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Practical testing of distance relays under power swing conditions is becoming all the more essential. This is in view of the increasing use of power electronic apparatus due to penetration of renewable sources and/or FACTS controllers now-a-days. To perform such practical tests, a hardware platform emulating power system swing occurrences, as caused by electromechanical oscillation of alternators, is necessary. As a first step it is required to model the phenomenon before its implementation. In this paper an analytical small-signal model of the low-frequency electromechanical oscillations in a grid-connected alternator is presented. Off-line simulation-based validation for a Single Machine Infinite Bus (SMIB) system is done. To emulate an open-loop alternator, a prototype of a controlled grid synchronised VSI with AC-side reactor is developed and practically tested. A control scheme is proposed and implemented to emulate the active power swing phenomenon. Effects of machine inertia and initial power angle on the swing characteristics are investigated. In-process estimation of apparent impedances, as seen from the distance relay terminals downstream towards the grid, is done. Principle of estimating the apparent impedance during power swing is presented with corresponding experimental results. Both real-time and off-line simulation results are in close agreement with the experimental results thus establishing the accuracy of the model and the precision of the experiments. [ABSTRACT FROM AUTHOR]

The shift from traditional fossil fuel-based power systems to renewable energy sources heightens the importance of frequency regulation. The lack of inertia in this new generation increases the risk of low-frequency oscillatory events, a significant concern in power systems stability. To mitigate these stability problems, it is crucial to study the effectiveness of damping controllers. This paper delves into the analysis of three damping controllers: the power system stabilizers (PSS) installed in synchronous generators, and two Power Oscillation Damping (POD) controllers, one with active power modulation (POD-P) and the other with reactive power modulation (POD-Q), typically installed in environments with high renewable penetration.The main objective is to critically evaluate the comparative advantages of PSS, POD-P, and POD-Q controllers in local and inter-area oscillations by exploring their flexibility and performance under various initial conditions and oscillatory scenarios. The proper choice of damping controllers will ensure the stability of the grid in future scenarios of high renewable production, thus allowing the definition of future technology needs. This research is of utmost importance as it aims to dampen different oscillations by employing uniform control parameters in the PSS, POD-P, and POD-Q controllers. Five scenarios are defined on a system based on the IEEE 39 Bus New England System model and simulated by DIgSILENT PowerFactory. The results are analyzed methodically per scenario, facilitating a comparative evaluation of the controllers and reaching promising conclusions.

With the expansion of power grid scale and the increase of power components, the maintenance methods of power system become more and more complex. It is difficult to evaluate the low-frequency oscillation risk of power grid under massive maintenance only by traditional methods. To solve this problem, a risk prediction method of low-frequency oscillation in maintenance power network based on long short term memory (LSTM) neural network was proposed. Firstly, the unified coding method of power system maintenance mode was proposed, so that the computer can quickly and accurately identify the operation state of power grid under various maintenance modes. Then, based on the historical data measured in real time by phasor measurement unit (PMU), the number of low-frequency oscillation of power grid under different maintenance modes was predicted by using LSTM neural network, so as to evaluate the risk of low-frequency oscillation of power grid under maintenance. Finally, a regional power grid in central China was taken as an example to verify the accuracy and rapidity of the proposed method.

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Low-frequency oscillations (LFO) are generated in interconnected electric networks because of the weak tie lines between the parts of the networks. Such oscillations have been a significant challenge for engineers that may lead to system instability if appropriate measures are not taken. This article proposes two new metaheuristic algorithms, the jellyfish search algorithm (JSA) and the tunicate swarm algorithm (TSA), to design the power system stabilizers (PSS) for single machine infinite bus (SMIB) and multimachine power system (MPS) networks. The proposed method uses the JSA and TSA to dampen out the LFOs by modifying the vital parameters of lead-lag type conventional PSS (CPSS). A damping ratio-based objective function improves both models' system damping. These methods are tested on an SMIB system and two distinct MPS networks exposed to the three-phase fault under various loading conditions. The effectiveness of the suggested approach has been studied by comparing the system eigenvalues and minimum damping ratio (MDR) produced from JSA and TSA-tuned PSS and the CPSS. In addition, time domain simulation results are compared, demonstrating that the new approach outperforms the standard techniques, such as particle swarm optimization (PSO) and backtracking search algorithm (BSA). In the SMIB system, MDR produced by JSA and TSA-based PSS is 2.55 times higher than that of CPSS. Similarly, in comparison to PSO and BSA-based PSS, JSA, and TSA-tuned PSS offer >1.4 times greater MDR in the Two Area Four Machine network and up to 8.4 times larger MDR for the IEEE-39 Bus network. Furthermore, the efficacy of the suggested JSA and TSA approaches' prediction capacity is validated by satisfying the values of statistical performance metrics.

