Showing papers on "Frequency response published in 2014"

Security-Constrained Unit Commitment With Linearized System Frequency Limit Constraints

Abstract: Rapidly increasing the penetration level of renewable energies has imposed new challenges to the operation of power systems. Inability or inadequacy of these resources in providing inertial and primary frequency responses is one of the important challenges. In this paper, this issue is addressed within the framework of security-constrained unit commitment (SCUC) by adding new constraints representing the system frequency response. A modified system frequency response model is first derived and used to find analytical representation of system minimum frequency in thermal-dominant multi-machine systems. Then, an effective piecewise linearization (PWL) technique is employed to linearize the nonlinear function representing the minimum system frequency, facilitating its integration in the SCUC problem. The problem is formulated as a mixed-integer linear programming (MILP) problem which is solved efficiently by available commercial solvers. The results indicate that the proposed method can be utilized to integrate renewable resources into power systems without violating system frequency limits.

A Systematic Method for Designing a PR Controller and Active Damping of the LCL Filter for Single-Phase Grid-Connected PV Inverters

Abstract: The Proportional Resonant (PR) current controller provides gains at a certain frequency (resonant frequency) and eliminates steady state errors. Therefore, the PR controller can be successfully applied to single grid-connected PV inverter current control. On the contrary, a PI controller has steady-state errors and limited disturbance rejection capability. Compared with the L- and LC filters, the LCL filter has excellent harmonic suppression capability, but the inherent resonant peak of the LCL filter may introduce instability in the whole system. Therefore, damping must be introduced to improve the control of the system. Considering the controller and the LCL filter active damping as a whole system makes the controller design method more complex. In fact, their frequency responses may affect each other. The traditional trial-and-error procedure is too time-consuming and the design process is inefficient. This paper provides a detailed analysis of the frequency response influence between the PR controller and the LCL filter regarded as a whole system. In addition, the paper presents a systematic method for designing controller parameters and the capacitor current feedback coefficient factor of LCL filter active-damping. The new method relies on meeting the stable margins of the system. Moreover, the paper also clarifies the impact of the grid on the inverter output current. Numerical simulation and a 3 kW laboratory setup assessed the feasibility and effectiveness of the proposed method.

Electrostatic energy harvesting device with out-of-the-plane gap closing scheme

Abstract: In this paper, we report on an electrostatic energy harvester with an out-of-the-plane gap closing scheme. Using advanced MEMS technology, energy harvesting devices formed by a four wafer stack are batch fabricated and fully packaged at wafer scale. A spin coated CYTOP polymer is used both as an electret material and an adhesive layer for low temperature wafer bonding. The overall size of the device is about 1.1 cm × 1.3 cm. At an external load resistance of 13.4 MΩ, a power output of 0.15 μW is achieved when vibration at an acceleration amplitude of 1 g (∼9.8 m/s2) is applied at a low frequency of 96 Hz. The frequency response of the device is also measured and a broader bandwidth is observed at higher acceleration amplitude.

Fast Frequency Response Capability of Photovoltaic Power Plants: The Necessity of New Grid Requirements and Definitions

Abstract: In recent years, only a small number of publications have been presented addressing power system stability with the increased use of large-scale photovoltaic (PV) generation around the world. The focus of these publications was on classical stability problems, such as transient and small signal stability, without considering frequency stability. Nevertheless, with increased PV generation, its effects on system frequency response during contingencies can no longer be ignored, especially in the case of weakly interconnected networks or isolated power systems. This paper addresses the impacts of large scale PV generation on the frequency stability of power systems. The positive effects of deloaded PV power plants (PV-PPs) able to support system frequency recovery during the initial seconds after major contingencies are also examined. Because this type of frequency support is not covered by current definitions, a new terminology is proposed that includes the frequency response of inertia-less generation units immediately after major power imbalances. We refer to this type of frequency support as fast frequency response (FFR). Finally, a discussion is also presented regarding the applicability and pertinence of frequency-related grid requirements for PV-PPs in the case of real power systems. The investigation is based on the isolated power system of northern Chile. The obtained results indicate that in the case of major power imbalances, no significant effects arise on the system frequency response until PV penetration levels exceed approximately 20%. From a system security perspective, the problems arise for PV penetration levels of approximately 50%, in which case, the frequency response capability in PV-PPs would be justified during certain hours of the year.

