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This paper presents a new method for studying electromechanical transients in power systems using three phase, combined transmission and distribution models (hybrid models). The methodology models individual phases of an electric network and associated unbalance in load and generation. Therefore, the impacts of load unbalance, single phase distributed generation and line impedance unbalance on electromechanical transients can be studied without using electromagnetic transient simulation (EMTP) programs. The implementation of this methodology in software is called the Three Phase Dynamics Analyzer (TPDA). Case studies included in the paper demonstrate the accuracy of TPDA and its ability to simulate electromechanical transients in hybrid models. TPDA has the potential for providing electric utilities and power system planners with more accurate assessment of system stability than traditional dynamic simulation software that assume balanced network topology. [ABSTRACT FROM PUBLISHER]

Small isolated power systems often experience generator outages, which are responsible for the activation of the under-frequency load shedding scheme with the corresponding negative impact on electricity consumers and, hence, market loss. There are three main causes of this problem: the power system's low inertia, the speed governors' low capacity, and a poor size-ratio between generator and system. The most extensive research line in this area is focused on the optimization of the load shedding scheme, which is a partial solution. Another research line is presented to solve the problem from the point of view of the system operator. This paper proposes an online method to predict and correct possible load shedding by redistributing load dispatching. This proposal uses artificial intelligence techniques, in particular neural networks, and a special-purpose power system simulator. In order to evaluate the proposal, the achieved solution is applied to a real case study: the island of Gran Canaria. This application shows the improvement that might be achieved by implementing this simple method. The method proposed in this paper is strongly recommended for regions that have suitable geographical sites as well as energy problems similar to those of the Canary Islands (see tech. rep. “Map of the Canary Islands Power Systems” by Red Electrica de Espana). [ABSTRACT FROM AUTHOR]

Large-scale wind farms (WFs) are gradually required to participate in power system frequency regulation, especially in a weak grid. Corresponding ancillary frequency control functionalities and the contribution of the WF to system frequency stability are well studied. However, the impact of WF ancillary frequency control on wind turbine generators (WTGs) is rarely considered. It is found in this paper that the ancillary frequency control deteriorates drive-train torsional oscillation of the WTG, which restricts application of the ancillary control. To overcome this problem, this paper proposes an adaptive damping control scheme based on reactive power modulation of the WTG to suppress the drive-train torsional oscillation, which can assist the WF to meet the grid code requirements. Superior to the traditional active power modulation method, the proposed adaptive control scheme can achieve satisfactory damping improvement with less control effort. Furthermore, the adaptive scheme with a torsional frequency updating mechanism can effectively counteract torsional damping deterioration caused by parameter uncertainties, operating condition or control mode variations. Feasibility and effectiveness of the proposed damping control are validated by simulations and real-time experiments. [ABSTRACT FROM AUTHOR]

This paper proposes some methods for the purpose of reactive power and voltage control. Real cases show them as potentially harmful for power systems, since dynamic instability and voltage collapse may appear. Control actions like tap changers, active and reactive power redispatch may help the system voltage stability, but may present reverse results for some operating conditions. This paper is firstly devoted to identify and classify an operating point under the voltage stability point of view. Following this classification, an index to assess the robustness of a bus is proposed. The studies are carried out with the help of the QV curves. Methods to change the region of operation of a bus are then discussed with the help of a real Brazilian system with all limits considered. [ABSTRACT FROM PUBLISHER]

Power generators contain control systems that are able to regulate system frequency, but the frequency setpoint values are rarely modified from nominal values. This paper describes design considerations for a communication system from generators to frequency-sensitive distributed energy resources (FS-DER) using changes to frequency setpoint values of generators. Signaling discrete system states by generating off-nominal system frequency values can be used as a novel narrowband unidirectional broadcast communications channel. This paper describes two protocols for utilizing off-nominal frequencies to carry information: First, a protocol for dispatching blocks of FS-DER that is suitable for systems restricted to relatively slow rates of change of frequency (ROCOF). Second, for systems that allow higher ROCOF values, the feasibility of using power generation resources as a power-line communication transmitter is shown. Data from an operating islanded power system with diesel generators are analyzed to demonstrate the feasibility of the proposed communication system in systems fed by rotating machines. The feasibility of the proposed communication system in systems fed by voltage-source inverters is shown with laboratory tests of a 20-kVA inverter. The inverter was found to have a maximum ROCOF of 2.2 Hz/s, sufficient to enable its use as a power-line communication transmitter. [ABSTRACT FROM AUTHOR]

This two-part paper presents a framework for the characterization and minimal representation of the feasibility regions of power systems in the demand space. These feasibility regions are called loadability sets, and they represent the projection of generation-demand-network space onto the demand space only. Loadability sets have been characterized previously for power systems with either no or a single active line flow constraint. In Part I of this two-part paper, we generalize this characterization to power systems with any number of active line flow constraints. The proposed characterization approach makes use of the Fourier–Motzkin elimination method which leads to the generation of a large number of constraints. We set course to address this shortcoming in the second part of this paper. The notion of umbrella set is revisited in Part II to identify and remove the redundant constraints produced in the loadability set characterization process. The outcome of the proposed framework is the minimal representation of the power system feasibility region in the demand space. We envision multiple applications for the proposed framework in power system planning, operations planning, and real-time operation. [ABSTRACT FROM AUTHOR]

