Effect Of Frequency Modulation Research Articles

Research on active participation of distributed photovoltsics in power grid primary frequency control strategy

Distributed photovoltaic systems can actively contribute to the primary frequency regulation of the power grid by reserving capacity. Traditional power reduction methods often employ fixed load reduction ratios, potentially resulting in inadequate frequency regulation capacity and unnecessary reserve power. This paper centers on optimizing power reserve control, starting with the construction of a two-stage model for a photovoltaic grid-connected inverter power generation system. It includes the design of a maximum power estimation method and the implementation of photovoltaic power reduction operation. The article proposes a strategy to utilize photovoltaic backup capacity for achieving primary frequency modulation effects in a short time scale. Additionally, it adopts a variable power reserve ratio operation strategy over the long term, aiming to enhance photovoltaic power generation and optimize solar energy utilization without compromising the grid’s frequency and quality. Finally, a MATLAB/Simulink model is developed to validate the effectiveness of the control strategy. Simulation results indicate that the proposed strategy satisfies frequency regulation requirements, enhances power generation efficiency, and improves the economic viability of photovoltaic operations.

Change in Frequency Modulation of Electroencephalographic Activity in Imaginary and Real Limb Movement

INTRODUCTION: Investigation of electroencephalographic activity as a marker of cognitive processes in the brain traditionally focuses on the analysis in the frequency domain considering rhythms of encephalogram (EEG) as potential carriers of information needed for research. At the same time, analysis of the EEG frequency modulation effects requires improvement of approaches in the field of digital signal processing. Taking into account the fact that frequency modulation of EEG, as well as amplitude modulation, can be a marker of a number of states, it seems promising to develop a method for detecting this phenomenon and using it to evaluate a number of parameters of the brain dynamics associated with biological feedback systems. AIM: To evaluate the phenomena of frequency modulation when the user performs tasks associated with the control of external devices based on the brain–computer interface, implemented in the phenomena of electrical activity in the motor cortex area.
 MATERIALS AND METHODS: To obtain the data, a group of thirty volunteers of both genders aged 17 to 23 years was formed. The participants of the experiment had to execute four commands and repeat them in an unknown order set by the program. The experiment was conducted in two ways: physically and mentally. That is, in the first method, each command corresponded to a certain movement of a person, in the second — the same commands were executed in imagination, the movement was imagined mentally. The command was considered successfully executed if the volunteer managed to repeat and hold the position set by the program for two seconds.
 RESULTS: Based on the developed method for evaluating the frequency modulation of the EEG, the dynamics of the electrical activity of the brain was studied in the range of 9 Hz to 12 Hz when a user was performing real and imaginary movements. A comparative analysis showed that the differences were mostly recorded in the condition when the subject did not achieve the goal. At the same time, the differences to a greater extent were observed in the experiments where the subject had to make real, rather than imaginary movements. The significant differences between low- and high-frequency modulations were associated with the inability for the user to generate the requested command, which he could see by the biofeedback mechanism. It has been established that the greater the number of high-frequency restructures observed on the EEG, the smaller number of low-frequency restructures occur at the same epoch of analysis.
 CONCLUSION: The results obtained considerably expand the understanding of the mechanisms of frequency modulation of the EEG. In general, the methods and algorithms underlying the analysis that permitted their identification can be used to solve a wide range of tasks related to processing of EEG signals, including improvement of methods for detecting user errors by EEG when controlling brain-computer interface devices.

An Emergency Coordinated Control Strategy to Improve the Transient Stability of a Single-Ended Distribution Network with Flexible Interconnection Channel Blocking.