Comparative Performance Analysis of Hamming, Hanning and Blackman Window

Abstract: In the emerging field of medical image processing, computer vision, pattern recognition and other digital signal processing applications, window technique is vastly used. A window function is a mathematical function that is zero-valued outside of some chosen interval. When another function is multiplied by a window function, the product is also zero-valued outside the interval. In this paper, the performance of Hamming, Hanning and Blackman window have been mainly compared considering their magnitude response, phase response, equivalent noise bandwidth, sidelobe transition width, response in time and frequency domain using MATLAB simulation. To observe the responses, a FIR filter of low pass, high pass, band pass and band stop type have been designed and encountered them with each parameters stated above. The results that have been found is as same as its to be as stated in the theory. Comparing simulation results of different window, this paper has found Blackman window with best performance among them which is also expected from the theory. These windows have also been encountered with speech signal using MATLAB simulation and found the same expected result.

Self-interference cancellation

Abstract: A wireless communication device includes, in part, an analog interference cancellation circuit and a controller. The analog cancellation circuit includes a multitude of delay paths each including a delay element and a variable attenuator. The controller dynamically varies the attenuation level of each of the variable attenuators in accordance with the frequency response characteristic of that attenuator to remove a portion of a self-interference signal present in a signal received by the device. The device measures the frequency response characteristic of the communication channel, used in determining the attenuation levels, via one or more preamble symbols. A second portion of the self-interference signal is removed by the device using a multitude of samples of a transmitted signal and a multitude of samples of a signal to be transmitted.

Analysis and Design of Efficient and Flexible Fast-Convolution Based Multirate Filter Banks

Abstract: In this paper, we investigate fast-convolution based highly tunable multirate filter bank (FB) configurations. Based on FFT-IFFT pair with overlapped processing, they offer a way to tune the filters' frequency-domain characteristics in a straightforward way. Different subbands are easily configurable for different bandwidths, center frequencies, and output sampling rates, including also partial or full-band nearly perfect-reconstruction systems. Such FBs find various applications, for example, as flexible multichannel channelization filters for software defined radios. They have also the capability to implement simultaneous waveform processing for multiple single-carrier and/or multicarrier transmission channels with nonuniform bandwidths and subchannel spacings. This paper develops an effective model for frequency response analysis and optimization for such filter banks, explores various practical issues of fast-convolution processing and reports the optimized frequency response characteristics versus direct raised cosine based designs. The fast-convolution approach is shown to be a competitive basis for filter bank based multicarrier waveform processing in terms of spectral containment and complexity.

Nonlinear vibration of a rotating laminated composite circular cylindrical shell: traveling wave vibration

Abstract: In this paper, the large-amplitude (geometrically nonlinear) vibrations of rotating, laminated composite circular cylindrical shells subjected to radial harmonic excitation in the neighborhood of the lowest resonances are investigated Nonlinearities due to large-amplitude shell motion are considered using the Donnell’s nonlinear shallow-shell theory, with account taken of the effect of viscous structure damping The dynamic Young’s modulus which varies with vibrational frequency of the laminated composite shell is considered An improved nonlinear model, which needs not to introduce the Airy stress function, is employed to study the nonlinear forced vibrations of the present shells The system is discretized by Galerkin’s method while a model involving two degrees of freedom, allowing for the traveling wave response of the shell, is adopted The method of harmonic balance is applied to study the forced vibration responses of the two-degrees-of-freedom system The stability of analytical steady-state solutions is analyzed Results obtained with analytical method are compared with numerical simulation The agreement between them bespeaks the validity of the method developed in this paper The effects of rotating speed and some other parameters on the nonlinear dynamic response of the system are also investigated

Deterministic and band-limited stochastic energy harvesting from uniaxial excitation of a multilayer piezoelectric stack

