Showing papers on "Frequency response published in 2018"

Hierarchical Parameter Estimation for the Frequency Response Based on the Dynamical Window Data

Abstract: This paper studies the problem of parameter estimation for frequency response signals For a linear system, the frequency response is a sine signal with the same frequency as the input sine signal When a multi-frequency sine signal is applied to a system, the system response also is a multi-frequency sine signal The signal modeling for multi-frequency sine signals is very difficult due to the highly nonlinear relations between the characteristic parameters and the model output In order to obtain the parameter estimates of the multi-frequency sine signal, the signal modeling methods based on statistical identification are proposed by means of the dynamical window discrete measured data By constructing a criterion function with respect to the model parameters to be estimated, a hierarchical multi-innovation stochastic gradient estimation method is derived through parameter decomposition Moreover, the forgetting factor and the convergence factor are introduced to improve the performance of the algorithm The simulation results show the effectiveness of the proposed methods

Analytical Method to Aggregate Multi-Machine SFR Model With Applications in Power System Dynamic Studies

Abstract: The system frequency response (SFR) model describes the average network frequency response after a disturbance and has been applied to a wide variety of dynamic studies. However, the traditional literature does not provide a generic, analytical method for obtaining the SFR model parameters when the system contains multiple generators; instead, a numerical simulation-based approach or the operators’ experience is the common practice to obtain an aggregated model. In this paper, an analytical method is proposed for aggregating the multi-machine SFR model into a single-machine model. The verification study indicates that the proposed aggregated SFR model can accurately represent the multi-machine SFR model. Furthermore, the detailed system simulation illustrates that the SFR model can also accurately represent the average frequency response of large systems for power system dynamic studies. Finally, three applications of the proposed method are explored, with system frequency control, frequency stability, and dynamic model reduction. The results show the method is promising with broad potential applications.

Synthetic inertia versus fast frequency response: a definition

Abstract: This study discusses synthetic inertia from the perspective of a transmission system operator and compares it to fast frequency response based on frequency deviation. A clear distinction of the meanings between these concepts is discussed, the basis of which is a description of their characteristics. A contribution and the purpose is the clarification of these concepts in addition to share the perspectives of a transmission system operator. The frequency response of a power system based on the Nordic system is examined for future scenarios with large amounts of wind power. Conclusions are drawn regarding the benefit of synthetic inertia compared with fast frequency response based on frequency deviation.

Primary resonance analysis and vibration suppression for the harmonically excited nonlinear suspension system using a pair of symmetric viscoelastic buffers

Abstract: To reduce the severity of high-magnitude vibrations and shock, end-stop buffers was used for the most suspension cabs or seats of work vehicles. This paper employs a pair of symmetric linear viscoelastic end-stops to improve the performance of a single-degree-of-freedom nonlinear suspension system under primary resonance conditions, which has cubic nonlinearity. Firstly, a piecewise symmetry tri-nonlinear model is introduced. The frequency response of relative displacement corresponding to the steady-state motion is obtained by applying the multiple-scale method, which is found to be the same with the averaging method solution. And it is further verified by numerical simulation. Its stability is then studied. Subsequently, a design criterion is proposed for jump avoidance, which is caused by the saddle-node bifurcation. Also, parametric studies are carried out to illustrate effects of design parameters for the end-stop on the isolation performance at primary resonance, including responses of the relative displacement and the absolute acceleration. The results show that with dynamic parameters properly designed by using viscoelastic end-stops, the relative displacement response can be effectively suppressed and the jump can be eliminated for both hardening and softening primary isolators. Besides, the end-stop can effectively attenuate the absolute acceleration response for a hardening primary isolator, while more damping is needed to attenuate that for a softening primary isolator, although the degree of the softening nonlinearity is mitigated. It is suggested that a moderate stiffness compared to that of the primary isolator and also a high damping of the end-stop be beneficial to both vibration isolation and jump avoidance under primary resonance conditions.

Intelligent Demand Response Contribution in Frequency Control of Multi-Area Power Systems

Abstract: Frequency control is one of the most important issues in a power system due to increasing size, changing structure and the complexity of interconnected power systems. Increasing economic constraints for power system quality and reliability and high operational costs of generation side controllers have inclined researchers to consider demand response as an alternative for preserving system frequency during off-normal conditions. However, the main obstacle is calculating the accurate amount of load related to the value of disturbances to be manipulated, specifically in a multi-area power system. Dealing with this challenge, this paper makes an attempt to find a solution via monitoring the deviations of tie-line flows. The proposed solution calculates the magnitude of disturbances and simultaneously determines the area where disturbances occurred, to apply demand response exactly to the involved area. To address communication limitations, the impact of demand response delay on the frequency stability is investigated. Furthermore, this paper introduces a fuzzy-PI-based supervisory controller as a coordinator between the demand response and secondary frequency control avoiding large frequency overshoots/undershoots caused by the communication delays. To evaluate the proposed control scheme, simulation studies are carried out on the 10-machine New England test power system.