The paper proposes a new adaptive approach to power system model reduction for fast and accurate time-domain simulation. This new approach is a compromise between linear model reduction for faster simulation and nonlinear model reduction for better accuracy. During the simulation period, the approach adaptively switches among detailed and linearly or nonlinearly reduced models based on variations of the system state: it employs unreduced models for the fault-on period, uses weighted column norms of the admittance matrix to decide which functions to be linearized in power system differential-algebraic equations for large changes of the state, and adopts a linearly reduced model for small changes of the state. Two versions of the adaptive model reduction approach are introduced. The first version uses traditional power system partitioning where the model reduction is applied to a defined large external area in a power system and the other area defined as the study area keeps full detailed models. The second version applies the adaptive model reduction to the whole system. The paper also conducts comprehensive case studies comparing simulation results using the proposed adaptively reduced models with the linearly reduced model and coherency-based reduced model on the Northeast Power Coordinating Council 140-bus 48-machine system. [ABSTRACT FROM AUTHOR]

This paper extends the dynamic coherency determination (DCD) method by including Type-3 wind power plants (WPPs) models in the coherency evaluation process and quantifies impacts of the high depth of wind power penetration on the coherency phenomena of interconnected power systems. The method is based on frequency-deviation signals, measured at nongenerator buses and terminal buses of WPPs and synchronous generators. Salient features of the presented method are its ability to account for the hybrid nature of enhanced generic models of Type-3 WPPs and expanding notion of the power system coherency beyond the classical definition by including models of Type-3 WPPs. This paper also investigates impacts of the high depth of wind power penetration; i.e., up to 30%, on the coherency structure of the 16-machine/68-bus NPCC equivalent system. The studies are based on time-domain simulations in PSS/E software. The investigations reveal that Type-3 WPPs can introduce new coherent areas, significantly change areas’ boundaries and number of areas, and alter frequencies/dampings of interarea modes. [ABSTRACT FROM AUTHOR]

Transient stability simulation studies of large-scale power systems often generate large amounts of data. This can make it difficult for power system planners to understand the overall system response or to identify portions of the system with unusual signals. In this paper we present a novel approach that utilizes clustering to extract common features in the voltage magnitude and frequency response signals, and to identify outliers. The geographic visualization of the results is also discussed. Results are demonstrated using the IEEE 118-bus system and a 16\thinspace000-bus real-world system model. [ABSTRACT FROM AUTHOR]

Identification of optimal locations to deploy the phasor measurement units (PMUs) is a preliminary task in wide area monitoring and control of power systems. Given the cost and other associated restrictions, it is highly unlikely for any utility to install all the required number of PMUs to ensure the complete observability of the network. This necessitates judicious identification of locations in the network to deploy the PMUs. Ideally, the choice of location must depend on the intended purpose. In this paper, an approach for placement of PMUs considering both the stability and topological aspects is presented. First, a probabilistic framework based on proximity to instability is proposed to rank the generators/load buses in the order of vulnerability. Subsequently, a binary integer linear programming formulation is proposed to identify the optimal locations considering both stability and topological aspects. The optimal locations obtained using the proposed approach ensures a priori observability of most vulnerable buses in addition to enhancing the network observability. Results on IEEE 39-bus system and 246-bus equivalent system of Indian southern grid are presented to illustrate the proposed approach. [ABSTRACT FROM PUBLISHER]

This paper introduces a screening method to determine the potential risk of interactions between a dynamic device and a generator with torsional oscillations. The proposed method introduces a factor called the radiality factor (RF) which is an indicator of the radialness of the network between the device and the generator. TheRF is calculated in the sub-synchronous frequency range and plotted against the frequency (RF curves). The RF curves can then be used for screening of torsional interactions between the generator and other dynamic devices. The critical value for the RF is determined through a large number of sensitivity studies on a test system. This method surpasses the available screening method: unit interaction factor (UIF) calculations which is only applicable for inductive networks without series compensated lines. [ABSTRACT FROM AUTHOR]

Growing system sizes and complexity, along with the large amount of data provided by phasor measurement units (PMUs), are the drivers to accurate state estimation algorithms for online monitoring and operation of power systems. In this paper, a distributed weighted-least-square state estimation method using an additive Schwarz domain decomposition technique is proposed to reduce the computational execution time. The proposed approach divides a data set into several subsets to be processed in parallel using a multiprocessor architecture considering data exchange among distributed areas. The slow coherency method and balanced partitioning are utilized to reduce the communication overhead and increase accuracy. Moreover, bad data analysis is also investigated in a distributed manner. The performance of the proposed distributed state estimator, along with the speed-up for several test systems, was compared with the traditional centralized state estimator. The simulation results show a speed-up of 6.5 for a 4992-bus system. [ABSTRACT FROM AUTHOR]

