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The interline power-flow controller (IPFC) is a voltage-source-converter (VSC)-based flexible ac transmission system (FACTS) controller for series compensation with the unique capability of power-flow management among the multiline transmission systems of a substation. The reactive voltage injected by individual VSCs can be maintained constant or controlled to regulate active power flow in the respective line. While one VSC regulates the dc voltage, the others control the reactive power flows in the lines by injecting series active voltage. This paper presents the modelling of IPFC with 12-pulse, three-level converters and investigates the subsynchronous-resonance (SSR) characteristics of IPFC for different operating modes. The analysis of SSR is carried out based on eigenvalue analysis and transient simulation of the detailed system. It is illustrated with the help of a case study on a system adapted from the IEEE Second Benchmark Model. The analysis uses both D-Q model (neglecting harmonics in the output voltages of VSCs) and the three-phase model of VSCs using switching functions. While the eigenvalue analysis and controller design is based on the D-Q model, the transient simulation considers both models. [ABSTRACT FROM AUTHOR]

This paper presents the Cross-Border activation of the Regulating Reserve (CBRR) between participating Control Areas (CAs), which is being developed to reduce the costs of balancing energy. The main objective of the CBRR is to activate the regulating reserve in participating CAs, to release the regulating reserve and to reduce the balancing energy as part of the safe operation of the power system. However, the classic CBRR includes a frequency term and, therefore, inherently affects the frequency response of the participating CAs, which is not discussed in the literature. In this paper, the impact of the classic CBRR on frequency quality and the provision of Load-Frequency Control (LFC) is thoroughly evaluated with dynamic simulations of a three-CA test system and an eigenvalue analysis of a two-CA system. It is clearly demonstrated that the classic CBRR reduces the damping of the entire power system. Therefore, a modified implementation of the classic CBRR is presented, and a modified CBRR is proposed, which has no impact on the system's eigendynamics. Furthermore, the results of the dynamic simulations confirm that the frequency quality can be improved by the classic CBRR, although there are also cases where it can deteriorate. However, the modified CBRR improves the frequency quality in all cases. The modified CBRR also improves the indicators for the provision of LFC compared to the classic CBRR. Moreover, the modified CBRR reduces the unintended exchange of energy and the demand power, thus increasing the financial effects of the CBRR's activation.

This paper puts forward wavelet transform method to identify P and S phases in three component seismograms using polarization information contained in the wavelet transform coefficients of signal. The P and S wave locator functions are constructed by using eigenvalue analysis method to wavelet transform coefficient across several scales. Locator functions formed by wavelet transform have stated noise resistance capability, and is proved to be very effective in identifying the P and S arrivals of the test data and actual earthquake data. [ABSTRACT FROM AUTHOR]

In the traditional power grid, inverter-inter-faced distributed energy resources are widely used in microgrids such as conventional synchronous generators (SGs) in the traditional power grid. They are expected to decrease the rotational inertia and spinning reserve capacity that are specific to SGs, while synchronverters can compensate for the loss. Thus, an increasing number of interfaced inverters may act as synchronverters in a microgrid. The dynamic stability of the synchronverter-dominated microgrid must thus be carefully evaluated to ensure the reliable operation of this type of system. This paper presents a nonlinear model of a synchronverter-dominated microgrid. The eigenvalues of the system state matrix, along with the participation factors, are analyzed to determine the predominant parameters affecting the stability. Bifurcation theory is then used to predict and describe the unstable phenomenon as the system parameters fluctuate; the effect of these parameters on the system stability is then examined. A simulation on MATLAB/Simulink and experiments were performed and results validated the presented analysis. [ABSTRACT FROM PUBLISHER]

Small Signal Stability Analysis (SSSA) for a hybrid renewable energy system including uncertainties requires an extensive attention to make a system more stable. This paper analyses the method involved in the stability studies of integrated hybrid power system with the help of Lyapunov's stability criteria. The stability studies can be performed for different renewable energy sources like wind generation system, solar PV system and a micro hydro system. In this paper, a study is carried out on a wind generation system which is integrated with the Western System Coordinating Council (WSCC) four machine system. The stability analysis concentrates on the different states of operation of WSCC four machine system with random values of generation and demand. The simulation studies on WSCC four machine system are carried out with the help of MATLAB/Simulink to evaluate stability. This study is validated with the aid of Monte Carlo Approach for evaluations based on iterations. This investigation highlights the significant advantage of conducting stability studies with uncertainty constraints involved, over the deterministic stability studies like probable limitations for transfer capability to cancel out poorly damped oscillations from power system operation. [ABSTRACT FROM AUTHOR]

In this paper, the proposed hierarchical control scheme adds new control loop to control the reactive power reference by a fuzzy logic controller to have the benefit of increasing the system stability margins and moreover, eigenvalue, robustness and time delay analysis of proposed control scheme are presented. The reported droop-based control methods of VSI-based microgrids including hierarchical droop-based control scheme are limited to primary and secondary control levels while the proposed control scheme is completely analyzed so that the three hierarchical control levels modeled for both grid-connected mode and islanded mode. This scheme maintains the stability of microgrids not only for the small-signal events, but also for large-signal disturbances such as three phase and single phase to ground faults, heavy motor starting, etc. However, power sharing to loads and network is sufficiently done. To demonstrate the effectiveness of the proposed hierarchical controller, simulation studies have been performed on a microgrid consisting of four units of distributed generation with local loads and in presence of main grid using MATLAB/SIMULINK software and validated using OPAL RT real-time digital simulator. [ABSTRACT FROM AUTHOR]

