Showing papers on "Fundamental frequency published in 2016"

Small-Signal Dynamic DQ Model of Modular Multilevel Converter for System Studies

Abstract: This paper presents three dynamic linear state-space models of the modular multilevel converter (MMC) which are suitable for small-signal dynamic studies and controller design. The three models differ by the number of states (two, six, and ten) and, therefore, are suitable for different applications based on the required accuracy. The 2nd- and 6th-order models ignore dynamics of the second harmonics and circulating current suppression control (CCSC). The main challenges of dynamic analytical modelling of MMC are the nonlinear multiplication terms in ABC frame equations for modulating oscillating signals. The multiplication nonlinear terms are therefore considered directly in the rotating DQ frame. This requires simultaneous modeling in zero sequence, fundamental frequency DQ and double fundamental frequency DQ2 frames. The proposed linear analytical models are implemented in state space in MATLAB. The validity and accuracy of the models are verified against a detailed 401-level MMC model in PSCAD/EMTDC in both time and frequency domains. The results show very good accuracy for the 10th-order model and decreasing accuracy for the lower order models. The influence of phase-locked loop and CCSC gains on the MMC dynamic is also studied using the proposed 10th model, and the results verify the suitability of the model for this purpose.

Improved Nearest-Level Modulation for a Modular Multilevel Converter With a Lower Submodule Number

Abstract: This letter proposes an improved nearest-level modulation (NLM) method to enhance the quality of output voltage of a modular multilevel converter (MMC) with the low amount of submodules, as well as restrain the voltage fluctuation of the submodules. By adding a small offset, which is alternating at the double fundamental frequency to the reference signals, a small phase shift of the step-changing moment between upper and lower arms’ voltage emerges. As a result, an odd-level difference between the output voltage of lower arm and that of upper arm occurs, which can increase the level number of output voltage from $N + 1$ to $2N + 1$ , where N is the number of submodules per arm. With the proposed method, the total harmonic distortion (THD) of the output voltage is mitigated without increasing the switching frequency of IGBTs or changing the average voltage of submodules’ capacitor. In addition, within a special range of power factor angle, the circulating current can be reduced by choosing the proper phase between the fundamental and the double fundamental frequency. Simulation and experimental results verify the effectiveness and validity of the proposed NLM scheme.

A novel carbon fiber reinforced lattice truss sandwich cylinder: Fabrication and experiments

Abstract: To get a strong, stiff and weight efficient cylindrical shell, a novel carbon fiber reinforced corrugated lattice truss-core sandwich cylinder (LTSC) was designed and fabricated. The core is made up of orthogonal corrugated trusses and manufactured by mould pressing method. The LTSC is fabricated by filament winding and co-curing method. The face sheets have layups of [0°/30°/−30°/−30°/30°/0°] to improve the fundamental frequency as it is controlled by the circumferential stiffness. In end-free vibration the fundamental frequency of the LTSC is 112.18 Hz, higher than the referenced quasi-isotropic Isogrid-core sandwich cylinder. Determined by the skin fracture, the compression strength of the LTSC is 328.03 kN, stronger than the referenced Isogrid-core sandwich cylinder failed at rib buckling and the post-failure deformation is ductile. According to the optimization scheme jointly constrained by the strength and the fundamental frequency, an ultra-light and strong cylinder with high fundamental frequency was successfully fabricated.

Analytical and numerical studies of approximate phase velocity matching based nonlinear S0 mode Lamb waves for the detection of evenly distributed microstructural changes

