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This paper proposes a Principal Component Analysis (PCA)-based method to construct composite indices to rapidly assess power system transient stability. By assigning appropriate weights to a few selected sub-indicators, a composite index can be constructed to guarantee a better coverage of worst-case stability scenarios of the power system. This paper provides an automatic method to construct a composite index with four sub-indicators calculated by the integral of acceleration, speed deviation and rotor angle of generators over a certain integration period using PCA. The effectiveness of the sub-indicators is validated first, followed by a comprehensive example of process of composite index construction, and the assessment of the influence of the effect of integration period on the performance of the composite index. High accuracy of classification has been demonstrated using composite index with appropriate settings of the integration periods of the sub-indicators. [ABSTRACT FROM AUTHOR]

Transient stability of a power system can be significantly affected by wind power generators due to their stochastic power output and complex dynamic characteristics. This paper proposes a robust optimization approach for coordinating generation dispatch and emergency load shedding against transient instability under uncertain wind power output. The problem is modelled as a two-stage robust optimization (TSRO) model considering transient stability constraints, where the first-stage is to optimize the generation dispatch (preventive control) before a contingency and the second-stage decision is the emergency load shedding (emergency control) after the contingency occurrence under the worst case of wind power variation. To solve this TSRO problem, this paper also proposes a solution algorithm which integrates transient stability assessment and transient stability constraint construction in a column and constraint generation framework. The proposed method is validated on the New-England 39-bus system and the Nordic32 system, which shows high computational efficiency and stability robustness against uncertain wind power. [ABSTRACT FROM AUTHOR]

Co-simulation of heterogeneous systems allows for in-depth analysis of various aspects of power systems’ operation while staying within the environments of the simulation tools that are best fit to represent their respective domains. Equipped with a proprietary co-simulation platform, the paper focuses on the issue of power-conjugate coupling between parts of power grids modeled in transient stability and electromagnetic transient simulation tools. The problems of co-simulation stability and precision in presence of delays are tackled by means of designing a proper coupling interface. It is shown that two established interface methods – the V-I method and the Transmission Line Interface – are special cases of a generalized interface framework proposed in the paper. Moreover, a new interface algorithm is described by parametrizing the generalized framework. Analytical tools are also formulated to aid in the analysis of interface stability and precision via the concepts of passivity and transparency. Simulation results of benchmark systems of various complexity demonstrate the application of the developed power coupling interface. [ABSTRACT FROM AUTHOR]

The increasing complexity of modern AC/DC power systems poses a significant challenge to a fast solution of large-scale transient stability simulation problems. This paper proposes the hybrid parallel-in-time-and-space (PiT+PiS) transient simulation on the CPU-GPU platform to thoroughly exploit the parallelism from time and spatial perspectives, thereby fully utilizing parallel processing hardware. The respective electromechanical and electromagnetic aspects of the AC and DC grids demand a combination of transient stability (TS) simulation and electromagnetic transient (EMT) simulation to reflect both system-level and equipment-level transients. The TS simulation is performed on GPUs in the co-simulation, while the Parareal parallel-in-time (PiT) scheduling and EMT simulation are conducted on CPUs. Therefore, the heterogeneous CPU-GPU scheme can utilize asynchronous computing features to offset the data transfer latency between different processors. Higher scalability and extensibility than GPU-only dynamic parallelism design is achieved by utilizing concurrent GPU streams for coarse-grid and fine-grid computation. A synthetic AC/DC grid based on IEEE-118 Bus and CIGRÉ DCS2 systems showed a good accuracy compared to commercial TSAT software, and a speedup of 165 is achieved with 48 IEEE-118 Bus systems and 192 201-Level detail-modeled MMCs. Furthermore, the proposed method is also applicable to multi-GPU implementation where it demonstrates decent efficacy. [ABSTRACT FROM AUTHOR]

Online transient analysis plays an increasingly important role in dynamic power grids as the renewable generation continues growing. Traditional numerical methods for transient analysis not only are computationally intensive but also require precise contingency information as input, and therefore, are not suitable for online applications. Existing online transient assessment studies focus on the determination of post-contingency system stability or stability margin. This paper develops a novel graph-learning framework, Deep-learning Neural Representation or DNR, for online prediction, of the time-series trajectories of the system states using initial system responses that can be measured by phasor measurement units (PMUs). The proposed DNR framework consists of two sequential modules: a Network Constructor that captures network dependencies among generators, and a Dynamics Predictor that predicts the system trajectories. The key to improved prediction performance is the introduction of the spatio-temporal message-passing operations into graph neural networks with structural knowledge. Its effectiveness and scalability are validated through comparative studies, demonstrating the prediction performance under different contingency scenarios for systems of different sizes. This framework provides a solution to online predicting post-fault system dynamics based on real-time PMU measurements. Additionally, it can also be applied to facilitate the offline transient simulation without simulating the entire trajectories. [ABSTRACT FROM AUTHOR]

