Showing papers on "Fundamental frequency published in 2009"

Fundamental Frequency Switching Strategies of a Seven-Level Hybrid Cascaded H-Bridge Multilevel Inverter

Abstract: This paper presents a cascaded H-bridge multilevel inverter that can be implemented using only a single dc power source and capacitors. Standard cascaded multilevel inverters require n dc sources for 2n + 1 levels. Without requiring transformers, the scheme proposed here allows the use of a single dc power source (e.g., a battery or a fuel cell stack) with the remaining n-1 dc sources being capacitors, which is referred to as hybrid cascaded H-bridge multilevel inverter (HCMLI) in this paper. It is shown that the inverter can simultaneously maintain the dc voltage level of the capacitors and choose a fundamental frequency switching pattern to produce a nearly sinusoidal output. HCMLI using only a single dc source for each phase is promising for high-power motor drive applications as it significantly decreases the number of required dc power supplies, provides high-quality output power due to its high number of output levels, and results in high conversion efficiency and low thermal stress as it uses a fundamental frequency switching scheme. This paper mainly discusses control of seven-level HCMLI with fundamental frequency switching control and how its modulation index range can be extended using triplen harmonic compensation.

Analysis of Emotionally Salient Aspects of Fundamental Frequency for Emotion Detection

Abstract: During expressive speech, the voice is enriched to convey not only the intended semantic message but also the emotional state of the speaker. The pitch contour is one of the important properties of speech that is affected by this emotional modulation. Although pitch features have been commonly used to recognize emotions, it is not clear what aspects of the pitch contour are the most emotionally salient. This paper presents an analysis of the statistics derived from the pitch contour. First, pitch features derived from emotional speech samples are compared with the ones derived from neutral speech, by using symmetric Kullback-Leibler distance. Then, the emotionally discriminative power of the pitch features is quantified by comparing nested logistic regression models. The results indicate that gross pitch contour statistics such as mean, maximum, minimum, and range are more emotionally prominent than features describing the pitch shape. Also, analyzing the pitch statistics at the utterance level is found to be more accurate and robust than analyzing the pitch statistics for shorter speech regions (e.g., voiced segments). Finally, the best features are selected to build a binary emotion detection system for distinguishing between emotional versus neutral speech. A new two-step approach is proposed. In the first step, reference models for the pitch features are trained with neutral speech, and the input features are contrasted with the neutral model. In the second step, a fitness measure is used to assess whether the input speech is similar to, in the case of neutral speech, or different from, in the case of emotional speech, the reference models. The proposed approach is tested with four acted emotional databases spanning different emotional categories, recording settings, speakers and languages. The results show that the recognition accuracy of the system is over 77% just with the pitch features (baseline 50%). When compared to conventional classification schemes, the proposed approach performs better in terms of both accuracy and robustness.

Multi-Pitch Estimation

Abstract: Periodic signals can be decomposed into sets of sinusoids having frequencies that are integer multiples of a fundamental frequency. The problem of finding such fundamental frequencies from noisy observations is important in many speech and audio applications, where it is commonly referred to as pitch estimation. These applications include analysis, compression, separation, enhancement, automatic transcription and many more. In this book, an introduction to pitch estimation is given and a number of statistical methods for pitch estimation are presented. The basic signal models and associated estimation theoretical bounds are introduced, and the properties of speech and audio signals are discussed and illustrated. The presented methods include both single- and multi-pitch estimators based on statistical approaches, like maximum likelihood and maximum a posteriori methods, filtering methods based on both static and optimal adaptive designs, and subspace methods based on the principles of subspace orthogonality and shift-invariance. The application of these methods to analysis of speech and audio signals is demonstrated using both real and synthetic signals, and their performance is assessed under various conditions and their properties discussed. Finally, the estimators are compared in terms of computational and statistical efficiency, generalizability and robustness. Table of Contents: Fundamentals / Statistical Methods / Filtering Methods / Subspace Methods / Amplitude Estimation