Power system stabilizers (PSSs) are generally used to solve the low-frequency oscillation problem. To overcome this type of oscillation, this paper presented a new method by using the genetic algorithm (GA) to identify PSS settings. The tuning of PSS parameters was formulated relying on an eigenvalue-based objective function aiming at maximizing the stability margin. This was achieved by increasing the sum of the squares of negative real parts of the system eigenvalues. The small disruptions in the form of load change take place routinely; the controller parameters should be adjusted to the changing conditions. To remedy this defect, an adjustment of parameters as a function of the load was required. Thus, a neuronal model by using a historical database determined by the GA solutions for various load levels can approximate the simulation studies, since it could estimate the stabilizer parameters in real time after the learning phase. The validity of the proposed technique was checked through the evolution simulation of the regulator parameters for a load forecast curve. These concepts were discussed in details on a multi-machine network Western System Coordinating Council (WSCC) comprising three generators and nine nodes. The eigenvalue analysis and time domain simulation results were presented at different operating conditions and under various disturbances in order to show the effectiveness of this study. [ABSTRACT FROM AUTHOR]

This paper proposes a new type of generalized droop-based proportional power sharing scheme during load change for parallel inverter-interfaced islanded microgrids, which is an automatic strategy and is independent of any particular nature of transmission lines, i.e., resistive or inductive. Real and reactive powers are shared in proportion to the droop gains by implementing the voltage control law proposed in this paper; in which the inverter-interfaced voltage-sources are kept at equal reference values. The control gains are chosen based on eigenvalue analysis in a way that the system stability is ascertained. The performance of the designed controller is simulated under different microgrid structures such as load variation and various types of transmission lines; in which the results show superior dynamic performance in comparison to the conventional droop-based control strategy. [ABSTRACT FROM AUTHOR]

The (multistep) one-shot method for design optimization problems has been successfully implemented for various applications. To this end, a slowly convergent primal fixed-point iteration of the state equation is augmented by an adjoint iteration and a corresponding preconditioned design update. In this paper we present a modification of the method that allows for additional equality constraints besides the usual state equation. A retardation analysis and the local convergence of the method in terms of necessary and sufficient conditions are given, which depend on key characteristics of the underlying problem and the quality of the utilized preconditioner. [ABSTRACT FROM PUBLISHER]

The high-voltage voltage-source converter (VSC)-based multi-terminal dc (MTDC) grid is a key technology for integrating offshore wind energy and enabling bulk power transmission across nations and continents. This paper addresses the small-signal stability of an MTDC grid equipped with a power flow controller (PFC) under extremely weak ac system interconnections. Using a comprehensive linearized state-space model, eigenvalue analysis uncovers that beyond the well-documented low-frequency oscillations (LFO), an MTDC grid may experience unstable medium-frequency oscillations (MFO) under rectifier operation of droop voltage-controlled VSCs when interfaced to an extremely weak ac system. Moreover, it was shown that the most challenging scenario is when multiple droop voltage-controlled VSCs are interfaced to very weak ac systems, with unstable LFO and MFO observed at short-circuit ratio values of 1.4 and 1.8, respectively. Sensitivity analysis is conducted to assess the impact of the droop voltage control gains, PFC control parameters, and dc breaker reactor on the system dominant eigenmodes in such critical weak conditions. Simple yet efficient LFO and MFO compensators are proposed to stabilize the system, and their parameters design was detailed. Extensive simulation studies and real-time validation tests verify the analytical analysis and demonstrate the effectiveness of the proposed compensators and their feasibility for real-time implementation.

The significant increase of converter interfaced generation, consumption, storage, and transmission in power systems, results in the need to consider converter-driven stability in detail, as well as to study modelling and analysis methods with which such stability effects can be represented and investigated. Due to the multiple causes of converter-driven stability effects, a classification into further categories of fast and slow converter-driven stability is necessary, which is systematically presented in this paper. We further provide a detailed overview on appropriate modelling methods including static, quasi-dynamic and dynamic modelling and their respective applications. Typical analysis methods such as eigenvalue and impedance based analysis are explained and related to the previous modelling approaches. Based on that, a guide to which modelling and analysis method is appropriate for which type of converter-driven stability, is provided. In addition, open and recent research questions with regard to studies on nonlinear analyses of large systems with acceptable computational costs are pointed out.

Power converters and their interfacing networks are often treated as modular state-space blocks for small-signal stability studies in microgrids; they are interconnected by matching the input and output states of the network and converters. Virtual resistors have been widely used in existing models to generate a voltage for state-space models of the network that require voltage inputs. This paper accurately quantifies the adverse impacts of adding the virtual resistance and proposes an alternative method for network modelling that eliminates the requirement of the virtual resistor when interfacing converters with microgrids. The proposed nonlinear method allows initialization, time-domain simulations of the nonlinear model, and linearization and eigenvalue generation. A numerically linearized small-signal model is used to generate eigenvalues and is compared with the eigenvalues generated using the existing modelling method with virtual resistances. Deficiencies of the existing method and improvements offered by the proposed modelling method are clearly quantified. Electromagnetic transient (EMT) simulations using detailed switching models are used for validation of the proposed modelling method.

