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This paper presents a method for small-signal dynamic studies of power systems including utility-scale PV energy systems considering the effects of dc-side components. Existing methods commonly model a PV energy system as a dc source connected to a grid-tied inverter. This paper shows that the dc components of a PV energy system can also contribute in the dynamics of the power system in the range of small-signal studies. The paper first develops the model of a PV energy system by merging the submodels of dc- and ac-side components. Then, a method to obtain the augmented model of the power system including a PV energy system will be explained using a study system. The study system consists of a PV energy system in parallel with a synchronous generator connected to a grid. Then, based on eigenvalue analysis, verified by time-domain simulations, it is shown that the dc-link capacitor, front-end converter, and its controller can introduce oscillatory modes in subsynchronous range of frequencies. Furthermore, it is shown that the damping of the sensitive modes can significantly vary with respect to the parameters of the dc-side components. [ABSTRACT FROM PUBLISHER]

The static series synchronous compensator (SSSC) has demonstrated its capability in providing voltage support and improving power system stability. The objective of this paper is to analyze the dynamic interaction stability mechanism of a hybrid renewable energy system connected with doubly-fed induction generators (DFIGs) and solid oxide fuel cell (SOFC) energy with the SSSC. For this purpose, a linearized mathematical model of this modified hybrid single-machine infinite-bus (SMIB) power system is developed to analyze the physical mechanism of the SSSC in suppressing oscillations and the influence on the dynamic stability characteristics of synchronization. Typical impacting factors such as the series compensation level, the SOFC penetration and tie-line power are considered in the SMIB and two-area systems. The impact of dynamic interactions on enhancing damping characteristics and improving transient performance of the studied systems is demonstrated using eigenvalue analysis and dynamic time-domain simulations, which validates the validity of the proposed physical mechanism simultaneously. [ABSTRACT FROM AUTHOR]

As the installed capacity of the power system is scaled up and the distance of transmission increases constantly, high-voltage direct current (HVDC) transmission technology has been widely applied across the power system. The HVDC system can lead to sub-synchronous oscillations (SSO) in the turbine and new energy generation systems. When the SSO caused by HVDC are studied through small signal analysis, it is usually necessary to establish the detailed state space model and electromagnetic transient model, which shows various disadvantages such as the high complexity of the model, the high order of the state space matrix, the complex calculation of eigenvalues, and the slow pace of simulation. In the present study, a simplified model intended for the HVDC transmission system is proposed, which can be used to simplify the calculation model and accelerate the simulation by omitting the high-frequency component and simultaneously keeping the sub-synchronous frequency component unchanged. The time domain simulation method is used to compare the dynamic response of the proposed simplified simulation model with that of the original detailed model, and the accuracy of the proposed model is demonstrated. The proposed simplified simulation model is applied to explore the SSO of wind-thermal power bundling in the HVDC transmission system. Additionally, the simulation results of SSO are compared by using the simplified model and the detailed model; the results of which demonstrate the effectiveness and rapidity of the simplified simulation model. The simplified model proposed can greatly improve the efficiency of SSO risk assessment. By selecting reasonable types and parameters of new energy units, SSO of the system can be avoided under risky operation mode, and the power grid operation mode can be monitored and adjusted to ensure the safe operation of the system. Finally, it can promote the sustainable development of the power system. [ABSTRACT FROM AUTHOR]

Wind power integration through the voltage source converter-based high-voltage direct current (VSC-HVDC) system will be a potential solution for delivering large-scale wind power to the "Three-North Regions" of China. However, the interaction between the doubly-fed induction generator (DFIG) and VSC-HVDC system may cause the risk of subsynchronous oscillation (SSO). This paper establishes a small-signal model of the VSC based multi-terminal direct current (VSC-MTDC) system with new energy access for the problem, and the influencing factors causing SSO are analyzed based on the eigenvalue analysis method. The theoretical analysis results show that the SSO in the system is related to the wind farm operating conditions, the rotor-side controller (RSC) of the DFIG and the interaction of the controller in the VSC-MTDC system. Then, the phase lag characteristic is obtained based on the signal test method, and a multi-channel variable-parameter subsynchronous damping controller (SSDC) is designed via selecting reasonable parameters. Finally, the correctness of the theoretical analysis and the effectiveness of the multi-channel variable-parameter SSDC are verified based on time-domain simulation. [ABSTRACT FROM AUTHOR]

The ITER pulsed power electrical network (PPEN) supplies the superconducting magnets and the heating and current drive systems. During the experimental pulses, about several hundreds of seconds long, active power consumption of 500 MW and reactive one of 950 Mvar are expected. The ITER power supply system is very large and complex, and a careful design is required to assure a safe operation. Stability of ITER PPEN has been already investigated in recent studies by numerical simulation and analytical methods. Now, a new dynamic analytical model of the ITER power supply system is being developed, based on the state-space theoretical approach, which allows the application of the linear control theory to study the stability of the whole system. For each subsystem of the ITER power supply, a state-space model was developed, and in this paper, the ac/dc converter model is presented and validated for six and twelve pulse operation, and circulating current mode. [ABSTRACT FROM AUTHOR]

