Search

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.

A coupled-inductor-based fourth-order buck converter is introduced in this article. The salient features of this topology are lower source current ripples like in conventional buck converter with input filter, no need of connecting an additional damping network across the input filter capacitor, additional flexibility provided by the coupling in the performance tuning, and the existing input C1–L1m structure itself acts as a ripple steering network. The detailed steady-state analysis is evolved and conditions for source current ripple reductions are formulated. Subsequently, small-signal analysis is established and a proportional plus integral plus derivative type controller is designed to ensure load voltage regulation. To enhance the dynamic performance, a two-loop voltage-mode controller is designed. The stability analysis of the closed-loop coupled-inductor-based buck converter is carried out through the eigenvalue sensitivity and participation factors approach. The impact of converter parameters on the converter system stability is discussed. In comparison with the single-loop voltage-mode controller, the two-loop voltage-mode controller is able to ensure that the closed-loop poles stay away from the jω-axis and, thus, the two-loop voltage-mode controller exhibits better dynamic performance. Analytical findings are validated on a 75 W, 60 to 36 V prototype converter. Steady-state and dynamic performance characterizing measurement results are given for validation of the concept. [ABSTRACT FROM AUTHOR]

Applying droop-based hierarchical control for islanded microgrids would face several unavoidable operation issues, such as large frequency deviation, high dynamic fluctuation, and inefficient coordination between different control layers. To this end, droop-free control has been explored to achieve the power sharing goal through neighboring communication, while maintaining system frequency levels (i.e., keeping the average nodal frequency constant). Although droop-free control shows potential in mitigating the defects of droop-based control, current research on the theoretical understanding of its stability performance remains limited. Hereby, this paper discusses the stability performance of droop-free controlled islanded microgrid via eigenvalue-based analysis. Specifically, a modified eigenvalue analysis method is first proposed to prove that all effective system eigenvalues under the symmetric communication network are located in the left half-plane, indicating that the symmetric droop-free controlled microgrid is asymptotically stable. Then, the asymmetric communication network is discussed, and the analytical eigenvalues with symmetric/asymmetric communication network designs are deduced under the homogenized electrical network. With the deduced analytical eigenvalues, stability performances of the symmetric/asymmetric designs are assessed via stability margin analysis and vulnerability analysis. Numerical case studies illustrate stability performance of the proposed designs, demonstrating that the asymmetric cycle design outperforms symmetric cycle and symmetric/asymmetric chain designs in overall convergence speed and stability against communication errors between droop-free controllers. [ABSTRACT FROM AUTHOR]

Unconventional reservoirs usually have strong anisotropy. Generally, they can be regarded as transversely isotropic media with a vertical symmetry axis [(VTI) media] in the absence of fractures. Therefore, it is of great significance to develop high-accuracy inversion method for VTI media. The three elastic parameters and two Thomsen anisotropy parameters of VTI media are usually obtained by indirect calculation or inversion methods based on the approximate formulas. However, the cumulative errors caused by indirect calculation and low calculation accuracy of the approximate formulas limit the estimation accuracy of these parameters. In this article, we propose a new method based on the exact reflection coefficients equations (ERCEs) of VTI media to improve the inversion accuracy of these elastic and anisotropy parameters. The new method adopts the Bayesian deterministic inversion (BDI) strategy to solve the inversion problem, which becomes highly nonlinear when using the ERCEs. We analyze the feasibility of the new method using the residual function maps (RFMs) and eigenvalue analysis of Hessian matrix. The analysis results show that the BDI strategy can well solve a series of problems brought by the ERCEs for nonlinear inversion, such as strong nonlinearity and more target parameters need to invert. Both synthetic and field data examples show that the proposed method can accurately estimate the elastic and anisotropy parameters, which verifies the feasibility and effectiveness of the method. [ABSTRACT FROM AUTHOR]