Back-to-Back (B2B) HVDC systems can enhance cross-regional transmission capacity and overall power system stability. However, their use in interconnecting two extremely weak grids can compromise system stability. This paper presents a comprehensive stability analysis of a B2B HVDC system to distinguish the root causes of instability mechanisms and identify the critical short circuit ratio (CSCR) of each converter station under inverter and rectifier operations considering the impact of power feedforward compensation of the dc-bus voltage controller. The study also investigates the stability implications and CSCR changes when a dc transmission line connects the converter stations, creating a point-to-point (P2P) HVDC system. Eigenvalue analysis, based on detailed small-signal modeling, showed that three distinct instability mechanisms, high-, low-, and medium-frequency instabilities, can compromise the operation of VSC stations under extremely weak grid conditions. Notably, the medium-frequency instability observed in the P2P HVDC system during inverter operation is predominantly caused by the power feedforward compensation of the dc-bus voltage controller. Furthermore, the analysis reveals that the CSCRs for dc-bus voltage-controlled VSC stations are higher in comparison to power-controlled ones. This suggests that a dc-bus voltage-controlled VSC is more susceptible to instability in weak grid scenarios than its power-controlled counterpart. Active compensators are designed based on participation factor analysis to mitigate the identified instabilities. The findings are validated with extensive simulations and real-time hardware-in-the-loop tests, demonstrating the analysis's accuracy and the proposed compensators' efficacy.

This study examines the influence of a direct-power control technique for a DFIG (Doubly-Fed Induction Generator)-based wind generator on sub-synchronous resonance (SSR). A series capacitor of a transmission line will exchange power with the synchronous generator when it runs via an SSR. DFIG includes power converters built into its rotor circuit, allowing for quick control of both the active and reactive power of the device. This is made possible by the rotor converter circuit's fast IGBT switching. Examining the ability of the LQR (Linear Quadratic Regulator) on the DFIG to provide the required active power and reactive power during SSR is the primary goal of this work. Additional DFIG is added to the test system in addition to the original test system, and during SSR its performance is evaluated using an additional control signal that is obtained from the synchronous generator and supplied to DFIG through LQR. The analysis of SSR was completed based on eigenvalue analysis utilizing the D-Q model test system and transient simulation using MATLAB Simulink. Independent model control is used to control the DFIG rotor converter that dampens multimodal SSR oscillations. The test system was developed using the IEEE first benchmark model's adopted system. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of non-dispatchable energy sources on the dynamic stability of stand-alone MicroGrids (MGs) with autonomous control of frequency and voltage based on inverters. The analysis considers the use of eigenvalue techniques. Although this methodology is well known, the contribution of this paper is twofold. First, it proposes an algorithm for designing the inverter interface to meet the requirements associated with the harmonic distortion (THD) and dynamic performance of the inverter. Second, it provides an analysis of the dynamic stability of MG considering different levels of penetration of non-dispatchable energy sources, variations in the network parameters and the presence of dynamic loads (i.e., induction motors). [ABSTRACT FROM AUTHOR]

As an important manufacturing process, mechanical assembly affects directly product quality. Conventional quality inspections and estimations of mechanical assembly are primarily concentrated in "static quality", such as size coordination, shaping and positioning tolerances, etc. However, mechanical assembly actually has its own dynamic quality, which contributes to that of whole product. Inspecting only static quality is thus incomplete for quality estimation of the assembly. On the basis of substructuring method, this paper at first applies eigenvalue analysis to investigate the effects of assembling process on the dynamic transfer-functions, expressed by spectral-based frequency response functions (FRFs), of substructural components involved in the process. Eigenvalue modules of FRF-matrix-ratios of FRF before assembling to that after assembling are analyzed to quantify the effects, which are consequently indicated by the mean module. Then, according to the explicit definition of "dynamic quality of mechanical assembly" introduced in this paper, dynamic quality matrix of mechanical assembly and its mean eigenvalue module are worked out and chosen to be the right quantitative measure and indicator for dynamic quality estimation of assembly system. Meanwhile, a lumped-parameter model and its experimental counterpart are employed to validate effectiveness of the analytical outcomes obtained and the quality estimation method established in the study. [ABSTRACT FROM AUTHOR]

This paper explores the potential of hydrogen as an energy carrier for deep-sea applications. Finite element analysis of a type III pressurised cylinder to the intended working pressures of 300 bar internal and up to 600 bar external were carried out for different designs and safety factors. Design parameters such as helical angle, liner, helical, and hoop thicknesses were studied and optimised. A buckling analysis was carried out for the optimised designs and recommendations to increase the maximum allowable external pressure are given. Image 1 • A parametric study was carried out varying several pressure vessel parameters. • Parameters included liner, helical, and hoop thickness, among others. • The designs were optimised to endure 300 bar internal pressure. • Eigenvalue and nonlinear buckling analysis were carried out for optimised designs. • Designs without hoop reinforcement have a stronger buckling response. [ABSTRACT FROM AUTHOR]

