Showing papers on "Frequency response published in 1997"

Control topology options for single-phase UPS inverters

Abstract: Four control topologies for single-phase uninterruptible power system (UPS) inverters are presented and compared, with the common objective of providing a dynamically stiff, low total harmonic distortion (THD), sinusoidal output voltage. Full-state feedback, full-state command controllers are shown, utilizing both filter inductor current and filter capacitor current feedback to augment output voltage control. All controllers presented include output voltage decoupling in a manner analogous to "back EMF" decoupling in DC motor drives. Disturbance input decoupling of the load current and its derivative is presented. An observer-based controller is additionally considered and is shown to be a technically viable, economically attractive option. The accuracy transfer function of the observer estimate is used to evaluate its measurement performance. Comparative disturbance rejection is evaluated by overlaying the dynamic stiffness (inverse of output impedance) frequency response of each controller on a single plot. Experimental results for one controller are presented.

Free-space electro-optics sampling of mid-infrared pulses

Abstract: We report on the coherent detection of ultra-broadband mid-infrared electromagnetic pulses using a 30-μm-thick ZnTe electro-optic sensor. The detected frequency spectrum exceeds 37 THz, extending from microwave to the mid-infrared. The frequency response can be further improved by reducing the sensor thickness to 10 μm.

Small-signal analysis of DC-DC converters with sliding mode control

Abstract: This paper deals with small-signal analysis of DC-D converters with sliding mode control. A suitable small signal model is developed which allows selection of control coefficients, analysis of parameter variation effects, characterization of the closed loop behavior in terms of audiosusceptibility, output and input impedances, and reference to output transfer function. Unlike previous analyses, the model includes effects of the filters used to evaluate state variable errors. Simulated and experimental results demonstrate model potentialities.

High-frequency response of atomic-force microscope cantilevers

Abstract: Recent advances in atomic-force microscopy have moved beyond the original quasistatic implementation into a fully dynamic regime in which the atomic-force microscope cantilever is in contact with an insonified sample. The resulting dynamical system is complex and highly nonlinear. Simplification of this problem is often realized by modeling the cantilever as a one degree of freedom system. This type of first-mode approximation (FMA), or point-mass model, has been successful in advancing material property measurement techniques. The limits and validity of such an approximation have not, however, been fully addressed. In this article, the complete flexural beam equation is examined and compared directly with the FMA using both linear and nonlinear examples. These comparisons are made using analytical and finite difference numerical techniques. The two systems are shown to have differences in drive-point impedance and are influenced differently by the interaction damping. It is shown that the higher modes must be included for excitations above the first resonance if both the low and high frequency dynamics are to be modeled accurately.

Identification of Wiener-type nonlinear systems in a noisy environment

Abstract: Wiener systems are widely encountered in engineering and science applications. This paper proposes a straightforward approach to the identification of Wiener systems in a noisy environment. The obtained models are represented in terms of the frequency response for the linear subsystem and the inverse of the static nonlinearity. A variety of input excitation signals, including random binary and periodic, can be used with the proposed method. Simulation studies using a pH neutralization continuous stirred tank reactor show that excellent results are obtained with relatively short data lengths.

Traveling-wave photodetector theory

Abstract: Photodetector efficiency decreases as bandwidth increases, Bandwidth-efficiency limitations of traveling-wave photodetectors (TWPDs) are substantially greater than those of lumped-element photodetectors because the velocity-mismatch bandwidth limitation is independent of device length. TWPDs can be long for high efficiency without significantly compromising bandwidth. The TWPD is modeled by a terminated section of transmission line with a position-dependent photocurrent source propagating on it at the optical group velocity. A wave model for the transmission line confirms the accuracy of an equivalent-circuit model for electrical wave propagation. The velocity-mismatch impulse and frequency response are determined by absorption coefficient and wave velocities rather than junction capacitance and load resistance. The velocity-mismatch bandwidth limitations can be written in a simple form which elucidates the factors affecting device response, A discretized periodic TWPD is described by the same equations as the fully distributed version. This more complicated device offers additional degrees of freedom in design and potentially improved performance.

A new frequency-weighted balanced truncation method and an error bound

Abstract: In this paper, a new frequency weighted model reduction method with an error bound is proposed. The method is a generalization of Enns's technique and yields stable models even when both input and output weightings are included. The proposed method is compared with other existing methods using numerical examples.

Low-Order Modeling from Relay Feedback

Abstract: There have recently been considerable interests in extensions of PID relay autotuning to model-based controllers, and this necessitates transfer function modeling from relay feedback. The methods reported in the literature for this purpose require two tuning tests, and their results are approximate in nature. In this paper, exact expressions for the periods and amplitudes of limit cycles under relay feedback are derived for processes which may be modeled by first-order plus dead-time dynamics. This time-domain information is then combined with frequency response point estimation using Fourier series expansions of the limit cycles so that a first-order plus dead-time model can be identified with a single relay test. Furthermore, no approximation is made in our derivations and the resultant model will be precise if it matches the structure of the process. In the case of the mismatched structure, it is shown through extensive simulations that our procedure yields very accurate results in the sense that the i...