Deep learning (DL) techniques have shown promising performance for designing data-driven power system transient stability assessment (TSA) models. However, due to the deep structure of the DL, the resulting model is always a black-box and hard to explain, which hinders its practical adoption by the industry. This paper proposes an interpretable DL-based TSA model to balance the TSA accuracy and transparency. The proposed method combines the strong nonlinear modelling capability of a deep neural network and the interpretability of a decision tree (DT). Through regularizing DL-based model with the average DT path length in the training process, the proposed interpretable DL-based TSA method can visually explain the TSA decision-making process. Simulation results have shown that the proposed method can deliver highly accurate TSA results and interpretable TSA decision-making rules, which can be used for designing preventive control actions. [ABSTRACT FROM AUTHOR]

This paper proposes a Transient Stability Constrained Optimal Power Flow (TSCOPF) formulation that models non-synchronous renewable generation equipped with synthetic inertia. The proposed optimization problem calculates the optimal operating point of the system, accommodating high shares of non-synchronous renewable generation while ensuring transient stability in the event of critical incidents. Synthetic inertia controllers are used to improve the dynamic stability of the system in cases of very high share of renewable generation. The proposed tool is tested in the North-West Spanish system, a network with a high penetration of wind energy that causes a reduction in the total system inertia. The results of the study show that 1) synthetic inertia in renewable power plants can diminish electromechanical oscillations after a severe contingency, reducing the cost of ensuring transient stability; 2) using synthetic inertia the system becomes more stable when conventional generation is decommissioned following de-carbonization and renewable promotion policies; and 3) the proposed model can be used to calculate the parameters of the synthetic inertia control. [ABSTRACT FROM AUTHOR]

Since the wide application of virtual synchronous generators (VSGs), the power grid faces great challenges in the safe and stable operation due to their limited thermal capacity and weak anti-disturbance ability. During transient period, for example, a fault occurs in the transmission line, the VSG may lose the transient angle stability and provoke the current hard limit. Even if the fault is cleared by tripping of line, it still faces the problem of instability and voltage dips. To address this problem, in this paper, the post-fault large-signal model of VSG is derived first via the travelling waves based fault information acquisition. Subsequently, with the effect of both active and reactive power loops taken into account, a two-stage simultaneous control scheme is proposed for improving the transient stability of VSG, while considering the current limitation during fault state and voltage support after fault clearance. This method is fulfilled by mode switching and an additional feedback control based on the fault signal. Finally, the effectiveness of the proposed method under both symmetrical and asymmetrical faults is verified. Moreover, the application of the proposed method in a multiple VSGs system is also verified. Besides, the robustness to parameter mismatch and the feasible operating region for the method are discussed. [ABSTRACT FROM AUTHOR]

Machine learning approaches have exhibited high potential in power system transient stability assessment (TSA), yet their initial preparation stages of stability knowledge base generation (SKBG) based on time-domain simulations often undergo high computational costs. In fact, how to ease the heavy computational burden of SKBG without sacrificing the reliability is still a significant challenge. To address this problem, this paper develops a semi-supervised ensemble learning (SSEL) framework for reliable SKBG acceleration, without additional need for computing hardware upgrading. In particular, it performs detailed simulations for a minority of cases and fast simulations for the majority ones to reduce the total computation time. Considering the absence of stability status information of those fast simulated cases, an SSEL scheme is systematically designed to reliably label their stability status. Before implementing SSEL, two concise feature descriptors are first introduced to efficiently extract transient features from multiplex system trajectories. Then, all the cases are characterized in a unified feature space, whereby a series of semi-supervised support vector machines are trained in randomly formed subspaces. Afterward, these single machines are systematically combined to derive an enhanced SSEL model, which is able to make reliable and robust labeling decisions. Further, a backtrace strategy is carefully devised for SSEL, so as to maintain the high reliability of SKBG. Test results on the IEEE 39-bus system and the realistic GD Power Grid in South China illustrate the excellent performances of the proposed framework on SKBG acceleration. [ABSTRACT FROM AUTHOR]

