Power-frequency Characteristics Research Articles

Self-adaptive system state optimization based on nonlinear affine transformation for renewable energy volatility

The short-term power variations of renewable energy sources result in system state fluctuations and deviations from the scheduled operating point. Tracking short-term power variations and maintaining the system's optimality is challenging for traditional optimization methods due to their highly time-consuming nature. This paper proposes a short-timescale self-adaptive optimization strategy based on the nonlinear affine transformation to deal with this problem. Firstly, the multi-period optimization model is established and solved by considering static power-frequency characteristics to obtain an optimal operating point on a longer temporal scale, with the state security margins reserved using chance constraint programming. Next, analogously with the Taylor series, the nonlinear relationship between the system state variable and short-term power fluctuations is revealed through an analytic expression of the nonlinear affine transformation. Then, a self-adaptive optimization algorithm based on the nonlinear affine transformation is proposed to achieve frequency and voltage optimizations on a shorter temporal scale. With less communication, self-adaptive optimization is implemented at the local bus level to achieve more optimal states for short-term renewable power variations rapidly. Finally, simulations demonstrate that the proposed optimization strategy can effectively enhance frequency and voltage qualities, and decrease objective function, thereby improving the operation safety and economy.

A cascading failure model of cyber-coupled power system considering virus propagation

Cyber attacks from the information layer can have a serious impact on the operation of the cyber-coupled power system. In this paper, a practical cascading failure model used for investigating the impact of virus propagation on the cascading failure of cyber-coupled power system is proposed. The model takes into account the actual functionality of cyber-coupled system and the dynamic virus propagation in cyber network, and describes the effects of cyber node failure caused by virus infection and power flow overload on the cascading failure. Moreover, the impact of defense upgrade on the virus propagation is considered. Centralized control based on dispatching center and local regulation based on static power-frequency characteristic are introduced to describe the actual monitoring function of cyber system on the power grid. Then, the effects of defense upgrade strategy and modular community structure on the failure evolution are analyzed. The results indicate that the spread of virus destroys the monitoring function of cyber network on the power network and leads to more serious failure results. The effectiveness of defense upgrade strategies is related to the upgrade probability of information stations. In addition, the stronger community structure of cyber network can improve the robustness of cyber-coupled power system.

ОБРАТИМЫЙ ПРЕОБРАЗОВАТЕЛЬ ЭНЕРГИИ С МАХОВИЧНЫМ НАКОПИТЕЛЕМ В СИСТЕМАХ ЭЛЕКТРОСНАБЖЕНИЯ

The problem of voltage unbalance and the need to power factor correction remain a relevant objective for electric power engineering. A variable load profile reduces the operating efficiency of electric power plants and leads to an overestimation of the power of transformer substations and the wire size of supply lines. Thus residential buildings power equipment remains underloaded for a significant part of the time. The decrease of power-frequency characteristic is becoming increasingly noticeable. This situation is not a problem yet, but in the future it may complicate the task of frequency stabilization. Finding solutions to existing and predicted problems is an important topic of research. To solve the problems posed, the work proposes the concept of a reversible energy converter, that is an electrotechnical complex with a flywheel energy storage and a two-section frequency converter based on two reversible voltage converters (active front end). The planning area of application of a reversible energy converter is transformer substations of residential and public buildings of urban power supply systems. The reversible energy converter is designed to solve such problems as load leveling, reactive power compensation (power factor correction), balancing voltages and power-frequency characteristic control. The work presents a connection scheme a reversible energy converter to the supply system and provides an expression for the phase load voltage.

Comprehensive evaluation of corroded grounding electrodes considering the impulse characteristics

