Fast Frequency Research Articles

Concise and Compatible MOR-Based Self-Adjoint EM Sensitivity Analysis for Fast Frequency Sweep

It is of great significance to perform adjoint electromagnetic (EM) sensitivity analysis when designing or optimizing a microwave component. Recent advances in adjoint EM sensitivity analysis using a fast frequency sweep have gained a considerable speedup over that using discrete frequency sweep. However, it needs complex computational loops for calculating the adjoint vectors, resulting in extra time for an increased number of forward/backward (F/B) substitutions of the original system matrix along with additional large matrix multiplications. The proposed method addresses this situation and proposes a novel model order reduction (MOR)-based self-adjoint EM sensitivity analysis for a fast frequency sweep. This method derives more concise and more compatible formulations for calculating adjoint sensitivities to decrease the number of F/B substitutions and matrix multiplications. The proposed method subsequently develops a new self-adjoint EM sensitivity analysis algorithm for a fast frequency sweep which further decreases half of the number of F/B substitutions. Compared with the existing adjoint sensitivity method for a fast frequency sweep, the technique we proposed can take less time due to the more concise sensitivity formulations while additionally obtaining better sensitivity accuracy in a relatively wide frequency range, especially when a higher MOR order is needed. Besides, the self-adjoint EM sensitivity analysis formulation can be compatible with various MOR techniques. Two EM examples of microwave components are used to demonstrate the proposed technique.

Dynamic Virtual Power Plant Design for Fast Frequency Reserves: Coordinating Hydro and Wind

To ensure frequency stability in future low-inertia power grids, fast ancillary services such as fast frequency reserves (FFR) have been proposed. In this work, the coordination of conventional (slow) frequency containment reserves (FCR) with FFR is treated as a decentralized model matching problem. The design results in a dynamic virtual power plant (DVPP) whose aggregated output fulfills the system operator’s (SO’s) requirements in all time scales, while accounting for the capacity and bandwidth limitation of participating devices. This is illustrated in a 5-machine representation of the Nordic synchronous grid. In the Nordic grid, stability issues and bandwidth limitations associated with non-minimum phase zeros of hydropower is a well-known problem. By simulating the disconnection of a 1400 MW importing dc link, it is shown that the proposed DVPP design allows for coordinating fast FFR from wind, with slow FCR from hydro, while respecting dynamic limitations of all participating devices. The SO’s requirements are fulfilled in a realistic low-inertia scenario without the need to install battery storage or to waste wind energy by curtailing the wind turbines.

The role of hydrogen electrolysers in frequency related ancillary services: A case study in the Iberian Peninsula up to 2040

This paper investigates the contribution of hydrogen electrolysers (HEs) for frequency related Ancillary Services (AS), namely Frequency Containment Reserve (FCR), Synthetic Inertia (SI) and Fast Frequency Response (FFR) in future operation scenarios in the Iberian Peninsula (IP) considering low system inertia. The proposed framework for analysis consists of a dynamic model developed in MATLAB/Simulink. Simulations show that an instantaneous inverter based resource (IBR) trip induced by a grid fault may lead to the occurrence of values of Rate of Change of Frequency (RoCoF) close to undesirable thresholds if the FCR is provided solely by the conventional generators. The obtained results illustrate that HEs can outperform conventional generators on the provision of FCR. Furthermore, the FCR is unable to unlock the full potential of fast responding HEs. This suggests the advantage of providing additional AS such as SI or FFR in critical periods. Simulations also show that the benefit of additional AS can be limited in specific conditions, especially depending on the evolution of HEs’ ramping capabilities, but are still a relevant complement to other solutions designed to deal with low inertia in power systems such as synchronous compensators.

