System Frequency Research Articles

Numerička analiza titrajnog odziva dalekovoda velikog raspona prijenosnih vodova izazvanog vjetrom

Based on the engineering background related to ±800 kV ultra-high voltage (UHV) transmission lines spanning the Yellow River, finite element models were developed for single-tower and transmission tower-line systems, with their wind-induced responses under wind loads were simulated and analysed. In addition, the coupling effect in a large-span transmission tower line system was investigated. The results showed that the natural vibration frequency of the tower-line system was slightly lower than that of a single tower and that the torsional natural frequency was the most significantly reduced. The transmission tower-line system has a maximum displacement of 1.92 times that of a single tower when the wind angle is 0°. The maximum axial force and stress in the tower-line system are 1.6 times and 1.37 times higher than those in a single tower. The interaction between the tower and wires significantly affects the wind-induced response of the tower body. Hence, considering the dynamic coupling effect of the tower-line transmission system is important when designing a tower.

An overview of grid-forming technology and its application in new-type power system

To address the global climate crisis, achieving energy transitions is imperative. Establishing a new-type power system is a key measure to achieve CO2 emissions peaking and carbon neutrality. The core goal is to transform renewable energy resources into primary power sources. The large-scale integration of high proportions of renewable energy sources and power electronic devices will dramatically change the operational mechanisms and control strategies of power systems. Existing wind and solar converters mostly adopt the grid-following control mode, which leads to significant challenges in system security and stability as it is insufficient to support the frequency and voltage of the grid. On the other hand, grid- forming control technology (GFM) can provide voltage and frequency support for the system, and thus becomes an effective measure to improve the inertia and damping characteristics of power systems. This paper illustrates the principles, control strategies, equipment types, application scenarios, and project implementation of grid-forming technology. The simulation and analysis based on a renewable-dominated real new-type power system show that GFM can significantly enhance the frequency and voltage support capacity of the power system, improve renewable energy accommodation capacity and grid transmission capacity under weak grid conditions, and play an important role in enhancing the stability and power supply reliability of renewable-dominated new-type power systems.

Rolling planning model for high proportion renewable energy generation power system considering frequency security constraints

In this paper, a rolling planning model for high proportion renewable energy generation power systems is proposed, considering frequency security constraints, to address the frequency stability challenges posed by increased integration of wind and solar energy into the power grid under the “double carbon” goal. First, this study establishes a frequency response model for a thermal generation unit (TGU) and analyzes the impact of the high proportion of renewable energy on system frequency stability. Subsequently, a dynamic frequency security constraint is formulated, which can be used in generation planning to address the frequency issues. Second, a bi-level rolling planning model for high proportion renewable energy generation power systems considering dynamic frequency security constraints is established. The upper level focuses on investment decisions. The lower level incorporates frequency security constraints into the operational simulation to guarantee the frequency stability of the power system when making decisions on the size of newly built TGUs annually. Finally, case studies are conducted to demonstrate the validity and effectiveness of the proposed rolling planning model.

Minimizing phase delay of feedback control signals for electromagnetic vibrators to reduce measurement uncertainty in ultra-low frequency vibration calibration

Suppressing the distortion of ultra-low frequency (ULF) vibration waveforms produced by an electromagnetic vibrator (EMV) presents significant challenges, leading to considerable measurement uncertainty during vibration calibration. A phase delay minimization method for feedback control signals is proposed to reduce the harmonic distortion of ULF vibration waveforms. The method quantitatively describes the influence law of the active viscoelastic approach on system frequency response characteristics. By selecting appropriate active stiffness and damping coefficients, the method minimizes the phase delay of the feedback control signal, thereby enhancing the disturbance suppression capability of the displacement and velocity composite negative feedback control. Experimental results indicate that harmonic distortion of the vibration waveform is reduced to less than 1.70 % within the ULF frequency range of 0.001 Hz ≤ f ≤ 1 Hz. Furthermore, the amplitude sensitivity calibration uncertainty, which arises from vibration waveform distortion, has been reduced to 0.038 % (k = 1.8), thereby improving the accuracy of vibration calibration.