A novel approach to extracting small-signal model parameters of silicon MOSFET's

Abstract: We present a simple and accurate method to extract a small-signal equivalent circuit model of Si MOSFET's, based on the novel approach to determining parasitic inductances and resistances by fitting the frequency response of new analytic expressions with Z-parameters. This method is proposed to overcome the serious problem that conventional cold-FET methods cannot be applied for MOSFET's, and is also superior to the traditional optimization of the entire model parameters to fit the measured S-parameters. In particular, this technique is simple and reliable because no additional measurements are needed. The excellent correspondence is achieved between modeled and measured S-parameters from 0.5 to 39.5 GHz.

Integrated tunable inductance network and method

Abstract: An integrated, tunable inductance network features a number of fixed inductors fabricated on a common substrate along with a switching network made up of a number of micro-electromechanical (MEM) switches. The switches selectably interconnect the inductors to form an inductance network having a particular inductance value, which can be set with a high degree of precision when the inductors are configured appropriately. The preferred MEM switches introduce a very small amount of resistance, and the inductance network can thus have a high Q. The MEM switches and inductors can be integrated using common processing steps, reducing parasitic capacitance problems associated with wire bonds and prior art switches, increasing reliability, and reducing the space, weight and power requirements of prior art designs. The precisely tunable high-Q inductance network has wide applicability, such as in a resonant circuit which provides a narrow bandwidth frequency response which peaks at a specific predetermined frequency, making possible a highly selective performance low noise amplifier (LNA), or in an oscillator circuit so that a precise frequency of oscillation can be generated and changed as needed.

Tunable microwave network using microelectromechanical switches

Abstract: A desired frequency response of a microwave network on a monolithic microwave integrated circuit (MMIC), a microwave integrated circuit (MIC), or a hybrid circuit is achieved by selectively switching MEM switches to change the network topology. In a filter network, MEM switches connected between capacitors and inductors are selectively switched to change the network configuration to achieve a desired frequency response. In an amplifier network, the MEM switches are selectively switched to tune the amplifier to a desired frequency response and to reduce harmonic output.

Gain and phase constrained adaptive equalizing filter in a sampled amplitude read channel for magnetic recording

Abstract: A sampled amplitude read channel for magnetic disk recording which asynchronously samples the analog read signal, adaptively equalizes the resulting discrete time sample values according to a target partial response, extracts synchronous sample values through interpolated timing recovery, and detects digital data from the synchronous sample values using a Viterbi sequence detector is disclosed. To minimize interference from the timing and gain control loops, the phase and magnitude response of the adaptive equalizer filter are constrained at a predetermined frequency using an optimal orthogonal projection operation as a modification to a least mean square (LMS) adaptation algorithm. Further, with interpolated timing recovery, the equalizer filter and its associated latency are removed from the timing recovery loop, thereby allowing a higher order discrete time filter and a lower order analog filter.

Identification of probabilistic system uncertainty regions by explicit evaluation of bias and variance errors

Abstract: A procedure is developed for identification of probabilistic system uncertainty regions for a linear time-invariant system with unknown dynamics, on the basis of time sequences of input and output data. The classical framework is handled in which the system output is contaminated by a realization of a stationary stochastic process. Given minor and verifiable prior information on the system and the noise process, frequency response, pulse response, and step response confidence regions are constructed by explicitly evaluating the bias and variance errors of a linear regression estimate. In the model parametrizations, use is made of general forms of basis functions. Conservatism of the uncertainty regions is limited by focusing on direct computational solutions rather than on closed-form expressions. Using an instrumental variable method for identification, the procedure is suitable also for input-output data obtained from closed-loop experiments.

Structural Acoustics and Vibration: Mechanical Models, Variational Formulations and Discretization

Abstract: A Strategy for Structural-Acoustic Problems. Basic Notions on Variational Formulations. Linearized Vibrations of Conservative Structures and Structural Modes. Dissipative Constitutive Equation for the Master Structure. Master Structure Frequency Response Function. Calculation of the Master Structure Frequency Response function in the LF Range. Calculation of the Master Structure Frequency Response Function in the MF Range. Reduced Model in the MF Range. Response to Deterministic and Random Excitations. Linear Acoustic Equations. Internal Acoustic Fluid Formulation for the LF and MF Ranges. External Acoustic Fluid: Boundary Integral Formulation for the LF and MF Ranges. Structural-Acoustic Master System in the LF Range. Structural-Acoustic Master System in the MF Range. Fuzzy Structure Theory. Appendix: Mathematical Notations. References. Subject Index. Symbol Index.

