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With the expansion in recent power systems, the boost in renewable energy resources with multiple interconnections, overloading of existing power networks, increased load growth, and equipment failures, power system transient instability issues have exponentially increased. Transient stability in power systems is of particular importance even while performing the steady state analysis of a power system. Power system transient stability assessment is mandatory regularly for power system operation and has a major impact on power system planning. Potential risks of blackouts and failures in power systems can be avoided or minimized with the prompt prediction of transient instability. This research work presents a predictive approach for power system transient instability. The case study is a 735kV, 29-bus, 7-powerplant network involving precise modeling of generators. In particular, the proposed method is represented by different machine learning models through extraction and regression, in which the variables of the power-generating units are used as primary sources/features. Data cleaning and sorting out techniques are being used for refining data. Feature extraction has also been implemented for further cleansing of the data. The result is in the form of concrete and robust classifier models that can overcome power systems’ instability concerns through prompt prediction.

A system's stability is affected by the generation types in the interconnected power system. For example, synchronous generators usually have high inertia sharing with the power system since they have rotating mass, and they usually have primary frequency response capability. On the other hand, renewable energy sources (RES) neither provide inertia to the system nor have a primary frequency response capability; hence, adding RES will impact the power system's voltage, angle, and frequency stability. Battery energy storage systems (BESSs) have many applications in the future electric grid. From the stability perspective, BESSs can be used to increase the power system's stability. A case study was conducted on the Rafha microgrid in the Kingdom of Saudi Arabia (KSA) to inspect a BESS's influence on the Rafha microgrid's stability and the impact of changing the BESS's location, which might cause changes in the system stability after contingencies. In addition, we investigated which dynamic stability is affected if the BESS's capacity changes. The microgrid is tested using contingencies that affect the system's frequency, angle, and voltage stability using the power system simulator for engineering (PSS/E) software as a simulation platform. Finally, we investigated the technical impact of utilizing a BESS and its influence on economic operation. [ABSTRACT FROM AUTHOR]

The fast development of renewable energies leads to an increase in the power electronics penetration in transmission systems. This is particularly true if one considers a 100% renewable energies power system, where wind and solar photovoltaic energies, which make most of the renewable energies connections today, are connected to the grid through power electronics converters. Because power electronics-based generators and synchronous machines-based generators have very different dynamic behaviours, some approximations usually used to run transient simulations of transmission systems might not be optimal for future grids. The systematic use of the phasor approximation applied to the power lines, implemented in most of the Transient Simulation Programs, is indeed not relevant any more. To avoid the use of Electromagnetic Transient simulations, that are resource-demanding and time-consuming, this paper presents a novel Model Order Reduction technique for large grids with a high penetration of power electronic devices. Compared to the classical phasor approximation, this event-based state residualization approximation allows accurate transient simulations and at the same time an optimal reduction of the number of the system’s state variables depending on the observed variables, the considered events and the tolerated approximation error. [ABSTRACT FROM AUTHOR]

Grid modernization and innovations in clean energy are leading to a rapid increase in the penetration of inverter-based resources (IBRs) like wind power and solar photovoltaic (PV) plants in the bulk power system (BPS). To study the implications on BPS dynamics and mitigate potential risks to grid reliability, the second-generation generic renewable energy system model has been developed earlier. However, this model has three modules with 86 user-defined parameters and eight control flags to facilitate the utility-scale solar PV plant operation in different control modes. It presents a major challenge to the transmission system planning engineers. There is a critical need to identify the key parameters of the dynamic model that are highly sensitive to grid events causing large-scale voltage and frequency disturbances. In this work, a sensitivity analysis based on modified Sobol’ method is proposed for identification of the key parameters in the utility-scale solar PV plant model. The total Sobol’ sensitivity index captures even the higher-order effects of the variations in the parameters. Validation of the identified key parameters was carried out on a modified IEEE 9-bus system and 200-bus synthetic grid using PSS®E for plant-level control and local coordinated control operation of the solar PV plant. The reduced set of parameters identified in this work offer help to utility grid planning teams while conducting dynamic studies to meet the interconnection requirements. [ABSTRACT FROM AUTHOR]