As the penetration of wind energy into the power system continues to grow, wind energy conversion systems (WECSs) are increasingly expected to be able to control their output real power, while retaining their maximum power-point tracking (MPPT) capability. This paper proposes a simple real power control strategy, which augments the MPPT feature of modern WECSs, and is based on rapid torque control as opposed to the traditional pitch-angle control. This paper presents the implementation of the proposed control strategy for a direct-drive WECS that employs the permanent-magnet synchronous generator, even though the proposed method can also be extended to other classes of electronically interfaced WECSs. The paper also presents a parameter-tuning procedure for the proposed control strategy. The effectiveness of the proposed control strategy is demonstrated through mathematical analysis and time-domain simulation studies. [ABSTRACT FROM PUBLISHER]

This paper deals with modeling and stability analysis of a doubly-fed induction generator (DFIG)-based wind-power unit that is interfaced with the grid via a series-compensated transmission line. A detailed mathematical model is developed in this paper that takes into account dynamics of the flux observer, phase-locked loop (PLL), controllers of the power-electronic converter, and wind turbine. Using the model and based on eigenvalue/participation-factor analysis, the system and controller parameters that substantially influence the system stability have been identified. The developed model is validated through a comprehensive set of simulation studies in the Matlab/Simulink and PSCAD/EMTDC software environments. [ABSTRACT FROM AUTHOR]

Summary: The traditional droop control method in a DC microgrid (DCMG) fails to achieve accurate current sharing among parallel‐connected dispatchable units when the connecting feeders have unequal resistances, or when the units supply local loads apart from loads at the common dc bus. In this paper, a novel modification of the droop control strategy (additional feedback term in the outer control loop) is suggested to overcome the above limitations. The proposed method is robust, noise‐resilient, amenable to the "plug and play model", and employs local measurements, thereby, dispensing with the need for communication between remote nodes. A small‐signal model of the system with the proposed control strategy is derived for carrying out eigenvalue and participation factor analysis. A sensitivity analysis is also carried out to inspect the impact of variation of system parameters on small‐signal stability. The effect of time delay and noise on system small‐signal stability is also studied. A robust stability analysis is also carried out. The proposed control strategy is easily implementable on digital hardware. Time domain simulations using PSCAD (Power System Computer Aided Design)/EMTDC(Electromagnetic Transients including DC) is carried out to validate and compare the performance of the proposed technique vis‐a‐vis other existing methods. Performance of the proposed method is good even with time delay and noise. [ABSTRACT FROM AUTHOR]

This paper is concerned with polynomial approximations of the spectral abscissa function (defined by the supremum of the real parts of the eigenvalues) of a parameterized eigenvalue problem, which are closely related to polynomial chaos approximations if the parameters correspond to realizations of random variables. Unlike previous work, we highlight the major role of this function smoothness properties. Even if the eigenvalue problem matrices are analytic functions of the parameters, the spectral abscissa function may not be differentiable, and even non-Lipschitz continuous, due to multiple rightmost eigenvalues counted with multiplicity. This analysis demonstrates smoothness properties not only heavily affect the approximation errors of the Galerkin and collocation based polynomial approximations, but also the numerical errors in the evaluation of coefficients in the Galerkin approach with integration methods. A documentation of the experiments, conducted on the benchmark problems through the software Chebfun, is publicly available. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology to predict behavioural changes in manufacturing supply chains due to endogenous and/or exogenous influences in the short and long term horizons. Additionally, the methodology permits the identification of the causes that may induce a negative behaviour when predicted. Initially, a dynamic model of the supply chain is developed using system dynamics simulation. Using this model, a neural network is trained to make online predictions of behavioural changes at a very early decision making stage so that an enterprise would have enough time to respond and counteract any unwanted situations. Eigenvalue analysis is used to investigate any undesired foreseen behaviour, and principles of stability and controllability are used to study several decision configurations that eliminate or mitigate such behaviour. A case study of an actual electronics manufacturing company demonstrates how to apply this methodology and its real benefits for enterprises. [ABSTRACT FROM AUTHOR]

