For renewable energy penetration, a frequency control strategy is proposed to assure the multi-area hybrid power system stable operation. The load frequency control (LFC) and the battery energy ...storage system (BESS) are used together to design the frequency control strategy. Furthermore, in order to improve the control accuracy and reduce the battery capacity, the area control error and active power disturbance are divided into low-frequency components and high-frequency components. Therefore, LFC is designed by using sliding mode algorithm for the low-frequency deviation and BESS is adjusted by using the designed disturbance observer for the high-frequency disturbance. Finally, the effectiveness of the proposed frequency control strategy is proved by the real-time digital simulator which can optimise the frequency quality and reduces the capacity of the BESS.
In this study, a Koch snowflake frequency reconfigurable antenna for wideband applications is presented including experimental verification. The frequency reconfigurable approach is obtained for UHF ...band using RF PIN diodes, lumped capacitor and inductors. Proposed antenna is compact, therefore, it can be used as an array element. It has three measured frequency bands. These bands are: case I, 3.34– 4.52 GHz (30%); case II, 2.2–3.4 GHz (43%); and case III, 1.45–4.1 GHz (95.49%). In cases I and II, two different bands are obtained and case III covers almost the frequency band of case I and case II. Thus, the impedance bandwidth of the proposed antenna provides continuous wideband frequency coverage from 1.45 to 4.52 GHz (103%). In addition, the measurements are carried out to validate the performance of the antenna. The proposed antenna has good agreement between simulated and measured results with reasonably low cross polarisation.
A microwave frequency divider based on an optically injected semiconductor laser is presented. It has a very simple structure as it only requires an optical circulator and a DFB laser in a ...conventional microwave photonic link. Period-two oscillation in the DFB laser, introduced by injecting an RF modulated optical signal into the DFB laser, generates optical frequency components with half of the input RF signal frequency separation. Beating of these optical frequency components at the photodetector produces a divide-by-two frequency component. The proposed microwave frequency divider is free of electrical components. It can operate over a wide input RF signal frequency range without the need of altering the system physical configuration. Experimental results demonstrate generation of a 1/2 frequency component for different input RF signal frequencies, by adjusting the forward bias current of a DFB laser.
A frequency domain reflection (FDR) method has been widely used to locate cable defects. Generally, the performance of the FDR method can be enhanced by extending the sweeping frequency range of the ...signal. However, with the increase in the signal frequency, misdiagnosis can easily occur owing to the attenuation of the signal and noise. Thus, this paper's authors propose the upper sweeping frequency (UF) selection method of FDR to improve the accuracy of cable defect location. First, the cable's three-dimensional location spectrum, including the frequency and spatial information, is obtained at a wide frequency range based on short-time Fourier transform with excellent time-frequency aggregation characteristics. Second, the reasonable UF is selected through the energy change characteristics of the cable end. Then, the optimal localization result of the cable defect is calculated by interpolating the sum of energy among the effective frequency bands. Finally, two single-and multi-defect cases are used for the YJV-8.7/10kV XLPE power cable in the experiment to demonstrate the performance of the proposed method. The experimental results show that with the UF selection method, the impact of high-frequency signal attenuation on defect location is eliminated, and cable defect can be localized with more accuracy.
•Built-up steel sections as seismic metamaterial is studied.•Attenuation of surface waves is reported in single and six layered soil medium.•Low frequency wide bandgaps with relative bandwidth ...greater than 1.5 is achieved.•The competency of bandgaps is validated by frequency and time domain analyses.•More than 50% wave signal amplitude reduction is observed.
The purpose of this work is to investigate the propagation of surface waves through periodically arranged built-up steel section (resonator) in single and multiple layered soil medium (substrate) and to study the feasibility of surface waves attenuation by finite element technique. Two types of simple and small geometric size built-up sections are taken into consideration. Due to occurrence of local resonance between resonator and surface waves propagating on the surface of semi-infinite substrate, low frequency wide bandgaps are reported. Generation of local resonance is mainly governed by (i) impedance mismatch between the resonator and substrate (ii) coupling of longitudinal resonance modes of resonator with surface waves propagating on the surface of semi-infinite substrate. To have a more general and realistic study, surface wave propagation in single and six-layered soil medium is considered and the bandgaps are compared. Furthermore, with the variation in geometrical configuration of built-up section and change in material properties (soil profile), bandgap width and location changes. In the case of a layered soil medium, a relative bandwidth greater than 1.5 for both types of resonator is achieved. This implies that the proposed built-up sections are capable of attenuating surface waves in an extremely low frequency range. The position and width of bandgaps are further validated through finite unit cell based frequency response and time transient analyses. The findings substantiate the infinite unit cell model proposed here with the conclusion of more than 50% reduction in surface wave amplitude. The feasibility study manifests that the built-up structural steel sections can be applied as resonant barriers for mitigating seismic waves to protect important civil infrastructures from earthquake hazards.