The grounding electrodes are buried in a harsh soil environment, which will cause corrosion. Corroded grounding electrodes directly affect the safe and stable operation of the power system. Therefore, it is particularly important to detect the corrosion degree of the grounding electrodes accurately. The existing methods have the following problems: 1) Power-frequency grounding resistance is used as a single criterion, and lack of considering the impulse characteristics, which is difficult to accurately judge the corrosion degree and could cause a potential safety hazard. 2) Lacking considering the environmental PH value, water content, salt content, and other factors of the buried soil, which is easy to lead to misjudgment of corrosion degree. To solve the problems, this paper studies a comprehensive evaluation of corroded grounding electrodes considering impulse characteristics. Based on thermal stability, impulse characteristics, and power frequency characteristics, the minimum safety diameter of grounding electrodes and the factors that affect the corrosion of the soil environment are studied. According to the relationship between each evaluation factors and corrosivity, the membership is calculated and combined with the comprehensive weight determined by the sum of the squares of deviation. The fuzzy evaluation method is adopted to obtain the corrosive evaluation matrix Y, and the corrosive index C is proposed to quantify the corrosive strength. Combined with the minimum safety diameter, the residual life range of the grounding electrodes is predicted and the corrosion degree is divided. Finally, a comprehensive corrosion evaluation algorithm considering impulse characteristics is proposed. The results show that this method not only considers the soil environmental factors but also considers the grounding characteristics of the grounding electrodes, especially the impulse characteristics. This method is more comprehensive than other evaluation methods which only consider the soil environment and can realize trenchless corrosion detection of grounding electrodes. Therefore, the contribution of this work is of great significance to the operation and maintenance of tower grounding electrodes.

Cascading Failure Analysis of Cyber–Physical Power Systems Considering Routing Strategy

In this brief, we develop a novel model to study the cascading failure in cyber-physical power systems. We use a discrete packet traffic model that follows a specific routing strategy to describe the dynamic data transmission in the information network. Moreover, the dynamic load flow model that takes into account the power-frequency characteristics of loads and generators is applied to describe the dynamic flow process of the power network. Our proposed model allows to consider the impacts of data packet transmission failures and voltage-related failures in the cascading process. Furthermore, we analyze the effects of routing strategy and information network topology on the severity of cascading failure. Simulation results verify the applicability of the proposed model and reveal the way in which routing strategy affects the cascading failure of cyber-coupled systems. In addition, we show that when the main hub in the information network is used as a dispatching center, a spreadout degree distribution of the information network reduces the severity of cascading failure in the cyber-coupled system.

An Electronic Voltage Transducer Based on Electrostatic Charge Escape

An electronic voltage transducer (EVT) based on electrostatic charge escape is proposed in this paper. Its working principle is to apply the electric field (or voltage) to the electrostatic charges of the electrode, and the electrostatic charges are forced to escape directionally to form an escape current, so the voltage measurement can be achieved by detecting the escape current. Based on Gauss’s theorem and dielectric polarization principle, the mathematical models of the new EVT’s power frequency characteristics, harmonic transfer characteristics and transient response characteristics are studied. And the COMSOL multiphysics coupling simulation is employed to verify these characteristics. The simulation shows that the new EVT can linearly transform the primary voltage, realize harmonic measurement, and have satisfactory transient response. Finally, the experiment verification system is established to examine the new EVT. And the result demonstrates that the EVT has a 0.5 class accuracy, and enables to accurately reflect the characteristics of harmonics and impulse voltage.

Dynamics of Electrical Activity of Olfactory Structures under Conditions of Calypsol / Ketamine Anesthesia

