Power Frequency Response Research Articles

Ancillary Services Market Design in Distribution Networks: Review and Identification of Barriers

The high proliferation of converter-dominated Distributed Renewable Energy Sources (DRESs) at the distribution grid level has gradually replaced the conventional synchronous generators (SGs) of the transmission system, resulting in emerging stability and security challenges. The inherent characteristics of the SGs are currently used for providing ancillary services (ASs), following the instructions of the Transmission System Operator, while the DRESs are obliged to offer specific system support functions, without being remunerated for these functions, but only for the energy they inject. This changing environment has prompted the integration of energy storage systems as a solution for transfusing new characteristics and elaborating their business in the electricity markets, while the smart grid infrastructure and the upcoming microgrid architectures contribute to the transformation of the distribution grid. This review investigates the existing ASs in transmission system with the respective markets (emphasizing the DRESs’ participation in these markets) and proposes new ASs at distribution grid level, with emphasis to inertial response, active power ramp rate control, frequency response, voltage regulation, fault contribution and harmonic mitigation. The market tools and mechanisms for the procurement of these ASs are presented evolving the existing role of the Operators. Finally, potential barriers in the technical, regulatory, and financial framework have been identified and analyzed.

Characterization of a Gm-C Filter Based on CNTFETs for Use in Digital Audio Broadcasting Systems

Anti-aliasing filters play an important role in analog front-end circuits, and their suitable design can improve the performance of digital audio broadcasting systems. In this paper, a Gm-C anti-aliasing filter based on carbon nanotube field effect transistors (CNTFETs) is proposed. Using CNTFETs provides low power consumption and appropriate frequency response. Simulation results show that these characteristics are widely dependent on the physical parameters of CNTFETs. The effects of chirality, the number of CNTs in each CNTFET, and distance of CNTs from each other on power consumption and frequency response are investigated. Among these parameters, the chirality and number of CNTs respectively have nonlinear and linear relationships with both power consumption and cutoff frequency. On the other hand, changing the distance between CNTs has the least effect on the output characteristics. Also, the output features of the filter for different gate oxides and channel lengths are studied. The overall result of the simulations demonstrates that the filters based on CNTFETs are promising candidates to be used in future nano-scale integrated circuits.

Analysis of bimorph piezoelectric beam energy harvesters using superconvergent element

Cantilever-based piezoelectric energy harvesters have been utilized as structures to extract mechanical energy from the ambient mechanical vibrations and transfer it into the electrical output. In this article, the performance of bimorph piezoelectric beam energy harvesters is investigated. The cantilever beam is modeled by using both Timoshenko and Euler–Bernoulli beam theories. The equations are discretized using the conventional finite element method and superconvergent element. Besides the high rate of convergence, easy switching between the above beam theories is enabled by such type of element. The current model is presented for a Timoshenko beam model, but it could as well be used for a Euler–Bernoulli beam model. In addition, voltage, current, and power frequency response functions for different ranges of load resistance varying from the short-circuit to open-circuit conditions are determined to reach the maximum values. Effects of the slenderness ratio and the required beam model based on the geometric properties of the piezoelectric energy harvesters are discussed in the final part of this study. The results show that only for smaller values of the slenderness ratio (below 5), it is necessary to model the beam using the Timoshenko assumptions; otherwise both beam theories provide approximately the same responses.

Nonlinear piezoelectric vibration energy harvester with frequency-tuned impacting resonators for improving broadband performance at low frequencies

The paper reports on a nonlinear frequency up-converting vibration energy harvester with enhanced broadband performance below 50 Hz, which is attained by leveraging vibro-impact interaction between two high-frequency piezoelectric generators and two low-frequency resonators with commensurate natural frequencies in the 2:1 ratio. Finite element model was implemented to assess the proposed concept by treating the harvester as a vibro-impact coupled piezoelectric-circuit system. The model accommodates multiple mechanical contact pairs defined by nonlinear dissipative Hunt–Crossley contact force formulation. Effective design principles were applied to maximize power output including near-optimal positioning of the neutral plane in the generators and rational adjustment of response settling time. The fabricated proof-of-concept device was tested in different clearance configurations and under varying harmonic excitation conditions to reveal rich nonlinear dynamics behavior. The measured hardening-type power frequency responses were examined to gain better insight into nonlinear resonance characteristics (instability jumps, frequency hysteresis, etc), which determine effectiveness of micro-power generation. It was demonstrated that the proposed dual-resonator energy harvester favorably harnesses nonlinear resonance amplification to deliver larger average power output (up to 37 μW) and useable bandwidth (up to 9.5 Hz) in comparison to the conventional single-resonator counterparts (delivering up to 26 μW and up to 7 Hz, respectively). The maximum normalized power density of the device is 41 μW cm−3 g−2, while volume figure of merit and 3 dB or 1 dB bandwidth-based figures of merit reach 0.18%, 11 μW cm−3 g−2 and 1.5%, respectively. The latter value indicates superior broadband performance of the device. Adoption of mean performance index and coefficient of variation as complementary figures of merit proved to be valuable in identifying device configuration that yields the most effective and stable broadband operation in a targeted frequency range.