Abstract: Deterministic and band-limited stochastic energy harvesting scenarios using a multilayer piezoelectric stack configuration are investigated for uniaxial dynamic pressure loading. The motivation for exploring this off-resonant energy harvesting problem derives from typical civil infrastructure systems subjected to dynamic compressive forces in deterministic or stochastic forms due to vehicular or human loads, among other examples of compressive loading. Modeling of vibrational energy harvesters in the existing literature has been mostly focused on deterministic forms of mechanical vibration as in the typical case of harmonic excitation, while the efforts on stochastic energy harvesting have thus far considered second-order systems such as piezoelectric cantilevers. In this paper, we present electromechanical modeling, analytical and numerical solutions, and experimental validations of piezoelectric energy harvesting from harmonic, periodic, and band-limited stochastic excitation of a multilayer piezoelectric stack under axial compressive loading in the off-resonant low-frequency range. The deterministic problem employs the voltage output-to-pressure input frequency response function of the harvester for a given electrical load, which is also extended to periodic excitation. The analytical stochastic electromechanical solution employs the power spectral density of band-limited stochastic excitation to predict the expected value of the power output. The first one of the two numerical solution methods uses the Fourier series representation of the excitation history to solve the resulting ordinary differential equation, while the second method employs an Euler–Maruyama scheme to directly solve the governing electromechanical stochastic differential equation. The electromechanical models are validated through several experiments for a multilayer PZT-5H stack under harmonic and band-limited stochastic excitations at different pressure levels. The figure of merit is also extracted for this particular energy harvesting problem to choose the optimal material. Soft piezoelectric ceramics (e.g. PZT-5H and PZT-5A) offer larger power output as compared to hard ceramics (e.g. PZT-8), and likewise, soft single crystals (e.g. PMN-PT and PMN-PZT) produce larger power as compared to their hard counterparts (e.g. PMN-PZT-Mn); and furthermore, single crystals (e.g. PMN-PT and PMN-PZT) generate more power than standard ceramics (e.g. PZT-5H and PZT-5A) for low-frequency, off-resonant excitation of piezoelectric stacks.

Frequency limitations in generating multi-scroll chaotic attractors using CFOAs

Abstract: The current-feedback operational amplifier (CFOA) allows us to implement any kind of circuit useful in analogue signal processing applications. However, it has limited performance in implementing nonlinear circuits. That way, this investigation highlights the experimental results of implementing a multi-scroll chaotic oscillator by using the commercially available CFOA AD844. The chaotic oscillator is based on saturated nonlinear function (SNLF) series, and we show and discuss its frequency limitations to generate 3- to 10-scrolls from 1 kHz to 100 kHz. Finally, we conclude that the frequency limitations are due to the nonideal characteristics of the CFOA-based SNLF block, imposed by the AD844.

Experimental Investigation and Design Optimization of Targeted Energy Transfer Under Periodic Forcing

Abstract: In this paper, the dynamic response of a harmonically forced Linear Oscillator (LO) strongly coupled to a Nonlinear Energy Sink (NES) is investigated both theoretically and experimentally. The system studied comprises a LO with an embedded, purely cubic NES. The behavior of the system is analyzed in the vicinity of 1 : 1 resonance. The complexification-averaging technique is used to obtain modulation equations and the associated fixed points. These modulation equations are analyzed using asymptotic expansion to study the regimes related to relaxation oscillation of the slow flow called Strongly Modulated Response (SMR). The zones where SMR occurs are computed using a mapping procedure. The Slow Invariant Manifolds (SIM) is used to derive a proper optimization procedure. It is shown that there is an optimal zone in the forcing amplitude-nonlinear stiffness parameter plane, where SMR occurs without having a high amplitude detached resonance tongue. Two experimental setups are presented. One is not optimized and has a relatively high mass ratio (≈ 13%) and the other one is optimized and exhibits strong mass asymmetry (mass ratio ≈ 1%). Different frequency response curves and associated zones of SMR are obtained for various forcing amplitudes. The reported experimental results confirm the design procedure, and the possible application of NES for vibration mitigation under periodic forcing.