Construction of the linearized state-space model is the key step of eigenvalue analysis for SSO study of power systems with large-scale renewable power generation (RPG) integrated. This paper proposes a novel method to construct the state matrix of the AC/DC hybrid power system with RPG within the discrete-time domain. The continuous-time state-space model of each AC/DC component as well as RPG units in the power system, is discretized together with their corresponding control. The discretized equation of each component is then represented by an equivalent circuit consisting of parallel historical current and conductance. According to the power system configuration, the discrete-time equivalent circuit of the whole AC/DC hybrid system is established, and the nodal analysis method is applied for the construction of the discrete-time state-space model of the power system. In this way, the state matrix can be acquired much more conveniently than that of continuous-time state-space method, which needs topology analysis to find independent state variables of the network from the proper tree. The proposed method has been applied in the eigenvalue analysis for the SSO study of a case system adapted from the AC/DC hybrid transmission system in northwest China. Eigenvalue results are in high accordance with time-domain simulation results in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

This paper presents the small-signal stability performance of a dc microgrid (MG) and investigates the interactions between the converter controllers by studying the critical modes. A comprehensive small-signal analysis using both the impedance-based method and eigenvalue-based analysis method has been presented thoroughly to investigate the high-frequency oscillation in the dc MG. The results show that there are inherent weak modes within the dc MG which could destabilize the MG in the presence of disturbances. Moreover, the controller gains and dc-link capacitance are found to be the most sensitive to substantial disturbance and have a significant influence on the weak modes leading to oscillation and resonance. The source side converter is found to be more influential than the load side converter in regard to various disturbances.

This paper is dedicated to presenting control-tuning methodologies for the rotor-side converter (RSC) and grid-side converter (GSC) of series-compensated DFIG-based wind farms (WF) and to determining the origin of subsynchronous resonance (SSR). Unlike conventional approaches to re-tuning controller gains to achieve desirable performance, these methodologies only consider the mathematical models of the states variables to be controlled. A PI cascade topology is used to control the RSC and GSC. An inner loop is required for current control and an outer loop for voltage control. Special consideration is taken for tuning the RSC because this converter is coupled with the mechanical variables as mechanical rotor speed of the DFIG. Compared with standard tuning, a better system behavior during a resonance condition is achieved with the proposed tuning methodology. Regarding the analysis of the SSR origin, the modal impedance (MI) technique is used as a tool to study SSR issues; its advantages compared to the driving point impedance technique are highlighted. In this context, the small-signal-stability (SSS) analysis is performed to evaluate the overall system. With the combination of MI and SSS, the phenomena of induction generator effect, torque interaction, and torque amplification are analyzed. As a result, the modes involved in the SSR phenomenon are identified and a discrimination procedure is described to determine the origin of the SSR.

We study the behavior of 3-D periodic composite media consisting of several types of split-ring resonators. By initially introducing the H-D periodic eigenmode finite element method (FEM) formulation, the dual counterpart of our formerly proposed E-B formulation, we are able to extract accurate dispersion diagrams and field distributions of electromagnetically complex structures and compare the returned characteristics of the supported modes. Using Babinet’s principle, we design the corresponding complementary resonators and evaluate their dual characteristics. Particular attention is given to the explanation of the behavior of these composite media under wave incidence perpendicular to the scatterers’ plane. Additionally, we perform a cross-check with excitation problem results, to interpret the response predicted by analytical models existing in literature and confirmed by the eigen-analysis of the structures. Useful conclusions are drawn concerning the potential utilization of the studied resonators in more complex structures in the field of microwave applications. [ABSTRACT FROM AUTHOR]

Interactions of identical inverters in weak grids have received wide attentions. However, in a practical wind farm, parameters of grid-side inverters and lengths of collecting lines are not completely the same. In this case, a multi-inverter system is not symmetric, and thus the interaction mechanism could be more complicated than that of identical inverters. To investigate the interaction mechanism of differently parameterized inverters, this paper proposes a clustering-based modeling method, in which inverters with identical parameters are classified as one group. The clustering-based model allows for efficient stability assessment using three low-order transfer function matrices, instead of a full-order dynamic model. The root locus analysis is applied in the clustering-based model for stability analysis. Results show that the interconnection of distinct groups of inverters deteriorates common current stability, but has no impact on interactive current stability. The simulation and rtlab-based experimental results validate the effectiveness of the proposed model and the interaction mechanism of differently parameterized inverters. [ABSTRACT FROM AUTHOR]

This paper develops an accurate small signal model for line commutated converter based HVDC (LCC-HVDC). The overall process of the model establishment is demonstrated from five parts: AC system, DC system, control system, phase-locked loop (PLL) and the converter. Considering the limitations of the traditional converter equations, the proposed small signal model takes the commutation process into account so that the overlap angle and AC current are calculated with the actual value rather than the estimated value. The accuracy of the proposed model is verified both in the time-domain simulation in PSCAD/EMTDC and by eigenvalue analysis. The results show better performance than the traditional modeling methods, which provides valuable guidance for future LCC-HVDC project design. [ABSTRACT FROM AUTHOR]