An Optimal Frequency Control Method Through a Dynamic Load Frequency Control (LFC) Model Incorporating Wind Farm

Abstract: In a high penetrated wind farm power system, wind farms can collaborate to control the power system frequency as like as conventional units. This paper presents a novel model to control the frequency of the wind farm connected to conventional units. Throughout the proposed frequency control, the integral controller, washout filter, and the PID controller could determine the active power variation value in different situations. In fact, a PID controller makes the wind farm aware of power variations. To improve the efficiency of the model, the defined frequency control parameters (i.e., PID coefficients) are optimized based on a multiobjective function using particle swarm optimization algorithm. This study has a unique perspective based on the wind farm collaboration through inertia control, primary frequency control, and supplementary frequency control of the system. A swift power reserve in a stable condition is needed in which wind farm can ameliorate the system frequency response. It is worth saying that the wind farm consists of variable speed turbines, such as a doubly fed induction generator, or a permanent magnet synchronous generator. To assess the performance of the proposed model, it is applied to a typical two-area system and the results are compared.

Small-Signal Stability Analysis of Inverter-Fed Power Systems Using Component Connection Method

Abstract: The small time constants of power electronics devices lead to dynamic couplings with the electromagnetic transients of power networks, and thus complicate the modeling and stability analysis of power-electronics-based power systems. This paper presents a computationally efficient approach to assess the small-signal stability of inverter-fed power systems. The power system is partitioned into individual components, including the power inverters, network impedances, and power loads. The state-space model of individual inverter is first built, where the frequency response and eigenvalue analysis collectively characterize the contributions of different controller parameters to the terminal behavior in a wide frequency range. These component models, together with the network equations, are then algebraically assembled based on the interconnection relations at their terminals. As a consequence, the state matrix of the whole system, which is essential to the system stability analysis, can be reformulated in a computationally efficient way. The experimental results are finally given to validate the effectiveness of the modeling method and system stability analysis.

A Novel Active Power Control Framework for Wind Turbine Generators to Improve Frequency Response

Abstract: Wind generation is expected to reach substantially higher levels of penetration in the near future. With converter interface, the wind unit's rotor inertia is effectively decoupled from the system, causing a reduction in inertial response. Moreover, the replacement of conventional synchronous generators with governors also reduces primary control capability. This paper proposes a novel active power control framework to enable doubly fed induction generator (DFIG) to participate in frequency regulation. The DFIG is controlled in different operating modes with switching among the different modes achieved by modifying reserve input. The DFIG is designed to provide both inertial and primary frequency support considering both underfrequency and overfrequency events. The effectiveness of the proposed control framework is demonstrated through case studies on a 181-bus WECC system with 50% wind penetration.

Forecast System Inertia Condition and Its Impact to Integrate More Renewables

Abstract: The system inertia is the inherent ability of the online synchronous machines to oppose sudden changes in generation or load. With increasing share of non-synchronous generation technologies (e.g., wind and solar generation) system inertia could decrease. One of the options to address system inertia decline is to increase frequency response reserves to achieve a satisfactory frequency control. This letter discusses a new prototype tool developed in Electric Reliability Council to forecast system inertia and to evaluate adequacy of frequency response reserves. The performance of this prototype tool is also evaluated.

Metamaterial beam with embedded nonlinear vibration absorbers

Abstract: In this work the multi-mode vibration absorption capability of a nonlinear metamaterial beam is investigated. A Euler–Bernoulli beam is coupled to a distributed array of nonlinear spring–mass subsystems acting as local resonators/vibration absorbers. The dynamic behavior of the metamaterial beam is first investigated via the classical approach employed for periodic structures by which the frequency stop bands of the single cell are determined. Subsequently, the frequency response is obtained for the metamaterial beam to study a multi-frequency stop band system by adding an array of embedded nonlinear local resonators. A path following technique coupled with a differential evolutionary optimization algorithm is adopted to obtain the optimal frequency-response curves of the metamaterial beam in the nonlinear regime. The use of the local absorbers, via a proper tuning of their constitutive parameters, allows a significant reduction of the metamaterial beam oscillations associated with the lowest three vibration modes.