A heterogeneous nonlinear attenuating full- wave model of ultrasound

Abstract: A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). Three-dimensional solutions of the equation are verified with water tank measurements of a commercial diagnostic ultrasound transducer and are shown to be in excellent agreement in terms of the fundamental and harmonic acoustic fields and the power spectrum at the focus. The linear and nonlinear components of the algorithm are also verified independently. In the linear nonattenuating regime solutions match results from Field II, a well established software package used in transducer modeling, to within 0.3 dB. Nonlinear plane wave propagation is shown to closely match results from the Galerkin method up to 4 times the fundamental frequency. In addition to thermoviscous attenuation we present a numerical solution of the relaxation attenuation laws that allows modeling of arbitrary frequency dependent attenuation, such as that observed in tissue. A perfectly matched layer (PML) is implemented at the boundaries with a numerical implementation that allows the PML to be used with high-order discretizations. A -78 dB reduction in the reflected amplitude is demonstrated. The numerical algorithm is used to simulate a diagnostic ultrasound pulse propagating through a histologically measured representation of human abdominal wall with spatial variation in the speed of sound, attenuation, nonlinearity, and density. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beam-forming algorithm to generate a images. The resulting harmonic image exhibits characteristic improvement in lesion boundary definition and contrast when compared with the fundamental image. We demonstrate a mechanism of harmonic image quality improvement by showing that the harmonic point spread function is less sensitive to reverberation clutter.

Event-Based Instantaneous Fundamental Frequency Estimation From Speech Signals

Abstract: Exploiting the impulse-like nature of excitation in the sequence of glottal cycles, a method is proposed to derive the instantaneous fundamental frequency from speech signals. The method involves passing the speech signal through two ideal resonators located at zero frequency. A filtered signal is derived from the output of the resonators by subtracting the local mean computed over an interval corresponding to the average pitch period. The positive zero crossings in the filtered signal correspond to the locations of the strong impulses in each glottal cycle. Then the instantaneous fundamental frequency is obtained by taking the reciprocal of the interval between successive positive zero crossings. Due to filtering by zero-frequency resonator, the effects of noise and vocal-tract variations are practically eliminated. For the same reason, the method is also robust to degradation in speech due to additive noise. The accuracy of the fundamental frequency estimation by the proposed method is comparable or even better than many existing methods. Moreover, the proposed method is also robust against rapid variation of the pitch period or vocal-tract changes. The method works well even when the glottal cycles are not periodic or when the speech signals are not correlated in successive glottal cycles.

On-line learning and modulation of periodic movements with nonlinear dynamical systems

Abstract: The paper presents a two-layered system for (1) learning and encoding a periodic signal without any knowledge on its frequency and waveform, and (2) modulating the learned periodic trajectory in response to external events. The system is used to learn periodic tasks on a humanoid HOAP-2 robot. The first layer of the system is a dynamical system responsible for extracting the fundamental frequency of the input signal, based on adaptive frequency oscillators. The second layer is a dynamical system responsible for learning of the waveform based on a built-in learning algorithm. By combining the two dynamical systems into one system we can rapidly teach new trajectories to robots without any knowledge of the frequency of the demonstration signal. The system extracts and learns only one period of the demonstration signal. Furthermore, the trajectories are robust to perturbations and can be modulated to cope with a dynamic environment. The system is computationally inexpensive, works on-line for any periodic signal, requires no additional signal processing to determine the frequency of the input signal and can be applied in parallel to multiple dimensions. Additionally, it can adapt to changes in frequency and shape, e.g. to non-stationary signals, such as hand-generated signals and human demonstrations.

Fundamental-Frequency-Modulated Six-Level Diode-Clamped Multilevel Inverter for Three-Phase Stand-Alone Photovoltaic System

Abstract: This paper presents a fundamental-frequency-modulated diode-clamped multilevel inverter (DCMLI) scheme for a three-phase stand-alone photovoltaic (PV) system. The system consists of five series-connected PV modules, a six-level DCMLI generating fundamental-modulation staircase three-phase output voltages, and a three-phase induction motor as the load. In order to validate the proposed concept, simulation studies and experimental measurements using a small-scale laboratory prototype are also presented. The results show the feasibility of the fundamental frequency switching application in three-phase stand-alone PV power systems.