Based on the scenario of high-penetration distributed photovoltaic connected to an AC/DC distribution network, this paper analyzes the dynamic characteristics of frequency and voltage in a distribution network after the blocking failure of the flexible interconnection channel. In order to enhance the transient stability of the system after the fault, this paper comprehensively considers the active regulation ability of photovoltaic units, and puts forward an emergency coordinated control strategy for a single-ended distribution network with flexible interconnection channel blocking. Firstly, the non-fault channel is overloaded for a short time, then the comprehensive influence of factors such as electrical distance, response time and adjustment cost on the frequency modulation effect of the system is quantitatively evaluated; according to the evaluation results, the photovoltaic and synchronous units are controlled by "control instead of tripping", and finally, the high-frequency tripping is carried out, based on the principle of "photovoltaics first". After the frequency control is completed, the reactive power optimization model of the system is established, and the improved tabu-particle swarm optimization algorithm is used to solve it, so as to optimize the voltage of the distribution network nodes. Finally, an equivalent simulation model is established to verify the coordinated control strategy.

Simulation of Secondary Frequency Modulation Process of Wind Power with Auxiliary of Flywheel Energy Storage

With the rapid increase in the proportion of wind power, the frequency stability problem of power system is becoming increasingly serious. Based on MATLAB/Simulink simulation, the role and effect of secondary frequency modulation assisted by Flywheel Energy Storage System (FESS) in regional power grid with certain wind power penetration rates are studied. First, the linear frequency control of the power system is used to establish the primary frequency modulation control model of FESS assisting wind power, and the frequency characteristics of FESS participating in primary frequency modulation are analyzed according to the transfer function. Then, in the case of step disturbance and continuous disturbance of load power, the frequency characteristics of a regional power grid are simulated and demonstrated through time domain simulation, and conclusions are drawn through comparison; a certain proportion of FESS can quickly respond to the frequency deviation signal. During secondary frequency modulation simulation, the maximum frequency deviation of the system is reduced by 57.1% and the frequency fluctuation range is reduced by 53.8%, effectively improving the frequency quality of the power grid.

Modality-dependent distortion effects of temporal frequency on time perception.

Time perception has been known to depend on the temporal frequency of the stimulus. Previously, the effect of temporal frequency modulation was assumed to be monotonically lengthening or shortening. However, this study shows that temporal frequency affects time perception in a non-monotonic and modality-dependent manner. Four experiments investigated the time distortion effects induced by modulation of temporal frequency across auditory and visual modalities. Critically, the temporal frequency was parametrically manipulated across four levels (steady stimulus, 10-, 20-, and 30/40-Hz intermittent auditory/visual stimulus). Experiment 1, 2, and 3 consistently showed that a 10-Hz auditory stimulus was perceived as shorter than a steady auditory stimulus. Meanwhile, as the temporal frequency increased, the perceived duration of the intermittent auditory stimulus was lengthened. A 40-Hz auditory stimulus was perceived as longer than a 10- Hz auditory stimulus, but did not differ significantly from a steady one. Experiment 4 showed that, for the visual modality, a 10-Hz visual stimulus was perceived as longer than a steady stimulus, and the perceived duration was lengthened as temporal frequency increased. This study demonstrated that within the scope of the temporal frequencies examined in this study, there were differential distortion effects observed across sensory modalities.

Forced vortex merging and splitting events in ferrofluidic Couette flow

Time-dependent boundary conditions are ubiquitous in numerous natural and industrial flows. However, to date, the influence of such temporal modulations has been given minor attention. This research addresses ferrofluidic Couette flow in between co-rotating cylinders in a spatially homogeneous magnetic field subject to time-periodic modulation. Using a modified Niklas approximation, we study the effect of amplitude and frequency modulation onto the transition scenarios between different toroidal flow structures, non-propagating vortex (nV) states, via vortex merging and splitting. Thereby, the system response appears to be quite sensitive/dependent on the driving frequency ΩH, which can cause a notable “delay” in the system response. Further, as a result of the inertia of the ferrofluid, resisting the fast-changing accelerating Kelvin force, new, temporal nV states appear within an alternating field. These states are unstable under static fields. Finally, we show that within the same nV state, while keeping similar flow dynamics, large discrepancies in angular momentum and torque can be observed.

