Showing papers on "Fundamental frequency published in 2008"

A unified framework for nonlinear combustion instability analysis based on the flame describing function

Abstract: Analysis of combustion instabilities relies in most cases on linear analysis but most observations of these processes are carried out in the nonlinear regime where the system oscillates at a limit cycle. The objective of this paper is to deal with these two manifestations of combustion instabilities in a unified framework. The flame is recognized as the main nonlinear element in the system and its response to perturbations is characterized in terms of generalized transfer functions which assume that the gain and phase depend on the amplitude level of the input. This 'describing function' framework implies that the fundamental frequency is predominant and that the higher harmonics generated in the nonlinear element are weak because the higher frequencies are filtered out by the other components of the system. Based on this idea, a methodology is proposed to investigate the nonlinear stability of burners by associating the flame describing function with a frequency-domain analysis of the burner acoustics. These elements yield a nonlinear dispersion relation which can be solved, yielding growth rates and eigenfrequencies, which depend on the amplitude level of perturbations impinging on the flame. This method is used to investigate the regimes of oscillation of a well-controlled experiment. The system includes a resonant upstream manifold formed by a duct having a continuously adjustable length and a combustion region comprising a large number of flames stabilized on a multipoint injection system. The growth rates and eigenfrequencies are determined for a wide range of duct lengths. For certain values of this parameter we find a positive growth rate for vanishingly small amplitude levels, indicating that the system is linearly unstable. The growth rate then changes as the amplitude is increased and eventually vanishes for a finite amplitude, indicating the existence of a limit cycle. For other values of the length, the growth rate is initially negative, becomes positive for a finite amplitude and drops to zero for a higher value. This indicates that the system is linearly stable but nonlinearly unstable. Using calculated growth rates it is possible to predict amplitudes of oscillation when the system operates on a limit cycle. Mode switching and instability triggering may also be anticipated by comparing the growth rate curves. Theoretical results are found to be in excellent agreement with measurements, indicating that the flame describing function (FDF) methodology constitutes a suitable framework for nonlinear instability analysis.

Multiple Reference Frame-Based Control of Three-Phase PWM Boost Rectifiers under Unbalanced and Distorted Input Conditions

Abstract: Many control algorithms and circuits for three-phase pulse width modulation active rectifiers have been proposed in the past decades. In most of the research, it is often assumed that the input voltages are balanced or contain only fundamental frequency components. In this paper, a selective harmonic compensation method is proposed based on an improved multiple reference frame algorithm, which decouples signals of different frequencies before reference frame transformation. This technique eliminates interactions between the fundamental-frequency positive-sequence components and harmonic and/or negative-sequence components in the input currents, so that fast and accurate regulation of harmonic and unbalanced currents can be achieved. A decoupled phase-locked loop algorithm is used for proper synchronization with the utility voltage, which also benefits from the multiple reference frame technique. The proposed control method leads to considerable reduction in low-order harmonic contents in the rectifier input current and achieves almost zero steady-state error through feedback loops. Extensive experimental tests based on a fixed-point digital signal processor controlled 2 kW prototype are used to verify the effectiveness of the proposed ideas.

A spectral/temporal method for robust fundamental frequency tracking

Abstract: In this paper, a fundamental frequency (F(0)) tracking algorithm is presented that is extremely robust for both high quality and telephone speech, at signal to noise ratios ranging from clean speech to very noisy speech. The algorithm is named "YAAPT," for "yet another algorithm for pitch tracking." The algorithm is based on a combination of time domain processing, using the normalized cross correlation, and frequency domain processing. Major steps include processing of the original acoustic signal and a nonlinearly processed version of the signal, the use of a new method for computing a modified autocorrelation function that incorporates information from multiple spectral harmonic peaks, peak picking to select multiple F(0) candidates and associated figures of merit, and extensive use of dynamic programming to find the "best" track among the multiple F(0) candidates. The algorithm was evaluated by using three databases and compared to three other published F(0) tracking algorithms by using both high quality and telephone speech for various noise conditions. For clean speech, the error rates obtained are comparable to those obtained with the best results reported for any other algorithm; for noisy telephone speech, the error rates obtained are lower than those obtained with other methods.