A novel approach for controlling the radiation patterns of antenna systems located on a complex platform is proposed in this paper. The proposed technique takes a cue from the traditional characteristic basis functions method and starts with the generation of characteristic basis functions (CBFs) by exciting a number of antenna elements on the platform. In order to account for the design constraints into consideration, the antennas are only placed at “allowable” locations (typically specified by the user). The CBFs are generated for the complex structure under analysis by using a suitable full-wave solver. Moreover, the antenna elements need not to be identical, and different types of antennas can be used at different locations on the platform depending on the application. A singular value decomposition can be employed to remove the redundancy of the CBFs, if necessary. Next, the corresponding characteristic basis function patterns are derived and used as basis functions in the “pattern space” to realize the desired radiation pattern. Rather than using a nonlinear optimization procedure to realize the desired pattern, the pattern design process is transformed into an eigenvalue problem – which is numerical considerably more efficient to solve – to find the best-fit solution that maximizes the energy radiated in the desired angular range, while minimizing the undesired radiation outside of this range. [ABSTRACT FROM AUTHOR]

Blind noisy image estimation is useful in many visual processing systems. The challenge lies in accurately estimating the image noise level without any priori information of the image. To tackle this challenge, an iterative texture-based eigenvalue analysis approach is proposed in this paper. The proposed approach utilizes the eigenvalue analysis to mathematically derive a new noise level estimator based on weak-textured image patches. Furthermore, a new texture strength measure is proposed to adaptively select weak-textured patches from the noisy image. Experimental results are provided to demonstrate that the proposed image noise level estimation approach yields superior accuracy and stability performance to that of conventional noise level estimation approaches, so that to improve the performance of image denoising algorithm. [ABSTRACT FROM AUTHOR]

This paper presents modeling and analysis of two variations of the multitaper detector namely multiple antenna detection of a single-user multiple-input-multiple-output (MIMO) node, and the multitaper method (MTM) combined with singular value decomposition (SVD), which is known as the MTM-SVD processor. Motivated by the reputation of the MTM as the best nonparametric power spectral density (PSD) estimator and after reviewing the limited previous research attempts, which focus on single-input-single-output (SISO) multitapering, we present the exact analytical models for the two considered derivatives of the multitaper method over fading channels by making use of the theory of Hermitian forms and Phase-Type distributions. In addition, using the Neyman–Pearson Approach (NPA), the performance of both detectors is optimized over Nakagami fading. For both multitaper variations, we accurately derive the eigenvalues of the Hermitian form of each detector, where the eigenvalues identify the Phase-Type distribution parameters. This yields generalized expressions for the probabilities of false alarm and missed detection when arbitrary multitaper weights are used. Finally, we investigate the impact of noise uncertainty on the performance of MIMO-MTM. The results show that performance of both detectors is dependent on the total number of discrete prolate spheriodal sequences (DPSSs), while for the MTM-SVD processor the performance is also dependent on the number of cooperating users and the employed frequency resolution. It is also shown that MIMO-MTM is robust under noise uncertainty. The obtained analytical models are proven to be accurate and enables further investigations on the multitaper detector. [ABSTRACT FROM PUBLISHER]

It is of paramount importance that power system operators be able to assess transient stability in order to realize a reliable and stable power supply. Transient stability analysis can be formulated as a large-scale system of differential and algebraic equations (DAE). However, as power systems are becoming larger and more complex, it is becoming difficult to solve DAE in a practical amount of time for system operations. Parallel computing based on the waveform relaxation method is an effective solution to achieve faster calculations for transient stability analysis. To enhance the performance of the waveform relaxation method, a proper partitioning of the original problem is essential. Although various partitioning approaches have been used, those approaches might not be effective when analyzing a weakly damped low-frequency oscillation. In particular, in the Japanese 60-Hz power system, this oscillation becomes an important problem. To resolve this issue, in this paper we have developed a new partitioning method that is better suited to analyzing a weakly damped low-frequency oscillation based on eigenvalue analysis. Specifically, effective partitioning can be automatically determined by the proposed index, which can evaluate the validity of the partitioning. The proposed method was tested using the Japanese standards of the IEEJ WEST10 system model and the WEST30 system model. [ABSTRACT FROM PUBLISHER]

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.)

This paper addresses modeling, stability analysis and control of the doubly fed induction generator (DFIG) for wind turbines (WTs). In the present work, imperialist competitive and artificial bee colony algorithms are used for optimizing parameters of controllers of a WT with DFIG. Algorithms for optimizing the controllers' parameters are described. Based on this, an eigenvalue-based objective function is utilized to optimize the parameters. To evaluate the optimized gains, simulations are performed on a single machine-infinite bus system, and the dynamic responses of system with parameters obtained from two optimization techniques are compared. [ABSTRACT FROM AUTHOR]