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, the damping of low-frequency oscillations (LFOs) in a power system containing Static VAR Compensator (SVC) is investigated based on Multiple-Model Linear Optimal Control (MMLOC) Strategy. The performance of MMLOC is enhanced using Polynomial Combination Algorithm (PCA). A linear optimal controller (LOC) generates the optimal control signal with linearization the nonlinear state equations of the system and solving the Riccati equation. One LOC generates synchronized control signals for the synchronous generator excitation system as well as SVC. The LOC is assigned to generate each model’s control signal. The final control signal is made by interpolating the LOC output signals obtained from each model using PCA. Considering a three-phase symmetrical fault on a near bus to the generator, the proposed control strategy is evaluated. This strategy not only maintains stability but also reduces LFO effectively. Furthermore, steady state error of rotor speed and rotor angle tend to zero favorably. Simulations are done for single- and multi-machine power systems via a MATLAB m-code.

Low frequency oscillations in power system with medium-pressure regulating valve of steam turbine occur from time to time， threatening the safe operation of generating units and power system. Three typical low frequency oscillations of power system induced by medium-pressure regulating valve are given. Given the roles of medium-pressure regulating valves in different types of steam turbines， the ways they induce or participate in low frequency oscillations are introduced. It is pointed out that one of the major reasons for low frequency oscillations occurring in deep peaking-shaving units is the reduction of the turbine’s integrated valve position command， resulting in the frequent participation of medium-voltage regulating valves of poor linearity in the power regulation of the units. In view of the current operating environment of thermal power units in China， six specific measures to prevent the medium-pressure valves from participating in low frequency oscillations in power system are given for reference.

Low-frequency oscillations (LFOs) pose a significant obstacle in achieving optimal power flow and utilizing transmission corridors in large interconnected power systems. In this study, linear matrix inequality (LMI) base robust H ∞ wide-area damping controller (WADC) is introduced to effectively address critical LFOs. The proposed WADC utilizes wide-area signals, which modulate the phase angle of a thyristor-controlled phase shifter device. To ensure that the concerned modes of LFOs lie in left half of the complex plane, a D-space sub-region approach is applied. However, using wide-area signals introduces time delays, which negatively impact the efficacy of the WADC; hence, a time delay compensator (TDC) is incorporated into the feedback path of the signals. The proposed approach involves four key steps: selecting feedback signals using a combined modal transformation and geometric approach, designing an appropriate TDC, building a generalized plant with mixed sensitivity weights, and solving the LMI. The dynamic efficacy is verified on IEEE 4-machine 11-bus system, and 10-machine 39-bus system. Poorly damped single and multiple critical modes are placed in the D-space region of interest with specified damping ratios viz. 10% and 15%. Furthermore, damping ratios of critical modes are maintained with TDC based proposed WADC while deteriorating with other counterparts. [ABSTRACT FROM AUTHOR]

With the development of new energy, energy storage, and flexible DC technology, AC/DC hybrid distribution networks have gradually become an important development direction for future distribution networks. The access of a large number of power electronic devices has brought dynamic problems such as low frequency oscillations to the distribution network. In order to deeply study the low frequency oscillation problem on the DC side of AC/DC distribution networks, detailed modeling of key links is conducted such as H-bridge series and isolated bidirectional active bridge structures, three-phase inverters, and three-phase Buck converters in the main valve tower of power electronic transformer. Through time domain simulation, the 4 Hz low frequency oscillation phenomenon on the DC side of the AC/DC distribution network in the actual project is reproduced, and the correctness of the established mathematical model is verified. Based on the established mathematical model, qualitative analysis is conducted on key influencing factors such as power and controller parameters, and the final conclusions are as follows: power level and Buck link voltage loop control parameters affect system stability, the integral coefficient of the current loop in the Buck link affects the oscillation frequency.

