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By addressing the phenomenon of carbody abnormal vibrations in the field, the acceleration of the carbody and bogie was measured using accelerometers, and the diamond mode of the carbody was identified. The equivalent conicity of the wheelset and the acceleration at the frame end indicated that the shaking of the carbody was caused by bogie hunting. In the SIMPACK simulation, the acceleration frequency and amplitude at the frame end and midsection of the side beam were calculated. The lateral deformation amplitude of the side beam in the finite element model was extracted, and a modal shape function for the diamond-shaped mode was established. By utilizing the modal vibration equation, the modal generalized forces of the carbody were computed, revealing that, during carbody shaking, the yaw damper force contributed significantly among the forces of the secondary suspension, with the phase difference between the front and rear bogies approaching 180°. This insight offers a novel perspective for subsequent active control strategies. Subsequently, these modal generalized forces were applied as external excitation to a coupled vibration model encompassing both the carbody and transformer. Aiming to reduce the acceleration amplitude at the side beam, the transformer was treated as a dynamic vibration absorber, allowing for the optimization of its lateral suspension parameters. As a result, the lateral and vertical acceleration amplitudes at the side beam were concurrently reduced, with the maximum decrease reaching 58.5%, significantly enhancing the ride comfort. [ABSTRACT FROM AUTHOR]

At present, great attention is being devoted towards resistive switching devices owing to lower switching voltage (<3 V), higher tolerance (> 10∧6 cycles), higher scalability (< 10 nm), multi-bit operations, and higher information storage time (10 years) compared to the existing broadly employed transistor technology. This was all possible owing to the accidental discovery of memristance by Hewlett Packard (HP) labs in 2008. In the past few decades, discoveries of such unique electronic properties have led to tremendous technological advancements. Consequently, it is very important to continually seek newer electronic characteristics. In this work, copper (Cu)-doped zinc oxide (ZnO) thin film was synthesized on Cu electrodes to form a Cu/Cu: ZnO/Cu resistive switching device. Function generator and oscilloscope were employed to obtain the electronic characteristics of the device instead of conventional techniques, which resulted in a 96.17% improvement in total equipment expenses. Most importantly, the proposed device exhibited hysteresis resonance and multi-pinched hysteresis; such phenomena have never been reported to date. These characteristics are extremely essential towards futuristic electronics for the development of computational circuits with meliorated performance, electronic systems with improved controllability, memory cells with higher data storage, and in-memory-based processing capabilities. [ABSTRACT FROM AUTHOR]

The neutron capture cross-section of 241Am was measured from 10 meV to about 500 keV using the NaI(Tl) spectrometer of the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) beamline in the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The total energy detection principle was applied in conjunction with the pulse-height weighting technique to derive the neutron capture yield. The present cross-section results were normalized using a 197Au sample measurement by applying the saturated resonance method. The thermal cross section was measured to be 708 ± 22 b, in agreement with the evaluation in JENDL-5 of 709 b within uncertainties. In the keV region, the evaluated libraries of JENDL-5, ENDF/B-VIII.0 and JEFF-3.3 are in good agreement with the present results over 10 keV but show values lower by 30% to 70% below that energy. Moreover, the results of a resonance shape analysis of the resolved resonance region are also provided in the present paper. [ABSTRACT FROM AUTHOR]

The resonance phenomena of a weakly nonlinear, damped, Duffing-van der Pol oscillation is studied analytically and numerically. The methods of multiple scales is used to obtain uniformly valid asymptotic approximate solutions of the governing equation for various cases of primary harmonic resonance, super-harmonic resonance and sub-harmonic resonance respectively. The study shows that the steady amplitudes in the solutions of the nonlinear equation demonstrate the nonlinear phenomena involving jump and bistability at some bifurcation points. The quantitative relations of Frequency-Amplitude involving the parameters of damping, nonlinear, external force in the oscillator are obtained. The asymptotic approximation and numerical solutions are in vertically perfect agreement for all the cases considered. The results enrich previous researches just for Duffing or van der Pol oscillation respectively. [ABSTRACT FROM AUTHOR]