Apply Honey Barger Algorithm to double integral sliding mode observer for stable load frequency in multi-area power system

A randomness of load demand and plant uncertainties causes frequency deviation in linked power plants. Based on the double-integral sliding mode observer (DISMO) integrated Honey Badger algorithm (HBA), a novel LFC for a multi-area power plant (MAPP) is introduced in this article. The main aim is to minimize frequency offset, finite time, and aggregate instability of controllable loads subject to the balance of the power on the MAPP. Firstly, the suggested observer is developed to ensure an exact estimation of the actual signal for the controller input signal. Secondly, a double-integral sliding surface (DISS) is introduced based on estimated signals the designed observer gains. Then, a new SMC rule is designed to ensure finite time reachability and eliminate the chattering and oscillating troubles. Thirdly, in this regard, the proposed sliding surface is designed with four selected parameters. Regarding this, to maximize the ability of the suggested SMCer, the optimized controller parameters are determined by HBA. The robustness of the suggested scheme is examined by various case studies on the LFC models in a single-area power plant (SAPP) and MAPP under different load disturbances and parameter uncertainties.

An Integrated Frequency Regulation Method Based on System Frequency Security Posture

As the share of renewable energy in a grid increases, the grid’s frequency support capability weakens, and the spatial distribution of grid frequency becomes more pronounced. As a result, control strategies based on system frequency consistency and traditional frequency regulation dominated by synchronous machines are becoming increasingly inadequate for meeting the frequency regulation requirements of new-type power systems. To enhance the system’s frequency support capability, it is imperative to fully utilize the frequency regulation resources within the power system. To address this issue, this paper first introduces a system frequency security posture assessment method that accounts for the spatial distribution characteristics of the grid. Subsequently, a parameter optimization method for diverse frequency regulation resources is proposed in conjunction with the proposed comprehensive evaluation method for frequency regulation. Next, using a renewable energy feeder regional grid as an example, an integrated frequency regulation method based on the system frequency security posture is presented. Finally, the frequency regulation performance and economic costs of different frequency regulation methods are analyzed under various operating scenarios and disturbances using a model based on actual data from the renewable energy feeder regional grid. The simulation and index calculation results demonstrate that the method proposed in this paper effectively enhances the system’s frequency support capability, reduces the frequency disparity between different nodes within the grid, and maintains high economic performance.

Piezoelectric Ultrasonic Local Resonant Ultra-Precision Grinding for Hard-Brittle Materials.

Hard-brittle materials are widely used in the optics, electronics, and aviation industries, but their high hardness and brittleness make it challenging for traditional processing methods to achieve high efficiency and superior surface quality. This study aims to investigate the application of ultrasonic local resonant grinding to sapphire to improve the efficiency and meet the requirements for the optical window in the surface roughness of the material. The resonant frequency of a piezoelectric ultrasonic vibration system and the vibration amplitude of a grinding head's working face were simulated and tested, respectively. The results of ultrasonic grinding experiments showed that the local resonant system reduced the surface roughness parameter (Ra) of sapphire to 14 nm and improved its surface flatness to 44.2 nm, thus meeting the requirements for the ultra-precision grinding of sapphire. Compared with a conventional resonant system, the surface roughness of the sapphire ground with the local resonant system was reduced by 90.79%, its surface flatness was improved by 81.58%, and the material removal rate was increased by 31.35%. These experimental results showed that ultrasonic local resonant grinding has better effects than those of conventional ultrasonic grinding in improving surface quality and increasing the material removal rate.

Research on The Influence of Continous Damping Control Shock Absorber on Frequency Response Function of Spindle Coupled Road Simulation Test Bench

When the semi-active suspension is tested based on the 6-DOF spindle coupled road simulation test bench, the traditional test method is no longer applicable, because the continous damping control shock absorber of the original vehicle controller cannot be used and the overall nonlinear of the system is stronger. At present, there are few related engineering applications in the industry. This paper introduces the current reproduction technology of semi-active suspension on the 6-DOF spindle coupled road simulation bench and researches the difference of the system frequency response function by excitation of continous damping control shock absorber with different control current.

Protección sísmica de estructuras civiles mediante dispositivo INERTER en la provincia de Huancayo

This research work proposes the use of a Tuned-Mass-Damper-Inerter (TMDI), which combines a new configuration of passive vibration control using an “Inerter”. This two-terminal mechanical flywheel device, based on the well-known Tuned-Mass-Damper (TMD), generates resistance forces proportional to the relative acceleration of its terminals. TMDI takes advantage of the “mass amplification effect” of Inerter to improve performance compared to TMD. For harmonically excited primary linear systems, closed-form analytical software is modeled to obtain optimal design and tuning parameters of the TMDI, using established methods. It is observed that, with proper distribution of the dampers, the TMDI system is more effective in suppressing vibrations close to the natural frequency of the uncontrolled primary system and is more resistant to the effects of detuning and misdistribution. Furthermore, the results of the modeled structures show the effectiveness of the TMDI, modeled as a classical damper, in suppressing the fundamental mode of vibration for linear MDOF structures. The incorporation of the Inerter in the proposed TMDI configuration can replace part of the vibrating mass, achieving lightweight passive vibration control solutions or improving structural performance. The solution proposed and modeled with traditional dampers behaves linearly, in line with current performance trends for minimally damaged structures protected by passive control devices. Additionally, optimized TMDI is applied for vibration suppression and displacement control, offering optimal seismic protection.