In order to study the characteristics of low frequency oscillation of summer precipitation over Qinghai-Xizang Plateau， based on the daily precipitation data of 62 meteorological stations over the Qinghai-Xizang Plateau from 1978 to 2017 and the high-resolution daily reanalysis data of ERA5.This paper adopted the collection of empirical mode decomposition （EEMD）， Lanczos filter and synthesis analysis method.Filter out the years of drought and flood， and analyzed the characteristics of low frequency oscillation， variation of meteorological elements and circulation of precipitation in dry and flood years in summer over the Qinghai-Xizang Plateau.Reveals the drought and flood years， the characteristics of low frequency oscillation period of precipitation in plateau area， the circulation characteristics and low frequency and other transmission characteristics of wind field and vorticity field.The results show that： （1） There is an oscillation period of 10~20 days in summer precipitation over the Qinghai-Xizang Plateau.The period frequency of drought and flood years is different， the oscillation frequency of flood years is obviously higher than that of drought years.In flood years， the significant oscillation is 10~20 days and 30-days oscillation， while in drought years， the oscillation is mainly 10~20 days.（2） In flood years， the low-frequency precipitation phase is strong， the high-altitude low-frequency cyclones control the plateau， the high-altitude divergence， the low-altitude convergence.The water vapor supply from the south of the Bay of Bengal， and the low-frequency disturbance is strong， which is conducive to the occurrence of precipitation， there is an abnormal circulation distribution of low-frequency anticyclone- low-frequency cyclone- low-frequency anticyclone from west to east.On the contrary， in the low frequency precipitation weak phase， the high frequency anticyclone controlled the main body of the plateau， high altitude convergence， low altitude divergence， the warm and wet southerly air is weak， the disturbance is weak， not conducive to the occurrence of precipitation.The distribution of low-frequency anticyclone， low-frequency cyclones and low-frequency anticyclone is not obvious in drought years， and the oscillation intensity is not as strong as that in flood years， and the intensity of low-frequency element field is weak.（3） The transmission of low-frequency fluctuation is different in drought and flood years.In flood years， the high and low plateau is the sink area of low-frequency oscillation， and the meridian is also the convergence area.The precipitation in the oscillation sink area is more frequent， so the precipitation in flood years is more.In the dry years， the low-frequency oscillation propagates upward from the plateau to the upper level， so the low-frequency precipitation occurs less in the dry years.

Copyright of Zhejiang Electric Power is the property of Zhejiang Electric Power Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Addressing the issue of system stability is a crucial step towards the successful integration of memristive devices in power electronics applications. This paper focuses on fluorescent lamps possessing memristive characteristics and investigates the instability phenomena and mechanisms within a full-bridge inverter with a fluorescent lamp load. Based on the memristive characteristics of fluorescent lamps, this paper establishes the averaged model of the system, whose coefficient matrix is nonlinear, periodic, and time-varying. This study identifies the occurrence of low-frequency oscillations within the system and elucidates the fundamental mechanism underlying the emergence of low-frequency oscillations. Furthermore, this paper establishes the stability boundaries of the system across different parameter planes. The research findings indicate that the low-frequency oscillations within the system are attributed to the occurrence of Hopf bifurcations in a frequency range higher than line frequency but significantly lower than switching frequency. Lastly, the PSpice circuit of the system is designed, and simulation results are provided for validation. This study can offer guidance on parameters and control strategies for ensuring the stable operation of a full-bridge inverter with fluorescent lamps. Moreover, it can facilitate the comprehension of instability mechanisms in systems incorporating memristive devices, thereby offering a foundation for the expansion of memristor applications. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The development of electric power systems determines the growing probability of low-frequency oscillations, which can be reason of system faults. Traditionally, the task of damping low-frequency oscillations is assigned to synchronous generators, by appropriate setting of the automatic voltage regulator parameters. However, as the installed capacity of renewable generation units increases, research aimed to analyse the impact of these generation units on the power oscillations in the electric power system is becoming more relevant. Moreover, an evaluation of the potential of renewables to solve the problems of power oscillation damping seems necessary to expand the operation functions of the these generation units and to increase the stability of the electric power systems. This paper presents an analysis of renewable energy plants, in particular photovoltaic stations, on damping of these power oscillations. Achieving such damping function is possible via upgrading the automatic control system of photovoltaic stations by using a synthetic inertia block and the possibilities of the “underload” mode. Different scenarios, including small disturbances and severe fault condition for strong and weak grids depending on the location and capacity of photovoltaic station were considered. To evaluate the impact of renewable generation unit to the damping properties of electric power system, the transient damping ratio was calculated. The calculation was carried out in accordance with the guidelines in case of three-phase short-circuit for a different penetration level of renewable generation unit, as well as with and without the synthetic inertia block.

The ActiGraph GT9X has been implemented in clinical trials to track physical activity and sleep. Given recent incidental findings from our laboratory, the overall aim of this study was to notify academic and clinical researchers of the idle sleep mode (ISM) and inertial measurement unit (IMU)'s interaction, as well as their subsequent effect on data acquisition. Investigations were undertaken using a hexapod robot to test the X, Y and Z sensing axes of the accelerometers. Seven GT9X were tested at frequencies ranging from 0.5 to 2 Hz. Testing was performed for three sets of setting parameters: Setting Parameter 1 (ISMONIMUON), Setting Parameter 2 (ISMOFFIMUON), Setting Parameter 3 (ISMONIMUOFF). The minimum, maximum and range of outputs were compared between the settings and frequencies. Findings indicated that Setting Parameters 1 and 2 were not significantly different, but both were significantly different from Setting Parameter 3. Upon inspection, it was discovered that the ISM was only active during Setting Parameter 3 testing, despite it being enabled in Setting Parameter 1. Researchers should be aware of this when conducting future research using the GT9X. [ABSTRACT FROM AUTHOR]