Abstract: Most previous studies on nonlinear Lamb waves are conducted using mode pairs that satisfying strict phase velocity matching and non-zero power flux criteria. However, there are some limitations in existence. First, strict phase velocity matching is not existed in the whole frequency bandwidth; Second, excited center frequency is not always exactly equal to the true phase-velocity-matching frequency; Third, mode pairs are isolated and quite limited in number; Fourth, exciting a single desired primary mode is extremely difficult in practice and the received signal is quite difficult to process and interpret. And few attention has been paid to solving these shortcomings. In this paper, nonlinear S0 mode Lamb waves at low-frequency range satisfying approximate phase velocity matching is proposed for the purpose of overcoming these limitations. In analytical studies, the secondary amplitudes with the propagation distance considering the fundamental frequency, the maximum cumulative propagation distance (MCPD) with the fundamental frequency and the maximum linear cumulative propagation distance (MLCPD) using linear regression analysis are investigated. Based on analytical results, approximate phase velocity matching is quantitatively characterized as the relative phase velocity deviation less than a threshold value of 1%. Numerical studies are also conducted using tone burst as the excitation signal. The influences of center frequency and frequency bandwidth on the secondary amplitudes and MCPD are investigated. S1–S2 mode with the fundamental frequency at 1.8 MHz, the primary S0 mode at the center frequencies of 100 and 200 kHz are used respectively to calculate the ratios of nonlinear parameter of Al 6061-T6 to Al 7075-T651. The close agreement of the computed ratios to the actual value verifies the effectiveness of nonlinear S0 mode Lamb waves satisfying approximate phase velocity matching for characterizing the material nonlinearity. Moreover, the ratios derived from the primary and secondary horizontal displacements generated from nonlinear S0 mode Lamb waves are closest to the real value, which indicates that using horizontal displacements is more suitable for detecting evenly distributed microstructural changes in large thin plate-like structure. Successful application to evaluating material at different levels of evenly distributed fatigue damage is also numerically conducted.

Nonlinear free vibration of temperature-dependent sandwich beams with carbon nanotube-reinforced face sheets

Abstract: In this research, large amplitude free vibrations of a sandwich beam with stiff core and carbon nanotube (CNT)-reinforced face sheets are analysed. The distribution of CNTs across the thickness of the face sheets may be uniform or functionally graded. The equivalent single- layer theory of Timoshenko is used to construct the Hamiltonian of the beam under the von Karman type of geometrical nonlinearity assumptions. A uniform temperature field through the beam is also included in the formulation. The Ritz method with polynomial basis functions is used to discrete the equations of motion and establish the matrix representation of the governing equations. A nonlinear eigenvalue problem is obtained and solved using a standard continuation procedure. After validating the developed solution method and formulation, parametric studies are conducted to examine the influences of thermal environment, core thickness-to-face sheet thickness ratio, boundary conditions, amplitude of vibrations, CNTs volume fraction and their distribution pattern. It is concluded that an increase in the volume fraction of CNTs results in higher fundamental frequency and decreases the nonlinear-to-linear frequency ratio.

Application of MEMS Accelerometer for Detection and Diagnosis of Multiple Faults in the Roller Element Bearings of Three Phase Induction Motor

Abstract: This paper presents a simple, non-electrical contact approach to detect and analyze multiple faults in the roller element bearings of three phase induction motor by vibration analysis using microelectromechanical systems (MEMS) accelerometer. The ability of the proposed method has been investigated experimentally under no load, single phase and unbalanced voltage conditions. The frequency analysis of motor vibration due to bearing fault has been carried out by fast Fourier transform algorithm. The appearance of fault frequencies in vibration spectrum will indicate multiple faults in the bearings and also the existence of side-band frequency components around fundamental frequency component indicates air gap modulation due to bearing fault. Experimentally obtained fault frequencies are compared with analytical values and found that both are closely matching. This indicates that the proposed method can be reliably employed to detect from simple to complex faults in the bearings of induction motor using MEMS accelerometers.

Small signal dynamic DQ model of Modular Multilevel Converter for system studies

Abstract: This article presents three dynamic linear state space models of Modular Multilevel Converter (MMC) which are suitable for small-signal dynamic studies and controller design. The three models differ by the number of states (two, six and ten) and therefore are suitable for different applications based on the required accuracy. The 2nd and 6th order models ignore dynamics of the second harmonics and circulating current suppression control. The main challenges of dynamic analytical modelling of MMC are the non-linear multiplication terms in equations for modulating oscillating signals. The multiplication non-linear terms is therefore considered directly in the rotating DQ frame. This requires simultaneous modeling in zero sequence, fundamental frequency DQ and double fundamental frequency DQ2 frames. The proposed linear analytical models are implemented in state-space in MATLAB. The validity and accuracy of the models are verified against detailed 401 level MMC model in PSCAD/EMTDC in both: time and frequency domains. The results show very good accuracy for the 10th order model and decreasing accuracy for the lower order models.