Demonstration and Characterization of High-Speed Silicon Depletion-Mode Mach–Zehnder Modulators

Abstract: High-speed silicon depletion-mode Mach-Zehnder modulators are demonstrated and characterized in this paper. Based on the structural dimensions and material parameters, transmission-line parameters and frequency response performances of the modulators are calculated and predicted by a proposed distributed circuit model. Parasitic coupled-slotline mode excited by the modulator is analyzed and suppressed by gold-wire bridges. Using a spectrum analysis method, the effect of this modification on the modulated optical signal is simulated. Over a broad frequency range from 10 MHz to 40 GHz, silicon depletion-mode Mach-Zehnder modulators with flat electro-optic modulation responses and broad bandwidths have been experimentally demonstrated.

Damage identification based on response-only measurements using cepstrum analysis and artificial neural networks

Abstract: This article presents a response-only structural health monitoring technique that utilises cepstrum analysis and artificial neural networks for the identification of damage in civil engineering structures. The method begins by applying cepstrum-based operational modal analysis, which separates source and transmission path effects to determine the structure’s frequency response functions from response measurements only. Principal component analysis is applied to the obtained frequency response functions to reduce the data size, and structural damage is then detected using a two-stage ensemble of artificial neural networks. The proposed method is verified both experimentally and numerically using a laboratory two-storey framed structure and a finite element representation, both subjected to a single excitation. The laboratory structure is tested on a large-scale shake table generating ambient loading of Gaussian distribution. In the numerical investigation, the same input is applied to the finite model, but...

Towards self-powered solar panel receiver for optical wireless communication

Abstract: In this paper, we experimentally demonstrate the feasibility of optical wireless communication (OWC) systems with a solar panel as a photo-detector. The advantage of a solar panel is that it is a passive device, which does not require an additional power supply for converting the received light signal into an electrical signal. The frequency response of a solar panel shows that its 3-dB modulation bandwidth is 350 kHz. The results demonstrate that for a 1-Mbit/s on-off keying signal, a bit error rate of less than 2 × 10 -3 could be achieved when the average irradiance on the solar panel is 3.5 × 10 -4 W/cm 2 . In the current experimental setup, this corresponds to a transmission distance of 39 cm. A data rate of 7.01 Mbit/s is achieved by using orthogonal frequency division multiplexing. In addition, the feasibility of using the solar panel for simultaneous communication and energy harvesting is investigated. A load is connected in parallel to the receiver circuit in order to simulate the conditions of charging a battery by using the received signal's DC component. It is shown that the load does not hamper the communication capabilities. Hence, an OWC system with a solar-panel-based receiver can satisfy the requirements of simultaneous communication and energy harvesting.

High-speed silicon modulator with band equalization

Abstract: Electro-optic modulation up to 70 Gbit/s has been demonstrated using a silicon Mach-Zehnder modulator with a bias voltage of -1.5 V. In a wide frequency range from DC, an increasing input impedance of the modulator was designed to equalize its electro-optic frequency response. Without a bias voltage, the 3 dB bandwidth was measured as 35 GHz and it is predicted to be as high as 55 GHz at -3 V bias. Frequency responses of the modulator operated with counter-propagating waves were tested to verify the proposed prediction model.

Three-Dimensional Dual-Polarized Frequency Selective Structure With Wide Out-of-Band Rejection

Abstract: A new three-dimensional bandpass frequency-selective structure (FSS) is proposed for dual-polarized applications. Each square unit cell of the proposed FSS consists of vertical and horizontal double-sided parallel-strip lines (DSPSLs) and a thin metallic plate. Furthermore, the parallel-strip lines of every DSPSL are connected together through via holes. Using this arrangement, multimode resonators are established in the proposed structure. At lower frequencies, the substrate mode propagates and two resonators along the DSPSL are constructed, leading to a bandpass response with two transmission poles. At higher frequencies, the air mode is reflected by two resonates along the inserted plate, resulting in a stopband with two transmission zeros. The operating principle for this FSS is explained with the aid of an equivalent circuit model. Moreover, a parametric study of the proposed FSS is also carried out and design guidelines are formulated. As an example, a prototype of the proposed FSS is designed, fabricated, and tested. Measured results demonstrate that the FSS exhibits dual polarizations, high out-of-band rejection, and stable frequency response under both transverse electric (TE) and transverse magnetic (TM) polarizations of an obliquely incident wave.