This paper presents a method that in real-time determines remedial actions, which restore stable operation with respect to aperiodic small signal rotor angle stability (ASSRAS) when insecure or unstable operation has been detected. An ASSRAS assessment method is used to monitor the stability boundary for each generator in real-time. The ASSRAS boundary represents the condition when a generator reaches the maximum steady state active power injection. The proposed control method exploits analytically derived expressions for the ASSRAS boundary and other characteristic curves in the injection impedance plane to determine an active power redispatch among selected generators to restore stable and secure operation. Since the method is purely based on analytically derived expression, the computation of the remedial actions is fast and well suited for real-time operation. The method was tested on the IEEE 14-bus and the Nordic32 test systems where results show that the method can efficiently determine the required active power redispatch to avoid an imminent instability. [ABSTRACT FROM AUTHOR]

Several transient stability software packages are widely used for power grid planning and operations. Prior research and software documentations have shown that packages can vary in the implementations of dynamic models, and hence could potentially yield different results for the same system simulation. This paper presents a systematic methodology to determine the sources of the discrepancies seen in results obtained from different transient stability packages. This methodology can be applied to various types of dynamic models and is illustrated with generator-associated dynamic models in this paper. Consistent metrics, data mining techniques, and engineering heuristics are used to determine the discrepancy sources. This hybrid top-down+bottom-up method has been implemented on a practical, large-system case to demonstrate its scalability and transferability to real-world system studies. [ABSTRACT FROM AUTHOR]

This paper proposes using phasor measurement unit (PMU) data to trigger one-shot control in response to loss of synchronism detection. Decision trees (DTs) are trained to associate voltage magnitude and angle measurements with loss of synchronism. Different approaches to the DT construction process are illustrated in an early section of the paper by restricting the input vector to only two elements. Response-based control is obtained by triggering one-shot control the first time the DT classifies measurements as “Unstable”. The same combination of one-shot controls is applied to any event the first time the DT outputs “Unstable”. The method is demonstrated on a 176-bus reduced-order model of the western U.S. interconnection. An effective one-shot control consists of a combination of fast power changes on four buses. This control is similar to 500-MW fast power increases on two HVDC interties and it reduces angle differences in the AC network. [ABSTRACT FROM PUBLISHER]

This paper proposes a fast and robust unscented Kalman filter based decentralized dynamic state estimator (DSE) for power system online monitoring and control. The proposed robust DSE is able to detect, identify, and suppress three types of outliers, namely the observation, innovation, and structural outliers. Observation outliers refer to the received PMU measurements providing unreliable metered values due to gross errors or cyber attacks; innovation outliers are typically caused by impulsive system process noise, whereas structural outliers are induced by incorrect parameters of the generators or its associated controllers, such as exciters and speed governors. To enable the fast estimation of generator states of large-scale power systems in a decentralized manner, two model decoupling approaches are presented and compared. It is shown that the generator decoupling approach presented in this paper achieves higher statistical efficiency than the ones proposed in the literature in the presence of both small and large measurement noise. To detect and distinguish three types of outliers, projection statistics based multiple hypothesis testing approach is proposed. Specifically, three hypotheses corresponding to the occurrence of three types of outliers are assumed by constructing three innovation matrices; these matrices are made up by time-correlated innovation vectors, and/or predicted states, and/or measurements; then projection statistics are applied to each of the innovation matrix and its calculated projection values are checked by a statistical test to validate the assumed hypothesis. The identified outliers are further suppressed by a generalized maximum-likelihood-type estimator. Numerical results carried out on the IEEE 39-bus system demonstrate the effectiveness and robustness of the proposed method. [ABSTRACT FROM AUTHOR]

The uncertainties of renewable energy may bring impacts to power system reliability. This paper proposes a novel generation rescheduling algorithm, which adjusts generation outputs to mitigate the variations of branch power flows and relieve the overload probability. This algorithm helps prevent power congestion and balance the aggregate renewable generations and loads in power systems. Besides, the paper also proposes a probabilistic method evaluating the system uncertainty issue in the power system considering generation rescheduling operation. The proposed generation rescheduling algorithm has been tested on the Arizona transmission system. The generation rescheduling method enhances power system reliability analysis with a high penetration of renewable energy resources. [ABSTRACT FROM PUBLISHER]

All-electric ship power systems include less generation capacity and smaller rotating inertia compared with large power systems. The systems include large portions of nonlinear loads and dynamic loads, which may reduce the stability margin. Moreover, various operational constraints, such as system frequency constraint, motor voltage constraint and dynamic cable constraint, need to be satisfied in operational real time. Further, pulse loads draw very high short-time power in an intermittent way, which may significantly deteriorate the power quality of the system. In this paper, a novel multi-agent system cooperative controller for a medium voltage AC (MVAC) system of all-electric ship power systems is developed to balance load and generation in real time while satisfying system's operational constraints and considering load priorities. The new method coordinates the pulse load and the propulsion load to reduce the impact of pulse load changes on the power quality of all-electric ship power systems. The dynamic behavior of the new method is evaluated using case studies in PSCAD software. [ABSTRACT FROM PUBLISHER]