To clarify the actual structural performance of an existing traditional timber structure in Japan, vibration measurements were carried out at a 17th century timber guest house (Gekkouden of Gokokuji temple). The results of the micro tremor measurement, earthquake monitoring, and analysis are discussed in this paper. For minute angles of less than 1/5000 rad, it was revealed through earthquake monitoring that each dominant frequency was strongly dependent on the vibration amplitude. It was also confirmed that the dominant frequencies of the lower vibration modes in 1/1000 rad declined to 65%‐75% of the frequencies obtained through micro tremor measurement. We propose a structural model that consists of a joint spring, column, beam, and hanging wall, based on previously reported experiments. In this study, it was clarified that the dominant frequencies determined by the analysis of the proposed structural model were in good agreement with the frequencies obtained through earthquake monitoring. The structural performance of a traditional timber architecture was evaluated through vibration analysis. We selected a 17th century guest house as a subject building, and performed vibration measurements and structural analysis. [ABSTRACT FROM AUTHOR]

It has become more and more demanding to investigate the impacts of wind farms on power system operation as ever-increasing penetration levels of wind power have the potential to bring about a series of dynamic stability problems for power systems. This paper undertakes such an investigation through investigating the small signal and transient stabilities of power systems that are separately integrated with three types of wind turbine generators (WTGs), namely the squirrel cage induction generator (SCIG), the doubly fed induction generator (DFIG), and the permanent magnet generator (PMG). To examine the effects of these WTGs on a power system with regard to its stability under different operating conditions, a selected synchronous generator (SG) of the well-known Western Electricity Coordinating Council (WECC three-unit nine-bus system and an eight-unit 24-bus system is replaced in turn by each type of WTG with the same capacity. The performances of the power system in response to the disturbances are then systematically compared. Specifically, the following comparisons are undertaken: (1) performances of the power system before and after the integration of the WTGs; and (2) performances of the power system and the associated consequences when the SCIG, DFIG, or PMG are separately connected to the system. These stability case studies utilize both eigenvalue analysis and dynamic time-domain simulation methods. [ABSTRACT FROM AUTHOR]

This paper deals with the stability analysis of a rotary power flow controller (RPFC). RPFC is a newly presented flexible alternating current transmission system device based on the rotary phase shifting transformer (RPST) configuration. This device comprises a shunt and a series transformer and two RPSTs. In this paper, a linear model is developed for RPFC in the dq-reference frame. The model includes two RPSTs, shunt, and series transformers. Stability of the device is studied using eigenvalues of the state matrix. Effects of system parameters such as resistance, reactance, and phase difference of the shunt and series transformers and RPSTs on stability are investigated using eigenvalue sensitivity analysis. Simulation results using PSCAD/EMTDC software and analytical results based on eigenvalue analysis are presented to evaluate effects of different parameters on stability of RPFC. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper shows the effects of microgrid (MG) integration, location, penetration and load levels on the power systems oscillating stability. The analysis work was carried out in the IEEE 14 bus test system which is widely used in stability studies. Stability studies were carried out with the help of eigenvalue analysis over linearized system models. HOPF bifurcation point detection was performed to show the effect of MGs on the system loadability margin. In the study results, it is seen that MGs affect system stability positively by increasing system loadability margin and has a damper effect on the critical modes of the system and the electromechanical local modes, but they reduce the damping amount of the electromechanical interarea modes. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes a probabilistic small-signal stability analysis method based on the polynomial approximation approach. Since the correct determination of unknown coefficients has a direct effect on the accuracy of the polynomial approximation method, this paper presents a method for determining these coefficients, with high coverage on the probabilistic input domain of the problem. In this method, by increasing the number of random input variables, the proposed method can continue to maintain its efficiency. After determining the unknown coefficients, the load flow results and the system state matrix are determined for random changes of all loads based on the Hermite polynomial approximation. Then, the small-signal stability of the system is probabilistically evaluated based on stochastic analysis of the system eigenvalues. The consistency and validity of the proposed method are demonstrated based on the simulation studies in the MATLAB® software environment. In the simulation studies, the performance of the proposed method is examined by comparison with Point Estimation, Cumulant, Monte Carlo, and Chebyshev polynomial-based methods, for IEEE 14-bus and IEEE 39-bus test systems. Article highlights Probabilistic small-signal stability analysis of power systems Modeling of governing equations of power system based on Hermite polynomial approximation Forming the Collocation matrix based on a robust method

This paper compares the IEEE-specified generator models such as the equivalent circuit (EC) models and the operational inductance (OI) models to understand their damping performances in the IEEE first-benchmark system for subsynchronous resonance study. These models are found to differ from one another only to an extent they accurately represent the standard transfer functions. By carrying out different case studies an effort is made to analyze the influence of these differences among the models on the damping performance of swing-mode and torsional modes. Through a detailed eigenvalue analysis and time-domain simulations, it is demonstrated that these models offer differing results with respect to swing-mode, thereby strongly influencing the power system stabilizer (PSS) performances, especially when the system is series compensated. Even the torsional mode interactions are found to exhibit dependency on the models employed for the generators. Such a study is expected to provide better insight into the behavior of generator models and controller design/tuning in system analysis. [ABSTRACT FROM PUBLISHER]