Asynchronous Machine Rotor Fault Diagnosis Technique Using Complex Wavelets

Abstract: This paper introduces a novel approach for the detection of rotor faults in asynchronous machines, based on wavelet analysis of the stator phase current. To be more specific, the measured stator phase current is filtered through a complex wavelet. Theoretical analysis validates that the spectrum of the modulus of the result of the filtering is free from the fundamental supply frequency component, and the fault characteristics can be highlighted. This is advantageous, especially if the induction machine operates at low slip values, where the characteristic frequency components of the rotor fault are very close to the fundamental frequency component. At the same time, by matching the wavelet function to the frequencies of the faulty components, a narrow bandpass filter at the frequency region of the fault characteristic spectral components is obtained. Furthermore, in the context of this paper, features extracted using the proposed technique are used as input to a support vector machine classifier that is employed for the detection of the rotor fault. Simulation and experimental results demonstrate the effectiveness of the proposed technique.

Alfvén quasi-periodic oscillations in magnetars

Abstract: We investigate torsional Alfven oscillations of relativistic stars with a global dipole magnetic field, via two-dimensional numerical simulations. We find that (i) there exist two families of quasi-periodic oscillations (QPOs) with harmonics at integer multiples of the fundamental frequency, (ii) the lower-frequency QPO is related to the region of closed field lines, near the equator, while the higher-frequency QPO is generated near the magnetic axis, (iii) the QPOs are long-lived, (iv) for the chosen form of dipolar magnetic field, the frequency ratio of the lower to upper fundamental QPOs is ∼0.6, independent of the equilibrium model or of the strength of the magnetic field, and (v) within a representative sample of equations of state and of various magnetar masses, the Alfven QPO frequencies are given by accurate empirical relations that depend only on the compactness of the star and on the magnetic field strength. The lower and upper QPOs can be interpreted as corresponding to the edges or turning points of an Alfven continuum, according to the model proposed by Levin (2007). Several of the low-frequency QPOs observed in the X-ray tail of SGR 1806-20 can readily be identified with the Alfven QPOs we compute. In particular, one could identify the 18- and 30-Hz observed frequencies with the fundamental lower and upper QPOs, correspondingly, while the observed frequencies of 92 and 150 Hz are then integer multiples of the fundamental upper QPO frequency (three and five times, correspondingly). With this identification, we obtain an upper limit on the strength of the magnetic field of SGR 1806-20 (if is dominated by a dipolar component) between ∼3 and 7 × 10 15 G. Furthermore, we show that an identification of the observed frequency of 26 Hz with the frequency of the fundamental torsional � = 2 oscillation of the magnetar's crust is compatible with a magnetar mass of about from 1.4 to 1.6 Mand an equation of state (EOS) that is very stiff (if the magnetic field strength is near its upper limit) or moderately stiff (for lower values of the magnetic field).

Optimal Harmonic Estimation Using A Particle Swarm Optimizer

Abstract: This paper presents a new algorithm for harmonic estimation. It utilizes the particle swarm optimizer with passive congregation (PSOPC) to estimate the phases of the harmonics, alongside a least-square (LS) method that is used to estimate the amplitudes. The PSOPC and LS method are executed alternately to minimize the error between the original signal and the signal reconstructed from the estimated parameters during the estimation process. Simulation results are presented to demonstrate that the estimation accuracy is greatly improved in comparison with that of the conventional discrete Fourier transform and genetic algorithms. The proposed algorithm is also used to estimate interhar- monics and the harmonics with frequency deviation. The results show that this new method, working in a corporative manner between PSOPC and LS, is capable of estimating power system integral harmonics and interharmonics, even in the case of the deviation of fundamental frequency.

Harmonic Contributions Evaluation With the Harmonic Current Vector Method

Abstract: A method to evaluate harmonic contributions at the point of common coupling is presented in this paper. The proposed approach is based on the harmonic current vector method where reference impedances are introduced. Resistance defined at fundamental frequency with measurements is used as the customer-side reference impedance. The presented method allows calculation of harmonic contributions without knowing the actual customer impedances. It also enables better evaluation of the customer and utility harmonic contributions in resonance conditions. The method is verified through a simulation study and with extensive field measurements. Long-term measurements are proposed for determination of harmonic contributions.