The paper proposes methodology for development of dynamic equivalent model of hybrid renewable energy source (HRES) plant suitable for reliable assessment of the overall transient stability of the realistic, large power systems. Transient stability index is used for system stability assessment, and consequently for the evaluation of the model performance. The historical plant production data and transmission network short-circuit fault statistics, together with probabilistically modelled uncertainties associated with system operation, are used to generate a set of realistic dynamic responses of the plant over the period of one year. The use of clustering algorithms enabled unsupervised grouping/clustering of responses and development of the low order equivalent models in the form of a transfer function with voltage as an input and real and reactive power as outputs. The methodology is illustrated on a number of case studies using two HRES plant configurations. It is demonstrated that a very few low order dynamic models can be used to model the HRES plant during the year for sufficiently accurate transient stability assessment of the power system. The possibility of deriving these equivalent models based on forecasted HRES plant composition makes them attractive for practical application in power system dynamic security studies. [ABSTRACT FROM AUTHOR]

Power system control and transient stability analysis play essential roles in secure system operation. Control of power systems typically involves highly nonlinear and complex dynamics. Most of the existing works address such problems with additional assumptions in system dynamics, leading to a requirement for a complete and general solution. This paper, therefore, proposes a novel control framework for various power system control and stability problems leveraging a learning-based approach. The proposed framework includes a two-module structure that iteratively and jointly learns the candidate Lyapunov function and control law via deep neural networks in a learning module. Meanwhile, it guides the learning procedure towards valid results satisfying Lyapunov conditions in a falsification module. The introduced termination criteria ensure provable system stability. This control framework is verified through several studies handling different types of power system control problems. The results show that the proposed framework is generalizable and can simplify the control design for complex power systems with the stability guarantee and enlarged region of attraction. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to dynamic phasor-based transient stability simulation. The proposed method is based on the modified nodal analysis (MNA) approach to circuit simulation, which is used to construct continuous differential-algebraic equations (DAEs). The proposed method makes use of the stamp technique, which makes it possible to construct a general purpose MNA-based simulator. Stamp-based models for common power system components are derived in this work. A new MNA-based synchronous machine model is presented, which represents machines as nonlinear inductances instead of subtransient equivalents. The resultant continuous DAEs are numerically solved using the general purpose variable step and variable order library IDA. Simulation results from the IEEE 68 bus test system, a real 400 bus power system, and the IEEE 39 bus test system with an embedded HVdc transmission system demonstrate that the proposed method is suitable for large ac networks with power electronic devices. The results demonstrate good agreement between the proposed method and electromagnetic transient (EMT) simulation. The results also demonstrate that the proposed method is fast and scalable with CPU times that are up to 200 times faster than EMT simulation. [ABSTRACT FROM AUTHOR]

While many machine learning approaches have been widely applied to power system online dynamic stability assessment, how to sufficiently learn spatial-temporal correlations from system transients without losing the interpretability is still a challenging issue. In this paper, a novel networked time series shapelet learning approach is proposed to learn spatial-temporal correlations for transient stability assessment (TSA) in an interpretable manner. Specifically, a network impedance-based adjacency matrix is first introduced to characterize spatial networked correlations. Based on graph structural regularization, this matrix is effectively incorporated into the subsequent learning procedure as spatial constraints. Taking time series trajectories acquired from multiple buses as the inputs, networked shapelet learning is heuristically performed to learn critical sequential features, i.e., networked shapelets, for TSA model derivation. With the learning procedure strategically guided by inherent spatial-temporal correlations of the system, the obtained data-driven TSA model is able to perform highly reliable and interpretable online TSA. Numerical test results on the IEEE 39-bus test system and the realistic GD Power Grid in China verify the superior performances of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper presents an optimal transient-stability control strategy that modulates the real power injected and absorbed by distributed energy-storage devices. These devices are located at the high-voltage bus of several generators in a synchronous power system. The system is broken into areas based upon groupings of generators. The control strategy consists of two parallel feedback loops. One loop focuses on preserving the synchronism of the generator to its own area. The second loop focuses on preserving the synchronism of a given area to the other areas. Each control loop strategy is based upon local and center-of-inertia frequency measurements. The strategy is derived from two perspectives. With the first, the goal is to remove as much kinetic energy gained during a disturbance as quickly as possible before it is converted to potential energy. With the second perspective, an optimal transient control cost-function is minimized. Both perspectives result in the same strategy. The performance of the control strategy is evaluated on a four-machine power system model and on a 34-generator reduced-order model of the western North-American grid. The results show that this control approach significantly improves the transient stability of power systems. [ABSTRACT FROM AUTHOR]