By addressing the phenomenon of carbody abnormal vibrations in the field, the acceleration of the carbody and bogie was measured using accelerometers, and the diamond mode of the carbody was identified. The equivalent conicity of the wheelset and the acceleration at the frame end indicated that the shaking of the carbody was caused by bogie hunting. In the SIMPACK simulation, the acceleration frequency and amplitude at the frame end and midsection of the side beam were calculated. The lateral deformation amplitude of the side beam in the finite element model was extracted, and a modal shape function for the diamond-shaped mode was established. By utilizing the modal vibration equation, the modal generalized forces of the carbody were computed, revealing that, during carbody shaking, the yaw damper force contributed significantly among the forces of the secondary suspension, with the phase difference between the front and rear bogies approaching 180°. This insight offers a novel perspective for subsequent active control strategies. Subsequently, these modal generalized forces were applied as external excitation to a coupled vibration model encompassing both the carbody and transformer. Aiming to reduce the acceleration amplitude at the side beam, the transformer was treated as a dynamic vibration absorber, allowing for the optimization of its lateral suspension parameters. As a result, the lateral and vertical acceleration amplitudes at the side beam were concurrently reduced, with the maximum decrease reaching 58.5%, significantly enhancing the ride comfort.

Abstract The medium‐ and high‐frequency resonance between modular multilevel converters (MMCs) and the AC grid has attracted increasing attention due to the frequent occurrence of resonance events in recent years. Therefore, resonance issues are analyzed, and corresponding suppression strategies are proposed in this paper. First, the analytical expression of the MMC AC‐side impedance is established. Then, the mechanism and influencing factors of different types of resonances, including active resonance and passive resonance, are analyzed to provide a more comprehensive perspective. To aid the suppression of these resonances, resonance risk indexes are defined to evaluate the resonance risk, and then the suppression effects of different strategies are compared through analytical calculations. Subsequently, coordinated resonance suppression strategies suitable for different resonance situations are proposed. The key points of the suppression strategies are to suppress the negative damping of MMC impedance at the resonance frequency and improve the integrated impedance of the MMC AC‐side system. Finally, the proposed suppression strategies are verified by simulation results.

The application of the multi-branch gear transmission in the power transmission system of high-power ships is increasing gradually. The elastic shaft structure used to realize the uniform load of each branch will lead to the reduction of the natural frequency of the transmission system, which will increase the possibility of resonance during operation. Based on the commercial finite element software (Ansys), a finite element model of a marine six-branch coaxial herringbone gear transmission system is established. The rotational degrees of freedom are reserved at each support, and the remaining degrees of freedom are constrained. The first 20 orders of natural frequencies and vibrations of the transmission system are calculated. Based on the Campbell diagram, the resonance characteristics of the system are analyzed for cruise speed. The influence law of the elastic shaft stiffness on the natural frequency of the system is studied, and the value range of the elastic shaft stiffness to avoid the resonance of the transmission system is obtained, which provide some reference for the vibration reduction design of the six-branch coaxial herring gear transmission system.

In this paper, a semi-analytical method is presented for nonlinear vibration analysis of rotating stiffened truncated conical shells with functionally graded materials (FGM) in the thermal environment subjected to harmonic excitation. Considering Coriolis acceleration and the centrifugal force, the governing equations of stiffened rotating FGM truncated conical shells are extracted utilizing the classical shell theory regarding the nonlinear von Karman relationships and the smeared stiffeners technique. The partial differential equations are discretized to a set of ordinary nonlinear equations by employing Galerkin's approach. The condensation method is utilized to reduce the equations of motion into the transverse direction. For analyzing the nonlinear resonance behavior, we use the multiple scales method. According to this approach, the primary resonance of the nonlinear vibration of the stiffened rotating FGM truncated conical shells is examined. Besides, linear free vibration of the stiffened rotating shell is analyzed to investigate the natural circular frequency. Numerical results are studied to investigate the influence of shell rotating speed on the frequency response curve. Also, the effects of force amplitude, volume–fraction index, temperature changes, and different vertex angles on the frequency response curve are examined for various rotating speeds. [ABSTRACT FROM AUTHOR]