Fast Frequency Control Strategy for Direct Drive Wind Turbines Considering the Suppression of Secondary Frequency Drop in the Power Grid

Inertia and damping in the power system are important parameters in frequency regulation and oscillation suppression. Inertia will reduce the rate and amplitude of frequency changes after active power sudden changes. Damping in the system can effectively suppress low-frequency oscillations after grid disturbances. As the penetration rate of wind turbines increases, it will significantly reduce the effective inertia in the power grid and reduce the friendliness of wind power grid connection. To provide better frequency support for the power grid in the event of large disturbances in the power system, this paper proposes a fast frequency control strategy for wind farms that considers the suppression of secondary frequency dips in the power grid. The strategy combines frequency droop control with grid frequency bias control and evaluates the kinetic energy reserve online based on wind power prediction and hourly speed, thus balancing the frequency regulation and suppression of secondary frequency dips in the power grid. A 2.5 MW direct drive wind turbine simulation model was built based on the PSCAD simulation platform, verifying the effectiveness of the proposed comprehensive control strategy.

Design of Energy Storage for Frequency Stability in Low-Inertia Power Grid

Short-term frequency instability is one of the major concerns in power systems with high percentage of converter-interfaced renewable energy sources. Energy storage system (ESS) has proven to be a viable solution for the problem of short-term frequency instability by fast frequency response (FFR). However, the appropriate location, size, and operating strategy of ESS are the main challenges for FFR. Power injection at some buses in large grids may lead to angular separation and instability. In addition, oversizing ESS could lead to huge investments without appropriate returns and under sizing may jeopardizes grid stability. Capacity estimation of ESS for FFR considering the suitable location and overall deployment strategies are missing in the current literature for large power grids. Hence, this research proposes a technique to place and size ESS for better FFR in power grids. The proposed technique consists of two steps. In the first step, a methodology based on frequency dynamic signature (FDS) is developed to identify the most suitable location. In the second step, the required capacity of the ESS is estimated based on a step reduction iterative algorithm (SRIA). SRIA and FDS consider the complete dynamics of power system components that affect the frequency dynamics of the system. The proposed methodology is thoroughly verified for various operating conditions in IEEE 39-bus using DIgSILENT PowerFactory.

Social Ecological Factors for Adolescent Obesity: Using the 2021 Korea Youth Risk Behavior Survey Data

Objectives: This study investigated obesity adolescents in Korean. Methods: This study was a cross-sectional, secondary analysis using the 2021 Korea Youth Risk Behavior Survey data. Among 54,848 adolescents in the raw data, 53,445 adolescents were selected as study participants. Results: It was found that sex, school achievement, fast food intake frequency, sitting time other than weekend learning, and weekend smartphone usage time were important individual factors influencing obesity in adolescents. It was found that school type was community and societal factors influencing obesity in adolescents. Conclusions: It is necessary to develop a obesity education program that considers eating habits, sedentary behavior, smartphone use, and school type of adolescents.

Ultrafine electro-optical frequency comb based on cascade phase modulation with cyclic frequency shifting.

An ultrafine electro-optical frequency comb (EOFC) with plentiful comb teeth is demonstrated. Adopting a single-frequency fiber laser as a light source, cascade phase modulation based on a sinusoidal signal and a frequency-time transformation (FTT) signal is executed to generate the EOFC with high fineness. Meanwhile, a cyclic fast frequency shifting strategy is introduced to boost the number of comb teeth and the bandwidth of the EOFC. As a result, an EOFC with 12600 comb lines covering a broad bandwidth from -6.3 GHz to 6.3 GHz is established, corresponding to an ultrafine comb space of 1 MHz. Moreover, the power fluctuation of a comb tooth is less than 0.5 dBm. This state-of-the-art EOFC has significant potential in the field of precision spectroscopy.

Inertia control method of direct drive permanent magnet wind turbine under high wind power permeability

Direct-drive permanent magnet wind turbine has high power generation efficiency, especially in low wind speed environment, and is widely used for wind power generation. Direct-driven permanent magnet wind turbines show no inertia response to the system through the grid connection of full-power converters, resulting in increased frequency fluctuation, poor response effect and reduced stability time of the system under sudden load and sudden wind speed conditions. Based on this, an inertia control method of direct-drive permanent magnet wind turbine under high wind power penetration is proposed, and the model of direct-drive permanent magnet wind turbine is built by designing functional modules to improve the synchronous control effect under high wind power penetration. The vector control calculation method is used to design the virtual inertia control parameters, and the decoupling quantity is introduced to decouple the parameters with filter inductance, so as to improve the supporting capacity of power grid frequency fluctuation. The simulation results show that the proposed method has a fast frequency response under sudden load change, and it drops to the lowest value of 49.16 Hz at 12.14 s. Under the condition of sudden change of wind speed, the system frequency rises to the highest value of 50.38 Hz at 12.94 s. It is proved that the proposed method has a certain suppression effect on the amplitude of frequency change, effectively shortens the time for the system frequency to return to steady state, and thus has more advantages.