Introduction. In this study, we have characterized high-frequency and low-frequency oscillations at several stages of olfactory processing under calypsol anesthesia in albino rats. While monitoring the animal's respiration, we also obtained field potentials from the olfactory bulb and piriform (olfactory) cortex and simultaneously recorded membrane potentials in piriform cortex pyramidal cells. Manifestations of the considered specific high-frequency components of electrical activity of rhinencephaly structures, in particular olfactory-amygdala rhythm and high-frequency synchronized activity, are obviously the resultof complex interaction of peripheral and central excitation mechanisms at the level of olfactory bulbs. We believe this finding has important functional as well as evolutionary implications.Purpose. To investigate the temporal dynamics of the manifestations of the phenomena of electrical activity of the olfactory bulb of rats and its changes under calypsol anesthesia.Methods.Stereotactic and electroencephalographic methods, correlation-spectral and coherent analysis of the obtained records of electricalactivity of the brain structures were used to study the bioelectrical activity of olfactory structures of the brain of experimental animals.The work was performed in a chronic experiment on 12 outbred white rats, males weighing 200 g. A premedication cocktail and calypsol at a rate of 25 mg / kg of animal weight were used for anesthesia. Implantation control was carried out according to specific patterns of electrical activity of the studied structures.The bioelectrical activity of the brain of each animal was studied for 10-20 days, followed by morphological control.Results. Olfacto-amygdala rhythm is registered against the background of polymorphic activity on the peak of respiratory waves in the form of spindle-shaped flashes of high-frequency oscillations in the range of 52-95 Hz, variable in amplitude. Simulation of the sustained suppression state of olfacto-amygdala rhythm in rhinencephalic structures was achieved using the technique of transferring animals to a state of deep ketamine (calypsol) anesthesia. This allowed not only to "exclude" flashes of olfactory-amygdala rhythm, but also to significantly suppress the high-frequency components of the spectra of electrical activity of olfactory bulbs, to increase the manifestation of low-frequency components (p <0.01-0.05) and to probably reduce the index of high-frequency waves (р<0.05). ISSN 2076-5835. Вісник Черкаського університету. 2021 No247Deep calypsol anesthesia caused differences in the spectra of electrical activity of olfactory bulbs at different depths of discharge only in terms of the spectral power density of the slow-wave range. At the same time, identical probable (p <0.05) suppression of high-frequency components of electrical activity of olfactory bulbs was observed.Under these conditions, the preservation of high-frequency components of the spectrum (unformed in spindles) in the electrical activity of olfactory bulbs at the border of mitral and granular cells was observed even under conditions of sharp depression of -activity in ECoG and identical dominance of high-amplitude low-frequency oscillations in the amygdala.Originality. The influence of narcotic substances on the dynamics of manifestations of the phenomena of electrical activity of rhinencephalic structures: respiratory waves, olfacto-amygdala rhythm, polymorphic activity, is revealed.Conclusions.It is expedient to use the following amplitude-time patterns for objective characterization of total electrical activityof olfactory structures of rats, whichprobably differ in power-frequency characteristics: polymorphic desynchronized activity, respiratory waves, olfacto-amygdala synchronous rhythm and high-frequency synchronous rhythm.Polymorphic activity is normally represented by low-amplitude oscillations (10-200 μV) in a wide frequency range (10-150 Hz) with a set of dominant extremes. Оlfactory-amygdala rhythmis registered against the background of polymorphic activity on the peak of respiratory waves in the form of spindle-shaped flashes of high-frequency oscillations in the range of 52-95 Hz, variable in amplitude.Experimental modeling of the state of stable suppression of olfacto-amygdala rhythm and high-frequency synchronized activity in the electrical activity of olfactory bulbs (under colipslol / ketamine anesthesia) revealed suppression of manifestations of high-frequency components of the spectrum, indicating the important role of centrifugal effects inthe mechanisms of olfactory rhythm generation.Key words:electrical activity, olfactory bulb, fast oscillations, slow oscillations, excitation, anesthesia

Recent Progress in Electrical Generators for Oceanic Wave Energy Conversion

Oceanic wave energy extraction through electrical generator is one of the most interesting topics in the field of power engineering. Almost all the existing relevant review paper focus on electrical generator with the working principle of electromagnetic induction or piezoelectric or triboelectric effect. In this paper, all the existing types (based on principle of operation) of electrical generator used for wave power harvesting are discussed. This paper not only covers recent progress in electrical power generation by electro-magnetic induction, piezoelectric generator, and electrostatic induction, but also presents critical comparative review as well where suitable use and weakness of each type of generators are discussed. Moreover, the application of advanced magnetic core, winding, and permanent magnets are discussed with extensive explanation which are not focused in the existing reviews. Various new constructional features of the electrical generators such as split translator flux switching, two-point absorber, triangular coil, dual port linear generator, piezoelectric, triboelectric nanogenerator, etc. are highlighted with principles of operation. It also includes emerging human intervened optimization method for determining optimum shape of generator and cooling system which is necessary to prevent demagnetization of the permanent magnet. Finally, the way of supply the generated electrical power form the generator to load/grid is thoroughly described in a separate section that would be obvious for successful operation. The comparison among all types of generators in terms of output voltage, current, scale of power production, power-frequency characteristics, power density, cascading, and approaches are tabulated in this paper.