Power system harmonics research: a survey

Abstract: The increased use of power electronic controlled equipment, such as variable speed drives, automated production lines, personal computers and non-linear electronic devices in power systems has given rise to a type of voltage and current waveform distortion called as ‘harmonics’. Harmonic can be defined as the undesirable components of a distorted periodic waveform whose frequencies are the integer multiples (non-integer multiples in case of inter-harmonics, and the frequency less than fundamental frequency in case of sub-harmonics) of the fundamental frequency. Presence of these harmonics results in increased losses, equipment heating and loss-of-life, and interference with protection, control and communication circuits as well as customer loads. The research has been underway since very beginning for control of power system harmonics and to supply consumers with reliable and ‘clean’ fundamental-frequency sinusoidal electric power that does not represent a damaging threat to their equipment. This paper, therefore, reviews the progress made in power system harmonics research and development since its inception. Attempts are also made to highlight the current and future issues involved in the development of quality and reliable electric power technology for future applications. A list of 145 research publications on the subject is also appended for a quick reference. Copyright © 2007 John Wiley & Sons, Ltd.

Real-Time Estimation of Fundamental Frequency and Harmonics for Active Shunt Power Filters in Aircraft Electrical Systems

Abstract: A novel algorithm for fundamental frequency and harmonic components detection is presented in this paper. The technique is based on a real-time implementation of discrete Fourier transform, and it allows fast and accurate estimation of fundamental frequency and harmonics of a distorted signal with variable fundamental frequency. It is suitable for active shunt filter applications, when fast and accurate tracking of the reference signal is required to achieve a good control performance. The main application for the algorithm is aircraft ac power systems, where the fundamental frequency can be either fixed on 400 Hz and its actual value fluctuates around the nominal value, or variable in the range 360-900 Hz. Hence, a real-time estimation of fundamental frequency is essential for active filter control. The proposed algorithm has been at first implemented in Matlab/Simulink for computer simulation, and it has been compared with a Phase Locked Loop (PLL) algorithm for frequency detection and the synchronous dq reference method for harmonic detection. Experimental tests have been carried out in order to validate the simulation results. The distorted current absorbed by a nonlinear load is analyzed and processed by means of a digital implementation of the algorithm running on the active shunt power filter control DSP, in order to calculate the active filter compensating current.

A Frequency-Doubling Optoelectronic Oscillator Using a Polarization Modulator

Abstract: A novel realization of a frequency-doubling optoelectronic oscillator (OEO) using a polarization modulator (PolM) is proposed and experimentally demonstrated. In the proposed system, the PolM in combination with two optical polarizers connected via two polarization controllers (PCs) is operating as a two-output intensity modulator. One output of the intensity modulator is connected to the radio-frequency port of the PolM, to form an optoelectronic loop for the generation of a microwave signal with the fundamental frequency determined by the center frequency of a narrowband electronic filter. The other output of the intensity modulator provides a fundamental or frequency-doubled optically modulated microwave signal depending on the static phase term introduced by the PC before the polarizer. The proposed OEO is experimentally demonstrated. A fundamental microwave signal at 10 GHz or a frequency-doubled microwave signal at 20 GHz is generated. The phase noise performance of the generated microwave signal is also investigated.

A converter topology for high speed motor drive applications

Abstract: In the area of natural gas industry, there is a large interest in converters for driving high speed, medium voltage induction motors. High-speed drive systems are capable of directly driving turbo-compressors at speeds of up to 20,000 rpm / 8MW. In high speed motor drive applications, the motor fundamental frequency can vary from 100Hz to 300Hz, which requires a high switching frequency. However, switching losses increase with switching frequency and these losses represent a critical point for high voltage semiconductors. Soft switching topology could represent a relevant solution to work at high switching frequency. The drawback of such a converter is the number of added components and the complexity of the control. Multilevel inverters provide output signals with low harmonic distortion. When the number of level increases, the output voltage THD decreases but the size and the cost of the system increases as well. The switching voltage is reduced when the number of level increases, depending on the topologies, or when a series connection of components is made. This paper reports a 3-level converter structure for high speed motor drive applications that allows decreasing switching losses in comparison with the well known 3-level NPC (Neutral Point Clamped) inverter [1]. This feature leads to the possibility to increase the switching frequency or the load current level thanks to series connection of IGBTs. As the neutral point is actively piloted, this structure is named NPP (Neutral Point Piloted).