A Fast Resonance Frequency Tracking Method for Photoacoustic Cell Based on the Hybrid Single-Frequency Excitation and FFT

A Fast Resonance Frequency Tracking Method for Photoacoustic Cell Based on the Hybrid Single-Frequency Excitation and FFT

Design and implementation of analog tracking filter for ac signal acquisition

SummaryThis paper presents an analog tracking bandpass filter that is intended to be applied in ac signal acquisition circuits to reduce measurement noise. A fast and accurate frequency tuning technique is developed based on the phase control loop. A complete derivation process is provided to build the mathematical model describing the control loop for the tracking filter. Accordingly, a zero‐crossing detector is designed to accurately extract signal phases in the proposed loop. As a closed‐loop control system, the loop dynamics such as stability, transient response, and steady‐state error are analyzed using the derived model. From both the simulations and measurements, the developed filter is found to provide excellent performance in frequency tracking, noise reduction, and linearity compared to existing work. The maximum and minimum Q value reaches 42.2 and 14, respectively, in the frequency tuning range of 34 to 107 kHz, while the frequency tracking error is less than 1.18% at 100 kHz.

Quantum Antireflection Temporal Coatings: Quantum State Frequency Shifting and Inhibited Thermal Noise Amplification

AbstractThe quantum optical response of antireflection temporal coatings (ATCs), that is, matching temporal layers that suppress the generation of backward waves in temporal boundaries, is investigated. The results reveal that quantum ATCs are characterized for inducing a frequency shift of the quantum state, while preserving all photon statistics intact. Thus, they can find application for fast quantum frequency shifting in photonic quantum networks. The quantum theory also provides additional insight on their classical mode of operation, clarifying which quantities are preserved through the temporal boundary. Last, it is shown that quantum ATCs allow for fast temporal switching without amplification of thermal fields.

Transient power equalization control strategy of virtual synchronous generator in isolated island microgrid with heterogeneous power supply

In the parallel supply system of synchronous generator and virtual synchronous generator, the physical structure and control structure of the two kinds of power supply are quite different, and it is difficult to distribute the transient power of the two kinds of power supply evenly when the load changes abruptly. Especially in the case of sudden load increase, virtual synchronous generator bears too much load in the transient process because of its fast adjustment speed, and even causes short-term overload, which makes the capacity of virtual synchronous generator can not be fully utilized. In view of this problem, firstly, the mechanism of transient power uneven distribution of two heterogeneous power sources is explained from the differences of frequency modulation, voltage regulation and output impedance. Secondly, virtual speed regulation, virtual excitation and dynamic virtual impedance are added to the traditional virtual synchronous generator control to simulate the speed regulation characteristics and electromagnetic transient characteristics of the synchronous generator, so as to realize the transient and steady-state power equalization between heterogeneous power supplies when the virtual synchronous generator and the synchronous generator run in parallel. Thirdly, in order to ensure the fast dynamic response characteristics of the virtual synchronous generator in independent operation mode, the traditional virtual synchronous generator control algorithm is still maintained in independent operation mode, and the mode switching control link based on state tracking is designed to realize smooth switching between the two working modes. Finally, the hardware in loop experiment results based on RT-LAB show that the proposed control method can realize the transient and steady-state power equalization when the virtual synchronous generator and the synchronous generator operate in parallel, it can keep the fast voltage regulation and frequency modulation ability when the virtual synchronous generator operates independently, and can realize smooth switching between independent and parallel operation modes.