This paper is devoted to the convergence problem for second-order signed networks that are associated with two signed graphs in the presence of heterogeneous topologies. An eigenvalue analysis approach is presented to develop convergence results for second-order signed networks, which employs a sign-consistency property for signed graph pairs. When the sign-consistency of two heterogeneous signed graphs and the connectivity of their union are given, bipartite consensus (respectively, state stability) can be derived for second-order signed networks if and only if the union signed graph is structurally balanced (respectively, unbalanced). Two examples are provided to illustrate the effectiveness of the obtained results.

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.

The metal shell vibratory gyro is a branch of Coriolis vibratory gyro, which has the advantage of overload resistance, simplify structure, low cost, wide range and long life. This paper focuses on multi-surface metal resonator. It is important that the eigenvalue analysis of multi-surface of hemisphere, cylinder and hyperbolic. Through analysis multi-surface characteristic, it presents a novel orthogonal curvilinear coordinate used machine error factor based on the traditional coordinate, which realizes boundary linear. We analyze its natural vibration characteristics, research on basic model distribution and built mode shape function of resonator; deeply research on dynamics characteristics of resonator under the condition of angular rate input, establish dynamics equation of multi-surface fusion metal shell vibratory gyroscope based on thin shell mechanics theory of elastic mechanics, solve out the eigenvalue of the resonator, and we also analyze this eigenvalue characteristics to lay the foundation of the follow-up study of the theory of the metal shell vibratory gyroscope. We test the gyro's temperature performance on the last. Finally, we test on the metal shell vibratory gyroscope, the ranges to ±3600°/s, zero-bias stability is 7.862°/h (25 °C), angular random walk is 1.487°/h1/2.

The wind turbine is usually integrated into the power grid via back to back converter, and the inertia is decreased. Virtual synchronous machine (VSM) control was proposed to improve inertia of the wind farm. While for the doubly-fed induction generator (DFIG)-based wind farm with traditional control strategy, sub-synchronous resonance (SSR) has become a significant problem when it is connected to series compensation transmission lines. Therefore, the impacts of VSM control strategy for DFIG on SSR need to be investigated. In this paper, a detailed small-signal stability analysis model of the VSM control strategy is first established and eigenvalue analysis is then carried out. SSR in the wind farm with the VSM control under different series compensation levels, controller parameters and wind speeds is analyzed, and it is also compared to that in the wind farm with the conventional vector control strategy (VC). Simulations are performed in PSCAD/EMTDC to verify the result of SSR analysis.

This paper presents small signal stability analysis of a hybrid microgrid from three different aspects. First, a generalized droop control of interlinking converter (ILC) is proposed which defines voltage and frequency droops at its terminals to achieve a bidirectional, autonomous power flow between grids. The impact of the droop gains on the stability is discussed and an operational range is defined for a stable system operation. Second, contrary to previous literature which have modeled the ac and dc grids by ideal sources and converters, the ac grid in this scheme is represented as a second-order synchronous generator and the dc grid is modeled as a PV system so as to analyze the dc grid dynamics in detail. It is observed that the dc link capacitor and inductor filter can lead to large system oscillations which can compromise stability. Third, the stability of the hybrid grid is analyzed from the aspect of short circuit ratio (SCR). Both rectifier and inverter mode of operation are used to understand how stability is affected with strength of ac grid. The time-domain simulations in PSCAD are used to confirm the validity of results obtained in frequency domain.

Abstract A small-signal model of photovoltaic (PV) generation connected to weak AC grid is established based on a detailed model of the structure and connection of a PV generation system. An eigenvalue analysis is then employed to study the stability of PV generation for different grid strengths and control parameters in a phase-locked loop (PLL) controller in the voltage source converter. The transfer function of the power control loop in the dq rotation frame is developed to reveal the influence mechanism of PLL gains on the small-signal stability of PV generation. The results can be summarized as follows: ① oscillation phenomena at a frequency of about 5 Hz may occur when the grid strength is low; ② the tuning control parameters of the PLL have a noticeable effect on the damping characteristics of the system, and larger proportional gain can improve the system damping;③ within a frequency range of 4-5 Hz, the PLL controller has positive feedback on the power loop of PV generation. A virtual inductance control strategy is proposed to improve the operational stability of PV generation. Finally, a simulation model of PV generation connected to weak AC grid is built in PSCAD/EMTDC and the simulation results are used to validate the analysis.