In transient stability simulators such as PSS/E, the bus frequency is estimated using a window of (positive-sequence) phasor angle measurements. A digital filter is often used to account for the filtering effect in actual measurement devices and to eliminate sudden changes during frequency computations. Although transient stability simulators label the filtered angle derivative as the “frequency,” the frequency provided by such programs does not match actual measurements reported by phasor measurement units (PMUs), which makes it difficult to gauge the validity of studies (e.g., wide-area event detection and control applications) that are based on such simulations. In this paper, we implement a frequency computation method directly using positive phasor angles provided by simulators. The proposed method is tested on two systems extensively and validated against the measurements of an actual PMU. The improved frequency measurements closely match PMU responses. Cross-validation results also suggest the method may be used for other systems without conducting full time-domain simulations. [ABSTRACT FROM AUTHOR]

Transient recovery characteristics of DC voltage are critical to analyze the stability criterion and the fault ride-through capability of voltage source converter (VSC)-based DC power systems. In this paper, the dynamic model of a flexible DC power grid was initially established, and then, the dynamic operation mechanism of the system was presented by analyzing the movement locus of the operating point when disturbances occur in the DC grid. Subsequently, the DC transient voltage limit and the DC fault clearing time were calculated in order to obtain the transient stability criterion of the DC power system. In addition, a novel voltage transient recovery control strategy was proposed by improving the droop control of the DC voltage to extend the transient stability margin of the power system. Finally, a typical multi-terminal flexible DC power grid was developed on a hardware-in-the-loop platform. The results demonstrated that the voltage recovery ability of the DC power system can be quantitatively estimated by the stability criterion, while the system transient stability can be improved by the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper proposes a fractional-order sliding mode controller (FOSMC) for fixed-time stability of multimachine power systems. Fractional calculus has been applied in sliding mode control (SMC) to design FOSMC which can better suppress the chattering phenomenon than the traditional integer-order SMC. Hence, a FOSMC is proposed to regulate the excitation of synchronous generators to improve the transient stability of the power system. In addition, the FOSMC can maintain the multimachine power systems stabilization in an upper bound and measurable convergence time independent of the initial operating conditions of the power system. The Lyapunov function is implemented to demonstrate the stability of multimachine power systems under the FOSMC, and the upper bound convergence time of the power system is generally estimated. The New England 10-machine 39-bus power system is taken into simulation to test the effectiveness and superior performances of the FOSMC than the existing control methods under different operating conditions. Meanwhile, the FOSMC with different orders are presented to verify that the FOSMC can better restrain the chattering phenomenon than traditional integer-order SMC. Simulation results show that the FOSMC can effectively reduce the chattering phenomenon and ensure the power system stabilization in an upper bound time, thus enhancing the dynamic performances of the power system. [ABSTRACT FROM AUTHOR]

The renewable energy source based generating technologies and flexible demand and storage devices exhibit significant temporal and spatial uncertainties in generating and loading profiles and introduce additional level of uncertainty in network operation. The dynamic behaviors of such a network can be affected and the stable operation may be compromised. This paper proposes a probabilistic analysis approach for the evaluation of the effect of uncertain parameters on power system voltage and angular stability. Load margin, the damping of critical eigenvalues and the transient stability index have been chosen as the relevant stability indices for voltage stability, small-disturbance stability, and transient stability analysis, respectively. The Morris screening sensitivity analysis method coupled with a multivariate Gaussian copula to account for parameter correlations is used for the priority ranking of uncertain parameters. The approach is illustrated on a number of case studies using modified IEEE 68-bus NETS-NYPS test system. The results obtained in this paper reveal that the critical parameters appear as groups if the input dataset is correlated, and, hence even a parameter (which may be uninfluential individually) can have a significant impact on system dynamic behavior due to its correlation with other influential parameters. [ABSTRACT FROM AUTHOR]

High-voltage direct-current (HVDC) transmission systems have been rapidly developing, whereas they also become the crucial factors that affect the power system's stability. The repetitive commutation failures (RCF) of the HVDC link will put the sending-end power system at risk of transient instability, which greatly raises the demand of the system to enhance its ability to cope with such events. This paper proposes a flexible control strategy supported by the fast-acting energy storage system (ESS) based on the combination of the model predictive control (MPC) principle and the extended equal area criterion (EEAC) to ensure transient stability of the sending-end system when RCF occurs in a single HVDC link. The formulas to forecast the system's dynamic behavior are constructed. The optimal power expected to be provided by the ESS for each commutation failure (CF) is obtained by assessing the system stability margin. The proposed strategy is to maintain the system's transient stability by the consecutive appropriate responses of the ESS during RCF. Additionally, the blocking conditions of the HVDC link and the required consequent control are studied. The simulation results demonstrate the ability of the proposed strategy to ensure the transient stability of the sending-end power system when the RCF occurs. [ABSTRACT FROM AUTHOR]

