Showing papers on "Frequency response published in 2013"

Enhanced broadband piezoelectric energy harvesting using rotatable magnets

Abstract: We investigate a magnetically coupled nonlinear piezoelectric energy harvester by altering the angular orientation of its external magnets for enhanced broadband frequency response. Electromechanical equations describing the nonlinear dynamic behavior include an experimentally identified polynomial for the transverse magnetic force that depends on magnet angle. Up- and down-sweep harmonic excitation tests are performed at constant acceleration over the range of 0–25 Hz. Very good agreement is observed between the numerical and experimental open-circuit voltage output frequency response curves. The nonlinear energy harvester proposed in this work can cover the broad low-frequency range of 4–22 Hz by changing the magnet orientation.

Primary Frequency Response From Electric Vehicles in the Great Britain Power System

Abstract: With the increasing use of renewable energy in the Great Britain (GB) power system, the role of electric vehicles (EVs) contributes to primary frequency response was investigated. A tool was developed to estimate the EV charging load based on statistical analysis of EV type, battery capacity, maximum travel range and battery state of charge. A simplified GB power system model was used to investigate the contribution of EVs to primary frequency response. Two control modes were considered: disconnection of charging load (case I) and discharge of stored battery energy (case II). For case II, the characteristic of the EV charger was also considered. A case study shows results for the year 2020. Three EV charging strategies: “dumb” charging, “off-peak” charging, and “smart” charging, were compared. Simulation results show that utilizing EVs to stabilize the grid frequency in the GB system can significantly reduce frequency deviations. However the requirement to schedule frequency response from conventional generators is dynamic throughout the day.

Measurement of Supercapacitor Fractional-Order Model Parameters From Voltage-Excited Step Response

Abstract: In this paper, we propose using a numerically solved least squares fitting process to estimate the impedance parameters of a fractional order model of supercapacitors from their voltage excited step response, without requiring direct measurement of the impedance or frequency response. Experimentally estimated parameters from low capacity supercapacitors of 0.33, 1, and 1.5 F in the time range 0.2-30 s and high capacity supercapacitors of 1500 and 3000 F in the time range 0.2-90 s verify the proposed time domain method showing less than 3% relative error between the simulated response (using the extracted fractional parameters) and the experimental step response in these time ranges. An application of employing supercapacitors in a multivibrator circuit is presented to highlight their fractional time-domain behavior.

Modulated pulses based distributed vibration sensing with high frequency response and spatial resolution.

Abstract: A distributed optical fiber sensing system merged Mach-Zehnder interferometer and phase sensitive optical time domain reflectometer (φ-OTDR) system for vibration measurement with high-frequency response and high spatial resolution is demonstrated, where modulated pulses are proposed to be used as sensing source. Frequency response and location information are obtained by Mach-Zehnder interferometer and φ-OTDR technology, respectively. In order to simulate high-frequency vibration of crack of cable and civil structure, experiments on detection of piezoelectric transducer and pencil-break are carried out. Spatial resolution of 5 m and the maximum frequency response of ~3 MHz are achieved in 1064 m fiber link when the narrow pulse width is 50 ns.

Three-Dimensional Magnetic Manipulation of Micro- and Nanostructures for Applications in Life Sciences

Abstract: We present a magnetic manipulation system capable of 5 degree-of-freedom (5-DOF) wireless control of micro- and nanostructures (3-DOF position, 2-DOF pointing orientation) The system has a spherical workspace with a diameter of approximately 10 mm, and is completely unrestrained in the rotational degrees-of-freedom This is accomplished through the superposition of multiple magnetic fields, and capitalizes on a linear representation of the coupled field contributions of multiple soft-magnetic-core electromagnets acting in concert The system consists of 8 stationary electromagnets with ferromagnetic cores, and is capable of producing arbitrary magnetic fields and field gradients up to 50 mT and 5 T/m at frequencies up to 2 kHz The capabilities of the system are evaluated through the introduction of the reachable magnetic workspace of the system as well as frequency response and calibration results Experimental results are presented which demonstrate different magnetic control strategies at sub-mm and sub-μm scale