Constructing navigation condition of oil supply vessels is of vital importance to both the research on the main engine and the safety of navigation. This paper carries out in-depth research and analysis based on the half-year shipping data derived from Hai Gong You 31, the oil supply vessel of Shanghai Chimbusco Marine Bunker Co., Ltd. After classifying 3946 pieces of shipping data, and there are 119 valid sequences. As for 13 characteristic parameters ,which include time, distance, average acceleration ,etc., they are eigenvalues of kinematics sequences ,and there are principal component analysis and contribution rate analysis relevant to them. Instead of original eigenvalues, three principal components whose contribution ratios are the highest and the accumulative one is around 85% are selected to be analyzed then. By means of between-groups linkage, this paper calculates the distance among clusters ,and the nearest two clusters are regarded as a new cluster. Afterward, calculations and combinations are made over and over till there is only one cluster. Eventually, the navigation condition of oil supply vessels is successfully formed, that is the one with a total length of 9240s.

A blackout can take place in entire power system or a part of the system due to extreme voltage instability (voltage collapse) that can appear abruptly. Instability prediction and continuous monitoring of the power system performance is, therefore, known exigent. This paper is conducted with a broad overview of the voltage stability indices, which are previously studied in the literature, and have the same foundation during their formulation. Afterward, an improved voltage stability indicator is introduced as a result of the multi-criteria integration and enhancement of the original indices by employing linear algebra methods. It is found that the proposed algorithm can overcome on the probable limitations from calculating point view. Then comparative analysis of the indices is presented in order to reach a unique consensus about the typical techniques of modal analysis (sensitivity, eigenvalue, right eigenvectors, and bus participation factor) as a precise algorithm. Finally, the IEEE 14-bus, and 30-bus test systems are selected to verify the algorithm, and compare the performance of the improved indicator approach with the existing indices. [ABSTRACT FROM AUTHOR]

New energy sources, storage facilities, power electronics devices, advanced and complex control concepts, economic operating doctrines, and cost-optimized construction and production of machines and equipment in power systems adversely affect small-signal stability associated with local oscillations. The objective of the article is to analyze local oscillations and the causes that affect them in order to reduce their negative impact. There are no recognized analyses of the oscillations of modern operating synchronous generators exposed to new conditions in power systems. The basic idea is to perform a numerical analysis of local oscillations of a large number of synchronous generators in the power system. The paper represents the local mode data obtained from a systematic analysis of synchronous generators in the Slovenian power system. Analyzed were 74 synchronous generators of the Slovenian power system, plus many additional synchronous generators for which data were accessible in references. The mathematical models convenient for the study of local oscillations are described first in the paper. Next, the influences of transmission lines, size of the synchronous generators, operating conditions, and control systems were investigated. The paper’s merit is the applicable rules that have been defined to help power plant operators avoid stability-problematic situations. Consequently, boundaries were estimated of the eigenvalues of local modes. Finally, experiments were performed with a laboratory-size synchronous generator to assess the regularity of the numerically obtained conclusions. The obtained results enable the prediction of local oscillations’ frequencies and dampings and will be useful in PSS planning.

Sub-synchronous oscillations (SSOs) in doubly-fed induction generator (DFIG)-based series compensated power systems are mainly caused by sub-synchronous control interaction (SSCI). SSCI is the most recently found type of sub-synchronous resonances. In this article, SSCI is elaborated and investigated by performing eigenvalue analysis on a mathematically modeled DFIG system. The occurrence of SSCI is observed and the results of eigenvalue analysis are validated through a down-scaled 7.5-kW experimental setup of a grid-connected DFIG. Based on the analysis, the proportional control parameters of the rotor-side converter (RSC) are found to be very sensitive towards the sub-synchronous modes of the system. The results obtained from both the simulation and the experimental analysis show that if the sensitive proportional parameters of the RSC are tuned properly, then the DFIG system can become immune to the SSCI for any level of series compensation. [ABSTRACT FROM AUTHOR]

Converters are the key for increasing the development of renewable energy generation but their dynamic interaction with the grid has an important impact on stability. Oscillatory instabilities in different grid‐connected converter systems at several frequency ranges are reported. In particular, sub and supersynchronous oscillatory instabilities in AC power systems with type‐3 and type‐4 wind turbine generators (WTGs) were recently registered at several wind farm areas. A number of works based on eigenvalue analysis and frequency domain approaches are carried out to analyse this new stability issue and more research is going on to analyse in detail the electric and control parameters that may affect this phenomenon. This study contributes analysing in detail the influence of system parameters on the subsynchronous oscillations (SSOs) in AC power systems with type‐4 WTGs. This study is based on a new approach for subsynchronous stability assessment which could also be used for analysing other types of SSOs (e.g. subsynchronous control interactions between doubly‐fed induction generators and series‐compensated networks) as well as supersynchronous oscillations. A representative example of weak AC grids with type‐4 WTGs is used to illustrate the contributions of the study. Results are validated with PSCAD/EMTDC time‐domain simulations. [ABSTRACT FROM AUTHOR]

This paper presents two modified Hager–Zhang (HZ) Conjugate Gradient methods for solving large-scale system of monotone nonlinear equations. The methods were developed by combining modified forms of the one-parameter method by Hager and Zhang (2006) and the hyperplane projection technique. Global convergence and numerical results of the methods are established. Preliminary numerical results show that the proposed methods are promising and more efficient compared to the methods presented by Mushtak and Keyvan (2018) and Sun et al. (2017). [ABSTRACT FROM AUTHOR]