Multi-Mode Active Inertia Support Strategy for MMC-HVDC Systems Considering the Constraint of DC Voltage Fluctuations

The Modular Multilevel Converter based High Voltage Direct Current Transmission (MMC-HVDC) systems can provide active inertia support for the connected ac grid for fast frequency recovery. However, the submodule (SM) capacitance voltages will be affected by the transient power flow and there exist dc voltage fluctuation issues during the active inertia support process. This paper proposes a multi-mode active inertia support strategy for MMC-HVDC systems considering the constraint of dc voltage fluctuations. The analytical relationship of dc voltage fluctuations and ac frequency variations when MMC adopts the virtual inertia control is firstly established, and then different inertia support operation modes are divided according to the allowable dc voltage fluctuation ranges. Next, the multi-mode active inertia support strategy for MMC-HVDC is proposed, which can provide flexible active inertia support on the premise of reasonable dc voltage fluctuations according to different frequency variations and recovery requirements. Besides, the inertia support process of MMC is equivalent to the zero-input response of first-order circuit to calculate the maximum sustainable supporting time, which ensures that the dc voltage fluctuation constraint can be well satisfied in different operation modes. Finally, several simulation results verify the effectiveness of the proposed control strategy.

Inverter fast frequency response is a low-cost alternative to system inertia

Inverter fast frequency response is a low-cost alternative to system inertia

Inverter-Fed Motor Drive System: A Systematic Analysis of Condition Monitoring and Practical Diagnostic Techniques

Due to their efficiency and control capabilities, induction motors fed with inverters have become prevalent in various industrial applications. However, ensuring the reliable operation of the motor and diagnosing faults on time are crucial for preventing unexpected failures and minimizing downtime. This paper systematically analyzes condition monitoring and practical diagnostic techniques for inverter-fed motor drive systems. This study encompasses a thorough evaluation of different methods used for condition monitoring and diagnostics of induction motors, with the most crucial faults in their stator, rotor, bearings, eccentricity, shaft currents, and partial discharges. It also includes an assessment of their applicability. The presented analysis includes a focus on the challenges associated with inverter-fed systems, such as high-frequency harmonics, common-mode voltages causing the bearing currents, and high voltage gradients (dv/dt) due to fast switching frequency, which can impact the motor operation, as well as its faults analysis. Furthermore, this research explores the usefulness and efficiency of various available diagnostic methods, such as motor current signature analysis and other useful analyses using advanced signal processing techniques. This study aims to present findings that provide valuable insights for developing comprehensive condition monitoring strategies, and practical diagnostic techniques that enable proactive maintenance, enhanced system performance, and improved operational reliability of inverter-fed motor drive systems.

Synchronization process expediting in nonlinear oscillators via reconfiguration of the potential well pattern

The synchronization phenomenon has garnered significant attention and extensive study due to its frequency locking effect, finding applications in diverse fields such as communication networks, neuroscience, and multi-robot systems. Fast frequency locking is crucial for synchronization applications, but there have been few investigations on it so far. In this study, we observed that when a nonlinear micro-oscillator synchronizes with a harmonic perturbation, the frequency and phase of the oscillator do not monotonically approach the locking state. Instead, they experience a period of frequency and phase fluctuations that can be divided into two stages: the slipping stage and the oscillation stage. The first slipping stage is affected by the frequency detuning between the perturbation force and oscillator, while the second oscillation stage time is determined by the configuration of the potential well. This configuration can be reconfigured by adjusting the nonlinearity terms of the micro system through phase delay, feedback strength, or perturbation strength. By reconfiguring the potential well pattern, we achieved a fivefold suppression of the synchronization process.