Long-Term Frequency Stability Assessment Based on Extended Frequency Response Model

Large frequency deviation degrades the operation performance of the boiler and its auxiliaries. It affects the output of thermal power units. A significant change in power generation leads to a great frequency deviation. An extended frequency response model for long-term frequency stability assessment is constructed to consider the effects of frequency deviations on boiler auxiliaries. The static power-frequency characteristic of the thermal power unit within an extensive frequency variation range is analyzed. It reveals that the active power output of the generating unit is not monotonically increasing with frequency dropping. An inflection point is observed on the static power-frequency characteristic curve when considering boiler auxiliary frequency characteristics. In the range of greater frequency deviation, the output power decreases rapidly with frequency declination, and an unstable equilibrium point (UEP) of frequency stability is identified. A quantitative index is proposed for frequency stability assessment based on UEP. The stability characteristic and the frequency stability quantitative index based on UEP are analyzed. The frequency dynamic behaviors of the extended model are demonstrated to analyze frequency stability characteristics within an extensive frequency variation range by a single machine system and the IEEE 39-bus system with considering boilers and its auxiliaries.

Research on Multifunctional High-Power Grid Source Simulator System with Synchronous Generator, Line Impedance Imitation, and ZIP Load Emulator

As the penetration of distributed power sources in the power grid is getting higher and higher, the adverse effects are also increasing. It is necessary to adopt control technology to make the distributed power source participate in the power regulation of the power system. In this paper, a multifunctional high-power grid source simulator system is presented. For wider control bandwidth and better performance, a high-power, back-to-back converter and an auxiliary lower-power, back-to-back converter connected in cascade mode topology is proposed in this paper. The basic principle and implementation method of virtual synchronous generator (VSG) in the high-power, back-to-back converter are described to reflect the same power frequency characteristics and voltage regulation characteristics as synchronous generators. Amplitude closed-loop control is proposed to realize zero steady-state error in the lower-power, back-to-back converter, also with line impedance imitation. Meanwhile, a constant-impedance, constant-current, and constant-power (ZIP) load model is used to emulate static load in the grid simulator system. At last, a set of experimental results for a 2 MW grid simulator system is provided to verify the effectiveness and validity of the proposed approach.

Electroencephalogram Resting State Frequency Power Characteristics of Suicidal Behavior in Female Patients With Major Depressive Disorder.

Difficulties in predicting suicidal behavior hamper effective suicide prevention. Therefore, there is a great need for reliable biomarkers, and neuroimaging may help to identify such markers. Electroencephalography (EEG) was used to investigate resting state spatial-frequency power characteristics of female patients with major depressive disorder (MDD); 19 were recent suicide attempters (within the previous 30 days), 36 were suicide ideators, and 23 were nonsuicidal. Patients were enrolled at neuroCare Clinic Nijmegen (Nijmegen, the Netherlands) between May 2007 and November 2016, and the primary diagnosis of nonpsychotic MDD was confirmed using the Mini-International Neuropsychiatric Interview, DSM-IV criteria, and a score of ≥ 14 on the 21-item Beck Depression Inventory. Nonparametric, cluster-based permutation tests were applied to detect robust power differences between the study groups on the EEG broadband signal (2-100 Hz). Furthermore, a nonadaptive distributed source imaging method (eLORETA) was utilized to examine if these suicide-based frequency characteristics are localized in brain areas previously reported in the neuroimaging literature. When compared to nonsuicidal depressed patients, attempters and ideators displayed both decreased beta and low gamma activity in the frontal regions. Moreover, ideators had increased alpha activity over the posterior regions and increased high beta, low gamma activity over the left occipital region when compared to psychiatric controls. Attempters had reduced beta and low gamma activity over the right temporal region when compared to ideators. In addition, eLORETA localized attempter and ideator reduced frontal activity within the orbito-, medial-, middle-, superior-, and inferior-frontal areas and the anterior cingulate cortex. In attempters, reduced right temporal activity was localized within the right inferior-, middle-, and superior-temporal cortices and the fusiform gyrus. Frequency power characteristics of attempters and ideators are consistent with findings from the neuroimaging literature concerning suicide, implying EEG resting state assessment could become a potential biomarker to predict suicide risk.