Nonlinear Characteristic Output Spectrum for Nonlinear Analysis and Design

Abstract: A systematic method for nonlinear analysis, design, and estimation in the frequency domain is proposed in this study using a new concept-nonlinear characteristic output spectrum (nCOS). The nCOS function is an analytical and explicit expression for the relationship between nonlinear output spectrum and system characteristic parameters of interest (including frequency, nonlinear parameters, and excitation magnitude), and can provide a significant insight into nonlinear analysis and design in the frequency domain. Given some simulation or experimental output data of a nonlinear system, the nCOS function of the system can be accurately determined up to any high nonlinear orders with less simulation trials and computation cost compared with a pure simulation-based study or traditional theoretical computations. Moreover, the method can also be used to accurately determine the linear and nonlinear components in the nonlinear output frequency response (or an output spectrum) of a nonlinear system. These results are definitely of significance to nonlinear analysis and design, nonlinear signal processing, system identification, fault detection, etc., in practice. Examples and case studies including analysis of a nonlinear vehicle suspension system are given to illustrate the results.

Towards higher accuracy and better frequency response with standard multi-hole probes in turbulence measurement with remotely piloted aircraft (RPA)

Abstract: . This study deals with the problem of turbulence measurement with small remotely piloted aircraft (RPA). It shows how multi-hole probes (MHPs) can be used to measure fluctuating parts of the airflow in flight up to 20 Hz. Accurate measurement of the transient wind in the outdoor environment is needed for the estimation of the 3-D wind vector as well as turbulent fluxes of heat, momentum, water vapour, etc. In comparison to an established MHP system, experiments were done to show how developments of the system setup can improve data quality. The study includes a re-evaluation of the pneumatic tubing setup, the conversion from pressures to airspeed, the pressure transducers, and the data acquisition system. In each of these fields, the steps that were taken lead to significant improvements. A spectral analysis of airspeed data obtained in flight tests shows the capability of the system to measure atmospheric turbulence up to the desired frequency range.

A Simplified Control Technique for a Dual Unified Power Quality Conditioner

Abstract: This paper presents a simplified control technique for a dual three-phase topology of a unified power quality conditioner—iUPQC. The iUPQC is composed of two active filters, a series active filter and a shunt active filter (parallel active filter), used to eliminate harmonics and unbalances. Different from a conventional UPQC, the iUPQC has the series filter controlled as a sinusoidal current source and the shunt filter controlled as a sinusoidal voltage source. Therefore, the pulse width modulation (PWM) controls of the iUPQC deal with a well-known frequency spectrum, since it is controlled using voltage and current sinusoidal references, different from the conventional UPQC that is controlled using nonsinusoidal references. In this paper, the proposed design control, power flow analysis, and experimental results of the developed prototype are presented.

Proportional–integral/proportional–integral-derivative tuning procedure of a single-phase shunt active power filter using Bode diagram

Abstract: This study presents a procedure for tuning proportional–integral/proportional–integral-derivative controllers using the frequency response method via Bode diagrams, which is relatively simple and easy to understand, and can be used when phase margin and 0 dB gain crossover frequency are project specifications. The method is validated in a practical power electronics application, considering the current and the DC-bus voltage loops of a shunt active power filter (SAPF). A detailed analysis related to the obtaining of the DC-bus voltage loop is also provided. In addition, a stability analysis is presented, considering how the SAPF compensation current is influenced according to the load current, taking into account different values of the grid impedance. Simulation and practical results show the effectiveness of the proposed scheme and its simplicity for being considered in practical cases.

Wideband Four-Way Filtering-Response Power Divider With Improved Output Isolation Based on Coupled Lines

Abstract: A planar 4-way power divider with bandpass filtering response based on the coupled line is presented. Its frequency response is similar to a coupled line filter. Moreover, open stubs are utilized to get good frequency selectivity by introducing transmission zeros and improve input match. Three isolation resistors are used to satisfy both transmission and isolation property. The equivalent even- and odd-mode circuits of the power divider are analyzed, while the design equations are derived. Comparison of the measured and simulated results is presented to verify the theoretical predications.