Fundamental bounds on the operation of Fano nonlinear isolators

Abstract: Nonlinear isolators have attracted significant attention for their ability to break reciprocity and provide isolation without the need of an external bias. A popular approach for the design of such devices is based on Fano resonators, which, due to their sharp frequency response, can lead to very large isolation for moderate input intensities. Here, we show that, independent of their specific implementation, these devices are subject to fundamental bounds on the transmission coefficient in the forward direction versus their quality factor, input power, and nonreciprocal intensity range. Our analysis quantifies a general tradeoff between forward transmission and these metrics, stemming directly from time-reversal symmetry, and that unitary transmission is only possible for vanishing nonreciprocity. Our results also shed light on the operation of resonant nonlinear isolators, reveal their fundamental limitations, and provide indications on how it is possible to design nonlinear isolators with optimal performance.

Design and Implementation of an Optimized 100 kW Stationary Wireless Charging System for EV Battery Recharging

Abstract: This paper presents the design, analyses and implementation of an optimized single stage high power wireless charging system capable of transferring 100 kW at an operating frequency of 22 kHz and a coil-to-coil distance of 5 inches. The detailed design and implementation of the power electronics including the high frequency inverter and rectifier and wireless power transfer coils along with the resonant stage are described. FEA simulation results of the coils and the resonant network analysis are validated by using a Venable frequency response analyzer. Experimental results corresponding to 50 kW operation are presented to validate the design process.

Broadband Terahertz Power Detectors Based on 90-nm Silicon CMOS Transistors With Flat Responsivity Up to 2.2 THz

Abstract: We present broadband high sensitivity terahertz (THz) detectors based on 90 nm CMOS technology with the state-of-the-art performance. The devices are based on bow-tie and log-spiral antenna-coupled field-effect transistors (FETs) for the detection of free-space THz radiation (TeraFETs). We report on optimized performance, which was achieved by employing an in-house developed physics-based model during detector design and thorough device characterization under THz illumination. The implemented detector with bow-tie antenna design exhibits a nearly flat frequency response characteristic up to 2.2 THz with an optical responsivity of 45 mA/W (or 220 V/W). We have determined a minimum optical noise-equivalent power as low as 48 pW/ $\sqrt {\textsf {Hz}}$ at 0.6 THz and 70 pW/ $\sqrt {\textsf {Hz}}$ at 1.5 THz. The results obtained at 1.5 THz are better than the best narrowband TeraFETs reported in the literature at this frequency and only up to a factor of four inferior to the best narrowband devices at 0.6 THz.

Inherent Self-Interference Cancellation for In-Band Full-Duplex Single-Antenna Systems

Abstract: We propose a new analog self-interference cancellation (SIC) technique for in-band full-duplex transmission in single-antenna systems. We use an RF circulator to separate transmitted (Tx) and received (Rx) signals. Instead of estimating the SI signals and subtracting them from the Rx signals, we use the inherent secondary SI signals at the circulator, reflected by the antenna, to cancel the primary SI signals leaked from the Tx port to the Rx port. We modified the frequency response of the secondary SI signals using a reconfigurable impedance mismatched terminal (IMT) circuit, which consists of two varactor diodes at the antenna port. We can also adjust the frequency band and the bandwidth by controlling the varactor diodes bias voltages. The IMT adjustability makes it robust to antenna input impedance variations and fabrication errors. We analyze and fabricate a prototype of the proposed technique at 2.45 GHz. We achieved more than 40-dB cancellation over 65 MHz of bandwidth. Our technique is independent of the RF circulator and antenna type and it can be applied to any frequency band. It is also very relevant to small mobile devices because it provides a simple and low-power and low-cost adjustable analog SIC technique.

π-Splicer: Perceiving Accurate CSI Phases with Commodity WiFi Devices

Abstract: WiFi technology has gained a wide prevalence for not only wireless communication but also pervasive sensing. A wide variety of emerging applications leverage accurate measurements of the Channel State Information (CSI) information obtained from commodity WiFi devices. Due to hardware imperfection of commodity WiFi devices, the frequency response of internal signal processing circuit is mixed with the real channel frequency response in passband, which makes deriving accurate channel frequency response from CSI measurements a challenging task. In this paper, we identify non-negligible non-linear CSI phase errors and report that IQ imbalance is the root source of non-linear CSI phase errors. We conduct intensive analysis on the characteristics of such non-linear errors and find that such errors are prevalent among various WiFi devices. Furthermore, they are rather stable along time and the received signal strength indication (RSSI) but sensitive to frequency bands used between a transmission pair. Based on these key observations, we propose new methods to compensate both non-linear and linear CSI phase errors. We demonstrate the efficacy of the proposed methods by applying them in CSI splicing and indoor distance ranging. Results of extensive real-world experiments indicate that accurate CSI phase measurements can significantly improve the performance of splicing and the stability of the derived power delay profiles (PDPs). Moreover, the estimated distance errors are reduced by 5.7 times on average comparing to the state-of-the-art schemes.