A novel polarimetric synthetic aperture radar (POL-SAR) image classification approach is proposed in this paper by exploiting coherency matrix eigenvalues for polarimetric information representation and understanding. The approach consists of two parts. Initially, the statistical distributions of eigenvalue for homogeneous areas are analyzed by taking eigenvalues as the features of polarimetric information. The Bayesian classification method is applied to verify the feasibility of distinguishing different homogeneous areas. As a result, this method can work well those pixels with the similar scatter mechanism by using different polarimetric intensity information from eigenvalues. But this process cannot adequately distinguish those pixels with similar eigenvalues distribution. So, an eigenvalues-based local operator is defined to overcome the insufficient of the similar pixels by introducing a similar measure and eigenvalues-based texture information. After all pixels are classified by Bayesian classification, if the similarity of the pixel is larger than the given threshold, this pixel will be further classified by support vector machine using texture information. The proposed method is tested on three POL-SAR datasets, in which the average classification accuracy of eight categories for the Flevoland data from our method reaches nearly 90%. [ABSTRACT FROM AUTHOR]

• New operators for splitting degenerate subspaces of symmetry group C 6v are proposed. • The operators are applied to the eigenvalue vibration analysis of two structural systems. • The computation of repeating frequencies of C 6v -symmetric systems is greatly simplified. • Obtained results for natural frequencies agree exactly with existing results in the literature. • New insights on the symmetries of vibration modes in degenerate subspaces are revealed. In considerations of the linear vibration of symmetric systems, group theory allows the space of the eigenvalue problem to be decomposed into independent subspaces that are spanned by symmetry-adapted freedoms. These problems usually feature one or more degenerate subspaces (i.e. subspaces that contain repeating solutions). For such subspaces, the associated idempotents, as calculated from the character table of the symmetry group, are not capable of full decomposition of the subspace. In this paper, and based on group theory, simple algebraic operators that fully decompose the two degenerate subspaces of structural problems belonging to the C 6v symmetry group are proposed. The operators are applied to the vibration of a spring-mass system, for which the results for natural frequencies are found to agree exactly with results from the literature. Their application to the vibration of a hexagonal plane grid reveals new insights on the character of the modes of degenerate subspaces. The overall conclusion is that, for problems belonging to the C 6v symmetry group, the proposed operators allow the mixed modes of degenerate subspaces to be separated into two distinct symmetry categories, and are very effective in simplifying the actual computation of the repeating eigenvalues of these subspaces. [ABSTRACT FROM AUTHOR]

Physical systems exhibiting symmetry properties may be conveniently studied using the mathematics of group theory. In structural mechanics, group theory has been successfully employed to simplify problems of the bifurcation, stability, statics, kinematics and vibration of symmetric configurations of space frames, space truss domes, double-layer and triple-layer space grids, plates and cable-net systems. Besides significantly reducing computational effort, group theory affords deeper insights on structural behaviour, and a better understanding of complex structural phenomena. The key to group-theoretic simplification is the decomposition of the space of the problem into independent subspaces that are spanned by symmetry-adapted variables obtained by applying idempotents of the symmetry group on the normal variables of the problem. However, for degenerate subspaces of a symmetry group (i.e. subspaces associated with repeating solutions), the associated idempotents do not sufficiently decompose the problem. The aim of this paper is to present, for the C 3 v symmetry group describing the symmetry of a regular 3-sided polygon, a pair of algebraic operators that fully decompose such subspaces. Compared with existing group-theoretic formulations, these operators offer an alternative approach that is simpler and more suited to practical engineering computations, and that affords clearer insights on the physical characteristics of the structural system (such as type of symmetries within the degenerate subspaces). The validity of the operators is confirmed through comparisons with results of eigenvalue vibration and stability problems drawn from the literature. • New group-theoretic operators for splitting degenerate subspaces are presented. • Subspace decomposition is illustrated by reference to a double-layer space grid. • Excellent agreement of results with those in existing literature is demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, we design a new kind of high order inverse Lax-Wendroff (ILW) boundary treatment for solving hyperbolic conservation laws with finite difference method on a Cartesian mesh. This new ILW method decomposes the construction of ghost point values near inflow boundary into two steps: interpolation and extrapolation. At first, we impose values of some artificial auxiliary points through a polynomial interpolating the interior points near the boundary. Then, we will construct a Hermite extrapolation based on those auxiliary point values and the spatial derivatives at boundary obtained via the ILW procedure. This polynomial will give us the approximation to the ghost point value. By an appropriate selection of those artificial auxiliary points, high-order accuracy and stable results can be achieved. Moreover, theoretical analysis indicates that comparing with the original ILW method, especially for higher order accuracy, the new proposed one would require fewer terms using the relatively complicated ILW procedure and thus improve computational efficiency on the premise of maintaining accuracy and stability. We perform numerical experiments on several benchmarks, including one- and two-dimensional scalar equations and systems. The robustness and efficiency of the proposed scheme is numerically verified. • Introduces high order finite difference boundary treatment for solving hyperbolic conservation laws. • Use a Cartesian mesh on domain with complex geometries and allow the boundary intersecting the grids in an arbitrary fashion. • Maintain stability with the same Courant-Friedrichs-Lewy number as the periodic boundary cases for any boundary locations. • Employ less terms using the relatively complicated ILW procedure and improve computational efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we perform an intensive study of the synchronization properties of interconnected network and the concepts of vital node, and the simplest and equivalent network is firstly introduced. We strictly derive the eigenvalues of Laplacian matrix and the synchronizability of interconnected network and its simplest and equivalent network through utilizing the master stability function approach. Firstly, we find the synchronizability of interconnected network is identical to its simplest and equivalent network. Secondly, we identify the general factors that determine the synchronizability of interconnected network and further analyze the impact of different factors on the synchronizability. Finally, theoretical analysis and numerical simulations are carried out to indicate the validity and effectiveness of current analysis. The current results are beneficial to understand the dynamical behaviors of complex networked systems. [ABSTRACT FROM AUTHOR]