Active Harmonic Load–Pull With Realistic Wideband Communications Signals

Abstract: A new wideband open-loop active harmonic load-pull measurement approach is presented. The proposed method is based on wideband data-acquisition and wideband signal-injection of the incident and device generated power waves at the frequencies of interest. The system provides full, user defined, in-band control of the source and load reflection coefficients presented to the device-under-test at baseband, fundamental and harmonic frequencies. The system capability to completely eliminate electrical delay allows to mimic realistic matching networks using their measured or simulated frequency response. This feature enables active devices to be evaluated for their actual in-circuit behavior, even on wafer. Moreover the proposed setup provides the unique feature of handling realistic wideband communication signals like multicarrier wideband code division multiple access (W-CDMA), making the setup perfectly suited for studying device performance in terms of efficiency, linearity and memory effects.

High frequency surgery apparatus and method of operating same

Abstract: The invention concerns a high frequency surgery apparatus for cutting and/or coagulating biological tissue and methods of operating same. The high frequency surgery apparatus includes at least one high frequency generator which in operation forms a high frequency circuit with the tissue to be treated, with the production of an arc, and at least one measuring and calculating device which is connected for signal transmission to the high frequency circuit and which is adapted in operation to ascertain both a DC voltage in the high frequency circuit and also the amplitudes of at least one even and at least one odd harmonic of a fundamental frequency of the high frequency generator and to form a first tissue parameter representative of the kind of tissue to be treated from the relationship of the sum of the amplitudes of the even and the odd harmonics to the DC voltage and to output a tissue signal dependent on the first tissue parameter for subsequent processing.

Correction of Current Transformer Transient Performance

Abstract: If a current transformer (CT) saturates while transforming the heavy primary current, in each period, there are sections when the magnetic core is unsaturated and transformation is correct, and when it is saturated, it causes enormous errors. The key to correct the errors is to detect instants of saturation and moments when the saturation ends. This paper presents simple and efficient methods of doing that. In addition, it shows the way how to predict up to three samples after saturation with the acceptable degree of accuracy, thus artificially expanding the unsaturated section. It may substantially facilitate operation of protective devices. The ultimate solution of the problem is to estimate the values of the fundamental frequency component amplitude and the decaying DC component in each period. This paper presents the method of doing that on the ground of four consecutive samples taken during the unsaturated section. If the primary current consists of the fundamental and DC exponential components only, the accuracy of the method is excellent. Neglecting contamination of the current signal with harmonics and noise, it is possible to reconstruct the CT primary current based on the measured values of fundamental and DC components.

Multiple fundamental frequency estimation using Gaussian smoothness

Abstract: The goal of a polyphonic music transcription system is to extract a score from an audio signal. A multiple fundamental frequency estimator is the main piece of these systems, whereas tempo detection and key estimation complement them to correctly extract the score. In this work, in order to detect the fundamental frequencies that are present in a signal, a set of candidates are selected from the spectrum, and all their possible combinations are generated. The best combination is chosen in a frame by frame analysis by applying a set of rules, taking into account the harmonic amplitudes and the spectral smoothness measure described in this work. The system was evaluated and compared to other works, yielding competitive results and performance.

The fundamental frequency variation spectrum

Abstract: This paper describes a recently introduced vector-valued representation of fundamental frequency variation – the FFV spectrum – which has a number of desirable properties. In particular, it is instantaneous, continuous, distributed, and well-suited to application of standard acoustic modeling techniques. We show what the representation looks like, and how it can be used to model prosodic sequences.

Specmurt Analysis of Polyphonic Music Signals

Abstract: This paper introduces a new music signal processing method to extract multiple fundamental frequencies, which we call specmurt analysis. In contrast with cepstrum which is the inverse Fourier transform of log-scaled power spectrum with linear frequency, specmurt is defined as the inverse Fourier transform of linear power spectrum with log-scaled frequency. Assuming that all tones in a polyphonic sound have a common harmonic pattern, the sound spectrum can be regarded as a sum of linearly stretched common harmonic structures along frequency. In the log-frequency domain, it is formulated as the convolution of a common harmonic structure and the distribution density of the fundamental frequencies of multiple tones. The fundamental frequency distribution can be found by deconvolving the observed spectrum with the assumed common harmonic structure, where the common harmonic structure is given heuristically or quasi-optimized with an iterative algorithm. The efficiency of specmurt analysis is experimentally demonstrated through generation of a piano-roll-like display from a polyphonic music signal and automatic sound-to-MIDI conversion. Multipitch estimation accuracy is evaluated over several polyphonic music signals and compared with manually annotated MIDI data.