Electromechanical wave propagation is present in power systems as a transient spatial delay of generator rotor angle variations when a disturbance occurs. The control and mitigation of the this wave phenomenon, which spreads out to different locations at a comparably slow speed, is important for enhancing power system transient stability, as shown in part two of this two-paper series. In an idealized power system consisting of infinitesimal generators and line impedances, this traveling wave can exist to infinite frequencies, its speed can be derived from a wave equation and its reflection can be eliminated by a characteristic termination. Part one of this paper series examines realistic power systems with finite size generators and line impedances. It shows that there is a finite approximation of the traveling wave in real power systems as the wave can exist only within a finite frequency range. This paper also examines aspects such as reflections due to discrete elements, controller design based on the load modulation effect, and the existence of traveling wave and its attenuation in the Australian power system. [ABSTRACT FROM AUTHOR]

Wind power generators will become increasingly useful in modern power systems; therefore, they should be able to support the system frequency in a way similar to that of conventional generators. Droop and virtual inertia are the most reported methods in the literature. However, their impact on the generator and system frequency stability, when the double-mass mechanical dynamics of a wind power generator are considered, has not been addressed thoroughly. In this paper, small-signal modeling, analysis, and eigenvalues studies are used to show that incorporating a wind power generator in the frequency regulation can expose its shaft to forces stimulating its natural resonance frequency dynamics and lead to instability. This paper shows that the mechanical resonance of frequency-regulating wind generators must be studied and enhanced not individually but as a part of the whole power system stability analyses. To overcome the stability problem caused by implementing frequency regulation in wind generators, this paper investigates different alternatives to stabilize the generator dynamics and, at the same time, minimize undesirable interference in the conventional wind power generator controllers. Time-domain simulation results validate the analytical results and discussions. [ABSTRACT FROM AUTHOR]

In a recent paper, we proposed a system identification method for constructing reduced-order models for the electro-mechanical dynamics of large power systems, divided into multiple coherent clusters, using Synchrophasors. Every cluster in the actual model was represented as an aggregate generator in the reduced-order model. An aggregate network graph connected one aggregate generator to another. In this paper, we extend this identification approach to differential-algebraic (DAE) models. First, every cluster is associated with a unique terminal bus, referred to as the pilot bus, that couples its internal network to the rest of the system. The proposed algorithm uses Synchrophasor measurements from the pilot buses to identify the dynamic model of the aggregate generator for each cluster using nonlinear least squares while retaining the identity of all the pilot buses. The resulting reduced-order model is in the form of a nonlinear electric circuit described by aggregate differential and algebraic equations. We illustrate our results using two case studies, one for the IEEE 9-bus power system and another for the IEEE 39-bus power system. We also discuss how these reduced-order DAE models may be useful for designing shunt controllers at the pilot buses by using Synchrophasor feedback. [ABSTRACT FROM AUTHOR]

This paper proposes a new approach for power system transient stability simulation, which is based on a semi-analytical solution (SAS) of power system differential-algebraic equations. In this paper, an SAS is derived using the Adomian decomposition method as a closed-form explicit function of symbolic variables such as time, the initial state, and other variables on system conditions and; hence, it can directly give a power system's dynamic trajectory being accurate for a certain time window. Unlike a traditional numerical integration based simulation approach, the proposed new approach offline derives an SAS and online evaluates the SAS by plugging in values of symbolic variables for a series of time windows making up the desired simulation period. This paper further studies the maximum length of the time window for an SAS being accurate and proposes a divergence indicator for simulation using adaptive time windows. Implementation of this new approach on parallel computers is also studied. The new approach is validated through contingency simulation of the IEEE 10-generator 39-bus system with detailed generator models. [ABSTRACT FROM AUTHOR]

This paper summarizes the technical activities of the Task Force on Power System Dynamic State and Parameter Estimation. This Task Force was established by the IEEE Working Group on State Estimation Algorithms to investigate the added benefits of dynamic state and parameter estimation for the enhancement of the reliability, security, and resilience of electric power systems. The motivations and engineering values of dynamic state estimation (DSE) are discussed in detail. Then, a set of potential applications that will rely on DSE is presented and discussed. Furthermore, a unified framework is proposed to clarify the important concepts related to DSE, forecasting-aided state estimation, tracking state estimation, and static state estimation. An overview of the current progress in DSE and dynamic parameter estimation is provided. The paper also provides future research needs and directions for the power engineering community. [ABSTRACT FROM AUTHOR]