This paper is concerned with the temperature effect on the vibration of a cable-stayed beam. The thermal effect is considered by using two non-dimensional factors for the cable tension force and sag. The nonlinear in-plane and out-of-plane vibration equations of motion of the cable-stayed beam with thermal effect are derived by using the extended Hamilton's principle. Eigenvalue analysis is performed to obtain closed-form eigenvalue solutions. It is shown that the effect of temperature variation plays a dominant role on the vibration behavior of the cable-stayed beam, and the effect is closely related with the initial tension force and the stiffness ratio. As to the in-plane motion, both positive and negative correlations between the temperature variations and natural frequencies are found, which depend on the mode order and the stiffness ratio of the cable-stayed beam. However, as to the out-of-plane motion, there only exist negative correlations between the temperature variation and natural frequencies, and the effect of temperature dropping condition seems more obvious. Moreover, both for the in-plane and out-of-plane motions, the locations of veering points between two natural frequencies are shifted under the thermal effect, which can significantly affect the internal resonance between different modes of the cable-stayed beam. [ABSTRACT FROM AUTHOR]

The accurate prediction of rotating stall inception is critical for determining the stable operating regime of a compressor. Among the two widely accepted pathways to stall, namely, modal and spike, the former is plausibly believed to originate from a global linear instability, and experiments have partially confirmed it. As for the latter, recent computational and experimental findings have shown it to exhibit itself as a rapidly amplified flow perturbation. However, rigorous analysis has yet to be performed to prove that this is due to global linear instability. In this work, an eigenanalysis approach is used to investigate the rotating stall inception of a transonic annular cascade. Steady analyses were performed to compute the performance characteristics at a given rotational speed. A numerical stall boundary was first estimated based on the residual convergence behavior of the steady solver. Eigenanalyses were then performed for flow solutions at a few near-stall points to determine their global linear stability. Once the relevant unstable modes were identified according to the signs of real parts of eigenvalues, they were examined in detail to understand the flow destabilizing mechanism. Furthermore, time-accurate unsteady simulations were performed to verify the obtained eigenvalues and eigenvectors. The eigenanalysis results reveal that at the rotating stall inception condition, multiple unstable modes appear almost simultaneously with a leading mode that grows most rapidly. In addition, it was found that the unstable modes are continuous in their nodal diameters, and are members of a particular family of modes typical of a dynamic system with cyclic symmetries. This is the first time such an interesting structure of the unstable modes is found numerically, which to some extent explains the rich and complex results constantly observed from experiments but have never been consistently explained. The verified eigenanalysis method can be used to predict the onset of a rotating stall with a CPU time cost orders of magnitude lower than time-accurate simulations, thus making compressor stall onset prediction based on the global linear instability approach feasible in engineering practice. [ABSTRACT FROM AUTHOR]

This work deals with doubly fed induction generator (DFIG) modeling and stability when connected to weak AC grids. A detailed state-space model that includes the phase-locked loop (PLL) is developed. This work aims to determine the influence of the network's strength on DFIG stability through the short-circuit ratio (SCR). The critical values of the proportional control parameters of the grid-side and rotor-side converters (RSC and GSC), as well as PLL, which make the system unstable, are calculated for different SCR values. Finally, PSCAD/EMTDC dynamic simulations are used to validate the critical control parameters obtained by studying the eigenvalues of the DFIG state-space model regarding system stability. [ABSTRACT FROM AUTHOR]

Copyright of Arabian Journal for Science & Engineering (Springer Science & Business Media B.V. ) is the property of Springer Nature 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.)