This paper proposes a new coordinated method for preventive generation rescheduling and corrective load shedding to maintain power system transient stability under uncertain wind power variation. A two-step bi-level optimization model is proposed where generation rescheduling and load shedding are coordinated by a risk coordination parameter, which adjusts the total coordination cost in the upper level. Then, based on Extended Equal Area Criterion (EEAC) and trajectory sensitivities, the non-linear risk and stability constraints are converted into the linear form for generation rescheduling cost and load shedding cost optimization in the lower level, respectively. Uncertain wind power output is modeled as a small number of robust test scenarios. Finally, the golden section search is applied to solve the bi-level problem. The proposed method is validated on the New-England 39-bus system by using commercial grade software. The computational efficiency, economic optimality, and stability robustness under random wind power of the method are demonstrated. [ABSTRACT FROM AUTHOR]

This paper proposes a novel wide-area control strategy to enhance the transient stability of a large inter-connected power grid. The proposed control strategy achieves maximal damping of the inter-area oscillations by calculating the optimal number of cluster centers based on a novel online coherency grouping. To achieve this objective, the critical electro-mechanical mode is selected using localness index method during transient conditions. In addition, the online identification of the full model is performed to estimate the states to be controlled during the grid disturbances. Thereafter, a discrete linear quadratic regulator (DLQR) is directly applied to the estimated states, and the corresponding signals are channelized through the loop of most controllable and observable machines of each coherent group. The efficacy of the proposed method is tested on IEEE 39 bus and IEEE 68 bus standard benchmark model. The results demonstrate faster damping with minimal computation burden compared to existing solutions such as a classical slow coherency and a multi-input multi-output (MIMO) based wide area damping controllers. [ABSTRACT FROM AUTHOR]

This paper develops a hierarchical deep learning machine (HDLM) to efficiently achieve both quantitative and qualitative online transient stability prediction (TSP). For the sake of improving its online efficiency, multiple generators’ fault-on trajectories as well as the two closest data-points in pre-/post-fault stages are acquired by PMUs to form its raw inputs. An anti-noise graphical transient characterization technique is tactfully designed to transform multiplex trajectories into 2-D images, within which system-wide transients are concisely described. Then, following the divide-and-conquer philosophy, the HDLM trains a two-level convolutional neural network (CNN) based regression model. With stability margin regressions hierarchically refined, it manages to perform reliable and adaptive online TSP almost immediately after fault clearance. Test results on the IEEE 39-bus test system and the real-world Guangdong Power Grid in South China demonstrate the HDLM's superior performances on both stability status and stability margin predictions. [ABSTRACT FROM AUTHOR]

This paper presents a sufficient and necessary condition for transient stability of multimachine power systems based on the passivity formalism. The condition derived using the extended classical model (ECM) with zero transfer conductance (TC). The ECM of power systems relaxes slightly the assumption of “voltage-behind-transient-reactance” from “constant”, which is used in the conventional classical model to “positive, bounded and independent of machine rotor angles”. The results of time domain simulation of a full model of Western Interconnection used for regular operation planning study are presented for verifying the model assumptions and the storage functions of the system in four different scenarios (well stable, marginally stable, marginally unstable and very unstable), thus illustrating the sufficiency and necessity of stability criterion based on passivity. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for generating restoration sequences in distribution systems and microgrids with emphasis on deriving optimal switching times for remote control switches. Microgrid architecture considered are assumed to be operating in islanded single master mode. Control methods for handling the unbalance inherent in distribution systems using single-phase controlled PQ inverters were developed and incorporated in the proposed method. The problem of considering simultaneously both energy optimization and dynamic stability of the system, which is lacking in existing methods, was addressed by studying the transient behavior of microgrids based on extended electromagnetic transients program (EMTP) simulations and then approximate and incorporate these behaviors into the optimization formulation for restoration. The approach is based on multi-objective optimization of final restored load and total restoration time. The methodology was studied on a modified IEEE 123 node test feeder. An EMTP simulation in PSCAD of the formed microgrids was used to validate the accuracy of the dynamic and steady-state characteristics of the resulting systems. By considering the transient behavior of distributed generators (DGs) during restoration, a better restoration sequence that does not trigger protection relays could be realized. [ABSTRACT FROM AUTHOR]