This paper provides the concept of design, implementation, and system integration of energy efficient power management solution for a fault-tolerant more electric engine/aircraft (MEE/MEA). The power management solution consists of three components, i.e., the power management system (PMS), the stability analysis module, and the condition-based control (CBC) module. The PMS is to optimize the electrical power system (EPS) level efficiency based on constraints with consideration of power limits of the dc system in the MEE/MEA architecture, which are calculated by the stability analysis module, and system reconfiguration, which is provided by the CBC module. This paper focuses on the design and implementation of PMS algorithm for EPS of a fault-tolerant MEE/MEA architecture. A PMS solution to optimize EPS level efficiency optimization is proposed, which is based on multiple objective optimization problem (MOOP). The proposed MOOP is solved with a modified nondominated genetic algorithm with local search mechanisms. The proposed power management solution are implemented in the MEE/MEA simulation model as well as hardware-in-loop virtual testbed and results show the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Large-scale integration of wind generation changes the power swing characteristics of a power system and may result in the misoperation of legacy power swing protection schemes. This paper presents a qualitative study on the impact of wind generation on power swing protection. The objective is to provide an understanding of the problem through case studies and present possible solutions and adjustments in protection schemes to ensure the efficiency of protection under large-scale integration of wind generation. The misoperation of power swing protection functions, namely power swing blocking and out-of-step tripping (OST), as a result of increased wind generation levels, are shown through case studies. It is also shown that the electrical center of a power system may move due to wind generation. In this case, it would be necessary to revise the optimal location of the OST protection. Finally, the impact of various factors, such as wind generator type, control scheme and fault-ride-through function, and wind generation level and capacity are investigated to determine the key features that need to be accounted for in practical protection studies. [ABSTRACT FROM AUTHOR]

A continuous Online Monitoring System (OMS) for power system stability based on Phasor Measurements (PMU measurements) at all the generator buses is proposed in this paper. Unlike the state-of-the-art methods, the proposed OMS does not require information about fault clearance. This paper proposes a convolutional neural network, whose input is the heatmap representation of the measurements, for instability prediction. Through extensive simulations on standard IEEE 118-bus and IEEE 145-bus systems, the effectiveness of the proposed OMS is demonstrated under varying loading conditions, fault scenarios, topology changes, and generator parameter variations. Two different methods are also proposed to identify the set of critical generators that are most impacted in the unstable cases. [ABSTRACT FROM AUTHOR]

This paper addresses the distributed optimal frequency control of power systems considering a network-preserving model with nonlinear power flows and excitation voltage dynamics. Salient features of the proposed distributed control strategy are fourfold, first, nonlinearity is considered to cope with large disturbances, second, only a part of generators are controllable, third, no load measurement is required, fourth, communication connectivity is required only for the controllable generators. To this end, benefiting from the concept of “virtual load demand,” we first design the distributed controller for the controllable generators by leveraging the primal-dual decomposition technique. We then propose a method to estimate the virtual load demand of each controllable generator based on local frequencies. We derive incremental passivity conditions for the uncontrollable generators. Finally, we prove that the closed-loop system is asymptotically stable and its equilibrium attains the optimal solution to the associated economic dispatch problem. Simulations, including small and large-disturbance scenarios, are carried on the New England system, demonstrating the effectiveness of our design. [ABSTRACT FROM AUTHOR]

Battery energy storage system (BESS) services will be of great help when operating power systems at high renewable energy penetrations. This paper demonstrates the requirements for effective frequency and inertia services. Some system operators currently apply scalars to financially reward improved performance. This paper demonstrates a method of validating and improving these scalars by considering the delay time and ramp time of the BESS. The importance of the method used to measure the rate of change of frequency is discussed in the paper. While the rate of change of frequency services improves with reduced delivery times, limits are identified where further reductions produce a negligible impact. This demonstrates the tangible benefits of a rapid response, and that current technology could meet the criteria. A variety of BESS capacities are trialed, which demonstrate consistency in performance and the occurrence of diminishing returns [ABSTRACT FROM AUTHOR]

This paper describes the use of large electric grids in university electric power system courses. Since much actual power system information is not publicly available, the application of public domain synthetic grids developed by the authors is presented including a 2000-bus grid. Discussion of the educational applications utilized in a senior level class are given for power flow analysis and sensitivity, economic dispatch, contingency analysis, optimal power flow (OPF), security-constrained OPF, transient stability, and real-time dynamic operations. In each of these, the application of the large synthetic grids give students insights and experience with cases closer to actual power systems in complexity and size. [ABSTRACT FROM AUTHOR]

This paper introduces a two-step methodology for online identification of the participation of generators in power system oscillatory modes, based on measured responses. The dominant modes in generator measured responses are initially identified using a mode identification technique and then introduced, in the next step, as input into a clustering algorithm. Critical groups of generators that exhibit poorly or negatively damped oscillations are identified, in order to enable corrective control actions and stabilize the system. The uncertainties associated with the operation of modern power systems with renewable energy sources (RESs) are investigated as well as the impact of the dynamic behavior of power electronic interfaced RESs. [ABSTRACT FROM AUTHOR]