Switching Frequency Analysis of Staircase-Modulated Modular Multilevel Converters and Equivalent PWM Techniques

Abstract: The large number of voltage levels in a modular multilevel converter (MMC) make staircase modulation a feasible alternative, particularly in high-power applications. However, staircase waveforms do not necessarily mean operation of the MMC submodules (SMs) at the fundamental frequency. This paper presents an analysis of SM switching frequencies in staircase-modulated MMCs and their correlation to the modulation index and load phase angle. A carrier-based pulsewidth-modulation (CB-PWM) equivalent technique is also developed. This analysis demonstrates that CB-PWM techniques provide a similar switching frequency with superior harmonic performance and improved voltage balancing characteristics at all modulation indices compared to staircase modulation. The theoretical analysis is verified with extensive simulation results for MMCs with different SMs and experimental results from a laboratory prototype.

Electron power absorption dynamics in capacitive radio frequency discharges driven by tailored voltage waveforms in CF4

Abstract: The power absorption dynamics of electrons and the electrical asymmetry effect in capacitive radio-frequency plasmas operated in CF4 and driven by tailored voltage waveforms are investigated experimentally in combination with kinetic simulations. The driving voltage waveforms are generated as a superposition of multiple consecutive harmonics of the fundamental frequency of 13.56 MHz. Peaks/valleys and sawtooth waveforms are used to study the effects of amplitude and slope asymmetries of the driving voltage waveform on the electron dynamics and the generation of a DC self-bias in an electronegative plasma at different pressures. Compared to electropositive discharges, we observe strongly different effects and unique power absorption dynamics. At high pressures and high electronegativities, the discharge is found to operate in the drift-ambipolar (DA) heating mode. A dominant excitation/ionization maximum is observed during sheath collapse at the edge of the sheath which collapses fastest. High negative-ion densities are observed inside this sheath region, while electrons are confined for part of the RF period in a potential well formed by the ambipolar electric field at this sheath edge and the collapsed (floating potential) sheath at the electrode. For specific driving voltage waveforms, the plasma becomes divided spatially into two different halves of strongly different electronegativity. This asymmetry can be reversed electrically by inverting the driving waveform. For sawtooth waveforms, the discharge asymmetry and the sign of the DC self-bias are found to reverse as the pressure is increased, due to a transition of the electron heating mode from the α-mode to the DA-mode. These effects are interpreted with the aid of the simulation results.

Interpretations of Frequency Domain Analyses of Neural Entrainment: Periodicity, Fundamental Frequency, and Harmonics

Abstract: Brain activity can follow the rhythms of dynamic sensory stimuli, such as speech and music, a phenomenon called neural entrainment. It has been hypothesized that low-frequency neural entrainment in the neural delta and theta bands provides a potential mechanism to represent and integrate temporal information. Low-frequency neural entrainment is often studied using periodically changing stimuli and is analyzed in the frequency domain using the Fourier analysis. The Fourier analysis decomposes a periodic signal into harmonically related sinusoids. However, it is not intuitive how these harmonically related components are related to the response waveform. Here, we explain the interpretation of response harmonics, with a special focus on very low-frequency neural entrainment near 1 Hz. It is illustrated why neural responses repeating at f Hz do not necessarily generate any neural response at f Hz in the Fourier spectrum. A strong neural response at f Hz indicates that the time scales of the neural response waveform within each cycle match the time scales of the stimulus rhythm. Therefore, neural entrainment at very low frequency implies not only that the neural response repeats at f Hz but also that each period of the neural response is a slow wave matching the time scale of a f Hz sinusoid.

Predicting Achievable Fundamental Frequency Ranges in Vocalization Across Species.

Abstract: Vocal folds are used as sound sources in various species, but it is unknown how vocal fold morphologies are optimized for different acoustic objectives. Here we identify two main variables affecting range of vocal fold vibration frequency, namely vocal fold elongation and tissue fiber stress. A simple vibrating string model is used to predict fundamental frequency ranges across species of different vocal fold sizes. While average fundamental frequency is predominantly determined by vocal fold length (larynx size), range of fundamental frequency is facilitated by (1) laryngeal muscles that control elongation and by (2) nonlinearity in tissue fiber tension. One adaptation that would increase fundamental frequency range is greater freedom in joint rotation or gliding of two cartilages (thyroid and cricoid), so that vocal fold length change is maximized. Alternatively, tissue layers can develop to bear a disproportionate fiber tension (i.e., a ligament with high density collagen fibers), increasing the fundamental frequency range and thereby vocal versatility. The range of fundamental frequency across species is thus not simply one-dimensional, but can be conceptualized as the dependent variable in a multi-dimensional morphospace. In humans, this could allow for variations that could be clinically important for voice therapy and vocal fold repair. Alternative solutions could also have importance in vocal training for singing and other highly-skilled vocalizations.