Aggregation Frequency Response Modeling for Wind Power Plants With Primary Frequency Regulation Service

High-penetration wind power access to grid requires wind turbine generator (WTG) to provide frequency regulation service. Consequently, the frequency dynamics of wind power plants (WPPs) integrated system are changing; thus, it is necessary to investigate the dynamic frequency response of WPPs. In this paper, an analytical approach for an aggregated frequency response model for WPPs with primary frequency regulation service is presented and validated. First, different operation region of WTGs is fully taken into account, and a low-order wind power frequency response (WPFR) model with combined frequency control is deduced based on small signal analysis theory, which has been given in the form of symbolic transfer function. Afterwards, a system identification (SI) analytical method is proposed to aggregate a multi-machine WPFR model with heterogeneous parameters into a single equivalent model, which is called an aggregated WPFR (AWPFR) model, and this aggregation method is validated by the mathematical proof. Finally, the accuracy and effectiveness of the AWPFR model is verified through comparisons of simulation results obtained from the multi-machine WPFR model, detailed wind power plant (WPP) model and individual WPFR models, and the impact of the WTG parameters on the system frequency characteristics is analyzed and discussed. Such an aggregation model can provide a convenient way to describe the dynamic frequency response of WPPs by avoiding the need for modeling complex transient processes while maintaining a satisfactory level of accuracy.

Frequency tuning of piezoelectric energy harvesters thanks to a short-circuit synchronous electric charge extraction

This paper introduces a new electrical strategy for maximizing the energy scavenged from highly coupled and lowly damped piezoelectric energy harvesters (PEHs). The proposed strategy named Short-circuit synchronous electric charge extraction (SC-SECE) introduces a SC phase whose start time ϕs and duration Δϕ can be adjusted. The control of ϕs and Δϕ allows to electrically adapt the dynamics of the electromechanical harvester. In a first part, we analytically derive the influences of ϕs and Δϕ on the harvester dynamics, and prove that they both affect the damping induced by the electrical interface on the mechanical resonator and its resonant frequency. Thereafter, we numerically evaluate the SC-SECE performances as a function of the intrinsic harvester’s characteristics. We expose that if the coupling and/or mechanical quality factor of the harvester are important enough, the SC-SECE leads to enhanced power frequency responses compared to SECE and SEH strategies. Experimental results on a high coupling PEH associated with the SC-SECE strategy have been realized and are in good agreement with the analytical predictions. Under various vibrations amplitudes, the harvester’s resonant frequency has been tuned on a frequency range as large as 35% of its natural resonant frequency. We have been able to harvest more than 92 μW for vibration frequencies ranging from 90 to 140 Hz, under an external acceleration of 0.2 G.

Resonance response interaction without internal resonance in vibratory energy harvesting

Abstract Resonance response interaction in nonlinear multiple degrees of freedom vibration systems has always involved internal resonance. In this article, bubble shaped response curve is uncovered without pre-designated resonances relationship that is a necessary condition for internal resonance. The objective of this article is twofold: first to explore the connection between the resonance response interaction and bubble shaped response curve that may appear in the forced response of a nonlinear magnetoelectric coupled system; and, second, to exploit resonance response interaction to enhance the vibratory energy harvesting bandwidth. A nonlinear magnetoelectric oscillator coupled linearly to an additional oscillator is used to demonstrate the phenomena and the enhanced performance. The lateral springs could produce the geometrical nonlinear stiffness and its stiffness to adjust the two resonance responses such that the bubble shaped response curve appears in the power-frequency response plot. The method of harmonic balance is well established method for the analysis of such the power-frequency response. The results are also validated by some numerical work. The power-frequency response curves are generated for distinct harvesting mass, manifesting the resonance response interaction could increase the bandwidth and output power. At last, the resonance response interaction designed energy harvesting from Gaussian white noise excitation is numerically addressed to illustrate positive effects of geometrical nonlinearity.