The medium‐ and high‐frequency resonance between modular multilevel converters (MMCs) and the AC grid has attracted increasing attention due to the frequent occurrence of resonance events in recent years. Therefore, resonance issues are analyzed, and corresponding suppression strategies are proposed in this paper. First, the analytical expression of the MMC AC‐side impedance is established. Then, the mechanism and influencing factors of different types of resonances, including active resonance and passive resonance, are analyzed to provide a more comprehensive perspective. To aid the suppression of these resonances, resonance risk indexes are defined to evaluate the resonance risk, and then the suppression effects of different strategies are compared through analytical calculations. Subsequently, coordinated resonance suppression strategies suitable for different resonance situations are proposed. The key points of the suppression strategies are to suppress the negative damping of MMC impedance at the resonance frequency and improve the integrated impedance of the MMC AC‐side system. Finally, the proposed suppression strategies are verified by simulation results. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) tends to cause resonance instability in interconnected systems. Current studies on the stability of MMC mainly focus on high-voltage and large-capacity power systems, while the impedance modeling process of MMC ignores the harmonics of the submodule (SM) capacitor voltages and the influence of voltage feedforward control. The applicability of the MMC impedance model with fewer submodules is doubtful. According to the circuit structure and control mode, the AC-side sequence impedance model of the MMC is established, which takes into account the capacitor voltage balance control of submodules and voltage feedforward control. Based on the RT-Lab control hardware-in-loop (CHIL) test platform, the MMC impedance frequency scanning was carried out to verify the accuracy of the impedance modeling method. The influence of control parameters in different frequency bands on the impedance characteristics of MMC was studied. The AC terminal voltage feedforward causes phase lag in the mid-/high-frequency range and increases the risk of resonance. In the low-frequency range, the dynamics and control of capacitor voltages reduce the impedance magnitude of MMC. Using the resonance phenomenon of an MMC connected to a weak grid as an example, the high-frequency resonance mechanism caused by control parameters is analyzed from the perspective of the negative damping effect. The simulation results show that the detailed wideband impedance model can improve the accuracy of the stability analysis results. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear vibration and resonance analyses of a rectangular hyperelastic membrane embedded within a nonlinear Winkler-Pasternak elastic medium subjected to a uniformly distributed hydrostatic pressure are investigated. The material of the membrane is incompressible, homogeneous, isotropic, and hyperelastic. The constitutive law of neo-Hookean is utilized for modeling the system. The elastic foundation includes two Winkler and Pasternak linear terms and a Winkler term with cubic nonlinearity. Using the theory of thin hyperelastic membrane, Hamilton's principle, and assuming the finite deformations, the governing equations are obtained. Then, the motion equation in the transverse direction is discretized by applying Galerkin's method. The transverse nonlinear oscillations of the membrane are considered in twomodes. Then, utilizing the multiple scales method, the secondary resonance for the case of V? 2x2 þ -1 is analyzed. Also, to analyze the nonlinear vibration behavior, numerical methods including the fourth-order Runge-Kutta methods are utilized. In addition, in analyzing the nonlinear vibration responses of the rectangular hyperelastic membrane, the bifurcation diagram, quasi-period motion responses, and the phase portrait are examined. Finally, the influence of the geometrical characteristics and elastic foundation parameters on the resonance analysis of a rectangular hyperelastic membrane is investigated. [ABSTRACT FROM AUTHOR]

The nonlinear characteristics of a general multiple degree-of-freedom suspension bridge under harmonic excitation are studied with an innovative approach consisting of the harmonic modes, the finite element modeling and the incremental harmonic balance method. The geometric nonlinearity induced by large-amplitude vibration is considered. The harmonic mode and mean kinetic energy of the system are proposed to describe the nonlinear responses. The harmonic mode can be expressed as a linear combination of different linearized system modes. The resonance responses of the structure are characterized with the participation ratio of these system modes. Its composition under harmonic excitations can easily be described in terms of the different harmonic mode shapes and then the system modes. The proposed method is further applied to analyze, in detail, the properties of the harmonic modes and the evolution of the steady-state nonlinear responses with variations in the excitation frequency. [ABSTRACT FROM AUTHOR]