Electrostatic Graphene Loudspeaker

Abstract: Graphene has extremely low mass density and high mechanical strength, and key qualities for efficient wide-frequency-response electrostatic audio speaker design. Low mass ensures good high frequency response, while high strength allows for relatively large free-standing diaphragms necessary for effective low frequency response. Here, we report on construction and testing of a miniaturized graphene-based electrostatic audio transducer. The speaker/earphone is straightforward in design and operation and has excellent frequency response across the entire audio frequency range (20 Hz–20 kHz), with performance matching or surpassing commercially available audio earphones.

Magnetic Field Response Measurement Acquisition System

Abstract: Magnetic field response sensors designed as passive inductor-capacitor circuits produce magnetic field responses whose harmonic frequencies correspond to states of physical properties for which the sensors measure. Power to the sensing element is acquired using Faraday induction. A radio frequency antenna produces the time varying magnetic field used for powering the sensor, as well as receiving the magnetic field response of the sensor. An interrogation architecture for discerning changes in sensor's response frequency, resistance and amplitude is integral to the method thus enabling a variety of measurements. Multiple sensors can be interrogated using this method, thus eliminating the need to have a data acquisition channel dedicated to each sensor. The method does not require the sensors to be in proximity to any form of acquisition hardware. A vast array of sensors can be used as interchangeable parts in an overall sensing system.

A 100-Channel 1-mW Implantable Neural Recording IC

Abstract: This paper presents a fully implantable 100-channel neural interface IC for neural activity monitoring. It contains 100-channel analog recording front-ends, 10 multiplexing successive approximation register ADCs, digital control modules and power management circuits. A dual sample-and-hold architecture is proposed, which extends the sampling time of the ADC and reduces the average power per channel by more than 50% compared to the conventional multiplexing neural recording system. A neural amplifier (NA) with current-reuse technique and weak inversion operation is demonstrated, consuming 800 nA under 1-V supply while achieving an input-referred noise of 4.0 μVrms in a 8-kHz bandwidth and a NEF of 1.9 for the whole analog recording chain. The measured frequency response of the analog front-end has a high-pass cutoff frequency from sub-1 Hz to 248 Hz and a low-pass cutoff frequency from 432 Hz to 5.1 kHz, which can be configured to record neural spikes and local field potentials simultaneously or separately. The whole system was fabricated in a 0.18-μm standard CMOS process and operates under 1 V for analog blocks and ADC, and 1.8 V for digital modules. The number of active recording channels is programmable and the digital output data rate changes accordingly, leading to high system power efficiency. The overall 100-channel interface IC consumes 1.16-mW total power, making it the optimum solution for multi-channel neural recording systems.

Towards an Assessment of Power System Frequency Support From Wind Plant—Modeling Aggregate Inertial Response

Abstract: With increasing wind penetration, it is likely that wind power plant will be expected to provide frequency response in support of the power system, in particular some form of inertial response. In these circumstances it is important to accurately quantify the type of inertial response available from wind plant (typically a wind farm) and how it is affected by varying wind conditions. Two different control schemes to provide this “synthetic” inertial response are investigated. The benefits of the non-standard control scheme are demonstrated by comparing the response with the conventional “ideal” inertial control scheme that exactly emulates synchronous generators in terms of their provision of inertial response. This paper proposes a novel probabilistic approach for estimation of the aggregate inertial response available from a wind farm by using a Gaussian probability distribution to model wind turbulence. The aggregate inertial response calculated in this way has been examined at various mean wind speed levels and has the advantage that it automatically takes into account wind speed variations during the transient event itself.