Electrically rectified piezoelectric energy harvesting induced by rotary magnetic plucking

A theoretical framework together with an experimental validation is developed for the investigation of a rotational piezoelectric energy harvester attached to the standard interface circuit for AC–DC conversion. The energy harvester consists of an electrically rectified piezoelectric cantilever beam mounted on a stationary base with a magnet attached to its free end. Energy is harvested by vibration of beam induced by non-contact rotary magnetic plucking. A theoretical model accounting for magnetic coupling and rotary plucking is developed and the phenomenon of frequency up-conversion is realized by the Fourier analysis of the impulsive-like driving force. The analytic estimate of DC harvested power is derived showing that the electric response can be imitated to the case of rectilinear harmonic force vibration whereas the multiplication of the driving frequency and the integer value closely matches the device’s fundamental resonance. As a result, it exhibits broadband frequency response due to frequency up-conversion. In addition, the prediction on the crests and troughs of ripples in the DC power frequency response is remarkably found in excellent agreement with experiment. Finally, several design guidelines are proposed. These include power enhancement by lowering the ratio of perpendicular distance of magnetics to the radius of revolution, and the reduction of ripples by requiring larger mechanical damping.

Intelligent frequency regulation in the wind integrated control area

Reduction in system inertia due to the higher levels of wind plants in a power system inherently necessitates the frequency regulation investigations and motivates new opportunities for the improvement of active power control techniques. This paper focus on the load-frequency regulation analysis of a control area in the presence of a proposed wind energy technology. The proposed variable speed wind turbine generator model incorporates a dynamic dead-band and moving average frequency filter-based algorithm to provide grid-code compatible power-frequency response. The proposed wind plant model provides better frequency response and increased electrical power generation in comparison to the other frequency responsive wind turbine generator models. This paper also highlights the superiority of gain scheduling concept in fuzzy logic controllers as an improved alternative to various other load frequency controllers under the stochastic conditions in a wind integrated control area.

Virtual Energy Storage: Converting an AC Drive to a Smart Load

This paper proposes a new smart-load concept using ac drives. The concept is based on a secondary control layer coordinated with the network and the load to provide active power support. The general smart-load concept is developed and synthesized for its practical implementation in network power–frequency support applications. A multi-power–frequency droop line is proposed. The final idea is applied to a fan load powered by an ac drive based on an induction motor and a two-level voltage source converter. Experimental results show that a full power–frequency response can be achieved by the smart load within 2 s of the network frequency deviation.

Analysis of multifunctional piezoelectric metastructures for low-frequency bandgap formation and energy harvesting

Vibration-based energy harvesting is a growing field for generating low-power electricity to use in wireless electronic devices, such as the sensor networks used in structural health monitoring applications. Locally resonant metastructures, which are structures that comprise locally resonant metamaterial components, enable bandgap formation at wavelengths much longer than the lattice size, for critical applications such as low-frequency vibration attenuation in flexible structures. This work aims to bridge the domains of energy harvesting and locally resonant metamaterials to form multifunctional structures that exhibit both low-power electricity generation and vibration attenuation capabilities. A fully coupled electromechanical modeling framework is developed for two characteristic systems and their modal analysis is presented. Simulations are performed to explore the vibration and electrical power frequency response maps for varying electrical load resistance, and optimal loading conditions are presented. Case studies are presented to understand the interaction of bandgap formation and energy harvesting capabilities of this new class of multifunctional energy-harvesting locally resonant metastructures. It is shown that useful energy can be harvested from locally resonant metastructures without significantly diminishing their dramatic vibration attenuation in the locally resonant bandgap. Thus, integrating energy harvesters into a locally resonant metastructure enables a new potential for multifunctional locally resonant metastructures that can host self-powered sensors.

High Figure of Merit Nonlinear Microelectromagnetic Energy Harvesters for Wideband Applications

We report a new approach for designing high-performance microelectromechanical system (MEMS) electromagnetic energy harvesting devices, which can operate at low frequency (<;1 kHz) over the ultrawide bandwidth of 60-80 Hz. The output from the devices is increased significantly at a low optimized load and this overall enhancement in performances is benchmarked using a power integral (Pf) figure-of-merit. The experimental results show that the efficient nonlinear designs produce large Pf values, giving rise to one of the highest normalized Pf densities among the reported MEMS scale nonlinear energy harvesting devices. This improvement is achieved by suitably designing the nonlinear spring architectures, where the nonlinearity arises from the stretching strain of the specifically designed fixed-fixed configured spring arms under large deflections and gives rise to wideband output response. Different fundamental modes of the mechanical structures are brought relatively close, which further widens the power-frequency response by topologically varying the spring architectures and by realizing the same using the thin silicon-on-insulator substrate using MEMS processing technology. In addition, we have used the magnet as proof mass to increase the output in contrary to conventional approach of using the coil as the proof mass in micro-electromagnetic energy harvesters. The high performance obtained from the MEMS energy harvesters with integrated double layer micro-coil is compared with the same using wire wound copper coil. The experimentally obtained results are qualitatively explained by using a finite-element analysis of the designed structures.