Online monitoring for underground power cable insulation has become an urgent need in distribution grids, which can lead to proactive maintenance and avoid severe insulation faults. Insulation capacitance has been selected as an effective insulation condition indicator in many researches, but the variation of insulation conductance is always overlooked, resulting in a limited monitoring range and sensitivity. To solve this problem, a novel online monitoring method for underground power cable insulation based on resonance frequency analysis under chirp signal injection is proposed in this article. An online monitoring scheme based on common-mode chirp signal injection is first designed, realizing online monitoring in a nonintrusive manner. The resonance frequency under the injected signal is then analyzed, providing an effective approach to monitor insulation capacitance regardless of the accompanied insulation conductance variation. Simulations and experiments are carried out, proving the effectiveness of the proposed method for different system operating conditions. [ABSTRACT FROM AUTHOR]

Based on the modal analysis theory of cyclic symmetric structure, the method for analyzing coupled vibration characteristics of large blades under the wheel assembly condition was established to evaluate the vibration characteristics and working reliability of the compressor rotor blades. A compressor stage was selected as the research object and the finite element model of blade-disc coupling structure was established by cyclic symmetry. The modal and stress distribution of the blade-disc system under static and working speeds were obtained. The reliability of the proposed method was verified by comparing with the experimental results. The dangerous rotational speed of the blade was determined using Campbell diagram, and the frequency margin of the system was evaluated at specific rotational speed, which provided numerical simulation technology support for the dynamic stress measurement of the compressor working blade. [ABSTRACT FROM AUTHOR]

With the move towards decarbonization of the energy system and increased use of renewable generation, the number of power electronics converter interfaced resources connecting to the grid is growing. These power electronics converters have fast dynamics determined by control algorithms, which leads to significant changes in the dynamics and impedance characteristics of the power system. Based on practical experience, concerns have grown about interactions between converters and between converters and the grid which can give rise to instability in a system with multiple grid–connected inverters operating in parallel. This paper reviews the recent work related to the understanding, modeling and mitigation of such interactions. The basic concepts which underpin the interactions are explained and discussed from an impedance stability perspective. The concepts are illustrated by means of an example case of multiple inverters operating in a low voltage distribution system. In recent years, several approaches have been proposed to prevent or mitigate the effects of these interactions. The mitigation approaches proposed in the most recent works are categorized and comprehensively reviewed. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) tends to cause resonance instability in interconnected systems. Current studies on the stability of MMC mainly focus on high-voltage and large-capacity power systems, while the impedance modeling process of MMC ignores the harmonics of the submodule (SM) capacitor voltages and the influence of voltage feedforward control. The applicability of the MMC impedance model with fewer submodules is doubtful. According to the circuit structure and control mode, the AC-side sequence impedance model of the MMC is established, which takes into account the capacitor voltage balance control of submodules and voltage feedforward control. Based on the RT-Lab control hardware-in-loop (CHIL) test platform, the MMC impedance frequency scanning was carried out to verify the accuracy of the impedance modeling method. The influence of control parameters in different frequency bands on the impedance characteristics of MMC was studied. The AC terminal voltage feedforward causes phase lag in the mid-/high-frequency range and increases the risk of resonance. In the low-frequency range, the dynamics and control of capacitor voltages reduce the impedance magnitude of MMC. Using the resonance phenomenon of an MMC connected to a weak grid as an example, the high-frequency resonance mechanism caused by control parameters is analyzed from the perspective of the negative damping effect. The simulation results show that the detailed wideband impedance model can improve the accuracy of the stability analysis results.