Real-Time Estimation of Power System Frequency Using Nonlinear Least Squares

Abstract: This paper presents a nonlinear least squares method for measuring the power system frequency, wherein the voltage at the measurement point is modeled by using the Fourier series. The estimation of the fundamental frequency is a nonlinear problem in this formulation and is solved by performing a 1-D search over the range of allowed frequency variation. The voltage signal is used for frequency estimation because it is typically less distorted than the line current, resulting in computational efficiency. The robustness of this algorithm with respect to change in various parameters is studied through simulation and the results are validated by hardware implementation using a Virtex IV field-programmable gate array. An application of this algorithm to a shunt active power filter is also presented.

Multiple second order generalized integrators for harmonic synchronization of power converters

Abstract: This paper presents a new frequency-adaptive synchronization method for grid-connected power converters which allows estimating not only the positive- and negativesequence components of the power signal at the fundamental frequency, but also other sequence components at multiple frequencies. The proposed system is called the MSOGI-FLL since it is based on a decoupled network consisting of multiple second order generalized integrators (MSOGI) which are frequency-adaptive by using a frequency-locked loop (FLL). In this paper, the MSOGI-FLL is analyzed and its performance is evaluated by both simulations and experiments.

Selective Harmonic Elimination PWM Control Scheme on a Three-Phase Four-Leg Voltage Source Inverter

Abstract: A selective harmonic elimination (SHE) control strategy on a three-phase four-leg inverter is reported in this paper. The control signals of the four legs are calculated as follows: 1) control signals of three legs are mathematically expressed using Fourier-based equations on line-to-line basis as conventional SHE technology, which eliminates lower order nontriplen harmonics, and 2) the fourth leg produces the harmonics that are equal to the lower triplen harmonics produced by the other legs. The inverter has almost symmetric three-phase output voltage with unbalanced load because the fourth leg provides a low-impedance path for the triplen harmonics. The switching-to-fundamental frequency ratio is only 13 and 27 (per unit) p.u. for the three legs and the fourth leg in the proposed prototype, which is with the total harmonic distortion of output voltage lower than 4%. Selected solutions for the switching angles are presented and verified by simulation and experimentation in order to confirm the effectiveness of the proposed scheme.

A Method for Extracting the Fundamental-Frequency Positive-Sequence Voltage Vector Based on Simple Mathematical Transformations

Abstract: In this paper, a novel scheme for obtaining the fundamental-frequency positive-sequence grid voltage is proposed. The method is based on four simple mathematical transformations; two of them are in the stationary reference frame, which are able to eliminate odd harmonics from the original signals. The other two transformations are implemented in a synchronously rotating reference frame in order to eliminate even harmonics. The output of the last transformation block is the input to a synchronous reference-frame phase-locked loop for detecting the frequency and position of the positive-sequence voltage vector. The proposed algorithm was verified through simulations and experiments by applying distorted and unbalanced signals, containing positive and negative-sequence components. The results are in agreement with those theoretically predicted and indicate that the proposed scheme has a great potential for use in grid-connected converter synchronization algorithms.

Optimization of the electrical asymmetry effect in dual-frequency capacitively coupled radio frequency discharges: Experiment, simulation, and model

Abstract: An electrical asymmetry in capacitive rf discharges with a symmetrical electrode configuration can be induced by driving the discharge with a fundamental frequency and its second harmonic. For equal amplitudes of the applied voltage waveforms, it has been demonstrated by modeling, simulation, and experiments that this electrical asymmetry effect (EAE) leads to the generation of a variable dc self-bias that depends almost linearly on the phase angle between the driving voltage signals. Here, the dependence of the dc self-bias generated by the EAE on the choice of the voltage amplitudes, i.e., the ratio A of high to low frequency amplitude, is investigated experimentally as well as by using an analytical model and a particle-in-cell simulation. It is found that (i) the strongest electrical asymmetry is induced for A<1 at pressures ranging from 6 to 100 Pa and that (ii) around this optimum voltage ratio the dc self-bias normalized to the sum of both voltage amplitudes is fairly insensitive to changes of A. T...