Common mode & differential mode filter for variable speed drive

Abstract: Systems and methods for improved Variable Speed Drives having active inverters include an input filter for filtering common mode and differential mode currents. A three-phase inductor has three windings, each winding of the three-phase inductor having a center tap dividing each winding into a pair of inductor sections; and a three-phase input capacitor bank connected in a wye configuration to the three center taps at one end, and to a common point at the opposite end. The three-phase input capacitor bank provides a short circuit for frequencies above a predetermined fundamental frequency for shunting such frequencies through the three phase capacitor bank, while passing the predetermined fundamental frequency to an input AC power source.

Sound analysis apparatus and program

Abstract: A sound analysis apparatus employs tone models which are associated with various fundamental frequencies and each of which simulates a harmonic structure of a performance sound generated by a musical instrument, then defines a weighted mixture of the tone models to simulate frequency components of the performance sound, further sequentially updates and optimizes weight values of the respective tone models so that a frequency distribution of the weighted mixture of the tone models corresponds to a distribution of the frequency components of the performance sound, and estimates the fundamental frequency of the performance sound based on the optimized weight values

Performance limit of a passive vertical isolator using a negative stiffness mechanism

Abstract: A passive vibration isolator using a negative stiffness mechanism (NSM) is being considered for small precision instruments since it does not need any outer power supply and pressurized air, and its fundamental frequency can be lowered down to 0.5 Hz. Although the working principle of the NSM and its patents are well known, neither the isolation performance limit related to the lowest fundamental frequency nor its nonlinear behavior have been studied. This paper discusses the performance limit of the passive vertical isolator using the NSM and presents the design guidelines for the isolator based on that performance limit. First, a nonlinear dynamic model of the passive isolator is derived through solid approximations, and the fundamental frequency or performance limit is obtained using nonlinear analysis, which entirely explains the nonlinear behavior of the isolator. In addition, the approximate design equations of the isolator are derived to analyze its performance limit. Finally, an approximate expression of the lowest fundamental frequency of the isolator is derived using nonlinear analysis and design equations, which provide substantial design guidelines to improve isolator performance.

Techniques for accurately deriving physiologic parameters of a subject from photoplethysmographic measurements

Abstract: Several techniques are disclosed for isolating either heart or breath rate data from a photoplethysmograph, which is a time domain signal such as from a pulse oximeter The techniques involve the use of filtering in the frequency domain, after a Fast Fourier Transform (FFT) has been conducted on a given photoplethysmograph also references as a given set of discrete time-domain data The filtering may be applied to an identified fundamental frequency and one or more harmonics for heart related parameters The filter may be truncated to the frequency data set and further applied multiple times to improve roll off After filtering, an Inverse FFT (IFFT) is used to reconstruct the time-domain signal, except with undesirable frequency content eliminated or reduced Calculation or measurement of parameters is then conducted on this reconstructed time-domain signal

Predicting Inverter-Induced Harmonic Loss by Improved Harmonic Injection

Abstract: This letter presents an improved harmonic injection method for determination of inverter-induced harmonic power loss across a range of induction motors rated at 1.1, 7.5, 15, and 30 kW. Techniques to obtain the necessary experimental precision and repeatability are investigated in detail. The harmonic injection method allows the machine to be tested under normal operating conditions while a range of selected harmonics are superimposed on the fundamental frequency of the pulse width modulation (PWM) waveform. This technique is validated by direct loss measurement using a specially built calorimeter capable of detecting power loss as low as a few watts in induction motors of up to 30 kW. Comparisons of segregated losses by IEEE 112 method B for the machines operating on sinusoidal and inverter-fed supplies show a good correlation between high frequency PWM harmonic loss and core loss. Core loss is not a constant proportion of total loss for any machine and neither is harmonic loss independent of machine design.

Pitch strength decreases as F0 and harmonic resolution increase in complex tones composed exclusively of high harmonics.