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]

This paper presents the modal analysis of different HVDC cable bundles. Using modal theory, specific transformation matrices are presented, and the modal equivalent circuits are illustrated. The behavior of the resulting modes is studied in a wide frequency range, the impact of different cable parameters and burial configurations on the modal characteristics are analyzed. A concept for online fault localization in HVDC cable transmission based on the difference between the modal velocities and consequently the arrival times of the modal traveling wave initial peaks is presented. In this method, modal voltages and currents are used instead of direct measurements and the proposed concept uses one-sided measurement without needing to detect the second TW reflections. Multiple faults are applied to CIGRE HVDC models in PSCAD/EMTDC and the modal analysis is obtained in MATLAB. The impact of different sampling frequencies, fault resistance, fault location and different grounding schemes on the proposed modal fault location principle is analyzed. The theoretical results show the accuracy of the proposed modal fault localization concept for different HVDC cable bundles. [ABSTRACT FROM AUTHOR]

Meshless time domain methods allow flexible distribution of nodes in the computational domain. The radial point interpolation method (RPIM) in electromagnetics with Gaussian radial basis functions (RBFs) requires global interpolation matrices with large condition numbers even for simple problems such as eigenvalue analysis of a circular waveguide. In addition, nonorthogonal grids in such problems demand divergence-free conditions to be enforced. In this letter, a divergence-free inverse multiquadric RBF has been proposed to efficiently solve such electromagnetic (EM) problems. Real parts in eigenvalues are nearly eliminated by this approach, thus removing spurious solutions. In addition, the proposed approach results in longtime stability of numerical analysis. [ABSTRACT FROM AUTHOR]

Objective: To demonstrate the role of surface charge and power dissipation in the analysis of EEG measurements. Methods: The forward EEG problem is formulated in terms of surface charge density. Using bounds based on power dissipation, the integral equations for forward solutions are shown to satisfy bounds on their eigenvalue structure. Results: We show that two physical variables, dissipated power and the accumulated charge at interfaces, can be used in formulating the forward problem. We derive the boundary integral equations satisfied by the charge and show their connection to the integral equations for the potential that are known from other approaches. We show how the dissipated power determines bounds on the range of eigenvalues of the integral operators that appear in EEG boundary element methods. Using the eigenvalue structure, we propose a new method for the solution of the forward problem, where the integral kernels are regularized by the exclusion of eigenvectors associated to a finite range of eigenvalues. We demonstrate the method on a head model with realistic shape. Conclusion: The eigenvalue analysis of the EEG forward problem is given a clear interpretation in terms of power dissipation and surface charge density. Significance: The use of these variables enhances our understanding of the structure of EEG, makes connection with other techniques and contributes to the development of new analysis algorithms. [ABSTRACT FROM AUTHOR]

In this article, a set of autonomous ac microgrids, interconnected by back-to-back converters, is taken into account, where they are supplied fully using voltage source converter-based distributed energy resources. A comprehensive and generalized small-signal model of the interconnected autonomous microgrids as a large-scale system is proposed using the interconnection method. The modeling is based on detailed module models to show the impact of each module on the dynamic modes, especially the dominant critical modes. It is generalized and scalable due to separate modeling of modules as well as using unlimited and expandable interconnecting. The proposed interconnection method deals with all electrical and control connections between individual modules including feedback, feed-forward, augmentation, and the order of module inputs and outputs. The model is validated employing Prony analysis method and using output results of an OPAL-RT real-time simulator. Using the proposed modeling method, the small-signal stability analysis and controller design can be realized simply for interconnected microgrids with any number of microgrids and different structures. Typically, for two interconnected microgrids, all dynamic modes and participant state variables in different frequency ranges are identified using the eigenvalue analysis and participation matrix in MATLAB. [ABSTRACT FROM AUTHOR]