An ant colony optimization approach to multi-objective optimal design of symmetric hybrid laminates for maximum fundamental frequency and minimum cost

Abstract: An ant colony optimization algorithm for optimum design of symmetric hybrid laminates is described. The objective is simultaneous maximization of fundamental frequency and minimization of cost. Number of surface and core layers made of high-stiffness and low-stiffness materials, respectively, and fiber orientations are the design variables. Optimal stacking sequences are given for hybrid graphite/epoxy-glass/epoxy laminated plates with different aspect ratios and number of plies. The results obtained by ant colony optimization are compared to results obtained by a genetic algorithm and simulated annealing. The effectiveness of the hybridization concept for reducing the weight and keeping the fundamental frequency at a reasonable level is demonstrated. Furthermore, it is shown that the proposed ant colony algorithm outperforms the two other heuristics.

Can temporal fine structure represent the fundamental frequency of unresolved harmonics

Abstract: At least two modes of pitch perception exist: in one, the fundamental frequency (F0) of harmonic complex tones is estimated using the temporal fine structure (TFS) of individual low-order resolved harmonics; in the other, F0 is derived from the temporal envelope of high-order unresolved harmonics that interact in the auditory periphery. Pitch is typically more accurate in the former than in the latter mode. Another possibility is that pitch can sometimes be coded via the TFS from unresolved harmonics. A recent study supporting this third possibility [Moore et al. (2006a). J. Acoust. Soc. Am. 119, 480–490] based its conclusion on a condition where phase interaction effects (implying unresolved harmonics) accompanied accurate F0 discrimination (implying TFS processing). The present study tests whether these results were influenced by audible distortion products. Experiment 1 replicated the original results, obtained using a low-level background noise. However, experiments 2–4 found no evidence for the use of TFS cues with unresolved harmonics when the background noise level was raised, or the stimulus level was lowered, to render distortion inaudible. Experiment 5 measured the presence and phase dependence of audible distortion products. The results provide no evidence that TFS cues are used to code the F0 of unresolved harmonics.

Harmonic-Suppressed Bandpass Filter Based on Discriminating Coupling

Abstract: This letter presents a novel method to suppress harmonic responses of parallel-coupled bandpass filters. The harmonic suppression is based on discriminating coupling. The coupling coefficient at fundamental resonant frequency can be tuned to desirable values whereas it is zero at the second harmonic. Hence, the coupling region blocks the second harmonic but still allows the transmission of signals at passband frequency. Benefiting from this feature, the second harmonic can be suppressed without degrading the passband performance. Furthermore, no additional circuit is needed. For demonstration purpose, two example filters are implemented. The experimental results are presented to verify the proposed method.

A Novel Three-Phase Hybrid Active Power Filter With a Series Resonance Circuit Tuned at the Fundamental Frequency

Abstract: In this paper, a novel three-phase hybrid active power filter (HAPF) with a series resonance circuit tuned at the fundamental frequency is proposed for simultaneously suppressing harmonic currents and compensating high-capacity reactive power in high- or medium-voltage power systems. To reduce its rated capacity, the active power filter is shunted to the series resonance circuit by a matching transformer and, thus, greatly reduces its current requirements as well as voltage ratings of semiconductor switching devices. The passive power filters are used to compensate the reactive power with a constant capacity. The validity and effectiveness of this novel HAPF system have been verified by simulation and industrial application results.

Multi-pitch estimation

Abstract: Periodic signals can be decomposed into sets of sinusoids having frequencies that are integer multiples of a fundamental frequency. The problem of finding such fundamental frequencies from noisy observations is important in many speech and audio applications, where it is commonly referred to as pitch estimation. These applications include analysis, compression, separation, enhancement, automatic transcription and many more. In this book, an introduction to pitch estimation is given and a number of statistical methods for pitch estimation are presented. The basic signal models and associated estimation theoretical bounds are introduced, and the properties of speech and audio signals are discussed and illustrated. The presented methods include both single- and multi-pitch estimators based on statistical approaches, like maximum likelihood and maximum a posteriori methods, filtering methods based on both static and optimal adaptive designs, and subspace methods based on the principles of subspace orthogonality and shift-invariance. The application of these methods to analysis of speech and audio signals is demonstrated using both real and synthetic signals, and their performance is assessed under various conditions and their properties discussed. Finally, the estimators are compared in terms of computational and statistical efficiency, generalizability and robustness. (Less)

Finding the pitch of the missing fundamental in infants.