Power system stability is an important problem for power system operation. Determination of different stability margins can result in the optimum utilization of power system with minimum risk. Voltage stability is an important subset of power system stability. To correctly analyze the voltage stability of a power system, suitable dynamic models are usually required. Therefore, in this paper, the Hopf bifurcation boundary of voltage stability feasible region is analyzed by combination of time domain simulation (TDS), bifurcation theory and modal analysis of dynamic Jacobian matrices of power systems. Effect of different load models, branch contingencies and excitation system parameters on critical eigenvalues and participation factors of system states is evaluated. The test results are given for IEEE14 bus test system. [ABSTRACT FROM AUTHOR]

This paper presents the dynamic-stability analyzed results of an 80-MW offshore wind farm (OWF) connected to a power grid through a line-commutated high-voltage direct-current (HVDC) link. The studied OWF is simulated by an equivalent 80-MW doubly-fed induction generator (DFIG) driven by an equivalent wind turbine through an equivalent gearbox using an aggregation method. The damping controller of the rectifier current regulator (RCR) of the proposed HVDC link is designed by using modal control theory to contribute adequate damping to the studied OWF under various wind speeds and different disturbance conditions. A systematic analysis using a frequency-domain approach based on eigenvalue calculations and a time-domain scheme based on nonlinear model simulations is performed. The eigenvalue analysis is performed to validate the effectiveness of the designed damping controller under different wind speeds. The nonlinear model simulations are carried out to demonstrate the effectiveness of the designed damping controller under various disturbance conditions. It can be concluded from the simulation results that the proposed line-commutated HVDC link joined with the designed damping controller not only can render adequate damping characteristics to the studied DFIG-based OWF under various wind speeds but also effectively mitigate the fluctuations of the OWF under disturbance conditions. [ABSTRACT FROM PUBLISHER]

This paper describes a study to determine the optimal parameter of a resistive superconducting fault current limiter (SFCL) applied to an electric power grid. The resistive SFCL, which is designed to provide the quick system protection during a fault, affects the entire system by reducing the fault current and improving the transient stability. In order to determine the optimal parameter of the resistive SFCL systematically, the eigenvalue analysis for an entire system is used. Generally, the eigenvalue analysis is useful to evaluate the relationship between parameter of a controller and stability of an electric power system. Therefore, the optimal parameter of the SFCL is determined based on the analysis of eigenvalues corresponding to low-frequency oscillations. Moreover, this optimal parameter obtained by the proposed method is compared with that determined by applying the equal-area criterion. The effectiveness of the optimal parameter for the SFCL is evaluated by time-domain simulation. The results show that the optimal resistive value determined by the eigenvalue analysis improves the damping performance of low-frequency oscillations effectively. [ABSTRACT FROM AUTHOR]

This paper presents an effective control scheme using a line-commutated high-voltage direct-current (HVDC) link with a designed rectifier current regulator (RCR) to simultaneously perform both power-fluctuation mitigation and damping improvement of four parallel-operated 80-MW offshore wind farms delivering generated power to a large utility grid. The proposed RCR of the HVDC link is designed by using modal control theory to contribute adequate damping to the studied four offshore wind farms under various wind speeds. A systematic analysis using a frequency-domain approach based on eigenvalue analysis and a time-domain scheme based on nonlinear model simulations is performed to demonstrate the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed HVDC link combined with the designed RCR can not only render adequate damping characteristics to the studied offshore wind farms under various wind speeds but also effectively mitigate power fluctuations of the offshore wind farms under wind-speed disturbance conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a control strategy for a single-stage, three-phase, photovoltaic (PV) system that is connected to a distribution network. The control is based on an inner current-control loop and an outer dc-link voltage regulator. The current-control mechanism decouples the PV system dynamics from those of the network and the loads. The dc-link voltage-control scheme enables control and maximization of the real power output. Proper feedforward actions are proposed for the current-control loop to make its dynamics independent of those of the rest of the system. Further, a feedforward compensation mechanism is proposed for the dc-link voltage-control loop, to make the PV system dynamics immune to the PV array nonlinear characteristic. This, in turn, permits the design and optimization of the PV system controllers for a wide range of operating conditions. A modal/sensitivity analysis is also conducted on a linearized model of the overall system, to characterize dynamic properties of the system, to evaluate robustness of the controllers, and to identify the nature of interactions between the PV system and the network/loads. The results of the modal analysis confirm that under the proposed control strategy, dynamics of the PV system are decoupled from those of the distribution network and, therefore, the PV system does not destabilize the distribution network. It is also shown that the PV system dynamics are not influenced by those of the network (i.e., the PV system maintains its stability and dynamic properties despite major variations in the line length, line X/R ratio, load type, and load distance from the PV system). [ABSTRACT FROM AUTHOR]