A Simple Planar Dual-Band Bandpass Filter With Multiple Transmission Poles and Zeros

Abstract: A simple and planar design structure for dual-band bandpass filter (BPF) with multiple transmission poles and zeros is proposed in this brief. According to frequency response transformation, two passbands are realized on both sides of the operation frequency. Sharp selectivity and high isolation level with eight transmission poles and seven transmission zeros are achieved just by employing three-section coupled lines and three short-circuit stubs. Besides, the analytical (closed-form) extraction process for the transmission poles and zeros of the proposed dual-band BPF is presented based on the rigorous scattering-parameters theory and the even- and odd-mode analysis method. A prototype for the dual-band BPF with 3-dB fractional bandwidth of 41.1% and 19.0% is designed and fabricated. The measured and simulated results are in good agreement to verify the validity of the proposed design principle.

Optimizing DER Participation in Inertial and Primary-Frequency Response

Abstract: This paper develops an approach to enable the optimal participation of distributed energy resources (DERs) in inertial- and primary-frequency response alongside conventional synchronous generators. Leveraging a reduced-order model description of frequency dynamics, DERs’ synthetic inertias and droop coefficients are designed to meet time-domain performance objectives of frequency overshoot and steady-state regulation. Furthermore, an optimization-based method centered around classical economic dispatch is developed to ensure that DERs share the power injections for inertial- and primary-frequency response in proportion to their power ratings. Simulations for a modified New England test-case system composed of ten synchronous generators and six instances of the IEEE 37-node test feeder with frequency-responsive DERs validate the design strategy.

Thermal Rectification of Integrated Microheaters for Microring Resonators in Silicon Photonics Platform

Abstract: Heating elements are used to tune the optical properties of silicon photonic devices, to stabilize operating temperatures, and to compensate for fabrication variations. In this paper, we characterize the transient thermal response and develop models for silicon photonic devices equipped with such heating mechanisms. To demonstrate the usefulness and practicality of the proposed models, we investigate pulse width modulation (PWM) drive scheme for microheaters and experimentally demonstrate its use in stabilizing microring resonators by digital driving signals (two-level voltage). Requirements on the drive frequency and duty cycle of the PWM signal to minimize optical power penalties owing to the undesired thermal ripples are discussed based on the accurately modeled thermal frequency response of the heater-ring system. It is shown that smaller duty cycles require higher drive frequencies and the maximum optical ripple for a microring resonator occurs at 65% duty cycle.

A comprehensive study of 2:1 internal-resonance-based piezoelectric vibration energy harvesting

Abstract: This work exploits a 2:1 internal resonance mechanism to enhance broadband vibration energy harvesting. It is achieved by adding a properly tuned auxiliary oscillator to the primary energy harvesting oscillator coupled by a nonlinear magnetic force. A theoretical study is conducted on the nonlinear dynamic and energy harvesting performance of the proposed harvester by various analytical approximations, and the accuracy of these analytical models is investigated. Given harmonic base excitation, the output voltage frequency response is derived by the multi-scale method and harmonic balance method (HBM), which are then verified by equivalent circuit simulations and experiments. The necessity of taking into account the zeroth-order harmonic component in the HBM is verified and discussed. The HBM result without this component and the multi-scale method fail to accurately predict the nonlinear dynamic behaviour. With the validated HBM model and the equivalent circuit model, key features of internal resonance are revealed by investigating modal interaction and saturation phenomena under varying excitation. By and large, the operational bandwidth of the vibration energy harvester is enlarged due to the 2:1 internal resonance.