Investigation of the multiple characteristics of the self-mixing effect subject to a single particle.

As a compact interferometry technique, self-mixing interferometry (SMI) is a promising tool for micro particle detection in biochemical analysis and the monitoring of laser manufacturing processing, and currently SMI based micro particle detection is attracting increasing attention. However, unlike the typical displacement or vibration measurement driven by a macro target, only a small amount of literature has targeted the SMI effect induced by a single micro moving particle. In this paper, two numerical models were investigated to describe the characteristics of the signal sparked by individual particle. We compared the measurement results with the two models' simulations in three signal characteristic aspects: the temporal waveform, frequency spectrum, and phase profile. From these results, we established that both amplitude modulation and frequency modulation effects apply under different conditions in the self-mixing process. And for the first time, we analyzed the effect of the laser illumination spot size on the particle-induced SMI signal features with two optical arrangements. When the laser beam size is larger than the particle size, the signal bursts are likely to result from frequency modulation, and vice versa. Our results can improve the capability of SMI technology in particle size discrimination and particle sorting.

Ferrofluidic wavy Taylor vortices under alternating magnetic field.

Many natural and industrial flows are subject to time-dependent boundary conditions and temporal modulations (e.g. driving frequency), which significantly modify the dynamics compared with their static counterparts. The present problem addresses ferrofluidic wavy vortex flow in Taylor-Couette geometry, with the outer cylinder at rest in a spatially homogeneous magnetic field subject to an alternating modulation. Using a modified Niklas approximation, the effect of frequency modulation on nonlinear flow dynamics and appearing resonance phenomena are investigated in the context of either period doubling or inverse period doubling. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)'.

Energy storage economy research and sensitivity analysis applied to photovoltaic primary frequency modulation scenario

In practical engineering applications, the investment, income, subsidies and other costs of energy storage batteries have a certain impact on the overall economic benefits of primary frequency modulation. The larger the capacity of the configured battery energy storage system, the better the primary frequency modulation effect will be, but at the same time, the problem is that the cost of investment in the energy storage system will increase, which will offset the benefits of primary frequency modulation loss reduction of its auxiliary photovoltaic station from an economic perspective. Therefore, this paper will clarify the benefits and costs of the primary frequency modulation application environment of the energy storage system, and establish an economic analysis model from delaying the investment of photovoltaic station equipment, reducing the cost of light waste, environmental benefits, direct benefits, government subsidies, energy storage investment costs and other aspects. Finally, a photovoltaic station is taken as an example to simulate and analyse the sensitivity.

A Hybrid Multistep Procedure for the Vibroacoustic Simulation of Noise Emission from Wind Turbines

This paper proposes an efficient hybrid analytical-computational approach for the simulation of mechanical vibrations and sound radiation in wind turbine drive trains.The computational procedure encompasses the detailed modeling of vibrational sources and structural sound paths as well as the major panels of airborne noise radiation. The angle-varying mesh stiffness is obtained from a series of quasi-static finite element simulations. A novel procedure is proposed to obtain the time-varying mesh stiffness at fluctuating speed. The varying mesh stiffness is introduced as a parametric excitation in an analytical gear model, and the Fourier-transformed results are used as vibrational sources in a finite-element-based harmonic response analysis of the drive train. The present paper focuses on the modeling of gear contact and gearbox vibrations. The models and procedures are outlined, and computational results are compared to physical measurements on a 2.5 MW wind turbine. The results are in good qualitative agreement at tonal frequencies. This is particularly the case at fluctuating speed, where both the simulation and the measurement show the characteristic effect of frequency modulation. The computational procedure has been expanded to the whole drive train and is effectively applied in the conception and evaluation of design measures for the reduction of tonal amplitudes.