Adaptive Harmonic Steady‐State Disturbance Rejection with Frequency Tracking

Abstract: This paper is concerned with the rejection of sinusoidal disturbances of unknown frequency acting at the output of unknown plants. Disturbance rejection is based on an adaptive harmonic steady-state (ADHSS) algorithm combined with a magnitude/phase locked-loop (MPLL) frequency estimator. The harmonic steady-state method assumes that the plant can be approximated by its steady-state frequency response. For high-order plants such as those encountered in active noise and vibration control (ANVC), this assumption greatly reduces the number of parameters and enables online estimation of the plant response using simple algorithms. The paper shows that when the MPLL is integrated with the ADHSS algorithm, the two components work together in such a way that the control input does not prevent frequency tracking by the MPLL, and so that the order of the ADHSS can be reduced. Thus, the addition of the MPLL allows disturbances of unknown frequency to be considered without significantly increasing the complexity of the original ADHSS. After analyzing the reduced-order ADHSS in the ideal case, the equations describing the complete system are considered. The theory of averaging is used to gain insight into the steady-state behavior of the algorithm. It is found that the system has a two-dimensional equilibrium surface such that the disturbance is cancelled exactly. A subset of the surface is proved to be locally stable. Extensive active noise control experiments demonstrate the performance of the algorithm, even when disturbance and plant parameters are changing.

Electroelastic modeling and experimental validations of piezoelectric energy harvesting from broadband random vibrations of cantilevered bimorphs

Abstract: We present electroelastic modeling, analytical and numerical solutions, and experimental validations of piezoelectric energy harvesting from broadband random vibrations. The modeling approach employed herein is based on a distributed-parameter electroelastic formulation to ensure that the effects of higher vibration modes are included, since broadband random vibrations, such as Gaussian white noise, might excite higher vibration modes. The goal is to predict the expected value of the power output and the mean-square shunted vibration response in terms of the given power spectral density (PSD) or time history of the random vibrational input. The analytical method is based on the PSD of random base excitation and distributed-parameter frequency response functions of the coupled voltage output and shunted vibration response. The first of the two numerical solution methods employs the Fourier series representation of the base acceleration history in an ordinary differential equation solver while the second method uses an Euler‐Maruyama scheme to directly solve the resulting electroelastic stochastic differential equations. The analytical and numerical simulations are compared with several experiments for a brass-reinforced PZT-5H bimorph under different random excitation levels. The simulations exhibit very good agreement with the experimental measurements for a range of resistive electrical boundary conditions and input PSD levels. It is also shown that lightly damped higher vibration modes can alter the expected power curve under broadband random excitation. Therefore, the distributed-parameter modeling and solutions presented herein can be used as a more accurate alternative to the existing single-degree-of-freedom solutions for broadband random vibration energy harvesting.

Impedance-Based Resonance Analysis in a VSC-HVDC System

Abstract: Resonances can limit power transfer in a voltage-source converter-high voltage dc (VSC-HVDC) system. The objective of this paper is to develop impedance models for the rectifier ac system and the inverter ac system for a VSC-HVDC system. Resonance stability will be examined using Nyquist stability criterion and impedance frequency responses. The impedance models consider the outer control loop and the inner current control loops of VSCs. Impacting factors are then examined. Stability analysis demonstrates that the feedforward filter, line length, and power transfer level have a significant impact on resonances. Time-domain simulation results obtained by Matlab SimPowerSystems are used to validate the analysis.

A comparison of spectral magnitude and phase-locking value analyses of the frequency-following response to complex tones

Abstract: Two experiments, both presenting diotic, harmonic tone complexes (100 Hz fundamental), were conducted to explore the envelope-related component of the frequency-following response (FFRENV), a measure of synchronous, subcortical neural activity evoked by a periodic acoustic input. Experiment 1 directly compared two common analysis methods, computing the magnitude spectrum and the phase-locking value (PLV). Bootstrapping identified which FFRENV frequency components were statistically above the noise floor for each metric and quantified the statistical power of the approaches. Across listeners and conditions, the two methods produced highly correlated results. However, PLV analysis required fewer processing stages to produce readily interpretable results. Moreover, at the fundamental frequency of the input, PLVs were farther above the metric's noise floor than spectral magnitudes. Having established the advantages of PLV analysis, the efficacy of the approach was further demonstrated by investigating how different acoustic frequencies contribute to FFRENV, analyzing responses to complex tones composed of different acoustic harmonics of 100 Hz (Experiment 2). Results show that the FFRENV response is dominated by peripheral auditory channels responding to unresolved harmonics, although low-frequency channels driven by resolved harmonics also contribute. These results demonstrate the utility of the PLV for quantifying the strength of FFRENV across conditions.