Complex pitch perception mechanisms are shared by humans and a New World monkey

Abstract: The perception of the pitch of harmonic complex sounds is a crucial function of human audition, especially in music and speech processing. Whether the underlying mechanisms of pitch perception are unique to humans, however, is unknown. Based on estimates of frequency resolution at the level of the auditory periphery, psychoacoustic studies in humans have revealed several primary features of central pitch mechanisms. It has been shown that (i) pitch strength of a harmonic tone is dominated by resolved harmonics; (ii) pitch of resolved harmonics is sensitive to the quality of spectral harmonicity; and (iii) pitch of unresolved harmonics is sensitive to the salience of temporal envelope cues. Here we show, for a standard musical tuning fundamental frequency of 440 Hz, that the common marmoset (Callithrix jacchus), a New World monkey with a hearing range similar to that of humans, exhibits all of the primary features of central pitch mechanisms demonstrated in humans. Thus, marmosets and humans may share similar pitch perception mechanisms, suggesting that these mechanisms may have emerged early in primate evolution.

Doubling the spectrum of time-domain induced polarization by harmonic de-noising, drift correction, spike removal, tapered gating, and data uncertainty estimation

Abstract: The extraction of spectral information in the inversion process of time-domain (TD) induced polarization (IP) data is changing the use of the TDIP method. Data interpretation is evolving from a qualitative description of the subsurface, able only to discriminate the presence of contrasts in chargeability parameters, towards a quantitative analysis of the investigated media, which allows for detailed soil- and rock-type characterization. Two major limitations restrict the extraction of the spectral information of TDIP data in the field: i) the difficulty of acquiring reliable early-time measurements, in the millisecond range and ii) the self-potential drift in the measured potentials distorting the shape of the late time IP responses, in the second range. Recent developments in TDIP acquisition equipment have given access to full waveform recordings of measured potentials and transmitted current, opening a breakthrough for data processing. For measuring at early times, we developed a new method for removing the significant noise from powerlines contained in the data through a model-based approach, localizing the fundamental frequency of the powerline signal in the full-waveform IP recordings. By this, we cancel both the fundamental signal and its harmonics. Furthermore, a novel and efficient processing scheme for identifying and removing spikes TDIP data is developed. The noise cancellation and the de-spiking allow the use of earlier and narrower gates, down to a few milliseconds after the current turn-off. Furthermore, tapered windows are used in the final gating of IP data, allowing the use of wider and overlapping gates for higher noise suppression without signal distortion. For measuring at late times, we have developed an algorithm for removal of the self-potential drift. Usually constant or linear drift-removal algorithms are used, but these algorithms fail in removing the background potentials due to the polarization of the electrodes previously used for current injection. We developed a drift-removal scheme that model the polarization effect and efficiently allows for preserving the shape of the IP responses at late times. Uncertainty estimates are essential in the inversion of IP data. Therefore, in the final step of the data processing, we estimate the data standard deviation based on the data variability within the IP gates and the misfit of the background drift removal Overall, the removal of harmonic noise, spikes, self-potential drift, tapered windowing and the uncertainty estimation allows for doubling the usable range of TDIP data to almost four decades in time (corresponding to four responses in frequency), and will significantly advance the science and the applicability of the IP method. (Less)

Modeling the effects of material properties on the pull‐in instability of nonlocal functionally graded nano‐actuators

Abstract: Dynamic pull-in behavior of nonlocal functionally graded nano-actuators by considering Casimir attraction is investigated in this paper. It is assumed that the nano-bridge is initially at rest and the fundamental frequency of nano-structure as a function of system parameters is obtained asymptotically by Iteration Perturbation Method (IPM). The effects of actuation voltage, nonlocal parameter, properties of FGM materials and intermolecular force on the dynamic pull-in behavior are studied. It is exhibited that two terms in series expansions are adequate to achieve the acceptable approximations for fundamental frequency as well as the analytic solution. Comparison between the obtained results based on the asymptotic analysis and the reported experimental and numerical results in the literature, verify the effectiveness of the asymptotic analysis.