A piezoelectric energy harvester for broadband rotational excitation using buckled beam

Abstract: This paper proposes a rotational energy harvester using a piezoelectric bistable buckled beam to harvest low-speed rotational energy. The proposed harvester consists of a piezoelectric buckled beam with a center magnet, and a rotary magnet pair with opposite magnetic poles mounted on a revolving host. The magnetic plucking is used to harvest the angular kinetic energy of the host. The nonlinear snap-through mechanism is utilized to improve the vibration displacement and output voltage of the piezoelectric layer over a wide rotation frequency range. Theoretical simulation and experimental results show that the proposed energy harvester can yield a stable average output power ranging between 6.91-48.01 μW over a rotation frequency range of 1-14 Hz across a resistance load of 110 kΩ. Furthermore, dual attraction magnets were employed to overcome the suppression phenomenon at higher frequencies, which yields a broadband and flat frequency response over 6-14 Hz with the output power reaching 42.19-65.44 μW, de...

Frequency Response Enhancement of Direct-Detection Phase-Sensitive OTDR by Using Frequency Division Multiplexing

Abstract: The frequency division multiplexing (FDM) technique is first introduced into a direct-detection phase-sensitive OTDR to improve the distributed acoustic sensing performance by using a frequency step sweeping laser source and a dual-pulse heterodyne detection scheme. A raised-cosine-shaped pulse is used to suppress the crosstalk in the FDM technique. By using this technique, a 40-kS/s sampling rate to vibration is realized with a 10-km measurement range, which implies the tradeoff relationship between the frequency response and the measurement range is broken. In the experiment, vibrations with different frequencies are measured to validate the effectiveness of the proposed technique. A 20-kHz frequency response is achieved over a 10-km measurement distance, and the frequency response shows a good flatness with a fluctuation of $\sim$ 0.5 dB.

A New Polarization-Reconfigurable Antenna for 5G Applications

Abstract: This paper presented a new circular polarization reconfigurable antenna for 5G wireless communications. The antenna, containing a semicircular slot, was compact in size and had a good axial ratio and frequency response. Two PIN diode switches controlled the reconfiguration for both the right-hand and left-hand circular polarization. Reconfigurable orthogonal polarizations were achieved by changing the states of the two PIN diode switches, and the reflection coefficient |S11| was maintained, which is a strong benefit of this design. The proposed polarization-reconfigurable antenna was modeled using the Computer Simulation Technology (CST) software. It had a 3.4 GHz resonance frequency in both states of reconfiguration, with a good axial ratio below 1.8 dB, and good gain of 4.8 dBic for both modes of operation. The proposed microstrip antenna was fabricated on an FR-4 substrate with a loss tangent of 0.02, and relative dielectric constant of 4.3. The radiating layer had a maximum size of 18.3 × 18.3 mm2, with 50 Ω coaxial probe feeding.

Flexible Optical Fiber Fabry–Perot Interferometer Based Acoustic and Mechanical Vibration Sensor

Abstract: We have proposed and demonstrated a novel flexible optical fiber Fabry–Perot interferometer (FPI) based vibration sensor with broadband frequency response. The sensor consists of a flexible FP cavity formed by soft splicing using polydimethylsiloxane (PDMS) material with low Young's Modulus and a compact fiber cantilever of low moment inertia as the vibration receiver. Acoustic or mechanical waves experienced by the fiber cantilever can result in obvious change of the FPI cavity length and finally be transduced to the intensity variation of the sensor signal, which makes the sensor highly sensitive to external acoustic or mechanical vibrations. Taking advantage of the superior elasticity of PDMS and compact structure of cantilever, a broadband frequency response for vibration detection has been achieved together with high sensitivity without extra external vibration receiver. The vibration detection is theoretically analyzed, and acoustic vibrations up to 20 kHz and damped mechanical vibrations from tens of hertz to tens of kilohertz, covering both the sound and part of ultrasound range, have been experimentally detected. Moreover, each event of the ball hitting and rebounding has been accurately identified by our sensor, showing excellent vibration sensing only by a thin optical fiber. We believe such a broadband, compact and cost-effective sensor would be a promising candidate for monitoring both acoustic and mechanical vibrations.

WAMS Based Intelligent Under Frequency Load Shedding Considering Online Disturbance Estimation

Abstract: The use of wide area measurements at a central monitoring and control center has brought greater flexibility in the monitoring, control and protection of modern power systems. Under frequency load shedding (UFLS) is one of the many areas experiencing the advantages involved with using wide area measurement systems (WAMS). Conventional UFLS techniques follow a pre-set and rigid threshold of frequency to shed loads at dedicated load buses in the network without considering the magnitude of the disturbance. In this paper, based on the wide area phasor measurements, the actual disturbance in the system is determined a few seconds before performing load shedding. Time domain simulations on an analytic system frequency response model of wide area power system verify the efficiency of the proposed method.