Temporal Response of the Underwater Optical Channel for High-Bandwidth Wireless Laser Communications

Abstract: This paper describes a high-sensitivity, high-dynamic range experimental method for measuring the frequency response of the underwater optical channel in the forward direction for the purpose of wireless optical communications. Historically, there have been few experimental measurements of the frequency response of the underwater channel, particularly with regard to wireless communication systems. In this work, the frequency response is measured out to 1 GHz over a wide range of water clarities (approximately 1-20 attenuation lengths). Both spatial and temporal dispersions are measured as a function of pointing angle between the transmitter and the receiver. We also investigate the impact of scattering function and receiver field of view. The impact of these results to the link designer is also presented.

Control and quantification of kinetic energy released by wind farms during power system frequency drops

Abstract: High wind energy penetration levels in modern power systems draw attention towards wind farms expected role during frequency drops. Wind farms positive contribution required by system operators basically depends on the amount of kinetic energy stored in wind turbines rotating parts and how to manage it during frequency deviations elimination. This study presents an algorithm to estimate and control the quantity of extractable kinetic energy stored in a wind farm during frequency drops. Moreover, it manages stored kinetic energy release within a given time span to achieve positive participation in frequency drops clearance. The proposed method is based on tuning the tip speed ratio before and during the frequency drop according to several factors. The recovery time required by the wind turbine to retain its normal speed is also a function of several parameters including turbine inertia and the incoming wind speed. The proposed algorithm's impact on power system frequency is analysed by assessing the expected enhancement in frequency deviation. A hypothetical grid is considered as the benchmark including detailed modelling for wind speeds, wind turbine and wind farm to improve the creditability of the obtained results. Presented research work outcomes highlight the impact of wind farms replacement for conventional generators. Executed simulations proved that applying the proposed algorithm neutralises wind energy penetration influence on system frequency response, even more, it causes solid improvements unless the incident wind speed is too slow or the frequency drop is too high. Simulation environments are MATLAB and Simulink.

System Identification for Small, Low-Cost, Fixed-Wing Unmanned Aircraft

Abstract: This paper describes a practical system identification procedure for small, low-cost, fixed-wing unmanned aircraft. Physical size and cost restrictions limit the sensing capabilities of these vehicles. The procedure is demonstrated on an Ultra Stick 25e, therefore emphasizing a minimum complexity approach compatible with a low-cost inertial sensor. A linear model, obtained from the generic nonlinear equations of motion for aircraft, is used as a basis for system identification. This model is populated with results from a first principles analysis to form a baseline model. Flight experiments are designed using the baseline model and operational constraints to collect informative data. Parameters of the linear model are identified by fitting the model to frequency responses extracted from the data. The parameters are integrated into the nonlinear equations of motion, and both linear and nonlinear models are validated in the time domain. Verification of model accuracy is extended with a sensitivity and resid...

Frequency response of power systems with variable speed wind turbines

Abstract: Summary form only given. As wind penetration levels on power systems increase worldwide and synchronous generation is displaced, the dynamic characteristics of these systems, and hence the protocols for how they are operated, are changing. One issue, of particular concern, is the resulting reduction in system inertia since modern variable speed wind turbines do not inherently contribute to the inertial response of the system. Such devices can, however, be fitted with a control loop which provides an active power response to significant frequency deviations, similar to the inertial response of fixed speed wind turbines and synchronous generation. Unlike conventional machines, however, the response of variable speed turbines is dependent on local wind speeds and so cannot be quantified deterministically by system operators. As a result, it is likely that uncertainty will exist over the inertial response capability of the system at high wind penetration levels. In this paper, the frequency response capability is assessed on a test system and the effectiveness of wind turbines' contribution to system inertial response is evaluated in the context of future system requirements.