In this paper, we propose an improved sub-synchronous resonance (SSR) damping controller (SSRDC) and a related control strategy to mitigate the SSR in a capacitive series-compensated double-fed induction generator based wind farms, based on the damping torque analysis. The proposed strategy is utilized for enhancing the system stability. Compared with the traditional damping controller, the proposed SSRDC is simultaneously embedded into the $d$ -axis and $q$ -axis control channels in the inner current loop of the rotor-side converter. On this basis, combined with the eigenvalue analysis and improved particle swarm optimization algorithm, the optimum gain coefficients of the SSRDC can be determined for maximizing the mitigation effect under different operation conditions of the series compensation levels and wind speeds. Moreover, the effect of the weight coefficients in the objective function on the SSR suppression is also investigated. Finally, the time-domain simulations are carried out to demonstrate the effectiveness of the proposed control strategy for mitigating the SSR and suppressing the connected power system oscillations. [ABSTRACT FROM AUTHOR]

One mechanism to generate optical rogue waves is the soliton fusion phenomenon. The impact of initial parameters such as pulse spacing, frequency separation, and phase difference between adjacent soliton shape pulses for soliton fusion phenomenon has been analyzed based upon soliton's eigenvalue. Numerical simulation results reveal that the parameter space can be divided to three regions, i.e., co-propagation, soliton fusion, and repulsion, which are sensitively dependent on the initial parameter.

In this paper, some issues related to the impedance-based stability criterion, such as RHP poles in the minor-loop gain, how to specify source and load impedances, and node-dependent stability margins are discussed and the vector fitting method is used to improve the method. This results in an eigenvalue analysis of the system instead of using the Nyquist diagram, and leads to obtain more information about the system. Furthermore, a participation factor analysis can be used to identify the problematic subsystem. The proposed method is examined in the assessment of a stable and an unstable system, and simulation results are used for verification. [ABSTRACT FROM AUTHOR]

A contour integral based spectrum transform (CIST) is first introduced for computing critical eigenvalues of power systems. Different from commonly-used shift-invert and Cayley transforms, CIST is able to give equal dominance to the eigenvalue set in a customizable complex plane area, which is defined by a given integral curve. The spectral property of CIST brings high distinctiveness of eigenvalues enclosed by the integral curve in transformed spectrum, along with well convergence of these eigenvalues in subspace methods. With CIST, Rayleigh–Ritz process is used to build subspace and extract eigenvalues. An iterative scheme is proposed for subspace refinement. The iterative contour integral Rayleigh–Ritz method is implemented with full utilization of parallel potentiality in contour integral numerical evaluation. Experiments on three test systems of different scales are performed to validate the reliability, computational efficiency, and parallel scalability of the proposed method. [ABSTRACT FROM AUTHOR]

Subsynchronous control interaction (SSCI) is the interaction between the power-electronics control and the series-compensated transmission system that occurs at frequencies below the system nominal frequency. SSCI may occur between the doubly-fed induction generator (DFIG) control system and the series-compensated transmission line, to which the wind park (WP) is connected. Not only do the DFIG control system parameters, but also the WP operating conditions have a significant impact on SSCI. In this paper, the impact of WP operating conditions and DFIG control system parameters on SSCI is analyzed in detail. Guidelines are presented for modifying the DFIG control system parameters to ensure safe operation and acceptable transient responses due to faults. This paper also examines the accuracies of various analytical tools used for SSCI problem identification and proposes a new frequency scan analysis approach for accurate prediction of potential SSCI problems. [ABSTRACT FROM PUBLISHER]

A small signal model of a multi-infeed high-voltage direct current (HVdc) transmission system containing a line commutated converter (LCC) and a voltage source converter (VSC) is developed. This model represents the LCC and VSC converters as operational impedances as seen from the converter ac busbar. This permits the converters to be included in the effective short-circuit ratio (ESCR) calculations. The resulting ESCR is referred to in this paper as the “Impedance based Effective Short Circuit Ratio” (IESCR). It is shown that the maximum power transfer limit (referred to as the maximum available power or MAP) of the converters is better predicted by this index compared to the conventional ESCR which ignores the operational impedances of the converters. The question also arises as to how close to this theoretical maximum power transfer limit can the HVdc system operate. Using the small-signal model, it is shown that with commonly used control strategies, the predicted MAP can only be achieved by reducing the controller gains. The results are validated using detailed electromagnetic transients simulation of the multi-infeed VSC-LCC system. [ABSTRACT FROM PUBLISHER]