This paper proposes a novel variable-inertia emulation control (VIEC) scheme that enables voltage-source-converter based high-voltage DC (VSC-HVDC) transmission systems to flexibly support AC grid frequency stability like synchronous generators. The VIEC scheme allows us to extract the energy from the augmented DC capacitance for inertia emulation by controlling the DC voltage without affecting the stability of the AC system connected on the remote side. In particular, with the proposed VIEC scheme, the inertia time constant can be flexibly emulated and its value can be automatically adjusted according to the rate of change of grid frequency as well as grid frequency deviations. This leads to more effective inertial support across different timescales. Modal analysis is carried out to investigate the impacts of inertia and DC capacitance, and to obtain the optimal control parameters. The effectiveness and advantages of the proposed VIEC scheme are demonstrated on an IEEE benchmark system in the presence of faults and load changes. [ABSTRACT FROM AUTHOR]

To ensure successful islanding of microgrids after a fault has occurred, the transient stability should be analyzed under a set of expected operating conditions during the design and operation of microgrids. Transient stability analysis is conventionally performed with time-domain analysis which is computationally expensive and does not quantify the stability margin. Energy-based methodologies can determine the stability margin, however existing methodologies require significant simplifications to be applied to the microgrid model. The energy-based stability analysis methodology proposed in this paper enables the analysis of high-dimension nonlinear microgrid systems and quantification of the stability margin within reasonable time. The performance of the methodology is validated by analyzing a case study microgrid and comparing the results to time-domain analysis and to a state-of-the-art methodology proposed in the literature. The results indicate that the proposed methodology has a significantly lower computational burden and similar accuracy compared to existing energy-based methodologies. The methodology is able to improve the probability of stable islanding of the case study microgrid from 74% up to 94% when only optimizing the design, and up to 100% when optimizing design and control actions. [ABSTRACT FROM AUTHOR]

This paper introduces the concept of the operating region of a virtual synchronous generator (VSG). The main objective of the operating region is to help take a decision on choosing proper VSG parameters. A VSG based on a diesel generator (Genset) model was used as the study case. The theoretical analysis examined the impact of relevant genset-based VSG parameters, such as droop factor, mdr, inertia, J, and damping, D, on the output electrical frequency. The main result of this analysis showed that it is possible to define inertia-damping surfaces which are parameterized upon different values of the droop factor. The operating region of the VSG is then defined as the locus of the triples (mdr, J, D) where the frequency transient response satisfies certain specifications in terms of peak frequency, peak time and rate of change. Experimental results showed that the VSG achieved a satisfactory performance for different values of speed droop during a transient and also in steady-state, validating the model of the genset. In comparison with simulation results, the measured peak frequencies deviated with a mean absolute error of 0.2 % and the steady-state frequencies with a mean absolute error of 0.12 %, validating the concept of the operating region.

In this study, an advanced phase‐locked‐loop (PLL), which has a simple structure and a low computational burden is proposed. The proposed PLL also improves the dynamic performance and the filtering capability of the conventional three‐phase enhanced‐PLL (3pEPLL) significantly. The conventional 3pEPLL operates three individual EPLL blocks for each phase voltage and a fourth EPLL for estimation of the magnitude, frequency, and phase angle, which considerably increases the structural complexity and computational burden. However, the proposed PLL called enhanced‐3pEPLL (E2 PLL) employs only two single‐phase EPLL modules in its pre‐filtering stage. A moving‐average‐filter (MAF) is also supplemented on the error signal path of these EPLL modules, which allows smoother estimation of the magnitude, frequency, and phase angle, and improves the filtering capability of the EPLLs. Unlike the conventional 3pEPLL, the proposed E2 PLL employs a quasi‐type‐1 PLL (QT1‐PLL) to estimate the magnitude, frequency, and phase information of the fundamental grid voltage. The structure of QT1‐PLL is similar to a type‐1 PLL, which offers a low transient response time. The small‐signal model of the proposed PLL is derived for stability analysis and parameter design procedure. The effectiveness of the E2 PLL is verified owing to experimental results and comparison with the conventional 3pEPLL and QT1‐PLL. [ABSTRACT FROM AUTHOR]

