions are discussed. Various methods for the optimization of harmonic generation are analysed, such as the application of the second harmonic of driving radiation and the application of prepulses of different durations. The enhancement of harmonic generation efficiency during the propagation of femtosecond pulses through a nanoparticle-containing plasma is discussed.

A Harmonically Coupled Admittance Matrix Model for AC/DC Converters

Abstract: This paper proposes a new method to model the harmonic generating characteristics of AC/DC converters. The model transforms the time domain nonlinear characteristic of the converter into a frequency domain linear admittance matrix. The matrix represents the coupling among the converter AC side harmonic voltages and currents accurately and it does not vary with the harmonic conditions of the system. The proposed model opens up a new way to conduct harmonic power flow studies. This paper presents the theoretical foundation and analytical derivation of the admittance model for both single-phase and three-phase bridge rectifiers. Potential applications of the model are discussed.

A Novel Switching Sequence Design for Five-Level NPC/H-Bridge Inverters With Improved Output Voltage Spectrum and Minimized Device Switching Frequency

Abstract: This paper presents a novel switching sequence design for the space-vector modulation of high-power multilevel converters. The switching sequences are optimized for the improvement of harmonic spectrum and the minimization of device switching frequency. Compared to other commonly used switching sequences, the output spectrum of the proposed design shows higher inverter equivalent switching frequency. Meanwhile, the device switching frequency is reduced by using a flexible switching pattern. The proposed switching sequence has been simulated and experimentally tested on a 5-level neutral point clamped H-bridge based inverter. The results from both simulations and experiments consistently verify the above-mentioned features.

A Novel Method for Selective Harmonic Elimination in Power Electronic Equipment

Abstract: The algorithms for adaptive canceling of selected harmonic components have been well developed in digital signal processing. In those applications, "filtering" is a primary objective. However, in power electronic applications control, with objectives like fast response of system on reference and disturbance change, is of primary importance. This paper provides a novel and a systematic design approach for applying signal processing methods (like modified adaptive selective harmonic elimination algorithms) as an addition to conventional control. Thus, both control objectives like fast transient response and efficient harmonic (disturbance) filtering are achieved. The filtering algorithm does not interfere and has minimal impact on the stability of the primary control loop. Its sole function is to eliminate undesirable higher harmonic components from selected variable (current or voltage) and it requires only knowledge of the frequency of the component to be eliminated. The methodology is applicable for a wide range of equipment like uninterrupted power systems, regenerative converters, active power filters, etc. The application of the proposed method in a regenerative voltage source converter for dead time compensation is used as an example for illustrating its effectiveness and design procedure

Optimal Regular-Sampled PWM Inverter Control Techniques

Abstract: A survey of eight different advanced Regular-Sampled pulsewidth-modulation (PWM) strategies is presented and compared for three-phase inverters. The PWM strategies represent modifications of the basic Regular-Sampled technique and are designed to closely reproduce the "exact" switching angles and performance of the well-known Harmonic Elimination, Harmonic Minimization, Space Vector Modulation, High-Frequency, and Hysteresis Band PWM strategies. Each strategy is compared, and the advantages and disadvantages of each are emphasized in terms of complexity and implementation. Experimental and computer-aided design simulation results are presented to show the differences between the various strategies and to confirm the validity and accuracy of each of the techniques

A Comparative Analysis of Real-Time Algorithms for Power Signal Decomposition in Multiple Synchronous Reference Frames

Abstract: The monitoring and rejection of voltage and current harmonics in power electronics applications such as power quality conditioners or distributed generation systems require correct estimation algorithms especially if the harmonic amplitudes are time varying. Power signal decomposition in multiple synchronous rotating reference frames (MSRFs) is considered one of the best solutions. The most commonly employed implementations of this signal transformation are based on phase-locked loops (PLLs), recursive discrete Fourier transforms (RDFT), or discrete Kalman filtering (DKF). In this paper, a rigorous analysis of the performance of these implementations has been carried out. Complete tests have been performed to evaluate the computational burden, the frequency domain response, and the tolerance to low frequency amplitude variations. The results make it possible to select the proper method depending on the requirements of each application.

Josephson junctions with second harmonic in the current-phase relation: Properties of φ junctions

Abstract: Several recent experiments revealed a change of the sign of the first harmonic in the current-phase relation of Josephson junctions (JJs) based on, e.g., $d$-wave superconductors or JJs with ferromagnetic barrier. In this situation, the role of the second harmonic can become dominant; in this case, it determines the scenario of a $0\text{\ensuremath{-}}\ensuremath{\pi}$ transition. We discuss different mechanisms of the second harmonic generation and its sign. If the second harmonic is positive and the first harmonic changes sign as a function of any control parameter, e.g., temperature, the ground state phase changes abruptly between 0 and $\ensuremath{\pi}$. If the second harmonic is negative, the ground state phase changes continuously passing all values between 0 and $\ensuremath{\pi}$ and the realization of a so-called $\ensuremath{\varphi}$-junction is possible in the vicinity of the point where the first harmonic vanishes. We study the unusual properties of this kind of Josephson junction such as critical currents, magnetic field penetration, plasma gap, microwave response, and zero field steps. We also analyze the possible experimental techniques for the observation of predicted effects.