Sensitivity Analysis of Load-Damping Characteristic in Power System Frequency Regulation

Abstract: The smart grid initiative leads to growing interests in demand responses and the load models, especially the frequency-sensitive loads such as motors. The reason is that high-penetration controllable load may have substantial impact on system frequency response (SFR). However, the effect of the frequency-related load-damping coefficient is still not completely understood. This paper investigates the effect of frequency-sensitive load on system frequency using typical SFR model. Theoretic analyses based on transfer functions show that the frequency deviation under a different load-damping coefficient is relatively small and bounded when the power system is essentially stable; while the frequency deviation can be accelerated when a power system is unstable after disturbance. For the stable case, the largest frequency dip under a perturbation and the corresponding critical time can be derived by inverse Laplace transformation using a full model considering load-damping coefficient. Further, the error in evaluating the load-frequency coefficient gives the largest impact to frequency deviation right at the time when the largest frequency dip occurs. Multiple-machine cases and automatic generation control (AGC) are also included in the analyses with verifications by simulation studies. The conclusion can be useful for system operators for decision-making of load control or interruption.

Estimation of CNC machine–tool dynamic parameters based on random cutting excitation through operational modal analysis

Abstract: Dynamic properties of the whole machine tool structure including tool, spindle, and machine tool frame contribute greatly to the reliability of the machine tool in service and machining quality. However, they will change during operation compared with the results from static frequency response function measurements of classic experimental modal analysis. Therefore, an accurate estimation of the dynamic modal parameters of the whole structure is of great value in real time monitoring, active maintenance, and precise prediction of a stability lobes diagram. Operational modal analysis (OMA) developed from civil engineering works quite efficiently in modal parameters estimation of structure in operation under an intrinsic assumption of white noise excitation. This paper proposes a new methodology for applying this technique in the case of computer numerically controlled (CNC) machine tools during machining operations. A novel random excitation technique based on cutting is presented to meet the white noise excitation requirement. This technique is realized by interrupted cutting of a narrow workpiece step while spindle rotating randomly. The spindle rotation speed is automatically controlled by G-code part program, which contains a series of random speed values produced by MATLAB software following uniform distribution. The resulting cutting produces random pulses and excites the structure in all three directions. The effect of cutting parameters on the excitation frequency and energy was analyzed and simulated. The proposed technique was experimentally validated with two different OMA methods: the Stochastic Subspace Identification (SSI) method and the poly-reference least square complex frequency domain (pLSCF or PolyMAX) method, both of which came up with similar results. It was shown that the proposed excitation technique combined successfully with OMA methods to extract dynamic modal parameters of the machine tool structure.

A Case Study on the Application of the Nyquist Stability Criterion as Applied to Interconnected Loads and Sources on Grids

Abstract: As the penetration of complex grid-connected devices, such as power electronic inverters, increases, so too does the complexity of analyzing system stability. A graphical application of the Nyquist stability criterion is presented that indicates how an individual load and source each contribute to the closed-loop system grid eigenvalues. The case study is not limited to particular impedance forms or scenarios like the more common complex torque coefficient method or passivity theory method. From the individual frequency responses of the load and source impedances, the graphical technique indicates how each impedance contributes to the system stability. Examples are provided that successfully indicate the cause of instability for a digitally controlled voltage source inverter (VSI) operating as a microgrid, with a current source inverter as a load. A second example is provided that identifies the potential instability of a VSI running an induction machine. A 42-kW inverter system is used to confirm the findings, showing a close correlation with the theoretical analysis.

Frequency dependence and frequency control of microbubble streaming flows

Abstract: Steady streaming from oscillating microbubbles is a powerful actuating mechanism in microfluidics, enjoying increased use due to its simplicity of manufacture, ease of integration, low heat generation, and unprecedented control over the flow field and particle transport. As the streaming flow patterns are caused by oscillations of microbubbles in contact with walls of the set-up, an understanding of the bubble dynamics is crucial. Here we experimentally characterize the oscillation modes and the frequency response spectrum of such cylindrical bubbles, driven by a pressure variation resulting from ultrasound in the range of 1 kHz ≲f≲ 100 kHz. We find that (i) the appearance of 2D streaming flow patterns is governed by the relative amplitudes of bubble azimuthal surface modes (normalized by the volume response), (ii) distinct, robust resonance patterns occur independent of details of the set-up, and (iii) the position and width of the resonance peaks can be understood using an asymptotic theory approach. Th...