• Proposing a hierarchical battery sizing approach to improve dynamic performance of MG. • Optimal sizing of BESS based on stochastic models to minimize frequency fluctuations. • Secondary BESS optimal sizing and placement to improve static and dynamic stability. • Proposing a dynamic objective function based on system eigenvalues. Integration of energy storage systems (ESSs) to microgrids (MGs) due to the growing penetration of intermittent energy resources is a great motivation to develop studies in the context of optimal sizing and placement of these systems. In this paper, a multi-objective bi-level optimization problem is addressed based on the stochastic nature and dynamic model of power system elements. As a preliminary step, the optimal size and capacity of the battery energy storage system (BESS) are determined to minimize frequency fluctuations. This level has been performed based on three approaches considering the daily intra-hour stochastic data. In the secondary level, the dynamic behaviour of all MG elements has been considered and correspondingly a dynamic objective function based on system eigenvalues and voltage sensitivity index (VSI) has been developed. According to the proposed objective function, the secondary step for sizing and placement of the battery units has been performed by adaptive particularly tuneable fuzzy particle swarm optimization (APT-FPSO) algorithm to reduce power losses, improve the voltage profile/ stability, and mitigate low-frequency fluctuations. Finally, the effectiveness of the proposed approach is evaluated using time-domain simulations, voltage sensitivity studies, and eigenvalue analysis. [ABSTRACT FROM AUTHOR]

High-frequency oscillation is one of the critical issues threatening the stability of modular multilevel converter (MMC) based high-voltage direct current (HVDC) system. A new 2 kHz high-frequency oscillation has occurred in the wind farm-side MMC station of Rudong wind farm integrated MMC-HVDC project of China during no-load charging process. The mechanism of this high-frequency oscillation is different to previous ones. Apart from the time delay of MMC, the stray capacitance of converter transformer makes a significant contribution to the high-frequency oscillation. This paper investigates the high-frequency oscillation mechanism of wind farm-side MMC station during no-load charging process. First, the harmonic state space (HSS) model of a wind farm-side MMC station is established. In addition to the leakage inductance, the stray capacitance is considered in the converter transformer model. To reveal the significance of the converter transformer stray capacitance in this new high-frequency oscillation, the root loci of the system are calculated with varying stray capacitance. Then, the state variables with high degree of participation in the high-frequency oscillation modes are determined by the participation factor analysis. A reduced-order model suitable for the high-frequency oscillation analysis is further established based on the participation factor analysis results. Next, the high-frequency oscillation mechanism is revealed by impedance analysis. Finally, the effects of system parameters are analyzed by the combination of eigenvalue analysis and impedance analysis. The analysis results are validated by electromagnetic transient simulations. • High-frequency oscillation mechanism of MMC charging with transformer is revealed. • The transformer stray capacitance must be considered in the oscillation analysis. • Participation factor analysis is carried out to determine main influencing factors. • A reduced-order model suitable for high-frequency oscillation analysis is proposed. • AC voltage control of MMC has significant effects on the high-frequency oscillation. [ABSTRACT FROM AUTHOR]

This research systematically analyzes the behaviors of correlations among stock prices and the eigenvalues for correlation matrices by utilizing random matrix theory (RMT) for Chinese and US stock markets. Results suggest that most eigenvalues of both markets fall within the predicted distribution intervals by RMT, whereas some larger eigenvalues fall beyond the noises and carry market information. The largest eigenvalue represents the market and is a good indicator for averaged correlations. Further, the average largest eigenvalue shows similar movement with the index for both markets. The analysis demonstrates the fraction of eigenvalues falling beyond the predicted interval, pinpointing major market switching points. It has identified that the average of eigenvector components corresponds to the largest eigenvalue switch with the market itself. The investigation on the second largest eigenvalue and its eigenvector suggests that the Chinese market is dominated by four industries whereas the US market contains three leading industries. The study later investigates how it changes before and after a market crash, revealing that the two markets behave differently, and a major market structure change is observed in the Chinese market but not in the US market. The results shed new light on mining hidden information from stock market data. [ABSTRACT FROM AUTHOR]

As wind power plants (WPPs) gradually replace the power production of the conventional generators, many aspects of the power system may be affected, in which the small signal stability is included. Additional control may be needed for wind turbine generators (WTGs) to participate in the power oscillation damping. The feasibility of implementing this control needs to be assessed. This paper studies how the damping contribution of a WPP is affected by different operating conditions and its dependence to selected feedback signals. The WPP model used includes individual WTGs to study how internal changes may affect this contribution. The study is based on the changes suffered by the residues of the electromechanical modes, which indicate the sensitivity of the modes to this particular feedback. The results show that a park level control for the entire WPP is possible, although it may not provide damping for a range of critical operating conditions. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a dynamic bandwidth selection method for thinning noisy point clouds into curves. Due to the nonhomogeneous distribution of noise or varying curvature of the data, the thinning procedure requires a dynamically adjusted bandwidth along the curve. On the other hand, the selected local region must be sorted along a suitable direction vector for local curve fitting purposes. The contribution of this paper to the field is 2-folded: first, a normalized eigenvalue analysis-based method is used to determine the best local bandwidth. The second task is getting a good regression line of the local region for ordering the data. In this step, a feature that is based on the Euclidean distances between points is used to determine the best regression line in the search space. Finally, a third-order parametric polynomial is fitted to the local data using the least squares method. We adapt and test our algorithm on the widely used k-nearest neighbor and constant radius methods. Our experiments show that the proposed methods automatically produce comparable results with these methods at their best parameter, which is empirically determined. Our methods also do not require any empirically determined parameter to adjust the best bandwidth or to select a good regression axis. Moreover, this method can be used with point sets that do not have a regression axis. [ABSTRACT FROM AUTHOR]