The leakage of the pilot stage of the 2D valve mainly depends on the size of its initial opening. According to the Routh criterion, the pilot stage of the two-dimensional magnetically levitated servo-proportional valve (2D-MSP valve) needs to be designed to have certain positive values to increase the damping ratio to improve valve stability, which leads to the leakage flow representing a non-negligible power loss. In order to reduce leakage flow and achieve goal of energy saving, this paper presents a novel resonance stability criterion by considering nonlinear characteristics of the fluid dynamic system. First, the 2D-MSP valve is regarded as a three-way valve-controlled differential cylinder system. Based on the frequency response of the resonance state, the energy conservation method is used to solve the flow "backfilling" area, the motion equation of the cylinder piston (valve spool displacement) and the pressure waveform of the sensing chamber under different opening and pressure amplitude ratio. Then, the analytical expression of the resonance peak amplitude is obtained and the resonance stability criterion is deduced. The result is compared with the Routh stability criterion, which illustrates that the positive openings of the pilot stage can be reduced to one-third of the original value. The prototype valve is then designed and manufactured based on the resonance stability criterion. The dynamic and static characteristics under different system pressures are measured. Experimental results show that the prototype valve is an over-damped system without any overshoot, which has excellent working stability, and its static and dynamic performance can meet the demands of the industry servo-proportional control system. The research work validates the effectiveness of the proposed resonance stability criterion. [ABSTRACT FROM AUTHOR]

In modular power converters, the dc-link capacitor has the highest failure rate due to thermal stress, reducing system performance and reliability. Current harmonics are one of the prominent causes of thermal stress on the dc-link capacitor that may get instigated by the resonance between the dc-link capacitor and stray inductance of the busbar. The dc-link capacitor current harmonics mitigation through busbar design optimization has not been reported. The challenge lies in analyzing the profound resonance characteristics of high order dc-link busbar impedance network as no insightful information can be obtained from impedance analyzers. This paper features a new strategy for high power modular converters that splits the high order dc-link busbar impedance network into corresponding lower-order sub-units. Then, the required relationship between resonating components and corresponding resonance frequencies is attained by exploiting the structural symmetry of the standard modular power unit as well as the inheritance relationship between sub-circuit units and the combined network. Finally, leveraging the derived resonant frequencies expressions, busbar structure is optimized, and up to 23% reduction in capacitor RMS current is achieved. Simulation and experimental results are provided to validate the efficacy of the proposed analysis method. The in-depth theoretical study featured in this paper can dictate not only the busbar design optimization but also a key to improve capacitor lifetime and reliability of the system.

This paper deals with reduction of oscillations of a continuous spinning shaft using proportional-derivative time delay controller. The stable and unstable zones of the system are obtained using the Routh-Hurwitz criteria. For small values of proportional coefficients, the Hopf bifurcation occurs in the high values of time delays while in the higher values of proportional coefficients instability occurs in the lower values. Also, in small values of derivative coefficients the Hopf bifurcation happens in the lower values of time delays, while in the higher values of derivative coefficients mentioned bifurcation occurs in the higher values. [ABSTRACT FROM AUTHOR]

Motivated by recent years' resonance incidents in wind-integrated power systems, this paper investigates the resonance-induced harmonic distortion and stability issues in doubly fed induction generator (DFIG)-based offshore wind farm (OWF) with high-voltage direct current (HVDC) grid connection. To accurately capture the dynamic characteristics of DFIG-based wind farm, a comprehensive impedance modelling considering the detailed PI control loop and DC dynamics of wind turbine as well as the cable connections of the medium-voltage (MV) collector system is conducted. Through stepwise simulation verifications, aggregated modelling of MV collector system is proved to be suitable for wideband resonance analysis. On this basis, the resonance analysis regarding grid topology change and controller parameter variation is conducted and the impact of frequency coupling on subsynchronous resonance (SSR), middle- and high-frequency resonances is analyzed using the aggregated models derived from a practical HVDC connected DFIG-based OWF. The strength or degree of the frequency coupling between the sequence impedances of wind farm, which is induced by the asymmetrical converter control of wind turbines, is found to be dependent on the impedances of all the components of the system. Moreover, case studies are conducted to demonstrate the importance of including the frequency coupling in SSR stability assessment. Simulations in MATLAB / Simulink validate the modelling and resonance analysis.