Over the last decade, many power systems have significantly changed with the proliferation of renewable generation sources, such as wind and solar photovoltaic. Due to their variability and nonsynchronous nature, new challenges and complexities have emerged regarding operational security of modern power systems. The 2016 South Australia (SA) blackout was the first known blackout due to such a high renewable situation. An official report has recently been published to review the causes and provide the corresponding recommendations for improvement of network operation, control, and security. However, there are still a number of critical issues and debates which remain unsolved, such as network bottleneck identification, overvoltage explanation, pole slip concern, frequency dip mystery, and frequency/voltage instability debate. In this paper, based on the reconstruction of the event, these unsettled issues are prudently analyzed to unveil their root causes. In addition, an innovative scheme is proposed to prevent the blackout by identifying the network separation at an early stage. This research will not only further advance the understanding of the 2016 SA blackout, but also will provide valuable guidelines for the management of future renewable-rich networks. [ABSTRACT FROM AUTHOR]

This paper proposes a novel voltage stability-constrained optimal power-flow (VSC-OPF) model utilizing a recently proposed sufficient condition on power-flow Jacobian nonsingularity. We show that this condition is second-order conic representable when load powers are fixed. Through the incorporation of the convex sufficient condition and thanks to the recent development of convex relaxation of OPF models, we cast a VSC-OPF formulation as a second-order cone program. An approximate model is introduced to improve the scalability of the formulation to larger systems. Extensive computation results on Matpower and NESTA instances confirm the effectiveness and efficiency of the formulation. [ABSTRACT FROM AUTHOR]

In this paper, a method for designing coordinated power system stabilizer (PSS) is presented. The proposed method is based on the reference model controller design. To this end, a model that is called single-machine non-infinite bus is presented for studying low frequency oscillations. Then a reference model is proposed for designing PSS based on the single-machine non-infinite bus model. Transfer functions of the understudy machine augmented with stabilizer are equated by transfer functions of the proposed reference model to compute the PSS's parameters. The damping of the reference model and consequently the damping of the designed PSS do not depend on the frequency of oscillations. Hence, the proposed PSS damps all intra- and inter-area oscillations and no incoordination will happen among the system's stabilizers. Two PSSs are designed using the proposed method for a test power system. To demonstrate the efficiency of the proposed method, the performance of the proposed PSSs are compared with the performance of multi-band PSS4B, conventional \Delta \omega PSS, conventional \Delta P_a PSS, and PSS designed based on particle swarm optimization. Robustness of stabilizers against variation of oscillations' frequency, variation of operating point, and existence of harmonics are used to measure their performances. [ABSTRACT FROM PUBLISHER]

The transition to a deregulated electric power system industry has created a highly competitive electricity market with immense power transfer activity performed between the market participants. A poorly-damped oscillation of small-signal instability is usually imminent during a stress power system condition attributed by the base case power transfer or available transfer capability (ATC) compounded with an outage of critical line. The contingency ranking by means of lowest damping ratio is introduced so that execution of the most critical line outage will incite to a poorly-damped oscillation during the base case ATC. The rescheduling of few critical generators determined by using the normalized participation factor is presented in this paper as a novel, non-intricate and cost-effective solution for estimating a new value of ATC while ensuring a secure power system operating condition. Sturdiness of the proposed method is verified through comparison with the weighted-average sensitivity of stability index required for rescheduling the critical generators performed in a case study of 39-bus New England system. Comparative study on the results of cost minimization in generators rescheduling has also been done based on the critical generators selected by the two methods. [ABSTRACT FROM AUTHOR]

This paper presents a decentralized wide-area coordinated supplementary control of multiple line-commutated converter (LCC)-HVDC links to 1) prevent interactions among the HVDC links and 2) enhance the damping of the inter-area oscillatory modes. The proposed approach is based on the sparsity-promoting optimal control. The main features of the proposed approach are 1) it requires minimal communication infrastructure to achieve the control objectives and thus reduces the impacts of communication delays and noise, 2) it entails in an optimal gain which preserves the closed-loop stability and 3) it does not require the estimates of the system states. The performance of the proposed controller is evaluated based on eigen analysis and time-domain simulation of an interconnected AC system that includes five LCC-HVDC links. Performance of the proposed controller is also compared with those of fully centralized and conventional local supplementary controllers and its merits are highlighted. The studies indicate the proposed controller, based on 13 remotely communicated signals, provides similar performance as that of a fully centralized optimal controller using 2050 communicated signals and is far superior to the conventional local supplementary controllers. [ABSTRACT FROM AUTHOR]

The small-signal stability analysis of power systems concerns the critical modes as well as the modes associated with a physical meaning, e.g., the interarea oscillation modes for weakly connected systems and the modes sensitive to a particular parameter. As the order of the power-system state matrix increases, it becomes more difficult to determine these modes. In this paper, a method is proposed to compute the interarea oscillation modes of large-scale power systems. The deviation in the active power of the transmission section is selected to identify the interarea oscillation modes. Then, the two-sided Jacobi-Davidson method combined with this selection is employed to compute these modes. Participation factors are used to separate the electromechanical oscillation modes. Numerical tests show that the proposed method is valid and efficient. [ABSTRACT FROM PUBLISHER]