Thermoelastic damping in asymmetric vibrations of nonlocal circular plate resonators with Moore-Gibson-Thompson heat conduction

Precise estimation of the amount of thermoelastic damping (TED) in small-sized resonators is one of the crucial issues in their optimal design. According to several experimental, numerical and theoretical findings, the behavior of structures with such small dimensions in structural and thermal domains does not follow classical elasticity theory and the Fourier law of heat conduction. The objective of this work is to develop a nonclassical formulation for computing TED in asymmetric vibrations of circular nanoplates according to nonlocal theory (NT) and Moore-Gibson-Thompson (MGT) heat transfer model. To do so, first, the coupled equations of motion and heat are derived in the purview of NT and MGT model. Then, the real and imaginary parts of the system frequency are extracted from the frequency equation affected by thermoelastic coupling. Finally, by means of the existing definition for TED, a mathematical expression including nonlocal parameter of NT and nonclassical constants of MGT model is obtained to make an estimate of TED value. In the numerical examples section, to ensure the credibility of the provided formulation, the results obtained through this model are compared with those reported in the literature in the context of simpler models. Then, by presenting various graphical data, the type and extent of the role of different factors in TED changes are appraised. The obtained results indicate that employing NT and MGT model can substantially impact the amount of TED compared to the estimations of the classical formulation. Furthermore, the comparison of results reveals that the magnitude of TED in asymmetric vibration modes surpasses that in symmetric ones, and consequently incorporating asymmetric vibration modes is crucial for thorough analysis of TED in circular nanoplates. Thus, the formulation presented in this article can aid in achieving an optimal design for such plates, particularly in terms of minimizing energy loss.

Genomic analysis of multi-drug resistant coagulase-negative staphylococci from healthy humans and animals revealed unusual mechanisms of resistance and CRISPR-Cas system.

Coagulase-negative staphylococci (CoNS) are evolving as major reservoirs and vectors of unusual and critical antimicrobialresistance (AMR) mechanisms. In this study, the genomic characterization of 26 multidrug-resistant (MDR)-CoNS (S. borealis, S. saprophyticus, S. sciuri, S. hominis, S. epidermidis, S. pasteuri, S. hyicus, S. simulans, S. haemolyticus, and S. arlettae) previously obtained from the nasal cavity of healthy nestling storks, humans who had no contact with animals, pigs, and pig farmers, as well as dogs and dog owners from Spain was performed. High-quality draft genomes obtained by Illumina sequencing technology were used to determine their resistome, virulome, mobile genetic elements, and CRISPR-Cas types. The relatedness of three CoNS species with publicly available genomes was assessed by core-genome single nucleotidepolymorphisms (SNPs). AMR genes to all classes of antibiotics in staphylococci were detected including unusual ones (mecC, ermT, and cfr), of which their corresponding genetic organizations were analyzed. About 96.1% of the MDR-CoNS strains harbored diverse adherence or immune evasion genes. Remarkably, one enterotoxin-C and -L-carrying S. epidermidis-ST595 strain from a nestling stork was detected. Moreover, various plasmid bound-biocide resistance genes (qacACGJ) were identified in 34.6% of the MDR-CoNS. Two genes that encode for cadmium and zinc resistance (cadD, czrC) were found, of which czrC predominated (42.3%). Complete CRISPR-Cas system was detected in 19.2% of the CoNS strains, of which cas-1, -2, and -9 predominated, especially in 75% of the S. borealis strains. The phylogenetic analysis identified clusters of related S. epidermidis lineages with those of other countries (SNP < 100). Also, highly related S. borealis isolates (SNP < 10) from pigs was confirmed for the first time in Spain. These findings showed that various ecological niches harbor CoNS that presented MDR phenotypes mediated by multiple AMR genes carried by mobile genetic elements with relatively low frequency of intact CRISPR-Cas systems. Furthermore, the transmission of some CoNS species in humans and animals is strongly suggested.