Highlights: [•] This paper presents an approach to the allocation and designs the PSSs. [•] The proposed approach has succeeded in determining the dominant generator. [•] Paper proposed a model for designing PSS regarding oscillation modes of the power. [Copyright &y& Elsevier]

This paper presents a method to analyze the Sub Synchronous Oscillation (SSO) problem based on broad learning system (BLS), which can quickly analyze the risk of SSO in a system and take measures. The simulation system is constructed by the eigenvalue analysis method to obtain training data, that solves the problem which is difficult to obtain actual data in SSO problem and makes the model more accurate and the conclusion more convincing. Subsequently, BLS is applied for feature extraction and the prediction model is constructed, the model can show the deep relationship between the oscillation source and topology of the system as well as various operating data, which is difficult to be expressed by formula. The system was tested and validated in the 41-bus system. The feature importance analysis method which comes from eXtreme Gradient Boosting (XGboost) algorithm is proposed and combined with the BLS prediction model, which can analyze the influence of each variable on the prediction results in different series compensation levels, and is validated in the 41-bus system, that makes the results of prediction more interpretable. Finally, the results of simulation show that the model can predict data with high accuracy and give adjustment plans for effective control of the system to avoid the risk of SSO.

• It is an attempt to develop an external SC based on current injection. The implementation mode of injecting AC current signals into current sampling loop of GSC controller has not been discussed before in the literature. • The entire CSI-ECSC is an independent modular design, which prevents redesigning the internal structure of the original controller. • The CSI-ECSC can be widely applied for diverse types of converter-based units. In other words, any DG or active load integrated to ADNs with electronic converter such as PMSG, PV, and ES, etc. can apply the CSI-ECSC, because it is made according to the specific existing control of converter controller. • This work is illustrated through comprehensive and detailed research and development process, including full eigenvalue analysis, interface circuit design, detailed simulation comparison, and effectiveness verification in hard-in-the-loop (HIL) testing based on real-time digital simulator (RTDS) system. Supplementary control (SC) technology is widely leveraged by power supply companies in active distribution networks (ADNs) to improve their stability and dynamic characteristics. Yet, the existed SCs are generally implemented from inside the converter controllers of distributed generators (DGs) or active loads, so there is a need to redesign the internal physical structure of the existing controller, resulting in the increasing work amount of assembling and workability. This paper studies the specific R & D process of a novel external coupling type SC (ECSC), which is based upon current source injection (CSI-ECSC) for improving the dynamic characteristics of ADN. The SC current signals are coupled to the current sampling loop from outside the converter controller. And the employment of the existing current sample makes it unnecessary to redesign the internal physical structure of the existing controller. As a result, the SC assembling is simplified and its workability is improved. In this paper, a detailed exemplary ADN with direct-drive permanent magnet synchronous generator (PMSG) is firstly set up in math for full eigenvalue analysis. Then, the CSI-ECSC is designed with its control loop, interface circuit, and parameter setting. Furthermore, by using PSCAD/EMTDC, groups of case studies are conducted in ADNs where photovoltaics (PVs) and energy storage (ES) are included. Finally, the real-time hardware-in-the-loop (HIL) testing validates the functionality of the realized CSI-ECSC in RTDS. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid algorithm combining chaotic Jaya (CJaya) and sequential quadratic programming (SQP), namely CJaya-SQP, for solving the coordinated design problem of static var compensator (SVC) and power system stabilizers (PSSs). The CJaya serves as a global optimizer and the SQP as a local optimizer for fine-tuning the solution. In the proposed algorithm, chaotic maps are used to generate the initial solutions and control the search process. In order to prove the performance of the CJaya-SQP, a set of benchmark optimization problems is used where the results are compared with those of the basic Jaya and other recognized algorithms. The proposed optimization method is then applied for the optimal tuning of PSSs and SVC controllers in such a way that damping ratios and damping factors of the electromechanical modes are optimally improved. To illustrate the robustness of the CJaya-SQP-based coordinated PSSs and SVC controllers, the four-machine, two-area system is used. Eigenvalue analysis and nonlinear time-domain simulation vividly show that the CJaya-SQP-based coordinated controllers improve greatly the system's dynamic stability with a robust damping of local and inter-area power oscillations. [ABSTRACT FROM AUTHOR]