With the move towards decarbonization of the energy system and increased use of renewable generation, the number of power electronics converter interfaced resources connecting to the grid is growing. These power electronics converters have fast dynamics determined by control algorithms, which leads to significant changes in the dynamics and impedance characteristics of the power system. Based on practical experience, concerns have grown about interactions between converters and between converters and the grid which can give rise to instability in a system with multiple grid–connected inverters operating in parallel. This paper reviews the recent work related to the understanding, modeling and mitigation of such interactions. The basic concepts which underpin the interactions are explained and discussed from an impedance stability perspective. The concepts are illustrated by means of an example case of multiple inverters operating in a low voltage distribution system. In recent years, several approaches have been proposed to prevent or mitigate the effects of these interactions. The mitigation approaches proposed in the most recent works are categorized and comprehensively reviewed.

Over the last decades, the resonance-related dynamics for bridge systems subjected to a moving train has been researched and discussed from mechanics, physics and mathematics. In the current work, new perspectives of train-induced resonance analysis are investigated through introducing random propagation process into the train–bridge dynamic interactions. Besides, the Nataf-transformation-based point estimation method is applied to generate pseudorandom variables following arbitrarily correlated probability distributions. A three-dimensional (3D) nonlinear train-ballasted track–bridge interaction model founded on fundamental physical and mechanical principles is employed to convey and depict train–bridge interactions with random properties considered. After that, extensive applications are illustrated in detail for revealing the statistical characteristics of the so-called "random resonance". Numerical results show that the critical train speeds associated with resonance and cancelation are random in essence owing to the variability of system parameters; the correlation between parameters exerts obvious influences on system dynamic behaviors; the last vehicle of a train will be in more violent vibrations compared to the front vehicles; the influences of track irregularities on the wheel–rail interactions are significantly greater than those of resonance. [ABSTRACT FROM AUTHOR]

The gearbox is a pivotal component in wind turbine,the dynamics performance of gearbox is one of the most critical factors determining the lifetime of gearbox and that of the wind turbine. A multi-body dynamics drivetrain model with rigid-flexible body coupled of a level MW wind turbine is built by using the Simpack software. The reliability and accuracy of this model is confirmed through comparing the nature frequency derived from Simpack drivetrain model and the nature frequency calculated by Bladed software and traditional approach. The modal analysis and torsional resonance analysis of gearbox is completed based on the multi-body dynamics simulation both in frequency domain and time domain,furthermore,the potential resonance is evaluated,the influence of shaft misalignment on the dynamics performance of gearbox is analyzed. The aforementioned analysis approach and evaluation method is confirmed to be correct by experimental.

Highlights • The suspension bridge with spatially inclined main cables is studied. • Nonlinear dynamics of a sectional model of suspension bridge is investigated. • The primary and secondary resonances of the first two modes are checked. • The effect of second and third order nonlinear stiffness of the system on the nonlinear dynamics are studied in details. Abstract The nonlinear dynamics of a suspended bridge deck with inclined main cables and its sensitivity to the nonlinear stiffness are investigated via a 6-DoFs sectional model in this study. Four configurations with different main cable inclination angles are investigated. Two higher order numerical models are analyzed to examine the effects of higher order nonlinear stiffnesses on the dynamic properties, with one considering the linear and quadratic stiffness terms and the other includes additionally the cubic stiffness term. Incremental harmonic balance method is adopted for the nonlinear dynamic analysis, and primary resonances at the first and second modes are studied in details. Results show that the nonlinearity introduced by the inclined main cables has only very minor effects on the first primary resonance modal response. However, the cubic stiffness term shows quite strong effect on the dynamic response of the second mode. If only the linear and quadratic stiffnesses are included in the model, the frequency-response curve from the first harmonic term shows weak softening features. The system, however, performs like a hard spring when the cubic stiffness is included which is totally different from existing published results. The observations on the super-harmonic resonance at the first two modes of the system also show great differences in the behavior of the two numerical models. Results from this study suggest that the cubic nonlinear stiffness should be included for better modeling of a sectional suspension bridge model. [ABSTRACT FROM AUTHOR]