A Capacitor Voltage Balancing Method With Fundamental Sorting Frequency for Modular Multilevel Converters Under Staircase Modulation

Abstract: A fundamental frequency-sorting algorithm with staircase modulation is proposed to balance the floating capacitors for modular multilevel converters. The driving pulses are assigned to the submodules at every fundamental period according to their charging capabilities for the capacitors. The charging capabilities of the driving pulses can be evaluated by sorting the voltage increments of the capacitors or derived from the symmetrical characteristic of the curve between the voltage increments and the pulse numbers. With this method, all the power devices switch only once per fundamental period, which is suitable for high-power applications. Meanwhile, the sorting frequency decreases to the fundamental frequency. Hence, a large number of calculation resources can be saved. Moreover, it does not need to measure the arm currents so that several current sensors can be saved and the communication protocol between the central and local controllers can be simplified. At last, a three-phase simulation platform with 20 submodules per arm and a down-scaled experimental prototype with eight submodules in each arm are built to validate the proposed voltage-balancing method.

Nonlinear analysis and power improvement of broadband low-frequency piezomagnetoelastic energy harvesters

Abstract: A significant impediment to the deploy- ment of vibration-based energy harvesting devices has been the limitation of most low-frequency transduc- ers, usually in the form of unimorph or bimorph can- tileverbeam,toextractenergyfromaverynarrowband- width around the transducer's fundamental frequency. In such devices, a slight deviation from the fundamen- tal frequency causes a significant reduction in the level of harvested power by several orders of magnitudes. Additionally,mostofthecurrentresearcheffortsonthe design of piezoelectric energy harvesters have had lim- ited success in achieving low resonance frequency. To overcome these challenges, we introduce an enhanced broadband low-frequency piezomagnetoelastic energy harvester. This harvester consists of a partially cov- ered piezoelectric cantilever beam with a fixed magnet mass at the top of the magnet tip mass. A nonlinear distributed-parameter model based on Euler-Bernoulli beam theory and Galerkin discretization is developed. This electromechanical model is validated with previ- ous experimental measurements for a specific value of the spacing distance between the two magnets. A para- metric study is performed to determine the effects of the spacing distance between the two magnets on the static position of the harvester, natural frequency, and level of the harvested power. It is demonstrated that a decrease between the two attractive magnets results in a decrease in the natural frequency of the harvester withastrongsofteningbehaviorwhichgivestheoppor- tunity to harvest energy at broadband low-frequency range. The results also show that the presence and importance of the softening behavior depends on the electrical load resistance. In conclusion, the results show that depending on the available low excitation frequency, an enhanced piezoelectric energy harvester can be tuned and optimized by changing the spacing distance between the two tip magnets.

Highly Tunable Electrothermally and Electrostatically Actuated Resonators

Abstract: This paper demonstrates experimentally, theoretically, and numerically for the first time, a wide-range tunability of an in-plane clamped–clamped microbeam, bridge, and resonator actuated electrothermally and electrostatically. Using both actuation methods, we demonstrate that a single resonator can be operated at a wide range of frequencies. The microbeam is actuated electrothermally by passing a dc current through it, and electrostatically by applying a dc polarization voltage between the microbeam and the stationary electrode. We show that when increasing the electrothermal voltage, the compressive stress inside the microbeam increases, which leads eventually to its buckling. Before buckling, the fundamental frequency decreases until it drops to very low values, almost to zero. After buckling, the fundamental frequency increases, which is shown to be as high as twice the original resonance frequency. Adding a dc bias changes the qualitative nature of the tunability both before and after buckling, which adds another independent way of tuning. This reduces the dip before buckling, and can eliminate it if desired, and further increases the fundamental frequency after buckling. Analytical results based on the Galerkin discretization of the Euler Bernoulli beam theory are generated and compared with the experimental data and simulation results of a multi-physics finite-element model. A good agreement is found among all the results. [2015-0341]

Utilizing intentional internal resonance to achieve multi-harmonic atomic force microscopy

Abstract: During dynamic atomic force microscopy (AFM), the deflection of a scanning cantilever generates multiple frequency terms due to the nonlinear nature of AFM tip-sample interactions. Even though each frequency term is reasonably expected to encode information about the sample, only the fundamental frequency term is typically decoded to provide topographic mapping of the measured surface. One of main reasons for discarding higher harmonic signals is their low signal-to-noise ratio. Here, we introduce a new design concept for multi-harmonic AFM, exploiting intentional nonlinear internal resonance for the enhancement of higher harmonics. The nonlinear internal resonance, triggered by the non-smooth tip-sample dynamic interactions, results in nonlinear energy transfers from the directly excited fundamental bending mode to the higher-frequency mode and, hence, enhancement of the higher harmonic of the measured response. It is verified through detailed theoretical and experimental study that this AFM design can robustly incorporate the required internal resonance and enable high-frequency AFM measurements. Measurements on an inhomogeneous polymer specimen demonstrate the efficacy of the proposed design, namely that the higher harmonic of the measured response is capable of enhanced simultaneous topography imaging and compositional mapping, exhibiting less crosstalk with an abrupt height change.