A Reconfigurable FSS Using a Spring Resonator Element

Abstract: Reconfigurable and tunable frequency selective surfaces (FSSs) are of significant interest in applications such as tunable radomes and adaptive screening of unwanted wireless transmissions Conventional FSSs require additional bias circuitry to tune the operating frequency or to change its characteristics In this letter, a new tuning technique using a spring resonator element is proposed This technique can be applied to FSS design to make it reconfigurable and/or to fine-tune the response The FSS frequency response can be adjusted by changing the spring height $h$ with applied pressure The functional characteristic of the FSS can also be altered between a bandstop and bandpass filter response A parametric analysis of the novel spring FSS is undertaken in CST software, and the results are validated with experimental measurement

Frequency domain analysis of pipe fluid transient behaviour

Abstract: Pipe transient signals are hyperbolic in nature where key features of the signal repeat periodically and are well suited to the analysis in the frequency domain. For this reason, a number of studies have been conducted on the use of frequency domain approaches for a variety of purposes, from fault detection to the prediction of the unsteady system response. Despite the number of papers on the topic over the past decades, there are no detailed review of the developments in the frequency domain analysis of pipe transient signals. This paper provides an assessment and review of the relevant research and provides a critical discussion of both the strengths and weaknesses of this approach. A method for extracting a system's frequency response function using conventional valve closure signals is proposed and the influence of various faults, friction and pipe wall viscoelasticity on this response function are compared with the corresponding impacts in the time domain. This study shows that most changes o...

Antenna Parametrization for the Detection of Partial Discharges

Abstract: Partial discharge (PD) detection is a widely extended technique for electrical insulation diagnosis. Ultrahigh-frequency detection techniques appear as a feasible alternative to traditional methods owing to their inherent advantages such as the capability to detect PDs online and to locate the piece of equipment with insulation problems in substations and cables. In this paper, four antennas are thoroughly studied by means of their theoretical and experimental behavior when measuring electromagnetic pulses radiated by PD activity. The theoretic study of the band of frequencies in which the pulse emits and the measurement of the parameters $S_{11}$ are complemented with the frequency response and wavelet transform of a set of 500 time signals acquired by the antennas, and the results are analyzed in detail.

Eastern Frequency Response Study

Abstract: This study was specifically designed to investigate the frequency response of the Eastern Interconnection that results from large loss-of-generation events of the type targeted by the North American Electric Reliability Corp. Standard BAL-003 Frequency Response and Frequency Bias Setting (NERC 2012a), under possible future system conditions with high levels of wind generation.

A wideband, frequency up-converting bounded vibration energy harvester for a low-frequency environment

Abstract: This paper presents a bounded vibration energy harvester to effectively harvest energy from a wide band of low-frequency environmental vibrations ranging from 10 to 18 Hz. Rigid mechanical stoppers are used to confine the seismic mass movement within the elastic limits of the spring. Experimental results show the effectiveness of the proposed technique in increasing the efficiency of the energy harvester. When excited at a frequency of 10 Hz with a peak acceleration of 1 g, the harvester responds at a higher frequency of 20 Hz and gives a peak power of 2.68 mW and a peak to peak voltage of 2.62 V across a load of 220 Ω. The average power density of 65.74 μW cm−3 obtained at 10 Hz 1 g excitation monotonically increases with frequency up to 341.86 μW cm−3 at 18 Hz. An analytical model describing the nonlinear dynamics of the proposed harvester is also presented. A simple technique to estimate the energy losses during impact and thereof a method to incorporate these losses in the model are suggested. The presented model not only predicts the experimental voltage waveform and frequency response of the device with good similarity but also predicts the RMS voltage from the harvester for the whole range of operating frequencies with an RMS error of 5.2%.