The paper introduces a probabilistic framework for online identification of post fault dynamic behavior of power systems with renewable generation. The framework is based on decision trees and hierarchical clustering and incorporates uncertainties associated with network operating conditions, topology changes, faults, and renewable generation. In addition to identifying unstable generator groups, the developed clustering methodology also facilitates identification of the sequence in which the groups lose synchronism. The framework is illustrated on a modified version of the IEEE 68 bus test network incorporating significant portion of renewable generation. [ABSTRACT FROM PUBLISHER]

Multi-stage Adomian decomposition method (MADM) is a proven semi-analytical approximation solution technique for ordinary differential equations (ODEs), which provides a rapidly convergent series by integrating over multiple time intervals. Applicability of MADM for large nonlinear differential algebraic systems (DAEs) is established for the first time in this paper using the partitioned solution approach. Detailed models of power system components are approximated using MADM models. MADM applicability is verified on 7 widely used test systems ranging from 10 generators, 39 buses to 4092 generators, 13659 buses. Impact of the step size and the number of terms is investigated on the stability and accuracy of the method. An average speed up of 42% and 26% is observed in the solution time of ODEs alone using the MADM when compared to the midpoint-trapezoidal (TrapZ) method and the modified-Euler (ME) method, respectively. MADM accuracy is found to be similar to the ME and comparable to the TrapZ method. MADM stability properties are found to be better than the ME and weaker than the TrapZ method. An average speed up of 13% and 5.85% is observed in the overall solution time using MADM w.r.t. TrapZ and ME methods, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents a novel method based on affine arithmetic (AA) for voltage stability assessment of power systems considering uncertainties associated with operating conditions, which may be attributed to intermittent generation sources, such as wind and solar. The proposed AA-based method reduces the computational burden as compared to Monte Carlo (MC) simulations, and also improves the accuracy as compared to some analytical approaches. The proposed method is tested using two study cases: first, a 5-bus test system is used to illustrate the proposed technique in detail, and thereafter a 2383-bus test system to demonstrate its practical application. The results are compared with those obtained using MC simulations to verify the accuracy and computational burden of the proposed AA-based method, and also with respect to a previously proposed technique to estimate parameter sensitivities in voltage stability assessment. [ABSTRACT FROM PUBLISHER]

Event-triggered control (ETC) is becoming increasingly popular in load frequency control (LFC) operation in power systems. So far, the existing literature has primarily focused on load disturbance rejection in face of communication delay without considering much on networked-induced measurement disturbances and messages sent. In this paper, we study the LFC operation as a problem of networked control system and propose, for the first time, an ETC based switching approach for frequency regulation. We derive delay-dependent conditions to obtain the lower bound on inter-event time during event-trigger mechanism which assures the robust stability under networked induced time-varying delays and measurement disturbance and reduction in the amount of sent measurements. The effectiveness of the proposed approach is verified via numerical examples based on single-, two-area power systems and single-area with electric vehicle (EV) participation. [ABSTRACT FROM AUTHOR]

This paper introduces a probabilistic framework for transient stability assessment (TSA) of power systems with high penetration of renewable generation. The critical generators and areas of the system are identified using a method based on hierarchical clustering. Furthermore, statistical analysis of several transient stability indices is performed to assess their suitability for TSA of reduced inertia systems. The proposed framework facilitates robust assessment of transient stability of uncertain power systems with reduced inertia. [ABSTRACT FROM AUTHOR]

This paper proposes the exploitation of multiterminal HVDC grids to improve transfer capability in power systems. Multiterminal HVDC systems based on voltage source converters (VSC-MTDC) have been recognized as a promising alternative for the wind power integration. Under low wind scenarios, these grids originally dedicated for wind power transmission can be exploited as an additional interarea transmission path, providing extra dynamic security. The paper focuses on small-signal stability assessment, especially in poor damped oscillations associated with interarea modes. Simulations performed through a generic computational framework have shown that the high level of flexibility and controllability provided by voltage source converters can considerably improve the transfer capacity, while preserving adequate dynamic performance. [ABSTRACT FROM AUTHOR]

This paper proposes a disturbance-adaptive short-term frequency support scheme of a doubly fed induction generator (DFIG) that can improve the frequency-supporting capability while ensuring stable operation. In the proposed scheme, the output of the additional control loop is determined as the product of the frequency deviation and adaptive gain, which is modified depending on the rate of change of frequency (ROCOF) and rotor speed. To achieve these objectives, the adaptive gain is set to be high during the early stage of a disturbance, when the ROCOF and rotor speed are high. Until the frequency nadir (FN), the gain decreases with the ROCOF and rotor speed. After the FN, the gain decreases only with the rotor speed. The simulation results demonstrate that the proposed scheme improves the FN and maximum ROCOF while ensuring the stable operation of a DFIG under various wind conditions irrespective of the disturbance conditions by adaptively changing the control gain with the ROCOF and rotor speed, even if the wind speed decreases and a consecutive disturbance occurs. [ABSTRACT FROM AUTHOR]