Abstract: Pitch perception is critical for the perception of speech and music, for object identification, and for auditory scene analysis, whereby representations are derived for each sounding object in the environment from the complex sound wave that reaches the ears. The perceived pitch of a complex sound corresponds to its fundamental frequency. However, removal of energy at the fundamental does not alter the pitch because adults use the harmonics to derive the pitch (Bendor and Wang, 2005; Trainor, 2008). Although sound frequency is represented subcortically, the integration of harmonics into a representation of pitch does not occur until auditory cortex (Bendor and Wang, 2005). Given that auditory cortex is immature in young infants, we examined the development of cortical representations for pitch by measuring electrophysiological (EEG) responses to pitch changes that required processing the pitch of the missing fundamental. Adults and infants 4 months and older showed a mismatch negativity response to these pitch changes, but 3-month-old infants did not. Thus, cortical representations of the pitch of the missing fundamental emerge between 3 and 4 months of age, indicating that there is a profound change in auditory perception for pitch in early infancy.

Radiation from a Josephson STAR-emitter

Abstract: We calculate the angular dependence of the radiation-zone output power and electric polarization of stimulated terahertz amplified radiation (STAR) emitted from a $dc$ voltage applied across cylindrical and rectangular stacks of intrinsic Josephson junctions. During coherent emission, a spatially uniform $ac$ Josephson current density in the stack acts as a surface electric current density antenna source, leading to an harmonic radiation frequency spectrum, as in experiment, but absent in all cavity modesl of cylindrical mesas. Spatial fluctuations of the $ac$ Josephson current cause its fundamental mode to lock onto the lowest finite energy cylindrical cavity mode, causing it to resonate, leading to a non-uniform magnetic surface current density radiation source, and a non-trivial combined fundamental frequency output power with linear polarization We also present a model of the superconducting substrate, and present results for rectangular mesas.

Dynamics of repulsive dual-frequency atomic force microscopy

Abstract: In bimodal atomic force microscopy, two flexural modes are driven at their resonances. The oscillation of the second eigenmode, which is usually an incommensurate multiple of the fundamental frequency, perturbs the dynamic system. Numerical simulations show that the tip motion is almost periodic at typical set points and that harmonics and intermodulation frequencies prevail in the spectrum. The simulations also predict a very small increase in the noise of the first mode amplitude and phase due to the second mode oscillation. At small average tip sample separations, however, phases with repulsive and purely attractive forces can occur intermittently.

Simple representation of signal phase for harmonic speech models

Abstract: A novel representation of the phase information in harmonic speech models is proposed. A transformation from instantaneous phases to initial phase shift differences with respect to the fundamental frequency provides a clear insight into the structure of the phase information and largely simplifies the manipulation of this information.

The Electrical Asymmetry Effect - A novel and simple method for separate control of ion energy and flux in capacitively coupled RF discharges

Abstract: If a temporally symmetric voltage waveform is applied to a capacitively coupled radio frequency (CCRF) discharge, that contains one or more even harmonics of the fundamental frequency, the sheaths in front of the two electrodes will necessarily be asymmetric even in a geometrically symmetric discharge. Optimally this is achieved with a dual-frequency discharge driven at a phase locked fundamental frequency and its second harmonic, e.g. 13.56 MHz and 27.12 MHz. An analytical model, a hybrid ∞uid/Monte-Carlo kinetic model as well as a Particle in Cell (PIC) simulation show that this Electrical Asymmetry Efiect (EAE) leads to the generation of a DC self bias as a function of the phase between the applied voltage harmonics in geometrically symmetric as well as asymmetric discharges. The DC self bias depends almost linearly on the phase angle and the role of the electrodes (powered and grounded) can be reversed. At low pressures the EAE is self-amplifying due to the conservation of ion ∞ux in the sheaths. By tuning the phase, precise and convenient control of the ion energy at the electrodes can be achieved, while the ion ∞ux remains constant. The maximum ion energy can typically be changed by a factor of about three at both electrodes. At the same time the ion ∞ux is constant within §5%.