This paper proposes a novel objective function and algorithm to obtain a set of optimal power system stabilizer (PSS) parameters that include a feedback signal of a remote machine and local and remote input signal ratios for each machine in a multi-machine power system under various operating conditions. A novel function called the damping scale is proposed and formulated as an objective function to increase system damping after the system undergoes a disturbance. Three existing objective functions of the damping factor, damping ratio, and a combination of the damping factor and damping ratio were analyzed and compared with the proposed objective function. A novel algorithm called gradual self-tuning hybrid differential evolution (GSTHDE) was developed for rapid and efficient searching of an optimal set of PSS parameters. GSTHDE uses the gradual search concept on STHDE to enhance the probability of searching for an optimal solution. Eigenvalue analysis and nonlinear time domain simulation results demonstrated the effectiveness of the proposed objective function and algorithm. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper a novel supplementary subsynchronous damping controller (SSDC) is proposed for the STATic synchronous COMpensator (STATCOM) which is capable of damping out subsynchronous oscillations in power system with series compensated transmission lines. An auxiliary subsynchronous damping controller (SSDC) for a STATCOM using the generator rotor speed deviation signal as the stabilizing signal has been designed to damp subsynchronous oscillations. Eigenvalue analysis and transient simulations of detailed nonlinear system are considered to investigate the performance of the controller. Robustness of the controller has been analyzed by facing the system with disturbances leading to significant changes in generator operating point. This paper deals with a cascaded multilevel converter model, which is a 48-pulse (three levels) source converter. The IEEE Second Benchmark (SBM) model is considered for the analysis and the complete digital simulation of the STATCOM within the power system is performed in the MATLAB/Simulink environment. [Copyright &y& Elsevier]

Summary: The grid‐connected system compensated by the series capacitor of the doubly fed induction generators (DFIGs) can easily lead to subsynchronous resonance (SSR) due to the interaction between the series capacitor and the rotor‐side converter. Eigenvalue analysis based on the small‐signal model shows the control parameters of rotor‐side current loop has a significant influence on SSR mode. The analysis of participation factors indicates SSR is most related to the rotor current. On this basis, this paper proposed a novel strategy to effectively suppress SSR based on phase‐shift average of rotor current. Firstly, the frequency information of subsynchronous mode is obtained through the analysis of rotor current. Then based on the rotor current transformed by the method of phase‐shift average, the obtained transformed signal is attached to the reference current of rotor‐side inner loop to suppress SSR. Without relying on system parameter information, this proposed strategy is able to suppress subsynchronous components effectively while the system steady‐state operating point is not changed. Simulation results based on a grid‐connected DFIG system validate this strategy can suppress the SSR effectively. Meanwhile, it has good robustness against the frequency measurement error. [ABSTRACT FROM AUTHOR]

Resource allocation and scheduling are fundamental issues in a Workflow Management System (WfMS). Effective resource management in WfMS should examine resource allocation together with task scheduling since these problems impose mutual constraints. Optimization of the one factor is subject to the other constraints and vice versa. Thus, an ideal algorithm should take into account not only performance metrics of the infrastructure, such as the number of resources and their utilization, but also quality criteria such as the percentage of tasks undergone violation in their temporal restrictions. In this paper, we propose an innovative algorithm which jointly optimizes the two aforementioned contradictory criteria. The algorithm, called Resource Conflicts Joint Optimization (Re.Co.Jo.Op.), minimizes resource conflicts subject to temporal constraints and simultaneously optimizes throughput or utilization subject to resources constraints. To achieve the optimization, the two factors are formulated in a matrix form and the optimal solution is found by applying concepts of the generalized eigenvalue analysis. A rough outline of an agent-based architecture is proposed to achieve runtime integration of our algorithm into a functional WfMS, while experimental results under different load environments and tasks assumption reveal the superiority of the proposed strategy than the other conventional approaches. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to develop a framework in which one can identify and predict the numerical instability of the steady state solution due to the solution reconstruction for cell-centered finite volume methods on unstructured meshes and to stabilize the problem by optimizing the reconstruction stencil. In this work, we first develop and extend a mathematical method, introduced by Haider and his colleagues, to measure the stability impact of the reconstruction phase for both linear and nonlinear problems regardless of the solution. Second order and third order accurate advection and Burgers problems as well as second order Euler problems are used to present detailed practical results and discussion around the use of the local reconstruction map for stability analysis. This method shows that for a range of different physical problems, increasing the stencil size will usually lead to more stable problems. Additionally, an empirical study is performed which sheds light on connections between the mesh properties and the stability of the reconstruction, which in turn helps choose the reconstruction stencil more wisely. Secondly, we propose a systematic approach to optimize both the shape and the size of the reconstruction stencil for better numerical stability through eigenvalue analysis. In this approach, one can directly optimize the solution reconstruction stencil for every control volume to obtain better numerical stability and convergence properties for steady state problems. A second order accurate Euler problem as well as a third order accurate laminar Navier-Stokes problem are used to showcase the applicability of the algorithm. • Identifying and predicting the numerical stability due to the solution reconstruction. • Better numerical stability through eigenvalue analysis and optimization of the solution reconstruction. • Extending solution reconstruction map theory to measure the impact of reconstruction for nonlinear and higher order problems. [ABSTRACT FROM AUTHOR]