The effect of time-varying operating condition on the crack induced impulses and its application to gearbox tooth crack diagnosis

Gearbox tooth crack diagnosis under Time-Varying Operating Conditions (TVOC) is a challenging issue. TVOC induce both Amplitude Modulation (AM) and Frequency Modulation (FM) effects into gearbox vibration signals, which results in difficulties in tooth crack diagnosis. To overcome this problem, the TVOC-induced AM and FM effects on vibration signals of gearboxes with tooth cracks need to be well studied. Many studies have been reported to investigate the influence of TVOC on gearbox vibration signals using dynamic modelling, some of which only focused on healthy gearboxes while others only considered piecewise constant operating conditions, failing to make comprehensive analyses involving both tooth cracks and TVOC. This paper aims to conduct a comprehensive study on how TVOC affect vibration signals of gearboxes with tooth cracks using dynamic simulation. Firstly, gear tooth mesh stiffness is evaluated considering both tooth crack severity progression and operating condition variations, through which gearbox vibration responses are generated under TVOC. A signal analysis procedure is proposed with its focus placed on the Crack Induced Impulses (CII), which are extracted from gearbox vibration signals using the adaptive harmonic decomposition method or its modified version. Envelope analysis is conducted on the CII to study how the CII are affected by TVOC, and a linear dependence of the AM effect of the CII on TVOC is identified. Based on the identified linear dependence, a novel Condition Indicator (CI), which is sensitive to crack growth while insensitive to operating condition variations, is proposed to track tooth crack severity progression under TVOC. The linear dependence of the AM effect of the CII on TVOC and the effectiveness of the proposed CI for tooth crack diagnosis are demonstrated using both simulated gearbox vibration signals and experimental gearbox vibration datasets.

Energy and Frequency Characteristics of Microseismic Particles in a Complex Geological Model

AbstractThis study aims to better understand the energy–frequency characteristics of microseismic wave propagation by monitoring particles in complex geology. Artificial seismic source experiments are conducted using a complex geological model, and variational mode decomposition method is applied to process the microseismic signals, obtain reconstructed microseismic signals and decomposition modes, and calculate the microseismic particle input energy and signal energy at each measurement point. Computations derived from the Sadoff empirical formula are used to evaluate the attenuation of the microseismic particle input energy with the propagation distance. The relationships between microseismic wave center frequency and energy and between the microseismic particle input energy and microseismic signal energy are elucidated. The results show that the microseismic particle input energy follows a power exponential decay trend with increasing propagation distance; the values and distributions of the microseismic particle input energy and signal energy conform to a Gaussian trend in the frequency domain; various geological structures and combinations thereof impose frequency modulation effects on the microseismic wave, where the frequency modulation interval depends on the microseismic waves across the different interfaces; and the linear slope describing the relationship between microseismic particle input energy and signal energy can reflect the microseismic wave propagation state.

Room temperature DNP of diamond powder using frequency modulation

Dynamic nuclear polarization (DNP) is a method of enhancing NMR signals via the transfer of polarization from electron spins to nuclear spins using microwave (MW) irradiation. In most cases, monochromatic continuous-wave (MCW) MW irradiation is used. Recently, several groups have shown that frequency modulation of the MW irradiation can result in an additional increase in DNP enhancement above that obtained with MCW. The effect of frequency modulation on the solid effect (SE) and the cross effect (CE) has previously been studied using the stable organic radical 4-hydroxy TEMPO (TEMPOL) at temperatures under 20 K. Here, in addition to the SE and CE, we discuss the effect of frequency modulation on the Overhauser effect (OE) and the truncated CE (tCE) in the room-temperature 13C-DNP of diamond powders. We recently showed that diamond powders can exhibit multiple DNP mechanisms simultaneously due to the heterogeneity of P1 (substitutional nitrogen) environments within diamond crystallites. We explore how the two parameters that define the frequency modulation: (i) the Modulation frequency, fm (how fast the microwave frequency is varied) and (ii) the Modulation amplitude, Δω (the magnitude of the change in microwave frequency) influence the enhancement obtained via each mechanism. Frequency modulation during DNP not only allows us to improve DNP enhancement, but also gives us a way to control which DNP mechanism is most active. By choosing the appropriate modulation parameters, we can selectively enhance some mechanisms while simultaneously suppressing others.