In this paper, a novel qualitative method is proposed to analyze the transient stability of power systems. Unlike the traditional methods, this method can illustrate the structural characteristics of the stability region and display the boundary on the global phase plane intuitively. Particularly, the stability boundary and phase portraits are investigated in three-dimensional space. Global phase portraits including the singularity at infinity (SAI) show the beginning and ending points of the portraits, and indicate the whole situation of an attractor's basin. To properly use the method to clarify the dynamic behavior at infinity, the multi-machine system is simplified by an equivalent method and the trajectories of the rotor angle near the unstable equilibrium point are projected into a closed ball based on the invariant submanifolds. The effects of damping coefficient, fault locations, and fault types on the transient stability region are discussed by the coordinate of the SAI, which are obtained based on the qualitative theory of differential equations. If the traditional generators are replaced with the distributed energy resources, the transient stability of the power system may be affected both positively and negatively. The simulation experiments of the IEEE 39-bus test system are carried out to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Nonlinear modal decoupling (NMD) was recently proposed to nonlinearly transform a multi-oscillator system into as many decoupled oscillators as the oscillation modes of interests with the original system. Those decoupled oscillators together provide a fairly accurate approximation of behaviors of the original system in an extended neighborhood of the equilibrium. Each oscillator has just one degree of freedom and hence can easily be analyzed to infer the nonlinear dynamics of the original system associated with one oscillation mode. As the first attempt of applying the NMD methodology to realistic power system models, this paper proposes an NMD-based approach for the early warning of the oscillation mode that may most likely develop into a mode of transient instability. For a multi-machine power system, the approach first derives decoupled nonlinear oscillators by a coordinates transformation, and then applies Lyapunov stability analysis to decoupled oscillators to assess the stability of the original system. For large-scale power grids, the proposed approach can be efficiently applied by conducting NMD regarding only selected modes. Case studies on a 3-machine 9-bus system and an northeast power coordinating council (NPCC) 48-machine 140-bus system show the potentials of the approach in early warning of transient instability for multi-machine systems. [ABSTRACT FROM AUTHOR]

This paper proposes a novel comprehensive model of a rectifier-controlled induction motor drive for use in positive-sequence transient stability simulation (PSTSS) programs. The model is implemented to approximately capture the behavior of the point-on-wave drive model, and applied to investigate the dynamic performance of the advanced drive loads in system-level simulations. This positive-sequence drive model is systematically developed by reducing the detailed three-phase electrical and control representations into $dq$ axes positive-sequence formulations. For the positive-sequence model, the line-side rectifier is interfaced to the grid through a voltage source with separate $dq$ axes controls to regulate the active and reactive power of the drive. The machine-side inverter control system is represented based on rotor flux oriented control. The dc-link of the drive converter is implemented by employing the average model of the pulse width modulated converter, and is utilized to integrate the line-side rectifier and machine-side inverter. The proposed motor drive model is validated by comparing the performance with the electromagnetic transient point-on-wave drive model. The VAr support capability of the drive load model is investigated by incorporating the developed model into a composite load structure in PSTSS programs. Multiple units of the developed drive models are represented in large-scale transmission systems to examine the system-level responses of drive loads. [ABSTRACT FROM AUTHOR]

This paper considers the use of hybrid simulation combining electromagnetic transients (EMT) simulation and transient stability (TSA) simulation to model large networks. By comparing with a full detailed EMT simulation, the paper shows that the hybrid approach gives more accurate results than TSA simulation alone, when power electronic equipment is included in the EMT part of the model. The paper also considers line switching and faults in the TSA part of the model which were ignored in earlier approaches, and shows that the accuracy is a function of the electrical distance of the fault to the interface bus bars. A new method to improve this accuracy with the use of switchable frequency dependent network equivalents (FDNE) is also introduced. [ABSTRACT FROM PUBLISHER]

Power system electro-magnetic transient programs (EMTP) have been popular among researchers and practitioners due to their detailed component modeling and high simulation accuracy for complex system operations. Despite broad applications in simulations with wide range of timescales, the small discretization step of these programs makes their use very time-consuming for system studies with long time span. Facing the increasingly complex power system transient characteristics and simulation demands, a multiscale algorithm that integrates the simulations of the electromagnetic and slower electromechanical transients is desirable. The multiscale simulation algorithm preserves the high fidelity of the EMTP and attains higher efficiency for the overall transient simulation. In this paper, we achieve this goal by exploiting the unique properties of the matrix exponential function. The proposed algorithm is capable of utilizing large step sizes to speed up the simulation of slow dynamics, whereas the fast transients are accurately reconstructed through efficient dense output mechanism, which is built upon the matrix exponential function computation. Numerical studies including a large-scale wind farm simulation are conducted to demonstrate the effectiveness of the proposed multiscale algorithm. [ABSTRACT FROM AUTHOR]