Equivalent model considering frequency characteristics and renewable uncertainties for probabilistic power flow

The data is not always shared among sub-networks due to concerns about information privacy or difficulties in synchronous information exchange. It is difficult or even impossible to obtain the probabilistic power flow (PPF) by the centralised analysis. In this paper, an equivalent model considering static power-frequency characteristics (SPFCs) and renewable uncertainties is proposed. In this model, SPFCs of equivalent loads and generators are derived to retain SPFCs of original external loads and generators, respectively. In addition, probabilistic characteristics and correlations of equivalent loads are formulated based on Cholesky decomposition to preserve original external renewable uncertainties. The proposed model is further applied to PPF and then PPF can be solved via Monte Carlo simulation method, which makes that the PPF results can be obtained when the detailed data of the original external network cannot be shared. Owing to efficiently preserving the external SPFCs and renewable uncertainties in the proposed equivalent model, the accuracy of PPF results can be guaranteed. Simulation results of IEEE 14-bus and IEEE-118 bus systems demonstrate the effectiveness and superiority of the proposed equivalent model and its applications to PPF, compared with existing well known equivalent models and their applications to PPF.

Consistency of Long-Term Subdural Electrocorticography in Humans.

Subdural electrocorticography (ECoG) can provide a robust control signal for a brain-computer interface (BCI). However, the long-term recording properties of ECoG are poorly understood as most ECoG studies in the BCI field have only used signals recorded for less than 28 days. We assessed human ECoG recordings over durations of many months to investigate changes to recording quality that occur with long-term implantation. We examined changes in signal properties over time from 15 ambulatory humans who had continuous subdural ECoG monitoring for 184-766 days. Individual electrodes demonstrated varying changes in frequency power characteristics over time within individual patients and between patients. Group level analyses demonstrated that there were only small changes in effective signal bandwidth and spectral band power across months. High-gamma signals could be recorded throughout the study, though there was a decline in signal power for some electrodes. ECoG-based BCI systems can robustly record high-frequency activity over multiple years, albeit with marked intersubject variability. Group level results demonstrated that ECoG is a promising modality for long-term BCI and neural prosthesis applications.

Simulation of Cascading Outages Using a Power-Flow Model Considering Frequency

Many steady-state power-flow-based models for cascading outage simulation have not considered frequency, which, however, is an important indicator of generation-load imbalance. This paper proposes a novel steady-state approach for simulating cascading outages. The approach employs a power-flow-based model that considers static power-frequency characteristics of both generators and loads. Thus, the frequency deviation due to active power imbalance can be calculated under cascading outages. Furthermore, a new ac optimal power-flow model considering frequency deviation is proposed to simulate the remedial control when system collapse happens as indicated by the divergence of power flows. Case studies first benchmark the steady-state frequency calculated by the power-flow-based model with time-domain simulation results on a two-area power system, and then test the proposed approach for simulation of cascading outages on the IEEE 39-bus system and an NPCC 48-machine 140-bus power system. The test results are compared with a traditional frequency-independent approach using the conventional power flow and ac optimal power-flow models, and verify that by capturing frequency variations under cascading outages, the proposed approach can more accurately simulate the mechanism of outage propagation.

Coordinated state‐estimation method for air‐conditioning loads to provide primary frequency regulation service

The penetration of large-scale renewable generation leads to a shortage of primary frequency regulation resources as well as increasing regulation demand. By exploiting the thermal capacity of buildings, the authors achieve linear power–frequency characteristics comparable to turbine droop control via clustering a number of air-conditioning units (ACs) to participate in primary frequency regulation without affecting indoor comfort. Due to the bandwidth limitations and latency in communication, the real-time centralised control method face great challenges. This study proposes a two-level coordinated state-estimation method to reduce the coordination burden, in which a central coordinator and local controller for each AC are involved. The central coordinator periodically gathers the working state of every AC and estimated thermal parameters individually, then broadcasts this identified model parameters – the coordination information – to each local controller. Resorting to a state-estimation method considering the coordinated information and local measurements, local controller determines whether to toggle the state of local AC to realise a fast frequency response. Simulation results show that the approach can effectively manage a large number of ACs with heterogeneous parameters to provide a primary frequency regulation service without inducing a rebound effect.