Stepwise inertial intelligent control for wind power frequency support based on modified stacked denoising autoencoder

Due to the large-scale popularization of renewable energy, the rotational inertia of modern power system is reduced, which increases the risk of power system failure and power outage when disturbance events occur. The wind turbine (WT) must be involved in frequency control to respond to power imbalance in the grid when it is detected. Stepwise inertial control (SIC) is one of the important frequency modulation strategies, but it will bring about secondary frequency drop (SFD). In order to minimize SFD while ensuring excellent frequency modulation effect, it is necessary to solve the optimal parameters of SIC, and the traditional method is very time-consuming to solve the parameters in different scenarios. In order to obtain the parameters quickly and accurately when the disturbance events occur, a stepwise inertial control of frequency modulation for wind power based on modified stacked denoising autoencoder is proposed in this paper. First, the sparrow search algorithm is used to obtain the required data. Then, the network model of the modified stacked denoising autoencoder is constructed. The “pre-training, fine-tuning” method is used to train the network parameters, and the Adamax optimization method is introduced to fine-tune the network parameters, which improves the training effect. Finally, the optimal SIC parameters are predicted by adding the scene data into the model. The proposed method is tested in IEEE 9 bus test system. Compared with the traditional method, the proposed method has faster computing speed, excellent prediction accuracy and generalization ability.

A Novel Vibration Model for Explanation of the Frequency Features in Multistage Wind Turbine Gearboxes Considering the Effects of Inter-stage Meshing Frequency Modulation

A Novel Vibration Model for Explanation of the Frequency Features in Multistage Wind Turbine Gearboxes Considering the Effects of Inter-stage Meshing Frequency Modulation

Design and Optimization of Laser Processing Control System and Process Parameters for Micro Crystal Resonator Frequency Modulation

The adjustment of the natural frequency of a micro crystal resonator (MCR) is the key requirement in its manufacturing, which determines the actual performance of the product. Laser processing is a new method for MCR frequency modulation, and its process parameters directly affect the frequency modulation effect. Aiming at the laser processing equipment for MCR frequency modulation, the structure of the laser processing control system for MCR frequency modulation is designed by analyzing the requirements of a laser processing control system. The working flow of the laser processing control system for MCR frequency modulation is studied, the motion control method of the laser processing platform for MCR frequency modulation is proposed, and the laser processing control system for MCR frequency modulation is designed. By analyzing the laser characteristics for MCR frequency modulation, an orthogonal experiment is carried out to optimize the laser processing parameters for MCR frequency modulation.

Structural Modifications and Electromagnetic Property Regulations of Ti3AlC2 MAX for Enhancing Microwave Absorption through the Strategy of Fe Doping

AbstractMicrowave absorption enhancements through atomic doping in traditional materials remain a significant challenge. Herein, the MAX phase materials of Fe‐doped Ti3AlC2 (xFe‐Ti3AlC2, abbreviated as TFAC‐x, x = 0, 0.2, 0.3, 0.4) are synthesized via solid‐phase reaction method. The X‐ray diffraction, Raman, and scanning electron microscopy confirm that the TFAC‐x samples are of high quality with multiphase coexistence structure and abundant interfaces. Relying on the improved impedance matching originating from structural modulation, the synergistic effects of dielectric loss and magnetic loss, as well as the enhanced interfacial polarization and defect dipole polarization, both the microwave absorption intensity and bandwidth are greatly strengthened. Accordingly, the minimum reflection loss of TFAC‐3 sample can achieve ‐33.3 dB and the absorption bandwidth could reach 3.9 GHz with the thickness of only 1.5 mm. Moreover, the investigated frequency can cover 86% through regulating their thickness from 1.5 to 5 mm, showing the excellent frequency modulation effect. The revealed improvements in both the microwave absorption performance and properties of TFAC‐x may enlighten the designing of microwave absorption materials and have potentials for widespread applications.