To address the challenges of integrating ever-increasing renewable energy generation such as wind power and photovoltaic (PV) to the power system concerned, the wind-PV-thermal-bundled (WPTB) transmission mode could be employed to mitigate the intermittent power output from wind and PV units. In this work, based on the mathematical models of thermal generation units, wind turbines and PV units, the WPTB transmission system model is developed. Each load demand is modeled as a random variable under various operating conditions of the concerned power system. The Lyapunov linearization method is used to obtain the system matrix of each operation mode, and then all eigenvalues of the system can be attained. According to the generator participation factor, the oscillation modes of the power system are classified. The eigenvalue and damping ratio of each oscillation mode are employed to formulate the objective function of the optimal strategy for enhancing probabilistic small-signal stability, and the particle swarm optimization algorithm is used for global optimization. The secure operation of the power system can be ensured in a wider range by the designed optimization strategy in this work. The effectiveness of the method is demonstrated by simulation results of a sample power system which can operate stably under some uncertain operation conditions. [ABSTRACT FROM AUTHOR]

Resonant pulse combustors, one of the deflagration-based pressure gain combustion devices, can significantly increase thermal efficiency in gas turbine engines. This experimental study investigates the stability characteristics of a newly designed actively valved resonant pulse combustor, capable of sustained operation and meaningful stagnation pressure gain. The resonant pulse combustor was fired with liquid gasoline fuel while ion and pressure sensors captured the temporally resolved heat release and chamber pressure. First, experimental results were used to demonstrate the general operating principle of the combustor. Then, the stability characteristics of the device were investigated through frequency domain analysis of the ion probe and pressure signal traces. A low frequency oscillation (also observed in steady flames and passively valved resonant pulse combustors), was observed as the device was brought near to its blowout limit. Finally, an index was defined to predict the stability characteristics of the resonant pulse combustor by quantifying the competition between low frequency oscillations and combustion-driven resonance. Experimental results demonstrated the ability of this index to provide early prediction of a blowout event for this device. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Engineering Technology is the property of Editorial Department of Electric Power Engineering Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Plateau Meteorology is the property of Plateau Meteorology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The appropriate design of the power oscillation damping controllers guarantees that distributed energy resources and sustainable smart grids deliver excellent service subjected to big data for planned maintenance of renewable energy. Therefore, the main target of this study is to suppress the low-frequency oscillations due to disruptive faults and heavy load disturbance conditions. The considered power system comprises two interconnected hydroelectric areas with heavy solar energy penetrations, severely impacting the power system stabilizers. When associated with appropriate controllers, FACTs technology such as the static synchronous series compensator provides efficient dampening of the adverse power frequency oscillations. First, a two-area power system with heavy solar energy penetration is implemented. Second, two neuro-based controllers are developed. The first controller is constructed with an optimized particle swarm optimization (PSO) based neural network, while the second is created with the adaptive neuro-fuzzy. An energy management approach is developed to lessen the risky impact of the injected solar energy upon the rotor speed deviations of the synchronous generator. The obtained results are impartially compared with a lead-lag compensator. The obtained results demonstrate that the developed PSO-based neural network controller outperforms the other controllers in terms of execution time and the system performance indices. Solar energy penetrations temporarily influence the electrical power produced by the synchronous generators, which slow down for uncomfortably lengthy intervals for solar energy injection greater than 0.5 pu. [ABSTRACT FROM AUTHOR]

• Evaluate PSS, POD-P, and POD-Q's efficiency, flexibility, and performance. • Comparative advantages and potential limitations of each control strategy. • Consider various oscillatory scenarios of a power system with renewables. • POD-P has a superior ability to manage oscillations across multiple scenarios. • PSS effectively damps inter-area oscillations with proper parameterization. The shift from traditional fossil fuel-based power systems to renewable energy sources heightens the importance of frequency regulation. The lack of inertia in this new generation increases the risk of low-frequency oscillatory events, a significant concern in power systems stability. To mitigate these stability problems, it is crucial to study the effectiveness of damping controllers. This paper delves into the analysis of three damping controllers: the power system stabilizers (PSS) installed in synchronous generators, and two Power Oscillation Damping (POD) controllers, one with active power modulation (POD-P) and the other with reactive power modulation (POD-Q), typically installed in environments with high renewable penetration. The main objective is to critically evaluate the comparative advantages of PSS, POD-P, and POD-Q controllers in local and inter-area oscillations by exploring their flexibility and performance under various initial conditions and oscillatory scenarios. The proper choice of damping controllers will ensure the stability of the grid in future scenarios of high renewable production, thus allowing the definition of future technology needs. This research is of utmost importance as it aims to dampen different oscillations by employing uniform control parameters in the PSS, POD-P, and POD-Q controllers. Five scenarios are defined on a system based on the IEEE 39 Bus New England System model and simulated by DIgSILENT PowerFactory. The results are analyzed methodically per scenario, facilitating a comparative evaluation of the controllers and reaching promising conclusions. [ABSTRACT FROM AUTHOR]