Mechanical Design and Control of a High-Bandwidth Shape Memory Alloy Tactile Display

Abstract: We have constructed a tactile shape display which can be used to convey small scale shape in teleoperation and virtual environments. A line of 10 pins spaced 2 mm on center are each actuated with a shape memory alloy wire. A combination of careful mechanical design and liquid cooling allows a simple proportional controller with constant current feed forward to achieve 40 Hz bandwidth. To quantify the value of increased bandwidth, an experiment involving a prototypical search task has been conducted using the display. A digital filter limited the frequency response of the display to three cutoff frequencies: 1, 5 and 30 Hz. Subjects were able to complete the search more than 6 times as quickly with 30 Hz bandwidth than with 1 Hz.

Method of up-converting and up-converter with pre-compensation filter

Abstract: An up-converter for digitally sampled baseband signals having the sinc(x) spectral replication functionality of a DAC, using a post-DAC, band pass filter to isolate a baseband replica that falls within that sidelobe of the DAC's sinc(x) frequency response containing the desired IF. The parameters of a pre-compensation filter and the gain of a post DAC amplifier are set to compensate for the distortion and attenuation imparted by the DAC's sinc(x) frequency response.

A frequency domain correlation technique for model correlation and updating

Abstract: Up to now, existent FRF based model updating methods use the differences between measured and analytical FRFs at a fixed frequency, as residual to minimize. This approach does not take into account that FRFs between a reference model (experimental) and a perturbed one (a finite elements model not yet updated), displace in two axes: amplitude and frequency. A more physical correlation, then, uses also the frequency shift. The problem is how to find it. Taking as base the well known Modal Assurance Criterion (MAC), the Modal Scale Factor (MSF), and the concept of frequency shift, two correlation techniques, the Frequency Domain Assurance Criterion (FDAC) and the Frequency Response Scale Factor (FRSF), are presented. They help to quantify the level of correlation between responses coming from the two models, determine the frequency shift at all measured frequencies, and establish a suitable set of frequencies to use during the updating procedure.

Adaptive quadrature filters and the recovery of phase from fringe pattern images

Abstract: A principled approach, based on Bayesian estimation theory and complex-valued Markov random-field prior models, is introduced for the design of a new class of adaptive quadrature filters. These filters are capable of adapting their tuning frequency to the local dominant spatial frequency of the input image while maintaining an arbitrarily narrow local frequency response; therefore they may be effectively used for the accurate recovery of the phase of broadband spatial-carrier fringe patterns, even when they are corrupted by a significant amount of noise. Also, by constraining the spatial variation of the adaptive frequency to be smooth, they permit the completely automatic recovery of local phase from single closed fringe pattern images, since the spurious discontinuities and sign reversals that one obtains from the classical Fourier-based methods are avoided in this case. Although the applications discussed here come from fringe pattern analysis in optics, these filters may also be useful in the solution of other problems, such as texture characterization and segmentation and the recovery of depth from stereoscopic pairs of images.

A Theoretical and Experimental Implementation of a Control Method Based on Saturation

Abstract: A novel approach for implementing an active nonlinear vibration absorber is presented. The absorber, which is built in electronic circuitry, takes advantage of the saturation phenomenon that occurs when two natural frequencies of a system with quadratic nonlinearities are in the ratio of two-to-one. When the system is excited at a frequency near the higher natural frequency, there is a small ceiling for the system response at the higher frequency and the rest of the input energy is channeled to the low-frequency mode.

Output frequencies of nonlinear systems

Abstract: An explicit expression for the output frequency range of nonlinear systems for general inputs is derived. This reveals the relationship between the input and output frequency ranges of a nonlinear system and extends the well-known concept in linear systems where the output frequency range is exactly the same as that of the corresponding input. The new results provide an important and basic relationship that can be applied in nonlinear system frequency domain analysis and design.

Time-varying effects and averaging issues in models for current-mode control

Abstract: This paper investigates issues in modeling of current-mode control in converters. The effects of the current-sampling intrinsic to current-mode control are analyzed, and inadequately recognized limitations of linear time-invariant (LTI) models at high frequencies (where the system behavior is time-varying) are exposed. The paper also examines the geometric methods used to derive duty-ratio constraints in averaged models of current-mode control and points out the sources of discrepancies among various models. The conclusions are supported by simulation and experimental results.