Individual Differences in the Frequency-Following Response: Relation to Pitch Perception

Abstract: The scalp-recorded frequency-following response (FFR) is a measure of the auditory nervous system’s representation of periodic sound, and may serve as a marker of training-related enhancements, behavioural deficits, and clinical conditions. However, FFRs of healthy normal subjects show considerable variability that remains unexplained. We investigated whether the FFR representation of the frequency content of a complex tone is related to the perception of the pitch of the fundamental frequency. The strength of the fundamental frequency in the FFR of 39 people with normal hearing was assessed when they listened to complex tones that either included or lacked energy at the fundamental frequency. We found that the strength of the fundamental representation of the missing fundamental tone complex correlated significantly with people's general tendency to perceive the pitch of the tone as either matching the frequency of the spectral components that were present, or that of the missing fundamental. Although at a group level the fundamental representation in the FFR did not appear to be affected by the presence or absence of energy at the same frequency in the stimulus, the two conditions were statistically distinguishable for some subjects individually, indicating that the neural representation is not linearly dependent on the stimulus content. In a second experiment using a within-subjects paradigm, we showed that subjects can learn to reversibly select between either fundamental or spectral perception, and that this is accompanied both by changes to the fundamental representation in the FFR and to cortical-based gamma activity. These results suggest that both fundamental and spectral representations coexist, and are available for later auditory processing stages, the requirements of which may also influence their relative strength and thus modulate FFR variability. The data also highlight voluntary mode perception as a new paradigm with which to study top-down vs bottom-up mechanisms that support the emerging view of the FFR as the outcome of integrated processing in the entire auditory system.

Empirical Formulation for Estimating the Fundamental Frequency of Slender Masonry Structures

Abstract: The fundamental frequency of a structure enables better assessment of its seismic demand for an efficient design and planning of its maintenance and retrofit strategy. The frequency is independent of the type of external loads, however, depends on structural stiffness, mass, damping and boundary conditions. In the case of slender masonry structures such as towers, minarets chimneys, and pagoda temples, it is influenced by mass and stiffness distribution, connection to adjacent structures, material properties, aspect ratio and slenderness ratio. In this present article, the data collected from various literature reviews on the slender masonry structures regarding dynamic, geometrical, and mechanical characteristics have been correlated to identify the major parameters influencing the fundamental frequency of such structures. The database has been used for developing an empirical formulation for predicting the fundamental frequency of such structures. The comparison between the experimental fundamen...

Multi-frequency acoustic metasurface for extraordinary reflection and sound focusing

Abstract: We theoretically and numerically present the design of multi-frequency acoustic metasurfaces (MFAMs) with simple structure that can work not only at fundamental frequency, but also at their harmonic frequencies, which breaks the single frequency limitation in conventional resonance-based acoustic metasurfaces. The phase matched condition for achromatic manipulation is discussed. We demonstrate achromatic extraordinary reflection and sound focusing at 1700Hz, 3400Hz, and 5100Hz, that is, they have the same reflection direction and the same focusing position. This significant feature may pave the way to new type of acoustic metasurface, and will also extend acoustic metasurface applications to strongly nonlinear source cases.

Common fate model for unison source separation

Abstract: In this paper we present a novel source separation method aiming to overcome the difficulty of modelling non-stationary signals. The method can be applied to mixtures of musical instruments with frequency and/or amplitude modulation, e.g. typically caused by vibrato. It is based on a signal representation that divides the complex spectrogram into a grid of patches of arbitrary size. These complex patches are then processed by a two-dimensional discrete Fourier transform, forming a tensor representation which reveals spectral and temporal modulation textures. Our representation can be seen as an alternative to modulation transforms computed on magnitude spectrograms. An adapted factorization model allows to decompose different time-varying harmonic sources based on their particular common modulation profile: hence the name Common Fate Model. The method is evaluated on musical instrument mixtures playing the same fundamental frequency (unison), showing improvement over other state-of-the-art methods.