A rail-borne piezoelectric transducer for energy harvesting of railway vibration

This paper investigates design, modelling, and test issues related to piezoelectric energy transducer. The model analyzes a rail-borne “seismic” energy harvester that is designed to generate electrical energy from local variations in rail acceleration. The energy harvester analyzed in this model consists of a piezoelectric PZT film clamped at one end to the rail with a tip mass mounted on its other end. It includes two sub-models in this paper: a vehicle-track interaction model considering vehicle travelling load; and a cantilevered piezoelectric beam model for the visualization of voltage and power profile and frequency response. Four rail irregularities (American 6th grade track spectrum, Chinese track spectrum, German high and low-disturbance track spectrum) are compared and implemented into the calculation script. The calculated results indicate a rail displacement of 0.2 mm to 0.8 mm. Vibration tests of the proposed rail-borne device are conducted; a hydraulic driven system with excitation force up to 140 kN is exploited to generate the realistic wheel-rail interaction force. The proposed rail-borne energy harvester is capable of energy harvesting at low-frequency (5 Hz to 7 Hz) and small railway vibration (0.2 mm to 0.4 mm rail displacement). The output power of 4.9 mW with a load impedance of 100 kOhm is achieved. The open circuit peak-peak voltage reaches 24.4 V at 0.2 mm/7 Hz/5 g wheel-rail excitation. A DC-DC buck converter is designed, which works at the resonance frequency of 23 Hz/5 g on a lab vibration rig, providing a 3.3 VDC output.

Comparative Analysis of Voltage Controlled Oscillator using CMOS

Objective: This research paper presents a review on performance comparison of different types of Voltage Controlled Oscillators to analyze power dissipation and frequency response. Methods: Designs from Ring Oscillator, Current Starved VCO, VCO with gates of PMOS transistors grounded, VCO with PMOS transistors as diode connected load, VCO with Source voltage applied to both PMOS and NMOS transistors and VCO with NMOS transistors as diode connected load are designed on 45nm CMOS Technology using Cadence Virtuoso Tool. Findings: The performance of different circuits as Transient response, Frequency Response, Stability, Power has been comparatively analyzed through different simulations. Current Starved VCO is concluded as most linear design. All design procedures, Circuit and simulation results are illustrated.

Experimental study of vibrational energy harvesting using Electro-Active paper

This paper presents an estimation of power output produced by an Electro-Active Paper (EAPap) energy harvesting transducer under base vibration. EAPap is very thin cellulose piezoelectric film, which exhibits a direct piezoelectric effect, when subjected to stress. A 50×50 mm2 EAPap patch was bonded on a 100×50×1 mm3 aluminum cantilever structure. Energy harvesting tests were performed on the energy harvesting transducer, without and with a 2 grams proof mass near the tip of the cantilever beam. The voltage, current and power frequency response functions (FRFs) with respect to the base acceleration are identified and presented. The Voltage FRFs show a monotonic trend with increasing the load resistor from 100 kΩ to 1 MΩ, and the current FRFs also demonstrate monotonic dynamic behavior, but the trend is opposite to the voltage FRFs. In contrast to the voltage and current FRFs, the output power FRFs do not show a monotonic trend, exhibiting the maximum value of 150 μW/g2 at 75.1 Hz without the proof mass. The output power increases to 392 μW/g2 at 62.2 Hz when the proof mass is attached. This preliminary study indicates that EAPap is promising for energy harvesting transducers under vibration environment.