The effect of high-pressure detonation products on fuel injection and propagation characteristics of detonation wave has been investigated in the form of ion voltage by varying the equivalence ratio (ER), air mass flux, and operation duration with hydrogen-air mixtures. It has been shown experimentally that the ion voltage decays gradually during the initial stage of rotating detonation wave (RDW). The attenuation of ion voltage is a general phenomenon, and the decay rate of ion voltage and its peak value of the trough state are related to the equivalence ratio and air mass flux. The analysis of interaction between the combustor and hydrogen plenum indicates that the feedback of high-pressure detonation products leads to the attenuation of ion voltage. In addition, the long-duration tests show that the ion voltage will recover to a steady state with the extension of reaction time, when the purgation (products leaving plenums) of detonation products is greater than feedback (products entering plenums) of detonation products in the hydrogen plenum. The recovery of ion voltage starts earlier at the higher equivalence ratio and air mass flux, and the peak value of ion voltage in the steady state also increases with the increase of equivalence ratio and air mass flux. A low frequency oscillation about 10–12 Hz occurs in the RDW at some operation conditions. This low frequency oscillation is related to the interaction between the combustor and hydrogen plenum, and can be eliminated by either increasing the equivalence ratio or decreasing the air mass flux.

Low frequency oscillation is one of the key problem affecting the safe and stable operation of interconnected power system, variational modal decomposition (VMD) was used to extract low-frequency oscillation signals from ambient data, and a method of low-frequency oscillation modal identification for power systems discrete Fourier transform (DFT)-based curve fitting was proposed in this paper. Firstly, the DC component of ambient data signals was filtered by VMD decomposition to extract low-frequency oscillation signals. The number of VMD decomposition was determined by modal correlation coefficient, which improved the timeliness of signal decomposition. Secondly, the auto regressive moving average (ARMA) model of ambient data was established to simulate the generation of data signals. The DFT curve fitting of low-frequency oscillation signal autocorrelation function was used to estimate the Laplace transform coefficient and extract characteristic parameters of electromechanical oscillation. Finally, Simulation data and some measured phasor measurement unit (PMU) data are used to verify the feasibility and effectiveness of the method. The experiment shows that the sampling VMD algorithm and the curve fitting method based on DFT can extract the characteristic parameters of low-frequency oscillation, which effectively improves the real-time performance of electromechanical small interference stability.

In order to study the influence of wind power grid connection on the small-signal stability of the multi-terminal VSC-HVDC system, based on the complete doubly-fed wind turbine model, damping characteristics of the multi-terminal VSC-HVDC system are qualitatively analyzed. Analyzed the influence of the doubly-fed induction generator (DFIG)-based wind turbine (WT) connection on the damping characteristics and stability of the multi-terminal VSC-HVDC system from multiple perspectives including the access point of the WT, the WT's capacity and transmission distance. The methods of the eigenvalue analysis and time-domain simulation analysis are adopted in this paper. Firstly, a complete three-terminal VSC-HVDC system model is built in PSCAD, and the systems after the WT connected to the grid are analyzed and compared. Then, based on the total least squares-estimation of signal parameters via rotational invariance techniques (TLS-ESPRIT) algorithm, some information of the system can be obtained such as eigenvalue, frequency, damping ratio and so on. The research results show that when the WT is connected to the inverter side, the damping ratio tends to be greater than connected to the rectifier side. In addition, within a certain range, as the capacity and transmission distance of the WT increase, the damping ratio also tends to increase. In this way, it provides a technical reference for the planning of wind farm access to multi-terminal VSC-HVDC system. [ABSTRACT FROM AUTHOR]

Addressing the issue of system stability is a crucial step towards the successful integration of memristive devices in power electronics applications. This paper focuses on fluorescent lamps possessing memristive characteristics and investigates the instability phenomena and mechanisms within a full-bridge inverter with a fluorescent lamp load. Based on the memristive characteristics of fluorescent lamps, this paper establishes the averaged model of the system, whose coefficient matrix is nonlinear, periodic, and time-varying. This study identifies the occurrence of low-frequency oscillations within the system and elucidates the fundamental mechanism underlying the emergence of low-frequency oscillations. Furthermore, this paper establishes the stability boundaries of the system across different parameter planes. The research findings indicate that the low-frequency oscillations within the system are attributed to the occurrence of Hopf bifurcations in a frequency range higher than line frequency but significantly lower than switching frequency. Lastly, the PSpice circuit of the system is designed, and simulation results are provided for validation. This study can offer guidance on parameters and control strategies for ensuring the stable operation of a full-bridge inverter with fluorescent lamps. Moreover, it can facilitate the comprehension of instability mechanisms in systems incorporating memristive devices, thereby offering a foundation for the expansion of memristor applications.