Frequency-Domain Digital Predistortion for OFDM Brihuega, Alberto; Anttila, Lauri; Valkama, Mikko
IEEE microwave and wireless components letters,
06/2021, Letnik:
31, Številka:
6
Journal Article
Recenzirano
In this letter, a novel frequency-domain (FD) digital predistortion (DPD) solution for orthogonal frequency division multiplexing (OFDM) transmitters (TXs) is proposed. The proposed approach allows ...to flexibly control the linearization performance, in FD, such that different degrees of linearization can be provided at different parts of the spectrum. Such a feature can be of special interest in the millimeter-wave (mmWave) bands, where the inband signal quality requirements can limit the feasible TX power, while also varying across the active subcarriers due to frequency multiplexing of different users with different modulation and coding schemes. The performance of the proposed FD DPD is demonstrated and validated through over-the-air (OTA) measurements on a 64-element phased-array operating at 28-GHz carrier frequency.
Fixing the frequency of the orthogonal signal generator is a classic way to improve the stability and dynamics of single-phase phase/frequency-locked loops (PLL/FLL). However, they exhibit undesired ...oscillation and bias under the fastly-time-variant frequency of low-inertia grids. It is very difficult to improve due to the absence of an internal model principle when this frequency-fixed property is still maintained. This paper aims to address the above challenge, and a typical orthogonal signal generator based on a second-order generalized integrator (SOGI) is researched. Firstly, it reveals that the frequency-fixed implementation inherently induces inaccuracies of the orthogonal signals generated by SOGI for two factors. One is the additional frequency offset, and the other is that the orthogonal signal is not achieved even when the amplitude is compensated. Then, these factors are considered in the PLL/FLL to interpret the problem of undesired estimation performance. The interpreted problem must be solved by the frequency derivative rather than the frequency itself. A frequency-derivative-adaptive loop is, thus, developed while maintaining the frequency-fixed property of SOGI. The loop analysis is further given to obtain the stabilization conditions and parameters design guidelines. Finally, comparative tests validate the improvement in estimating the voltage parameters under time-variant frequency and its potential merits for weak-grid-following inverters with inertia emulation.
Distributed injection-locked frequency division is introduced as a method to increase the locking range beyond that of conventional injection-locked frequency dividers. It is analytically shown that ...continuous frequency division can be achieved over a frequency range that spans over multiples of the self-oscillation frequency of the core divider. Design techniques in millimeter-waves are discussed in detail. A proof-of-concept prototype, realized in a foundry 130-nm BiCMOS SiGe HBT technology, achieves a measured locking range of 35-44 and 41-59.5 GHz while consuming 3.8 mW from a 1.15-V supply.
Empirical results are presented for a novel hexa-band coplanar waveguide (CPW)-fed antenna that consists of three asymmetric fork-shaped radiating elements incorporating U-shaped radiators with a ...slit. Each of the three branched radiators generates triple resonant frequencies within the L, S, C and X bands. U-shaped elements with a slit contribute toward generating resonant frequencies at lower band of the antenna. The asymmetrical fork-shaped elements enhance the impedance matching properties of the antenna and reduce its stopband. The proposed antenna design resonates at 1.3, 1.75, 3.35, 4.85, 6.5 and 7.6 GHz that covers the following wireless communications standards: global system for mobile communications (GSM) (880–960 MHz), digital cellular system (DCS) (1.71–1.88 GHz), personal communication system (PCS) (1.85–1.99 GHz), Bluetooth (2.402–2.480 GHz), wireless local area network (2.4/5.2/5.8 GHz), worldwide interoperability for microwave access (2.3–2.4/2.496–2.690/3.3–3.8 GHz), wireless fidelity (2.412–2.4835/4.9–5.9 GHz). A prototype hexa-band antenna was fabricated and tested. The measured results conform to the simulated ones. The proposed antenna essentially radiates omnidirectionally in both the E and H planes with a peak gain of 5.27 dBi and efficiency of 81.3% at 4.85 GHz. The antenna has dimensions of 35 × 26 mm2. The antenna is an excellent candidate for multiband and broadband communication applications.
To solve frequency stability problems caused by the high-power loss of ultra-high voltage faults and the high penetration levels of renewable energy, a method of active frequency response (AFR) based ...on model predictive control (MPC) for bulk power system is proposed. On the basis of the time-space distribution characteristics of the frequency in power system, a control framework of AFR is built, in which the frequency response control is transformed from decentralized feedback control to centralized feedforward control, and the theoretical basis for the coordination and optimization of multiple frequency regulation means is provided. By using MPC, not only the control hysteresis problems caused by the existing frequency response delay are overcome, but also the regulation characteristics of types of frequency regulation means and the operation constrains of power system are comprehensively considered. Furthermore, on the premise of ensuring system operation safety, the frequency response capability of power system is fully utilized. The analysis and simulation results for a two-area interconnected power system with multiple sources and a real large scale power system show that the proposed method is feasible and effective.