Echo spectrum modulation characteristics of plasma flow field simulated by wind tunnel

<sec>When the aircraft moves through the atmosphere at a very high speed, the aircraft will experience intense friction with the surrounding atmosphere, which causes the air to be ionized into plasma, thus producing a plasma flow field around it. Plasma is constantly generated on the windward side of the aircraft and flows backwards. The velocity of plasma is different from that of the aircraft. In addition to the dispersion characteristics of the plasma and the non-uniform distribution around the target, the plasma flow field will produce the effects of amplitude, frequency and phase modulation on the incident radar wave, which will change the electromagnetic scattering characteristics of the target. </sec><sec>In order to reproduce the non-uniform Doppler phenomenon in the flow field under electromagnetic wave irradiation, the plasma echo spectrum is measured experimentally in the JF-10 wind tunnel of the Institute of Mechanics, the Chinese Academy of Sciences. The echo spectrum data of S band and C band are obtained by using a measurement system composed of signal source, circulator, antenna and spectrometer, and based on the measured data the one-dimensional range profile of the plasma coated target is simulated, and the results show that the plasma flow field has a spectrum modulation effect on the target. When the speed of the flow field cannot be compensated for accurately, the spectral modulation effect will further cause the one-dimensional range profile to defocus, which will affect the ability of radar to detect and track the object. The preliminary analysis shows that the effect is caused mainly by the inhomogeneous velocity distribution of plasma flow field and the sudden change of medium parameters when the shock wave arrives. This experiment can provide data support for verifying the electromagnetic characteristics modeling method of plasma flow field. </sec>

Normalization of gearbox vibration signal for tooth crack diagnosis under variable speed conditions

AbstractVariable speed conditions introduce Amplitude Modulation (AM) and Frequency Modulation (FM) effects into gearbox vibration signals, which makes it difficult to distinguish between changes of tooth crack severity and speed changes. To overcome this problem, the AM and FM effects caused by speed variation need to be removed. Order tracking techniques are used to remove the FM effect. Some methods have been reported to reduce the AM effect. However, they attenuated crack information since they focused on the entire vibration signal. Besides, the performance of the reported methods on removing the AM effect was not quantitatively evaluated. In this study, a novel normalization method focusing on the Crack Induced Impulses (CII) is proposed to remove the AM effect without attenuating the tooth crack information. A modified Adaptive Chirp Mode Decomposition method is developed to obtain the CII under variable speed conditions. The peak envelope of the CII is determined using spline interpolation of its envelope peaks and is employed to remove the AM effect of the CII by normalization. Two metrics are introduced to quantitatively evaluate the performance of the proposed normalization method on removing the AM effect and preserving the tooth crack information. The effectiveness of the proposed normalization method is demonstrated using simulated gearbox signals and experimental gearbox datasets. The proposed method benefits tracking tooth crack severity progression under variable speed conditions.

Frequency-Modulated MEMS Gyroscopes: A Review

As a high-precision angular rate sensor, the Frequency-Modulated (FM) gyroscope based on MEMS craft has attracted more and more attention in recent years, owing to its advantages in low power consumption, low temperature sensitivity, very high bandwidth, and excellent scale factor stability. This review summaries the history and latest development of the FM gyroscope research. The theory of the frequency modulation effect of the Coriolis coupling is provided based on the method of rotating wave approximation in a systematic and explicit way. Typical FM gyroscope operation modes, such as QFM, IFM, LFM, and their working principles are introduced minutely. The error sources of FM gyroscopes, and the characters comparison between FM and AM gyroscopes are discussed in detail as well.