This paper summarizes the work of the Ad Hoc Task Force on Wind Generation Model Validation. The paper describes the concept of model validation, how this applies to wind turbine generation systems, and then gives clear examples of the most recent efforts to achieve model validation for wind turbine power plants. The document ends with a summary of the learning from the work presented and the conclusions which can be derived. Recommendations are made on the path forward for wind turbine generator modeling and model validation, primarily focused on generic models (i.e., standardized and publicly available) for stability analysis in power system studies. [ABSTRACT FROM PUBLISHER]

This paper investigates the impact of the overexcitation limiters (OELs) on the stability margin of a power system which is operating under stressed conditions. Several OEL modeling approaches are presented and the effect of their action has been examined in model power systems. It is realized that, more often than not, OEL operating status goes undetected by existing dynamic security assessment tools commonly used in the industry. It is found that the identification and accurate representation of OELs lead to significantly different transient stability margins. Unscented Kalman filtering is used to detect the OEL activation events. In the context of stressed system operation, such quantitative assessment is very useful for system control. This understanding is further reinforced through detailed studies in two model power systems. [ABSTRACT FROM AUTHOR]

This paper concerns a novel approach to the modeling and control design for transient stabilization of electric power systems using Flexible Alternating Current Transmission System (FACTS) devices. A nonlinear dynamic model of general interconnected electric power systems in the ordinary differential equation (ODE) form is proposed in terms of time-varying phasors of all dynamic components. This model captures previously unmodeled fast dynamics of inductors and capacitors of FACTS. Additionally, it allows us to observe the active power which is flowing through FACTS during transients. Using the derived model, an ectropy-based FACTS controller is proposed. The proposed controller regulates the active power through FACTS in order to shift the increment in energy created by disturbances. The energy increment is directed from generators into FACTS, preserving the synchronization between generators during disturbances. Simulation results obtained on the IEEE 14-bus system demonstrate the potential of this controller. The controller is shown to increase critical clearing time of the system in the case of a fault. [ABSTRACT FROM AUTHOR]

This paper analyzes the dc line fault transient stability characteristics of AC/DC power systems with three different modular multilevel converter based high voltage direct current (MMC-HVDC) configurations. The first configuration is half bridge sub-module based MMC (H-MMC) HVDC configuration, which clears dc line faults by tripping the ac circuit breakers. The clamp double sub-module (CDSM) based MMC (C-MMC) HVDC configuration with dc line fault clearance ability constitutes the second configuration. A line-commutated converter (LCC) and MMC hybrid HVDC configuration with dc line fault clearance ability, named LCC-diode-MMC (LCC-D-MMC), is the third configuration. The detailed processes of clearing dc line faults in three MMC-HVDC configurations are analyzed. The equal area criterion is utilized to analyze the dc line fault transient processes. Besides, to evaluate the power system transient stability characteristics in three MMC-HVDC configurations, an index, called critical ac transmitted power (Pac\_critical), is proposed. Under the same dc line to ground fault, transient stability characteristics of three test systems based on the three different MMC-HVDC configurations are compared. Excellent performance of the LCC-D-MMC HVDC configuration under the dc line fault is demonstrated through comparison of Pac\_critical in the three test systems. Finally, the study is extended to a modified New England 39-bus system, and the simulation results also correspond with the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents a decision tree based method for out-of-step prediction of synchronous generators. For distinguishing between stable and out-of-step conditions, a series of measurements are taken under various fault scenarios including operational and topological disturbances. The data of input features and output target classes are used as the input-output pairs for decision tree induction and deduction. The merit of decision tree based detection of transient instability lies in robust classification of new unseen samples. The performance of the proposed method is verified on two test cases including a 9-bus dynamic network and the practical 1696-bus Iran national grid. The simulation results are presented for various input features and learning parameters. [ABSTRACT FROM PUBLISHER]

Power system damping in the transient condition generally depends on system parameters and modeling hypotheses. The dependence can be very nonlinear. In this paper, a polynomial approximation method is proposed to obtain a representation of the damping torque and damping torque coefficient of the original detailed stability model. [ABSTRACT FROM PUBLISHER]