Adaptive Fuzzy Control for Power-Frequency Characteristic Regulation in High-RES Power Systems

Future power systems control will require large-scale activation of reserves at distribution level. Despite their high potential, distributed energy resources (DER) used for frequency control pose challenges due to unpredictability, grid bottlenecks, etc. To deal with these issues, this study presents a novel strategy of power frequency characteristic dynamic adjustment based on the imbalance state. This way, the concerned operators become aware of the imbalance location but also a more accurate redistribution of responsibilities in terms of reserves activations is achieved. The proposed control is based on the concept of “cells” which are power systems with operating capabilities and responsibilities similar to control areas (CAs), but fostering the use of resources at all voltage levels, particularly distribution grids. Control autonomy of cells allows increased RES hosting. In this study, the power frequency characteristic of a cell is adjusted in real time by means of a fuzzy controller, which curtails part of the reserves, in order to avoid unnecessary deployment throughout a synchronous area, leading to a more localised activation and reducing losses, congestions and reserves exhaustion. Simulation tests in a four-cell reference power system prove that the controller significantly reduces the use of reserves without compromising the overall stability.

Research on penetration of distributed generation considering fluctuation and load frequency characteristics

The high penetration rate of distributed generation brings a great impact to the security of the distributed network, and research on the penetration of distributed generation has significance on the planning and operation of the distributed network as well as the application of distributed generation. The calculation model of penetration of distributed generation is established under frequency stability constraints, considering the fluctuation characteristics of distributed generation and load requirement, and load frequency characteristics. The boundary of penetration of distributed generation under a different level of fluctuation, power-frequency characteristics and reserve capacity is defined. The effectiveness and accuracy of the model are verified by an example, providing a feasible solution for the large-scale access of distributed generation in the distribution network.

Security risk assessment using fast probabilistic power flow considering static power-frequency characteristics of power systems

Large scale blackouts in the world have aroused the study of security risk assessment (SRA) urgently. SRA difficulties brought about by uncertainties can be solved by probabilistic power flow (PPF). Conventional methods usually focus on the probabilistic density function (PDF) and the cumulative distribution function (CDF) of node voltages and branch flows only. A SRA scheme of power system using fast PPF is proposed in this paper. The scheme took static power-frequency characteristics (SPFCs) into account, and fast decoupled power flow (FDPF) was used to solve PPF. Besides node voltage and branch flows, the scheme can obtain the PDF and CDF of frequency. The computing speed of the proposed scheme considering wind power multi-scenarios is enhanced compared to conventional method. SRA indices are introduced to evaluate the power system quantitatively. The examples on the IEEE RTS-24 system demonstrate the feasibility, rapidity and validity of the proposed scheme.

An improved fast decoupled power flow model considering static power–frequency characteristic of power systems with large‐scale wind power

AbstractLarge‐scale wind power (LSWP) integration may cause significant impact on power system frequency, so it is necessary to take frequency regulation issues into account in power system steady‐state operation analysis. An improved fast decoupled power flow model considering static power–frequency characteristic of power systems with LSWP is proposed in this paper. In this scheme, the active power of generators and loads are presented with their static power–frequency characteristics. The slack bus degenerates to the nodal voltage phase angle reference bus of the system, and all the generators with frequency regulation capability participate in unbalanced power regulation. The power flow calculation results can reveal the impact to the system frequency of operation mode change and load variation, and present the output adjustment of the generators. The proposed model can be solved conveniently by the block solving technology based on the fast decoupled power flow algorithm. The scheme presented in this paper has been tested on the IEEE standard 30‐bus test system by simulating basic operation and primary and secondary frequency regulation of the generators, which demonstrated the validity by the method. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Wide-Range Dynamic Power Management in Low-Voltage Low-Power Subthreshold SCL

Power-frequency scaling in subthreshold source-coupled logic (STSCL) systems has been studied and analyzed. It is shown that the operating frequency of such systems can be adjusted over about three decades with linearly proportional power dissipation. The heart of such a system is a phase-locked loop (PLL)-based clock generator (CG) with a very wide tuning range controlling the dynamics of the STSCL system. The design of a wide tuning range PLL utilizing a novel self-adjustable loop filter that generates the reference clock as well as the bias current for the STSCL system is described. The PLL-based CG exhibits linear power-frequency characteristics in order to minimize its power consumption overhead (7 pJ with 350 nA standby current). Implemented in 0.13 μm CMOS, the CG occupies 0.06 mm2 with a supply voltage that can be reduced down to VDD = 0.9 V.