This paper presents stability-improvement results of a two-area power system connected with an integrated onshore and offshore wind farm (WF) using a static synchronous compensator (STATCOM). The onshore WF of 19.8 MW is based on dynamic-slip induction generator, while the offshore WF of 100 MW is based on doubly-fed induction generator. The qd axis equivalent-circuit model is derived to establish the complete system model under three-phase balanced conditions. A lead-lag power-oscillation damping controller (PODC) of the STATCOM is designed by using the phase-compensation method based on modal control theory to damp out low-frequency oscillations of the studied two-area power system. A systematic strategy using a frequency-domain approach based on eigenvalue analysis and a time-domain approach based on nonlinear-model simulations is performed to evaluate the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed STATCOM joined with the designed PODC is capable of improving stability of the studied two-area power system connected with the integrated onshore and offshore WF under various disturbance conditions. [ABSTRACT FROM PUBLISHER]

This paper addresses the power system model order reduction proposing an optimal formulation for identifying electromechanical modes present in active power flows. The reduced power system preserves the dynamic and physical characteristics of the studied system. The modal identification is achieved by the digital Taylor–Fourier transform, which decomposes an oscillating signal into monocomponents. Then, these ones are embedded into an objective function with the purpose of estimating the equivalent generators’ parameters. Results demonstrate a reduction in the computational burden and the computing time associated with transient stability studies for the preserved system, retaining its steady-state and dynamic conditions. [ABSTRACT FROM AUTHOR]

The inertia of modern power systems is decreasing and becoming more variable as more inverter-connected renewable energy sources and loads are integrated. This leads to a low and time-varied inertia power system that is more sensitive to disturbances and may not be robust enough to survive large disturbances. How to protect such a low and time-varied inertia system from blackouts is in question. This paper tries to answer this question using a graph spectra-based controlled islanding method. Eigenvector sensitivity, with respect to inertia, is used to identify the impact of reduced inertia on the spectral properties of power system graphs and, thus, coherent generator grouping. Constrained spectral clustering is then used to find the islanding boundary with minimal power-flow disruption to island low inertia systems. Simulation results, obtained using the IEEE 9-bus and 118-bus test systems, validate the effectiveness of the proposed algorithm in the case of low inertia systems. [ABSTRACT FROM AUTHOR]

This paper proposes an improved voltage regulation method in a multisource-based dc electrical power system in the more electric aircraft. The proposed approach, which can be used in terrestrial dc microgrids as well, effectively improves the load sharing accuracy under high droop gain circumstance with consideration of cable impedance. Since no extra communication line and controllers are required, it is easily implemented and also increases the system modularity and reliability. By using the proposed approach, the dc transmission losses can be reduced and the system stability is not deteriorated for normal and fault scenarios. In this paper, optimal droop gain settings are investigated and the selection of individual droop gains as well as the proportional power sharing ratio has been described. Simulation and experimental results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a method of estimating the electromechanical damping and frequency coefficients of interconnected power systems. The method combines AESOPS approach and eigenvalue analysis. Computation time is reduced by applying an approximation based on an eigenvalue sensitivity formula, which evaluates eigenvectors of the 2ng\times 2ng [A(\omegaK)] and [A(\omegaK)]^\rm T matrix and thereafter use them to obtain improved estimates of the eigenvalues. Numerical results from a 16-generator system demonstrate the feasibility of the proposed method. [ABSTRACT FROM PUBLISHER]

For the operators of a power system, underfrequency load shedding is important for maintaining the system in a stable and reliable state whenever it suffers from a severe disturbance. The underfrequency relay protects the power system against a blackout when the system frequency declines to predetermined settings. This paper determines the shed load at each stage for the underfrequency relay (81L). The genetic algorithm (GA) is employed to minimize the shed load and maximize the lowest swing frequency. Penalty functions and chromosomes with varying lengths are utilized in the GA to determine the optimal shed loads at all stages. The uncertainty in bus loads is modeled by a fuzzy set. A stand-alone power system with diesel and wind-power generators is adopted to demonstrate the applicability of the proposed method. [ABSTRACT FROM PUBLISHER]

With the increasing use of renewable energy resources and energy storage devices, inverter-based distributed energy resources (DERs) become the important components in microgrids. As diesel generators with direct ac connections are the current most cost effective and reliable power sources, the stability investigation of microgrids should include both types of DERs. In this paper, dynamics of diesel generation will be included and the interaction of the diesel generators and the inverter-based DERs will be investigated using eigenvalue analysis and time-domain simulations. The significant contributions of this paper include: 1) identification of the stability problem in microgrids with inverter-based DERs and conventional generators and 2) investigation of the interaction problem of inverter-based DERs and conventional generators in islanded microgrids. [ABSTRACT FROM AUTHOR]