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Abstract Curve squeal noise is a severe railway noise problem that can occur when a railway vehicle negotiates a sharp curve. It is usually characterised by a very loud tonal noise and can be very annoying for people in the vicinity. It is generally attributed to friction-induced instability, either due to a falling friction characteristic with increasing sliding velocity or to a mode coupling mechanism which can lead to instability even for a constant friction coefficient. The squeal frequency is usually associated with one or more wheel modes. However, the wheel is coupled dynamically to the track and insufficient attention has been paid in previous research to the role played by the rail dynamic behaviour. In this paper, the effect of the rail dynamics on curve squeal under constant friction conditions is investigated by means of different modelling approaches. The rail is firstly modelled using a waveguide finite element (WFE) model and it is found that the inclusion of the rail dynamics in the model can lead to squeal in some situations where it would otherwise not occur. Various effects are then considered that may introduce additional resonant behaviour into the rail dynamics. These include the effect of the rail cross mobility, rail cross-section deformation, the influence of the periodic support of the rail and reflections between multiple wheels on the rail. The effect of the rail pad stiffness is also explored. However, the results show that all these factors have little influence on the predicted curve squeal instabilities. By means of a reduced model, the main characteristics of the rail dynamics that can result in squeal are then assessed. It is shown that the mass and damping-like behaviour of the infinite rail are at the origin of the instabilities rather than any modal behaviour of the track. Curve squeal may occur for a single wheel mode even if the rail is represented by a damper, which is a close approximation to the vertical mobility of the track at high frequencies. This forms a third possible mechanism for curve squeal in addition to falling friction and wheel mode coupling. [ABSTRACT FROM AUTHOR]

Abstract The ITER large power supplies of the superconducting magnets and heating and current drive systems, fed by the Pulsed Power Electrical Network, can absorb from the grid active and reactive power up to 500 MW and 950 Mvar respectively. In this paper, a new analytical approach based on the state space formulation is proposed to investigate the dynamic stability of such complex system, including the main power components and their control, with the aim of identifying possible instability phenomena due to interactions among the ac/dc converters, reactive power compensation systems and related controllers. This model describes the dynamics of the main components of the ITER pulsed power supply systems and it is based on small signal approach to tackle the non linearity of the ac/dc conversion and reactive power compensation systems; the discrete phenomena have been approximated by continuous transfer functions, so the linear control theory can be applied for the stability analysis, making this method very effective and fast. Moreover a modular approach is adopted; thus this analytical model can be also easily adapted to other similar electrical power systems. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a method for PSS parameter tuning. The proposed method is based on the system identification using a Kalman filter. To eliminate the influence of inaccuracies of the mathematical model due to incomplete data of the system parameters, this paper proposes a procedure for identifying system parameters based on a Kalman filter. The identified system is the basis for determining the eigenvalue sensitivity function. PSS tuning is carried out based on the eigenvalue sensitivity analysis of changes of PSS parameters. In order to obtain the eigenvalue sensitivity function on the PSS parameter in a wider range of parameter values, it has been proposed to determine eigenvalues on the basis of the Bairstow method for solving polynomial equations. The entire procedure can be applied on-line, so the PSS structure and settings can be adaptive. Experimental tests carried out on a synchronous generator connected to an AC system demonstrate the effectiveness of the proposed method. Performance of the PSS tuned by using the proposed method was compared with the performance of the PSS tuned by using eigenvalue sensitivity. [Copyright &y& Elsevier]

Three commonly used methods to determine the principal moments of inertia of a plane area and their directions are based on: (i) the stationarity condition for the axial moment of inertia, (ii) the eigenvalue analysis, and (iii) Mohr's circle. In this paper we provide two new derivations, which are based on: (a) the matrix diagonalization and the invariant tensor properties, and (b) the conjugacy property of the moment of inertia vectors. A new general expression is derived which specifies the principal directions of inertia, as well as the directions of the maximum and minimum product of inertia. A comparative study of the five presented approaches is given, which is of interest from both conceptual and methodological points of view. The connection between the deviatoric part of the moment of inertia tensor and Land's circle of inertia is also given. The presented analysis applies to any two-by-two symmetric second order tensor. [ABSTRACT FROM AUTHOR]

In this paper we study the performances of generalized minimal residual method (GMRES) preconditioned with geometric multigrid (GMG), applied to steady and unsteady buoyancy driven flow problems, discretized with the finite element method. For the unsteady case, the second order Crank–Nicolson method is used for the temporal discretization. At each geometric multigrid level, we use Richardson iterative solvers preconditioned with different combinations of physics-based and domain decomposition preconditioners. Three different preconditioners are considered: incomplete LU decomposition (ILU), overlapping Vanka-type domain decomposition for additive Schwarz method (ASM), and field split (FS) physics-based decomposition. We also analyze the effect on the smoother of how the variables are ordered, and in particular whether the leading variable is the velocity or the temperature, resulting in six classes of preconditioners: ILU_VT, ILU_TV, ASM_VT, ASM_TV, FS_VT and FS_TV. The eigenvalue analysis for the six preconditioners is conducted to study the rate of GMRES convergence under several Prandtl numbers. The numerical performances of nested combinations of the above preconditioners are compared. Numerical results show that the pair of FS_VT and FS_TV preconditioners works better than the other two pairs, and that the FS_TV preconditioner always performs the best in terms of the computational time for all the steady and unsteady cases. [ABSTRACT FROM AUTHOR]