Design, fabrication and performances of MEMS piezoelectric energy harvester

MEMS piezoelectric energy harvester is optimally designed and fabricated, and its vibration characteristics, output voltage, power, power spectral density (SD) and frequency response function under harmonic and random excitation is studied by theory analysis, simulation and experimental test. For the designed MEMS piezoelectric energy harvester, the accurate solutions and expressions of amplitude, voltage, power and power spectral density are derived. Then, vibration characteristic, voltage, power and power SD with different load resistance, sinusoidal acceleration and random acceleration SD are simulated and tested; moreover, frequency response function of MEMS piezoelectric energy harvester is obtained by experimental test, and the results are consistent with theoretical model. When sinusoidal acceleration is 0.6 g, the maximal amplitude of mass is 116 µm and the power density is 0.1 mW/cm 3 . By testing results, output voltage of piezoelectric energy harvester is proportional to the amplitude, and the amplitude at optimal load is smaller than of at open circuit because of the feedback effect of load resistance. In addition, output power SD linearly increases with acceleration SD increasing. When acceleration SD is 5 × 10 −4 (m/s 2 ) 2 /Hz, power SD is 1.24 µW 2 /Hz.

Double-talk robust acoustic echo cancellation for CD-quality hands-free videoconferencing system

A novel monaural acoustic echo cancellation method developed for a 20-kHz wideband hands-free videoor teleconferencing system is presented. The method can effectively reduce undesired acoustic echo included in a signal arriving at a microphone from a loudspeaker and can emphasize the target talker's voice when near-end and farend talkers speak simultaneously (i.e. double-talk). The method estimates a power frequency response of an acoustic echo path between a loudspeaker and microphone (acoustic coupling level) whether or not double-talk has occurred, then calculates a post-filter that effectively reduces the undesired echo. In the echo cancellation processing, the calculation complexity is reduced to make the processing suitable for real-time implementation by using a low-complexity subband approach that employs a new subband filtering algorithm. Experiments were conducted to examine the performance of the proposed method. The results indicated that the proposed method delivered natural-sounding near-end speech even during double-talk periods while sufficiently suppressing the undesired echo.

Second-Order Spectral Statistics for the Power Gain of Wideband Wireless Channels

We derive closed-form expressions for the secondorder statistics of the power gain (as a function of frequency) of wideband microwave indoor channels. We obtain our results within a framework that is general enough to be compatible with several popular channel models, such as the Saleh-Valenzuela (SV) channel model and those proposed by the IEEE 802.15.3a and IEEE 802.15.4a task groups. As in all these models, our channel description is based upon clusters and rays with (possibly mixed) Poisson arrivals and random amplitudes. Our results consist of closed-form expressions for the second-order statistics of the channel power frequency response, where statistical averages involve expectations over ray amplitudes and arrival times. These expressions reveal that the autocovariance of the spectral power gain between any two frequencies decreases and tends to zero as the difference between these frequencies tends to infinity if and only if the cluster arrival rate goes to infinity. They also show that the variance-to-squared-mean ratio of the narrow-band power gain exhibits exactly the same behavior with respect to the center frequency. We then use these results to obtain closed-form expressions for the variance and the second-order moment of the aggregate channel power gain over any given interval of frequencies. This allows us to express the channel spectral diversity as a function of model parameters and bandwidth. In addition, we illustrate how these equations allow one to devise automatic cluster identification algorithms which, from empirical estimates of the second-order spectral statistics of the channel power gain, can confirm or deny the existence of clusters in a given scenario.

Power Handling Capability of Transmit HTS Stripline Filter with Shuttle-shape Resonators

The power handling capability and frequency response of transmit high-temperature superconducting stripline filter with shuttle-shape resonators were investigated. A cascaded quadruplet (CQ) design is used to produce a pair of attenuation poles for obtaining sharp cutoff characteristics. The shuttle-shape resonators improve power handling and out-of-band rejection. An electromagnetic simulator based on the moment method was used to design a four-pole SL CQ filter with shuttle-shape resonators (5.0-GHz center frequency and 100-MHz bandwidth). The filter was fabricated using YBa2Cu3O7-d thin films on an Al2O3 substrate and was formed Au ground plane. The filter showed good frequency response. From the result of the power-handling capability, the filter showed a liner property until 7.9W.

An omnidirectional loudspeaker based on a ring-radiator

Several (standardized) measurements require an omnidirectional sound source. Traditionally used sources offer either high power and flat frequency response, but limited omnidirectionality, or excellent point source characteristics with very irregular frequency response and limited power. In this paper, the development and performance of a different kind of source, consisting of two broadband speakers in face-to-face configuration, each with smooth conical enclosure, are presented. The proposed source, radiating the sound from a ring-like area, has a useable frequency range of 150Hz–10kHz, with 106dB sound power and good uniformity of pressure with angle. Data from two commercial sources is presented for comparison.