Robust Load Frequency Control of Interconnected Power Systems with Back Propagation Neural Network-Proportional-Integral-Derivative-Controlled Wind Power Integration

As the global demand for energy sustainability increases, the scale of wind power integration steadily increases, so the system frequency suffers significant challenges due to the huge fluctuations of the wind power output. To address this issue, this paper proposes a Back Propagation Neural Network-Proportional-Integral-Derivative (BPNN-PID) controller to track the output power of the wind power generation system, which can well alleviate the volatility of the wind power output, resulting in the slighter imbalance with the rated wind power output. Furthermore, at the multi-area power system level, to mitigate the impact of the imbalanced wind power injected into the main grid, the H∞ robust controller was designed to ensure the frequency deviation within the admissible range. Finally, a four-area interconnected power system was employed as the test system, and the results validated the feasibility and effectiveness of both the proposed BPNN-PID controller and the robust controller.

Investigation of dynamic characteristics of a vibration isolation system for impact resistance of the marine container

ABSTRACT To achieve impact load resistance for the marine container, the paper designs a novel vibration isolation system. The dynamic characteristics of the system are experimentally investigated to verify the mathematical model. Based on the model, the vibration isolation rate is predicted under different conditions and its sensitivity to different influencing factors is investigated. The system is optimally designed for multiple parameters using adaptive particle swarm optimization (APSO). The results show that the vibration isolation system temporarily enters the pressure building displacement stage which does not affect the properties of the system. The model calculations coincide with the test results by more than 97%, except for the pressure building displacement stage. The predictions of vibration isolation rate are more than 80% and the sensitivity to excitation direction, load mass, system frequency and damping ratio is significant. The optimal system can meet the design requirements of engineering applications.

Optimal Placement and Sizing of Battery Energy Storage Systems for Improvement of System Frequency Stability

Optimal Placement and Sizing of Battery Energy Storage Systems for Improvement of System Frequency Stability

Signal Components and Impedance Spectroscopy of Potential p‐Si/n‐CdS/ALD‐ZnO Solar Cells: EIS and SCAPS‐1D Treatments

AbstractA silicon heterojunction (SHJ) solar cell with the attractive and widely used atomic layer deposited (ALD)‐ZnO/n‐CdS/p‐Si configuration is examined in this work to learn more about its electrical properties. Using EIS and SCAPS‐1D, a comprehensive model of the device is created and then simulated. Theoretical aspects of the cell are examined through the use of similar electrical circuit models, focusing on the transmittance spectrum made possible by the ALD‐ZnO layer's low reflectance and high visible transmittance. In this study, the C–V tool is used to study the trap states in the silicon absorber layer under different lighting conditions and wavelengths. The doping concentration and built‐in potential are determined using the Mott–Schottky technique. In addition, the cell's properties are investigated by measuring its G–V, G–F, C–T, and C–F in different real‐world scenarios. As a means of visualizing the electrochemical impedance data, Nyquist plots—sometimes called Cole–Cole plots—are utilized. By utilizing absolute impedance and phase shifts, Bode plots are employed to examine the system's frequency response. Last, the results of the SHJ cell's spectral response measurements are given, which confirm the results of the Nyquist plots.

Unit commitment of power systems considering system inertia constraints and uncertainties

AbstractLarge‐scale integration of renewable energy into the power grid results in a lack of system inertia, posing challenges to the optimal operation and scheduling of systems considering frequency stability. This article proposes a unit commitment model that considers both inertia constraints and the uncertainty of load and renewable energy. First, the time‐domain expression of the system frequency response is calculated based on the aggregated System Frequency Response (SFR) model, considering the system's maximum frequency deviation and the maximum Rate of Change of Frequency (RoCoF) limit. This calculation determines the minimum inertia requirement for the system. Furthermore, inertia constraints suitable for mixed‐integer programming model are derived to address the nonlinearity of conventional frequency constraints. Second, considering the uncertainties of load and wind energy from renewable sources, a unit commitment model with inertia constraints is constructed, and a robust method is used to solve the uncertainties. Finally, the accuracy of the proposed inertia constraints and unit commitment model is validated using case study of IEEE standard test cases and a provincial power grid in China.