This paper presents three algorithms for identification of dominant inter-area oscillation paths: a series of interconnected corridors in which the highest content of the inter-area modes propagates through. The algorithms are developed to treat different sets of data: 1) known system model; 2) transient; and 3) ambient measurements from phasor measurement units (PMUs). These algorithms take feasibility into consideration by associating the network variables made available by PMUs, i.e., voltage and current phasors. All algorithms are demonstrated and implemented on a conceptualized Nordic Grid model. The results and comparison among three algorithms are provided. The applications of the algorithms not only facilitate in revealing critical corridors which are mostly stressed but also help in indicating relevant feedback input signals and inputs to mode meters which can be determined from the properties of dominant paths. [ABSTRACT FROM PUBLISHER]

This paper proposes and evaluates a strategy to mitigate the transients of an apparatus, e.g., an electronically-interfaced distributed energy resource (DER) unit. This strategy is based on response monitoring and can be implemented based on either set point automatic adjustment (SPAA) or set point automatic adjustment with correction-enabled (SPAACE). SPAA takes advantage of an approximate model of the system to calculate the intermediate set points. SPAACE monitors the trajectory of the variable of interest and bases its decisions on the trend of variations of that variable and accounts for the inaccuracies and unmodeled dynamics by switching the command input between alternative set points. Case studies are presented to demonstrate the application and effectiveness of the proposed strategy in limiting voltage or current excursions in balanced and unbalanced microgrid study systems, subsequent to a step change in set point, load switching, and black start. [ABSTRACT FROM PUBLISHER]

This paper presents a new, significantly improved, approach to formulate a global transient stability-constrained optimal power flow (TSC-OPF), where the sets of dynamic and transient stability constraints to be considered in the optimization process are reduced to one single stability constraint. This constraint is derived from dynamic information provided by the SIngle Machine Equivalent (SIME) method and is only expressed in terms of steady-state variables, which allows us to diminish the length of the time-domain simulation to be included into the global TSC-OPF to a single (initial) time step. In this way, the size of the resulting optimization problem is reduced to one very similar to that of a conventional OPF, overcoming the main drawback of global TSC-OPF techniques (its huge dimension) while maintaining its accuracy and improving its practical application to real power networks. Effectiveness of the proposal is demonstrated by numerical examples on the WSCC three-machine, nine-bus system and the Mexican 46-machine, 190-bus system. [ABSTRACT FROM PUBLISHER]

This paper presents a linearized technique to determine a risk-based index for dynamic security. The method is an extension to an existing technique in which the risk of steady state security is calculated using the mean and variance of load uncertainty. The proposed method is applied to calculate the risk indices for the IEEE New England 39-bus test system. The results obtained from the proposed method are validated against those estimated by Monte Carlo simulation. Both approaches produce virtually the same results for small load deviations. [ABSTRACT FROM PUBLISHER]

This paper introduces an approach which enables very large power systems to be modeled on real-time electro-magnetic transients (EMT) digital simulators. This is achieved using an improved wide-band multi-port equivalent, which reduces a large power network into a small manageable equivalent model that preserves wide-band behaviors. The low-frequency or electromechanical transients are captured with a transient stability analysis (TSA) type electromechanical equivalent derived using coherency-based reduction techniques. The high-frequency behavior is accurately captured by placing in parallel with the TSA equivalent, a passive frequency dependant network equivalent (FDNE). The validity of the proposed technique is demonstrated by comparing the approach with detailed electromagnetic simulations of a modified version of the New England 39-bus test system that includes an HVDC infeed. The power of the method is demonstrated by the real-time electromagnetic transient simulation of a large 2300-bus 139-generator system. [ABSTRACT FROM PUBLISHER]

The paper first shows that the transient stability status of a power system following a large disturbance such as a fault can be early predicted based on the measured post-fault values of the generator voltages, speeds, or rotor angles. Synchronously sampled values provided by phasor measurement units (PMUs) of the generator voltages, frequencies, or rotor angles collected immediately after clearing a fault are used as inputs to a support vector machines (SVM) classifier which predicts the transient stability status. Studies with the New England 39-bus test system and the Venezuelan power network indicated that faster and more accurate predictions can be made by using the post-fault recovery voltage magnitude measurements as inputs. The accuracy and robustness of the transient stability prediction algorithm with the voltage magnitude measurements was extensively tested under both balanced and unbalanced fault conditions, as well as under different operating conditions, presence of measurement errors, voltage sensitive loads, and changes in the network topology. During the various tests carried out using the New England 39-bus test system, the proposed algorithm could always predict when the power system is approaching a transient instability with over 95% success rate. [ABSTRACT FROM PUBLISHER]