The ActiGraph GT9X has been implemented in clinical trials to track physical activity and sleep. Given recent incidental findings from our laboratory, the overall aim of this study was to notify academic and clinical researchers of the idle sleep mode (ISM) and inertial measurement unit (IMU)’s interaction, as well as their subsequent effect on data acquisition. Investigations were undertaken using a hexapod robot to test the X, Y and Z sensing axes of the accelerometers. Seven GT9X were tested at frequencies ranging from 0.5 to 2 Hz. Testing was performed for three sets of setting parameters: Setting Parameter 1 (ISMONIMUON), Setting Parameter 2 (ISMOFFIMUON), Setting Parameter 3 (ISMONIMUOFF). The minimum, maximum and range of outputs were compared between the settings and frequencies. Findings indicated that Setting Parameters 1 and 2 were not significantly different, but both were significantly different from Setting Parameter 3. Upon inspection, it was discovered that the ISM was only active during Setting Parameter 3 testing, despite it being enabled in Setting Parameter 1. Researchers should be aware of this when conducting future research using the GT9X.

The integration of renewable energy has a significant impact on the stability of the power system, especially the unpredictable threat on the small-signal stability. The flexible AC transmission system (FACTS) devices can quickly adjust the fundamental wave power flow to improve the transmission capacity and stability of power systems. This paper proposes an improved steepest descent algorithm (SDA) to coordinate and optimize the control parameters of PSS, TCSC and UPFC-PODC, the initial values and ranges of parameters are determined by the critical eigenvalue locus movement (ELM). Extensive simulations on the eight machines twenty-four buses power system verify the effectiveness of the proposed method on improving the damping level and restraining the low frequency oscillation. [ABSTRACT FROM AUTHOR]

Recently, there has been a notable shift to increasingly more sedentary lifestyles, yet it remains unclear whether inexpensive accelerometers, such as those contained in Actigraph devices, can provide consistent measurements of low magnitude accelerations. This study sought to explore the ability of two Actigraph models to differentiate low frequency oscillations, in reference to higher-end accelerometers with the idle sleep mode disabled (ISM) (Part 1) and enabled (Part 2) in a controlled environment. Eight GT9X, fifteen wGT3X-BT and two higher-end accelerometers (Triaxial ICP) were mounted to a 6-degree of freedom robot, which introduced frequencies ranging from 0.5-2.0 Hz (Part 1) and 0.5-4.0 Hz (Part 2). To compare the models, the minimum, maximum and range of outputs were calculated for each of the frequencies. Part 1 revealed that the Actigraph monitors were able to detect low frequency oscillations; the captured output was similar across the different Actigraph models but was significantly greater than the higher-end devices. Part 2 demonstrated that amplitudes greater than the described 40 m g (0.392 m/s2) threshold were required for the Actigraph monitors to wake up. This study demonstrates that the GT9X and wGT3X-BT Actigraph accelerometers can detect low magnitude movements when the ISM is disabled. [ABSTRACT FROM AUTHOR]

The increasing number of low-frequency oscillation events has posed significant challenges to power system stability. It is imperative to accurately identify and properly control generators with poor or negative damping contribution for better oscillation damping. This paper proposes a hybrid energy and mode decomposition-based method for evaluating generators damping in multi-machine power systems. It is derived that the aggregate electric torque can be modeled as the superposition of electric torques in different modes. In each oscillation mode, the electric torque can be decomposed into the damping torque and the synchronizing torque. Moreover, a novel oscillation energy function is developed to evaluate generators' damping effect in each oscillation mode. The result proves that in each oscillation mode, generators with attenuated oscillation energies have negative damping effects. Simulation results in single and multinegative damping generators cases, as well as the comparison with other methods, demonstrate the effectiveness and robustness of the proposed method for damping evaluation.

Low frequency oscillation (LFO) in the electric multiple units (EMUs)-traction network cascade system (ETNCS) can lead to traction blockade and abnormal operation. Using the Chinese CRH3 EMUs as an example, a new LFO suppressing method by applying the energy storage (ES) device on EMUs is proposed in this paper and the ES is connected to the DC-link on board. The equivalent model of the ETNCS is established at first. The critical condition of LFO in the ETNCS is analyzed via impedance ratio criterion and Bode diagram. Then, the proposed on-board bidirectional DC-DC converter integrated with the ES system is controlled via a virtual DC machine (VDCM) strategy, and the VDCM small signal model derivation and the parameter design are carried out. Using the Bode diagram of the impedance ratio, the system stability with the ES device controlled by the proposed VDCM scheme is analyzed again; simulation results verify the effectiveness of the control algorithm to suppress the LFO adaptively. Compared with the traditional PI controller, the system steady-state and dynamic performance can be improved with the proposed method, including decreased overshoot, fluctuation, response time, and increased gain margin of the DC-link voltage.