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]

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]

One mechanism to generate optical rogue waves is the soliton fusion phenomenon. The impact of initial parameters such as pulse spacing, frequency separation, and phase difference between adjacent soliton shape pulses for soliton fusion phenomenon has been analyzed based upon soliton's eigenvalue. Numerical simulation results reveal that the parameter space can be divided to three regions, i.e., co-propagation, soliton fusion, and repulsion, which are sensitively dependent on the initial parameter. [ABSTRACT FROM PUBLISHER]

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]

In this paper, we investigate a frequency domain approach for eigenvalue-based detection of a primary user, based on equal gain combining (EGC) and spectrum estimation with Bartlett’s method. This paper considers two techniques for eigenvalue detection which are Maximum Eigenvalue Detection (MED) and the Maximum-Minimum Eigenvalue (MME) detector. We exploit the eigenvalues that are associated with the Hermitian form representation of Bartlett’s estimate to assess the performance of the aforementioned eigenvalue techniques in the frequency domain. For each case, we quantify the performance based on the probabilities of false alarm and missed detection over Rayleigh and Rician fading. A bivariate Mellin transform approach is employed to obtain the probability distribution function for the ratio of the extreme eigenvalues under each hypothesis. All obtained formulas are validated via Monte-Carlo simulations, and the results give a clear insight into the performance of the investigated methods. In frequency domain, MED outperforms both the MME detector and Periodogram-based energy detection even in a worst case scenario of noise uncertainty, while the MME detector exhibits heavy-tailed statistical characteristics and thus its receiver operating characteristics tend to stay on the line of no-discrimination. The performance of MED is further enhanced by careful choice of combinations of the total length of the sensing frame and number of sub-slots. [ABSTRACT FROM PUBLISHER]

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]

This paper investigates a special class of dynamic power system problem, namely subsynchronous resonance (SSR) resulted from a series-compensated network connecting doubly-fed induction generator (DFIG) based wind farms. A novel two-degree-of-freedom (2DOF) control strategy combined with a damping control loop is designed and analyzed for enhancing the system stability and alleviates the SSR that may arise due to the induction generator effect (IGE). The proposed control strategy is tested at different operating conditions of series compensation levels and low wind speeds to ensure the system stability. The doubly-fed induction generator based wind farms without the proposed control strategy leads to overall system instability during high series compensation and low wind speeds. Hence, the mitigation of the SSR and damping enhancement are critical to the entire power system stability. A reliable way of analyzing the system and designing effective control strategies against SSR based on the eigenvalue analysis and impedance based stability criterion is deployed. Moreover, analytical explanations have been elaborated to verify the procedure of the controller design. Fault ride-though capability has also been investigated with the proposed control strategy that is flexible to be integrated with the FRT schemes so as to assist the wind farm in mitigating the SSR during the fault recovery stage. Finally, time domain simulations are carried out to demonstrate the effectiveness of the proposed control strategy for mitigating the SSR and damping power system oscillations. [ABSTRACT FROM PUBLISHER]

This paper deals with subsynchronous resonance (SSR) phenomena in a capacitive series-compensated DFIG-based wind farm. Using both modal analysis and time-domain simulation, it is shown that the DFIG wind farm is potentially unstable due to the SSR mode. In order to damp the SSR, the rotor-side converter (RSC) and grid-side converter (GSC) controllers of the DFIG are utilized. The objective is to design a simple proportional SSR damping controller (SSRDC) by properly choosing an optimum input control signal (ICS) to the SSRDC block, so that the SSR mode becomes stable without decreasing or destabilizing the other system modes. Moreover, an optimum point within the RSC and GSC controllers to insert the SSRDC is identified. Three different signals are tested as potential ICSs including rotor speed, line real power, and voltage across the series capacitor, and an optimum ICS is identified using residue-based analysis and root-locus method. Moreover, two methods are discussed in order to estimate the optimum ICS, without measuring it directly. The studied power system is a \mathbf100\;MW DFIG-based wind farm connected to a series-compensated line whose parameters are taken from the IEEE first benchmark model (FBM) for computer simulation of the SSR. MATLAB/Simulink is used as a tool for modeling and designing the SSRDC, and power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) is used to perform time-domain simulation for design process validation. [ABSTRACT FROM PUBLISHER]