Characterization of dynamic coupling induced shifts of frequencies in vehicle-scanning method

A comprehensive strategy combining theory and experiment is proposed to characterize the dynamic coupling induced shifts of vehicle and bridge frequencies through both experimental investigation and numerical validation, in which the effect of vehicle-bridge interaction is theoretically incorporated in the vehicle-scanning method based on the experimental model. It is known that the measurement of bridge frequencies plays an important role in structural health monitoring as the shift of frequency can be served as an indicator of possible damage occurring in a bridge. Nevertheless, the attention has been mainly drawn on the accuracy improvement in developing the vehicle-scanning method so far, with limited discussion of dynamic coupling effect on the frequency shifts. As such, a combined theoretical–experimental approach is presented to show that the influence of vehicle-bridge interaction results in the coupled frequencies of a vehicle-beam system using the vehicle-scanning method, and adopting a heavy lumped test vehicle can lead to the underestimated bridge frequency and overestimated vehicle frequency. As a new finding, the effect of rolling frequency is experimentally observed in the vehicle spectrum for the first time.

Experimental investigation of stick-slip behaviors in dry sliding friction

Friction-induced vibration, particularly the bothersome stick-slip behavior, is a significant contributor to machine damage and component failure. In this study, the vibrational displacement, sound pressure, and coefficient of friction (COF) of several metal or alloy samples in dry conditions are tested using a reciprocating friction force test apparatus. It is found that the stick-slip behavior is more likely to occur at low sliding speeds and high normal loads. Furthermore, under the same working conditions, increasing the surface roughness of the sample or enhancing the hardness difference between the sample and the counterpart can mitigate the stick-slip behavior during the friction process. By analyzing the characteristic parameters of the stick-slip behavior, it is found that the temporal period and the stick-time decrease significantly with an increase in relative sliding speed. Additionally, the amplitude and intensity of the friction-induced noise increases with the increase of the relative sliding speed and normal load. The frequencies of the sound pressure are primarily concentrated around the natural frequency of the frictional system. Finally, we extract the COF and find that the average COF as well as the maximum and minimum COF first decreases sharply, and then becomes stable with the increase of the relative sliding speed due to the transition of friction state from stick-slip behavior to smooth sliding.

A new optimal 3° of freedom fractional order proportion integral derivative controller with model predictive controller for frequency regulation in high penetrated renewable based interconnected system

The increasing use of renewable energy sources (RESs) in conventional power systems is making them more complex. RES, such as solar and wind energy, reduce system inertia, affecting power system (PS) stability and frequency aberrations. Thus, the modern PS faces new concerns that arise from integrating RESs and struggles to manage frequency and stability, which can cause power outages and blackouts and lower industry production. The intelligent control mechanism is critical to the PS's operation to ensure frequency under its complicated structure. This study suggests a new best 3-DoF fractional order proportional integral derivative-model predictive controller (3DoF-FOPIDN-MPC) for controlling frequency when there is a lot of load going on quickly. The 3DoF-FOPID controls the outer loop using the area control error (ACE) signal, while MPC controls the inner loop using the output signal from the 3DoF-FOPIDN and the area's total power output response. For optimal controller functionality, the salp swarm algorithm (SSA) extracts optimized controller settings. To validate the suggested controller, it is tested under various load-changing scenarios and compared to state-of-the-art controllers. For 1 % and 3 % load changes, the suggested controller settles in 1.1 s and 1.78 s, respectively.

Effect of relative phase of loose tie rods on nonlinear dynamic behavior of rod-fastening rotor-bearing-seal system

Loosening of multiple tie rods in a circumferential rod-fastening rotor caused by thermal deformation and centrifugal loads is very common in engineering. The relative position of loose tie rods in the circumferential direction will also have an important impact on rotor dynamics. The relevant research has not been done yet. In this paper, a contact model of the rough machined surface is firstly established by combining the probability functions describing rough surfaces and fractal contact theory of asperities, then the contact stiffness model between disks is established based on the contact model. Finally, the dynamic model of the circumferential rod-fastening rotor-bearing-seal system is established and solved. The effect of relative phase of loose tie rods on the nonlinear dynamic characteristics of rod-fastening rotor-bearing-sealing system is studied. It can be concluded that relative phase of the loose tie rod has an important influence on the frequency, bifurcation, and periodic motion of the rotor system. At lower speed, the anisotropy of contact stiffness caused by loose tie rods has little effect on the rotor trajectory, while the generalized bending moment has a greater influence on dynamics of the system. At higher speed, the anisotropy of contact stiffness has a great influence on the axis rail of the rod-fastening rotor.