Abstract: A melodic pitch experiment was performed to demonstrate the importance of time-interval resolution for pitch strength. The experiments show that notes with a low fundamental (75Hz) and relatively few resolved harmonics support better performance than comparable notes with a higher fundamental (300Hz) and more resolved harmonics. Two four note melodies were presented to listeners and one note in the second melody was changed by one or two semitones. Listeners were required to identify the note that changed. There were three orthogonal stimulus dimensions: F0 (75 and 300Hz); lowest frequency component (3, 7, 11, or 15); and number of harmonics (4 or 8). Performance decreased as the frequency of the lowest component increased for both F0’s, but performance was better for the lower F0. The spectral and temporal information in the stimuli were compared using a time-domain model of auditory perception. It is argued that the distribution of time intervals in the auditory nerve can explain the decrease in perform...

Method and apparatus for estimating induction motor rotor temperature

Abstract: A method and apparatus to provide continuous and reliable rotor temperature estimates for line-connected induction motors during steady-state and/or dynamic motor operations. Rotor temperature is calculated from voltage and current measurements without any temperature or speed sensors. First, complex space vectors are synthesized from voltage and current measurements. Second, the instantaneous rotor speed is detected by calculating the rotational speed of a single rotor slot harmonic component with respect to the rotational speed of the fundamental frequency component. Third, the positive sequence fundamental frequency components are extracted from complex space vectors. Fourth, the rotor time constant is estimated in a model-reference adaptive system based on a dynamic induction motor equivalent circuit model. Finally, the rotor temperature is calculated according to the linear relationship between the rotor temperature and the estimated rotor time constant. Real-time induction motor thermal protection is achieved through this continuous tracking of the rotor temperature.

Ambiguous pitch and the temporal representation of inharmonic iterated rippled noise in the ventral cochlear nucleus.

Abstract: Neural coding of the pitch of complex sounds is vital for animals' ability to communicate and to perceptually organize natural acoustic scenes. Harmonic complex sounds typically have a well defined pitch corresponding to their fundamental frequency, whereas inharmonic sounds can exhibit pitch ambiguity: their pitch can have more than one value. Iterated rippled noise (IRN), a common “pitch stimulus,” is generated from broadband noise by a cascade of delay-and-add steps, with the delayed noise phase-shifted by φ degrees. By varying φ, the (in)harmonicity, and therefore the pitch ambiguity, of IRN can be manipulated. Recordings were made from single-units in the ventral cochlear nucleus of anesthetized guinea pigs in response to IRN and complex tones, systematically varying the inharmonicity. In their all-order interspike interval distributions, primary-like and chopper units tuned within the phase-locking range of best frequencies represent the waveform temporal fine structure (which varies with φ). In contrast, those units tuned to higher frequencies represent the temporal-envelope modulation (independent of φ). We show a temporal representation of ambiguous pitch for IRN and complex tones based on responses to the stimulus fine structure. Within the dominance region for pitch this representation follows the predictions of classic human behavioral experiments and provides a unifying contribution to possible neuro-temporal explanations for the pitch shift and pitch ambiguity associated with many inharmonic sounds.

Experimental Study on Impeller Blade Vibration During Resonance—Part I: Blade Vibration Due to Inlet Flow Distortion

Abstract: Forming the first part of a two-part paper, the experimental approach to acquire resonant vibration data is presented here. Part II deals with the estimation of damping. During the design process of turbomachinery components, mechanical integrity has to be guaranteed with respect to high cycle fatigue of blades subject to forced response or flutter. This requires the determination of stress levels within the blade, which in turn depend on the forcing function and damping. The vast majority of experimental research in this field has been performed on axial configurations for both compressors and turbines. This experimental study aims to gain insight into forced response vibration at resonance for a radial compressor. For this purpose, a research impeller was instrumented with dynamic strain gauges and operated under resonant conditions. Modal properties were analyzed using finite element method and verified using an optical method termed electronic-speckle-pattern-correlation-interferometry. During the experiment, unsteady forces acting on the blades were generated by grid installations upstream of the impeller, which created a distorted inlet flow pattern. The associated flow properties were measured using an aerodynamic probe. The resultant pressure fluctuations on the blade surface and the corresponding frequency content were assessed using unsteady computational fluid dynamics. The response of the blades was measured for three resonant crossings, which could be distinguished by the excitation order and the natural frequency of the blades. Measurements were undertaken for a number of inlet pressure settings starting at near vacuum and then increasing. The overall results showed that the installed distortion screens generated harmonics in addition to the fundamental frequency. The resonant response of the first and the second blade mode showed that the underlying dynamics support a single-degree-of-freedom model.