Modeling and Experimental Validation of the Frequency Response of Synthetic Jet Actuators

Abstract: A lumped-element mathematical model of the operation of a synthetic jet actuator driven by a thin piezoelectric disk is both analytically and numerically investigated to obtain information about the frequency response of the device. It is shown that the actuator behaves as a two-coupled oscillator system, and simple relationships are given to predict the two peak frequencies, corresponding to the modified Helmholtz and first-mode structural resonance frequencies. The model is validated through experimental tests carried out on three devices having different mechanical and geometrical characteristics, designed primarily to achieve an increasing coupling strength. A strict agreement between overall theoretical scaling laws and numerical computations is also found.

All-Dielectric Frequency Selective Surface for High Power Microwaves

Abstract: In this work, an all-dielectric frequency selective surface was developed for high power microwaves. By avoiding the use of metals, arcing at field concentration points and heating in the conductors was avoided. To do this in a compact form factor while still producing a strong frequency response, we based our design on guided-mode resonance (GMR). To make this approach viable for radio and microwave frequencies, we overcame three major challenges. First, conventional GMR devices have less than 1% fractional bandwidth and we extended this to 16%. Second, conventional GMR devices have a field-of-view less than 1 ° and we extended this to over 40 ° . Third, conventional GMR devices must be composed of hundreds of periods to operate, but our device operated very well with only eight. In this paper, we present our design and experimental results at 1.7 GW/m 2 .

Tuning the primary resonances of a micro resonator, using piezoelectric actuation

Abstract: Microbeam dynamics is important in MEMS filters and resonators. In this research, the effect of piezoelectric actuation on the resonance frequencies of a piezoelectrically actuated capacitive clamped-clamped microbeam is studied. The microbeam is sandwiched with piezoelectric layers throughout its entire length. The lower piezoelectric layer is exposed to a combination of a DC and a harmonic excitation voltage. The DC electrostatic voltage is applied to prevent the doubling of the excitation frequency. The traditional resonators are tuned using DC electrostatic actuation, which tunes the resonance frequency only in backward direction on the frequency domain. The proposed model enables tuning the resonance frequencies in both forward and backward directions. For small amplitudes of harmonic excitation and high enough quality factor, the frequency response curves obtained by the shooting method are validated with those of the multiple time scales technique. Unlike the perturbation technique, which imposes limitation on both the amplitude of the harmonic excitation and the quality factor to be applicable, the shooting method can be applied to capture the periodic attractors regardless of how big the amplitude of harmonic excitation and the quality factor are.

Injection locking of mid-infrared quantum cascade laser at 14 GHz, by direct microwave modulation

Abstract: Compact laser sources operating in mid infrared spectral region with stable emission are important for appli- cations in spectroscopy and wireless communication. Quantum cascade lasers (QCL) are unique semiconductor sources cover- ing mid infrared frequency range. Based on intersubband tran- sitions, the carrier lifetime of these sources is in the ps range. For this reason their frequency response to direct modulation is expected to overcome the limits of standard semiconductor lasers. In this work injection locking of the roundtrip frequency of a QCL emitting at 9 μm is reported. Inter modes laser fre- quency separation is stabilized and controlled by an external microwave source. Designing an optical waveguide embedded in a microstrip line a flat frequency response to direct modu- lation up to 14 GHz is presented. Injection locking over MHz frequency range at 13.7 GHz is demonstrated. Numerical so- lutions of injection locking theory are discussed and presented as tool to describe experimental results.

Finite-Element Modeling for Analysis of Radial Deformations Within Transformer Windings

Abstract: This paper develops computational models for undeformed and deformed transformers, using the finite-element method (FEM) to calculate frequency dependent parameters accounting for diamagnetic properties. In this manner, properly estimated inductances and capacitances can be derived and applied into a winding model for frequency response analysis (FRA). This research uses a hybrid winding model, so that frequency responses in the high frequency range ( >1 MHz) can be explored for the investigation of radial winding deformation. Meanwhile, computational models with respect to winding radial deformation are constructed, so that corresponding inductances and capacitances in specific radial deformed cases can be obtained by FEM. Therefore, the influence of the capacitances as well as the inductances can be taken into account for FRA of radial deformation in high frequencies. The frequency response in the undeformed case is compared with the experimental data to verify the accuracy of the frequency dependent parameters and mathematical winding models. The analyzed results in radial deformed cases are compared with the fault features derived from experimental studies reported in relevant literatures.