Multiple-point equalization of room transfer functions by using common acoustical poles

Abstract: A multiple-point equalization filter using the common acoustical poles of room transfer functions is proposed. The common acoustical poles correspond to the resonance frequencies, which are independent of source and receiver positions. They are estimated as common autoregressive (AR) coefficients from multiple room transfer functions. The equalization is achieved with a finite impulse response (FIR) filter, which has the inverse characteristics of the common acoustical pole function. Although the proposed filter cannot recover the frequency response dips of the multiple room transfer functions, it can suppress their common peaks due to resonance; it is also less sensitive to changes in receiver position. Evaluation of the proposed equalization filter using measured room transfer functions shows that it can reduce the deviations in the frequency characteristics of multiple room transfer functions better than a conventional multiple-point inverse filter. Experiments show that the proposed filter enables 1-5 dB additional amplifier gain in a public address system without acoustic feedback at multiple receiver positions. Furthermore, the proposed filter reduces the reflected sound in room impulse responses without the pre-echo that occurs with a multiple-point inverse filter. A multiple-point equalization filter using common acoustical poles can thus equalize multiple room transfer functions by suppressing their common peaks.

Resonator/Oscillator response to liquid loading.

Abstract: The resonant frequency of a thickness-shear mode resonator operated in contact with a fluid was measured with a network analyzer and with an oscillator circuit. The network analyzer measures changes in the device's intrinsic resonant frequency, which varies linearly with (ρη)1/2, where ρ and η are liquid density and viscosity, respectively. The resonator/oscillator combination, however, responds differently to liquid loading than the resonator alone. By applying the operating constraints of the oscillator to an equivalent-circuit model for the liquid-loaded resonator, the response of the resonator/oscillator pair can be determined. By properly tuning the resonator/oscillator pair, the dynamic range of the response can be extended and made more linear, closely tracking the response of the resonator alone. This allows the system to measure higher viscosity and higher density liquids with greater accuracy.

Design of two-dimensional FIR digital filters by a two-dimensional WLS technique

Abstract: For two-dimensional (2-D) FIR filter design, the conventional weighted least squares (WLS) technique rearranges the filter parameters of 2-D form into their corresponding one-dimensional (1-D) form, thus resulting in expensive computation. This paper presents a new computationally efficient WLS technique for the design of 2-D FIR filters. We introduce an updating desired frequency response which implicitly includes the weighting function such that the sum of weighted square errors to be minimized can be represented in a 2-D matrix form. This makes it possible to keep all filter parameters in their natural 2-D form, thereby reducing the computational complexity from O(N/sup G/) to O(N/sup 3/). It is confirmed through design examples that the new technique is computationally very efficient and leads to nearly optimal approximations. This technique is suitable for the design of 2-D real zero-phase FIR filters with quadrantal symmetric or antisymmetric frequency response and can also be applied to the design of 1-D FIR filters.

Fractional discrete-time linear systems

Abstract: In this paper, the class of discrete linear systems is enlarged with the inclusion of the discrete-time fractional linear systems. These are systems described by fractional difference equations and fractional frequency responses. It is shown how to compute the impulse response and transfer function. The theory is supported by the Cauchy integrals that perform projections of the frequency response into or outside the unit circle. The presented formalism is similar to that usually followed.

Identification of high frequency transformer equivalent circuit using Matlab from frequency domain data

Abstract: High frequency modelling is essential in the design of power transformers, to study impulse voltage distribution, winding integrity and insulation diagnosis. In this paper, a PC based, fully automated technique for identifying parameters of a high frequency transformer equivalent circuit is proposed. At each discrete measurement point, voltage ratio and phase between input and output is calculated to obtain the frequency response. A parametric system identification technique is utilised to determine the coefficients of an appropriate transfer function to model the measured frequency response from 50 Hz to 1 MHz, divided into low, medium and high frequency ranges. The proposed technique is simple to implement, fully computerised and avoids time consuming measurements reported earlier. Test results on several transformers indicate that the method is highly reliable, consistent and is sensitive to transformer winding faults.

Bifurcation Control of Parametrically Excited Duffing System by a Combined Linear-Plus-Nonlinear Feedback Control

Abstract: For a parametrically excited Duffing system we propose a bifurcation control method in order to stabilize the trivial steady state in the frequency response and in order to eliminate jump in the force response, by employing a combined linear-plus-nonlinear feedback control. Because the bifurcation of the system is characterized by its modulation equations, we first determine the order of the feedback gain so that the feedback modifies the modulation equations. By theoretically analyzing the modified modulation equations, we show that the unstable region of the trivial steady state can be shifted and the nonlinear character can be changed, by means of the bifurcation control with the above feedback. The shift of the unstable region permits the stabilization of the trivial steady state in the frequency response, and the suppression of the discontinuous bifurcation due to the change of the nonlinear character allows the elimination of the jump in the quasistationary force response. Furthermore, by performing numerical simulations, and by comparing the responses of the uncontrolled system and the controlled one, we clarify that the proposed bifurcation control is available for the stabilization of the trivial steady state in the frequency response and for the reduction of the jump in the nonstationary force response.