Highlight • Resonance mechanism is analyzed, and resonance damping is estimated using an aggregated RLC circuit. • The influence factors on the resonance are investigated. • A voltage feedforward approach, which can adjust the impedance characteristic, is introduced. • A virtual capacitor control is proposed to enhance the system inertia. • The design of controller parameters is discussed. Abstract In this paper, an impedance analysis method and resonance suppression strategies are proposed for the distributed controlled DC zonal distribution network. By combining with the grid impedance model and the node impedance matrix, the resonance mechanism of shipboard DC distribution network is investigated. The resonance damping is estimated using an aggregated RLC circuit. The proposed method is validated by the time-domain small signal model. Moreover, a multi-bus analysis method is proposed for the stability assessment of the system with multi-parallel, multi-cascade and ring-type structure, and the influence factors on the resonance are investigated. Further, a voltage feedforward approach is introduced, which can adjust the impedance characteristic of line regulating converter (LRC) at the resonance-frequency band effectively. Besides, a virtual capacitor control strategy analogized with virtual synchronous generator (VSG) is proposed to enhance the system inertia. By analyzing the control system stability, the appropriate controller parameters are selected. The simulation results show the effectiveness of the proposed analysis method and the control strategies. [ABSTRACT FROM AUTHOR]

High-impedance faults (HIF) occur frequently in resonant grounding systems and are difficult to detect. Thus, an effective HIF feeder identification technology is urgently needed. This paper establishes an HIF equivalent circuit in a resonant grounding system. The change rule of transient zero-sequence voltage, transient zero-sequence currents, and their projection components with respect to the transient zero-sequence voltage of the bus are analyzed in both underdamping and overdamping resonance conditions. Furthermore, the variation ranges of the resonant frequency, the magnitude, the attenuation factor, and other parameters are specified in detail. The magnitude and phase relationships of zero-sequence currents among the faulty feeder, healthy feeders, Petersen coil, and fault points, as well as the relationships between their projection components and quadrature components with respect to the transient zero-sequence voltage are analyzed and compared. A novel faulty feeder identification method based on a comparison of the magnitude and polarity of the transient zero-sequence current's projection component is proposed. The accuracy of the transient characteristics and the feasibility of the proposed method are verified by simulations and field data. [ABSTRACT FROM PUBLISHER]

As a basic building block in power systems, the three-phase voltage-source inverter (VSI) connects the distributed energy to the grid. For the inductor-capacitor-inductor (LCL)-filter three-phase VSI, according to different current sampling position and different reference frame, there mainly exist four control schemes. Different control schemes present different impedance characteristics in their corresponding determined frequency range. To analyze the existing resonance phenomena due to the variation of grid impedances, the sequence impedance models of LCL-type grid-connected three-phase inverters under different control schemes are presented using the harmonic linearization method. The impedance-based stability analysis approach is then applied to compare the relative stability issues due to the impedance differences at some frequencies and to choose the best control scheme and the better controller parameters regulating method for the LCL-type three-phase VSI. The simulation and experiments both validate the resonance analysis results. [ABSTRACT FROM AUTHOR]

• A coupling-strength factor is proposed for acoustic fluid–structure interaction. • An efficient numerical strategy is built by a fast dynamic flexibility algorithm. • Resonance analysis can verify the proposed coupling-strength analysis strategy. • The factor can high-efficiently predict the coupling-strength. The coupling-strength analysis can guide the proper modeling and efficient response analysis for acoustic fluid–structure problems. In this paper, a coupling-strength factor is proposed to quantify the dynamic interaction between acoustic fluid and structure, and its efficient computational strategy is established via a fast algorithm. This dimensionless factor expresses the average difference between the uncoupled and the coupled structural displacement (acoustic pressure) fields. The factor expression is related to the coupling matrix and the dynamic flexibility matrices of each physical field for the discrete system. Then a fast dynamic flexibility matrix algorithm of the non-positive definite system is deduced to ensure the feasibility of numerically calculating the factor, and the effects of the unconstrained structure and the acoustic rigid wall on the coupling-strength can be observed. Additionally, the strongly decoupling eigen-equations of each physical field are derived by the dynamic flexibility matrix expansion. Solving the resonance frequencies is adopted to verify the correctness of the proposed coupling-strength analysis strategy. In numerical examples, the coupling-strength factor is high-efficiently calculated with acceptable accuracy, the coupling-strength is investigated for the various acoustic fluid mediums and different boundary conditions, and the applicability and effectiveness of the factor are verified. [ABSTRACT FROM AUTHOR]