Fast Food Intake Frequency among Young Generation during COVID-19 Pandemic in Selected Area of Dhaka City

Introduction: Fast food is energy dense food with a high amount of refined sugar, wheat, flour, trans-fat, polyunsaturated fat, salt, numerous additives and low nutrient value in terms of protein, fiber, vitamins and mineral content. The nationwide lockdown due to COVID-19 forced people to stay at home for a prolonged period associated with anxiety, and boredom caused by home confinement influenced to change in lifestyle patterns, reduction diet quality and promote overconsumption. Objective: The study aimed to observe the frequency of junk food consumption among the young generation (15-25 years old) during the COVID-19 Pandemic and compare the change of before and during COVID-19 situation. Methods & materials: It was a cross-sectional study conducted in different area of north and south city corporation in Dhaka city focusing on the young generation aged 15-25 years old from September 2020 to April 2021. Total sample size was 315 and the sample was selected randomly following the inclusion and exclusion criteria. The data was collected from the participant through Online Google Form due to of pandemic issue. Data Analysis: Collected data was coded and analyzed by using SPSS for Windows, version 20 (SPSS Inc., Chicago, IL, USA). The statistical significance of difference between values was assessed by chi-square test. A probability level of 0.05 or less significant. Result: The study had found out among the 3-age category from 19-22 years preferred fast food more (64.78%) than others during the pandemic period (p=0.04). Male were taking fast food more than female. Female had increased fast food consumption 12.35% than before and male had increased 15.27% than before (p<0.01). That significantly stated male participants were more influenced by the Pandemic towards fast food. And a significant weight gain (57.14%) was noticed among the 19-22 years age participants, 32.4% male informed to gain weight more than 4kg and 37.4% female1-2 kg during that period. The physical activity level was significantly (p<0.01) dropped during the Pandemic both in male and female participants. Conclusion: The study exposed during pandemics people were taking fast food relentlessly more (13.81%) than normal period. But in spite of attempting to cut down the unhealthy habit of taking fast food, they couldn’t make it totally because of their slothful life and being quarantine in a long period in the home. The Journal of Ad-din Women's Medical College; Vol. 11 (2), July 2023; p 32-38

MWCAWE: A multivariate WCAWE approach for parametric model order reduction, and a sampling strategy for the bivariate case

In this paper, the multivariate well-conditioned asymptotic waveform evaluation (MWCAWE) algorithm is presented. It is based on a univariate version of the algorithm, previously introduced for fast frequency sweeps. Taking advantage of the robustness of this univariate algorithm, the MWCAWE enables to effectively generate multi-parameter reduced-order models. Additionally, a residue-based contour following approach is introduced for a two-stage generation of a projection basis, here applied on bi-variate acoustic problems where frequency and a material parameter are in focus. The effectiveness of the proposed method is demonstrated on two poro-acoustic problems, highlighting both the good convergence property of the algorithm and the potential of the multi-patch strategy for parametric applications.

Metasurface Antenna for Fast Frequency Scanning With Application to Conical Direction Finding

The functionality of a metadome to provide fast frequency conical beam scanning using a simple feeding, is reported in this letter. A metasurface composed by periodic patches covering a simple monopole antenna, acts as a partially reflective sheet to produce frequency-scanned conical beams. Then, the addition of a high impedance surface in the ground plane, is used to increase the scanning ratio. This is important to cover a wide scanning range using a narrow frequency bandwidth. A design example for conical direction finding with a field of view of 60 degrees and using the 200 MHz unlicensed band from 5.1 GHz to 5.3 GHz, is demonstrated with a metadome antenna prototype.

Impact of electric vehicles fast frequency regulation and charging strategies on grid frequency stability

With the gradual reduction of grid inertia, system sensitivity to load unbalances is increasing, compromising frequency stability. To face this problem, faster frequency regulation resources are required. In this context, vehicle-to-grid (V2G) is one of the concepts that is suggested for this purpose. When electric vehicles (EVs) are parked, their batteries can be used as distributed energy storage systems (EESs), injecting and absorbing power faster than conventional generation units (CGUs). The goal of this paper is to analyse the impact of fast frequency regulation of EVs in a small-scale grid, under sudden load variations. In this paper, the effect of charging strategies (CSs) is addressed, as they have a direct impact on the magnitude of the EV fleet regulation. In this way, different CSs can be used to achieve symmetrical up and down regulation, or to maximize one of them. The effect of the EV fleet dynamics in the frequency transient is also studied. The speed of response, and hence, the frequency transient, are influenced by these dynamics. The focus of the analysis will be the communication delay between the EV fleet and the central controller.