Using NCEP daily reanalysis and observation data, we analyzed the characteristics of the 2020 Meiyu in Shanghai and evaluated the effectiveness of the extended range forecast which is based on the atmospheric low-frequency characteristics. The results show that (1) the 2020 Meiyu in Shanghai was the most severe one since 2000. (2) The excessive precipitation during Meiyu is caused due to the influence by the cold phase of equatorial central-east Pacific and the anomalously warm SST of the tropical Indian Ocean in summer, the strong and stable anomalous anticyclone in the northwest Pacific Ocean and the abnormally strong water vapor transport from its western turn, and the frequent cold air transfer along the direction of wave-activity flux. (3) The precipitation events in the 2020 Meiyu show obvious quasi-biweekly oscillation characteristics, with all four strong precipitation events corresponding to the peaks of low-frequency precipitation. The extended range precipitation forecast method developed based on the low-frequency characteristics is more accurate in predicting the first strong precipitation event in the 2020 Meiyu season.

With the rapid development and wide range application of AC/DC distribution network,its stability has also become the focus. The low-frequency oscillation at the DC side in the commissioning stage of an AC/DC distribution network project is analyzed. Based on the small signal modeling,the eigenvalue analysis method is used to analyze the influence laws of short circuit ratio (SCR),power level and control parameters on low-frequency oscillation. Next,the measures of changing controller parameters and adding additional controllers to suppress oscillation are proposed. The theoretical analysis and simulation test show that weak grid affects the stability of voltage source converter (VSC). Low frequency oscillation occurs when the 375 V DC side power increases to exceed the rated power. The integral coefficient of the Buck converter current inner loop proportional integral (PI) controller does not affect the stability of the system,but it affects the oscillation frequency after the oscillation occurs. If the proportional coefficient of the voltage outer loop PI controller is too small or the integral coefficient is too large,the system is unstable. Changing voltage outer loop PI controller parameters of Buck converter and adding additional controller can effectively suppress low-frequency oscillations. The theory and simulation analysis of the actual AC/DC distribution network oscillation influence factors are of reference significance for the commissioning and operation analysis of other AC/DC distribution network projects.

The appropriate design of the power oscillation damping controllers guarantees that distributed energy resources and sustainable smart grids deliver excellent service subjected to big data for planned maintenance of renewable energy. Therefore, the main target of this study is to suppress the low-frequency oscillations due to disruptive faults and heavy load disturbance conditions. The considered power system comprises two interconnected hydroelectric areas with heavy solar energy penetrations, severely impacting the power system stabilizers. When associated with appropriate controllers, FACTs technology such as the static synchronous series compensator provides efficient dampening of the adverse power frequency oscillations. First, a two-area power system with heavy solar energy penetration is implemented. Second, two neuro-based controllers are developed. The first controller is constructed with an optimized particle swarm optimization (PSO) based neural network, while the second is created with the adaptive neuro-fuzzy. An energy management approach is developed to lessen the risky impact of the injected solar energy upon the rotor speed deviations of the synchronous generator. The obtained results are impartially compared with a lead-lag compensator. The obtained results demonstrate that the developed PSO-based neural network controller outperforms the other controllers in terms of execution time and the system performance indices. Solar energy penetrations temporarily influence the electrical power produced by the synchronous generators, which slow down for uncomfortably lengthy intervals for solar energy injection greater than 0.5 pu.

Low frequency oscillation (LFO) is one of the major concerns for reliable operation of the power system. This LFO occurs due to the failure of the rotor to supply sufficient damping torque to compensate the imbalance between mechanical input and electrical output. Hence, in this paper, we adopt a third generation flexible AC transmission system (FACTS) device named generalized unified power flow controller (GUPFC) based damping controller in order to investigate its effect for mitigating LFO for an single machine infinite bus (SMIB) system. To find an effective damping controller-optimizer pair, we integrate proportional–integral (PI) or lead–lag as a controller and grey wolf optimizer (GWO), differential evolution (DE), particle swarm optimization (PSO), whale optimization algorithm (WOA), and chaotic whale optimization algorithm (CWOA) as an optimizer. Later, we investigate the performances for the above mentioned controller-optimizer pairs through time domain simulation, eigenvalue analysis, nyquist stability test, and quantitative analysis. Moreover, we carry out two non-parametric statistical tests named as one sample Kolmogorov–Smirnov (KS) test and paired sample t − t e s t to identify statistical distribution as well as uniqueness of our optimization algorithms. Our analyses reveal that the GWO tuned lead–lag controller surpasses all other controller-optimizer combinations. • Adoption of third generation FACTs device such as GUPFC for mitigating LFO. • Identification of the most suitable GUPFC control input using controllability and residue indices. • Selection of efficient damping controller-optimizer pair from ten different combinations. • Demonstration of effectiveness for these combination through Eigen value analysis, time-domain analysis, quantitative analysis, and non-parametric statistical test. [ABSTRACT FROM AUTHOR]