This paper describes a methodology to identify potential conflicts among power flow control devices that may slow down or impair convergence. The proposed methodology is based on the eigenvalue analysis of the sparse Jacobian matrix associated with the Newton power flow with controls. Practically identical results are obtained from a smaller control sensitivity matrix. The implementation in a power flow program has been tested using both small- and large-scale systems. The results presented validate and clearly indicate the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

Abstract-The HVDC converter control can destabilize torsional modes of nearby turbogenerators. The first experience of HVDC-turbine generator torsional interaction was observed in 1977 during field tests at Square Butte. The development of power semiconductors, specially insulated-gate bipolar transistors and gate turnoff thyristors (GTOs) has led to the small power HVDC transmission based on voltage-source converters (VSCs). The self-commutated VSC-based HVDC installations have several advantages compared to conventional HVDC-based online-commutated current source converter. The main objective of this paper is to investigate and present the detailed analysis of subsynchronous resonance (SSR), arising from a VSC-based HVDC system connected close to generating units. The analysis considers different operating modes of the converters. Based on a case study, it is shown that the dc voltage control mode of VSC operation (rectifier/inverter) close to the generator units can contribute positive damping in the torsional-mode frequency range of interest. The investigations of SSR with VSC-based HVDC is carried out based on linear (damping torque and eigenvalue) analysis and nonlinear transient simulation. While the damping torque, eigenvalue analysis, and controller design are based on the D-Q model, the transient simulation considers the D-Q model and the three-phase detailed model of VSC using switching functions. The influence of the operating modes of the converters and effects of some important parameters, such as effective short circuit ratio and generator rating are investigated. [ABSTRACT FROM AUTHOR]

This paper focuses on the systematic optimal tuning of the power system stabilizer (PSS), which can improve, the system damping performance immediately following a large disturbance. As the PSS consists of both linear parameters (such as the gain and time constant) and nonsmooth nonlinear parameters (such as saturation limits of the PSS), two methods are applied for the optimal tuning of all parameters. One is to use the optimization technique based on the Hessian matrix estimated by the feedforward neural network, which identifies the first-order derivatives obtained by the trajectory sensitivities, for the nonlinear parameters. Moreover, the other is to use the eigenvalue analysis for the linear parameters. The performances of parameters optimized by the proposed method are evaluated by the case studies based on time-domain simulation and real-time hardware implementation. [ABSTRACT FROM AUTHOR]

Recently, it has been discovered that the dynamics of phytoplankton concentrations in an ocean exhibit a rich variety of patterns, ranging from trivial states to oscillating and even chaotic behavior [J. Huisman, N. N. Pham Thi, D. M. Karl, and B. P. Sommeijer, Nature, 439 (2006), pp. 322-325]. This paper is a first step towards understanding the bifurcational structure associated with nonlocal coupled phytoplankton-nutrient models as studied in that paper. Its main subject is the linear stability analysis that governs the occurrence of the first nontrivial stationary patterns, the deep chlorophyll maxima (DCMs) and the benthic layers (BLs). Since the model can be scaled into a system with a natural singularly perturbed nature, and since the associated eigenvalue problem decouples into a problem of Sturm-Liouville type, it is possible to obtain explicit (and rigorous) bounds on, and accurate approximations of, the eigenvalues. The analysis yields bifurcation-manifolds in parameter space, of which the existence, position, and nature are confirmed by numerical simulations. Moreover, it follows from the simulations and the results on the eigenvalue problem that the asymptotic linear analysis may also serve as a foundation for the secondary bifurcations, such as the oscillating DCMs, exhibited by the model. [ABSTRACT FROM AUTHOR]

This paper presents a practical approach for supplementary control of high voltage direct current (HVDC) system to damp subsynchronous oscillation (SSO) involving HVDC converters and turbine-generator shaft systems. A novel eigenvalue analysis (NEA) program, HVDC system modeling to consider steady-state and dynamic conditions in a combined ac/dc system, and an appropriate control scheme have been utilized. The design method proposed facilitates the design of a subsynchronous oscillation damping controller (SODC) to provide positive damping torque for the dominant torsional mode in combined ac/dc systems. The suggested SODC design method has been applied to an ac/dc system to verify its practicality using the EMTDC simulation program. [ABSTRACT FROM AUTHOR]

This paper presents the modal analysis of a grid-connected doubly fed induction generator (DFIG). The change in modal properties for different system parameters, operating points, and grid strengths are computed and observed. The results offer a better understanding of the DFIG intrinsic dynamics, which can also be useful for control design and model justification. [ABSTRACT FROM AUTHOR]