A Harmonic Suppression Method Based on Fractional Lower Order Statistics for Power System

Abstract: Impulse noise in power systems would seriously degrade the harmonic suppression performance. To remedy this problem, a novel harmonic suppression method based on fractional lower order statistics (FLOS) is proposed in this paper. In the proposed method, impulse noise is modeled by alpha-stable distribution. Then, the ESPRIT spectrum estimation algorithm is improved by FLOS for impulse noise and used to estimate the fundamental frequency of power signal, and the frequency of each harmonic component is obtained from this estimated frequency. Next, the amplitude of each harmonic component is estimated by a modified recursive least squares (RLS) algorithm. Finally, a harmonic compensation signal is generated by the active power filter based on the estimated frequencies and amplitudes to cancel original harmonics. The proposed method has a competitive advantage that it can suppress harmonics well even if the impulse noise activating and has a fast tracking ability for changing harmonics. Also, due to the use of self-sensing actuator principle, the proposed method can not only guarantee the performance of suppressing harmonics at normal operation states, but also ensure not to amplify harmonics in case of malfunction. The simulation results show that the proposed method has a better harmonic suppression performance than the existing ones under the impulse noise environment. The real experiments are also presented to verify the feasibility of the proposed method.

Evaluation of digital metering methods used in protection and reactive power compensation of micro-grids

Abstract: Stand-alone micro-grids (MGs) and grid-connected MGs with high penetration level of Distributed Generation (DG) are growing at a fast rate. In these grids, the power quality disturbances such as harmonics, inter-harmonics and deviation from the fundamental frequency are widespread. The influence of these disturbances on two categories of digital metering algorithms is evaluated in this paper. The first category is related to the measurement of the fundamental frequency component of current and voltage signals, which are used as inputs of the digital protection algorithms. Most of the relays only use fundamental frequency component of their input voltage and current signals to fulfill the desired protective functions. The accuracy of the protective relays highly depends on the performance of the applied algorithms for extracting the fundamental components. The second evaluated category is related to the reactive power calculation algorithms, which are used in the static VAr compensator (SVC) control system. Utilizing SVC is growing due to the DGs such as wind turbines magnify voltage fluctuations called flicker. Since the SVC compensates only the reactive power related to the fundamental frequency component, the reactive power signal should not be sensitive to the harmonics. In addition, the reactive power calculation should be fast enough that SVC can follow the abrupt changes to mitigate the flicker, efficiently. In this paper, frequency deviation, harmonic, and inter-harmonic phenomena are considered as the most causes for power quality problems. Their influence in digital metering algorithms is evaluated. It is confirmed that defining new indices is mandatory to fully reflect algorithms׳ accuracy and efficiency. Furthermore, the field measurements of instantaneous voltage and current of a wind farm and electric arc furnaces are used for the evaluation.

Maximum fundamental frequency of thick laminated composite plates by a hybrid optimization method

Abstract: As a first attempt, a combined method is introduced to obtain maximum fundamental frequency of thick laminated composite plates via finding optimum fibers orientation. The governing equations are obtained based on the higher order shear deformation theory (HSDT). The robust and accurate finite element method (FEM) is used to discretize the governing equations. The transferred form of the equations in frequency domain is obtained and the fundamental frequency of the plate is achieved. High sensitivity of the problem with the fibers orientations is shown. To find the optimum fibers orientation of the thick plate a mixed implementable evolutionary algorithm is used. In the proposed genetic algorithms (GAs) base method, particle swarm optimization (PSO) method is added to improve specified percent of GAs population. Applicability and usefulness of the method is demonstrated by solving different examples.

Vibration modeling of carbon-nanotube-based biosensors incorporating thermal and nonlocal effects:

Abstract: The vibration behavior of a bridged single walled carbon nanotube with a bio-mass adsorbed at various positions subjected to temperature change is investigated. The frequency equation of the sensor is derived analytically based on nonlocal Euler–Bernoulli beam theory. The relationship between the vibration frequency, the temperature change, the nonlocal parameter, the attached bio-mass and its location was obtained. Results without temperature change are compared with available results of analytical and molecular mechanics. It is found that the influence of thermal effect on the frequency and sensitivity of the biosensor is significant if its length-to-diameter ratio is large. On the other hand, the effect of nonlocal parameter on the frequency and sensitivity of the biosensor increases if its length-to-diameter ratio decreases.