Concerning the difficulty in unified modeling of direct-drive wind farm with virtual inertia and the unknown cause of low frequency oscillation, a detailed model of integrated dissipation energy of direct-drive wind farm is built. First, the dissipation energy model of wind generator and the integrated dissipation energy model of direct-drive wind farm containing virtual inertia and PLL is derived and built. On this basis, according to different sources of integrated dissipation energy, it is decomposed into free dissipation energy, resonant dissipation energy and forced dissipation energy. These three components respectively characterize the contribution of inherent damping, generator-grid coupled resonance and generator-grid interaction to the stability of system. And then, how the variation of wind speed and generator location affects the stability of system is analyzed quantitatively using the integrated dissipation energy. Finally, the model of IEEE 10-machine 39-bus system connected with direct-drive wind farm is built in RTDS for hardware-in-the-loop tests. Simulation results verify that, the detailed model exhibits three different oscillation states, and each generator in the wind farm contributes differently to system oscillation. The traditional equivalent model of wind farm only exhibits one oscillation state and cannot reflect the difference in contributions of generators, thus it may wrongly identify the stability of system, even aggravate oscillation. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Elevated carbon dioxide (CO2) in breathing air is widely used as a vasoactive stimulus to assess cerebrovascular functions under hypercapnia (i.e., "stress test" for the brain). Blood-oxygen-level-dependent (BOLD) is a contrast mechanism used in functional magnetic resonance imaging (fMRI). BOLD is used to study CO2-induced cerebrovascular reactivity (CVR), which is defined as the voxel-wise percentage BOLD signal change per mmHg change in the arterial partial pressure of CO2 (PaCO2). Besides the CVR, two additional important parameters reflecting the cerebrovascular functions are the arrival time of arterial CO2 at each voxel, and the waveform of the local BOLD signal. In this study, we developed a novel analytical method to accurately calculate the arrival time of elevated CO2 at each voxel using the systemic low frequency oscillations (sLFO: 0.01-0.1 Hz) extracted from the CO2 challenge data. In addition, 26 candidate hemodynamic response functions (HRF) were used to quantitatively describe the temporal brain reactions to a CO2 stimulus. We demonstrated that our approach improved the traditional method by allowing us to accurately map three perfusion-related parameters: the relative arrival time of blood, the hemodynamic response function, and CVR during a CO2 challenge. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydrofoil is the core unit of energy conversion for axial-flow pumps and hydro-energy turbines. The dynamic characteristics of hydrofoil significantly affect the operation stability of pumps and turbines, especially under the critical stall condition. In this paper, the unsteady flow field of NACA66 hydrofoil under critical stall condition at Reynolds number 0.75 × 10E6 is investigated by IDDES method. The low-frequency oscillations (LFO) under critical stall condition characterized by two typical frequencies with Strouhal number (St) 0.031 and 0.065 are reported in pressure pulsation and lift coefficient respectively. It is found that the merging phenomenon of separation vortices are the main reason of the wave peak of LFO with St 0.031, while the phenomenon of generation and shedding of separation vortices exist at the moment corresponding to the wave trough. The reason of the LFO of lift coefficient with St 0.065 is found to be the long-short switching of streamwise coverage of the leading edge separation vortex. The change of streamwise coverage is corresponding to the movement of the reattachment point of the separation area. The revelation of LFOs flow mechanism in hydrofoil under critical stall can provide reference for its unsteady flow control and applications. • LFO characteristic of hydrofoil NACA66 under critical stall condition is reported. • Two typical low-frequencies dominate the transient pressure and lift respectively. • The separation vortex merging fosters the first low-frequency. • Long-short switching of LE separation vortex leads to the second low-frequency. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a hybrid adaptive strategy to control virtual inertia of virtual synchronous generators (VSGs). The proposed technique can provide low frequency oscillation (LFO) damping and simultaneously improve primary frequency control (PFC) performance metrics. To this end, a control variable is defined to control extremum values of the VSG inertia during PFC process. The control variable uses an estimation of the grid frequency gradient to identify the PFC process stages following a power deficit event. The extremum of the VSG inertia to provide LFO damping is governed based on the control variable. In particular, the minimum value of the VSG inertia is restricted to its base value during the frequency arresting process in order to moderate the frequency rate of change. In contrast, the maximum value of the VSG inertia is limited to its base value in frequency recovery period to achieve a faster frequency recovery. The efficiency of the suggested method is validated through a power system with VSG penetration level as 50% of the system generation rating. The achieved results verify the superiority of the proposed scheme in the PFC improving and the LFO damping in comparison to the conventional strategy. Moreover, the suggested approach can efficiently decrease the required size of the VSG energy storage by about 50%. [ABSTRACT FROM AUTHOR]