With the continuous expansion of the power system scale and extensive application of phasor measurement units (PMUs), the secure operation of power systems has been increasingly concerned. In this paper, an integrated scheme for online dynamic security assessment (DSA) based on feature selection and regression prediction is proposed. First, partial mutual information (PMI) and the Pearson correlation coefficient (PCC) are used to select the key variables in the feature selection process. Second, an iterated random forest (IRF) is applied to predict the transient stability margin (TSM) based on the selected variables. Combining the feature selection process and regression prediction, a DSA model is constructed. Finally, a spatial-temporal dynamic visualization approach is proposed, which can intuitively provide real-time dynamic security information of power systems. The integrated scheme, which is tested on the IEEE 39-bus system and a practical 1648-bus system provided by the software PSS/E, exhibits desirable assessment accuracy and is suitable for online application. In the robustness test, some impact factors for power system operation are considered, such as topology change, variation of generator/load power distribution and variation of load characteristics. Moreover, the impacts of missing data and measurement noise are studied. [ABSTRACT FROM AUTHOR]

The isolated power system in Kinmen Island, Taiwan has already implemented the special protection system (SPS) to prevent various critical contingencies that occurred during the past decade. However, when a severe N-2 contingency occurred on July 26, 2013, the SPS has not properly armed its under-frequency load shedding. After reexamining transient recorded waveforms, it was observed that the system still has sufficient spinning reserve and the coordination between the under-frequency relay and the current SPS was not well considered. In this article, the current SPS is further modified in order to avoid the occurrence of the excessive load shedding under similar N-2 contingencies. Extensive time-domain dynamical simulations are performed first to study the relationship between the amount of the load shedding and frequency deviations under these extreme N-2 contingencies. Based on these simulation results, the remediation scheme of the SPS will be proposed by modifying the existing SPS design logic and the amount of load shedding. More comprehensive input triggered states are proposed for identifying these severe N-2 contingencies. Both simulation verifications under the proposed remedial scheme and actual transient recorded waveforms under a severe contingency after commissioning this remediated SPS are provided to demonstrate the effectiveness of this proposed remediation scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a new event-based logic of the breaker failure protection to improve power system transient stability by shortening the total clearing time of extreme contingencies involving circuit breaker failures. Stability improvement is achieved by using dual-timer protection with shorter safety margin for multi-phase faults close to the power plant and longer safety margin for remote multi-phase faults and single-phase faults. The use of the output signal obtained for a short safety margin depends on how the substation is configured. In the breaker-and-a-half configuration, this output signal is used to speed up the opening of all adjacent circuit breakers. In substations with the dual (or triple) busbar configuration the output signal obtained with a short safety margin is used to speed up the busbar splitting. A case study was performed for a real large-scale power system. Simulation results confirmed the advantages of the proposed logic. Breaker failure protection with the proposed logic has been implemented in a substation of a large power plant. [ABSTRACT FROM AUTHOR]

For low‐voltage autonomous microgrids, the essential goal is maintaining stable voltage and frequency throughout its network for the smooth operation of distributed loads. The other goal is to maintain proportionate power‐sharing between multiple sources connected through voltage source converters (VSCs). For the particular case of a heavily loaded microgrid, any further increase in demand poses new problems. The VSCs proximate to the loads may overshoot beyond its maximum ratings. Owing to which the stability of the power supply, as well as the longevity of VSCs, may get compromised. Also, these sources provide power under varying composite loading conditions comprising both linear and non‐linear loads resulting in unbalancing in its network. To overcome these problems, a decentralised fast terminal sliding mode control strategy for active power‐sharing between parallel VSCs has been proposed. A detailed mathematical model based on Lyapunov's stability theory‐based study is designed to establish the operating stability of the proposed controller. To validate the proposed control strategy, MATLAB‐based simulation results are provided for possible loading scenarios. A comparative study for performance evaluation between the proposed controller and a conventional proportional ‐integral‐based controller is further carried out. Finally, the performance of the proposed controller is also validated in real‐time scenario. [ABSTRACT FROM AUTHOR]

In order to mitigate most power quality issues in renewable power penetrated systems, load frequency control in automatic generation control based power systems and transient stability concerns in any power system, the deviation in frequency at the point of common coupling is chosen as the driving input for SMES active power control (Δf-control). We report a rate of change of frequency (ROCOF) controlled SMES as a resilient damping device to counter exogenous uncertainties in a wind based multi machine system. Primarily, the ROCOF is contingent on the active power mismatch. SMES reference active power command is issued using a genetic algorithm tuned scheme, participating through ROCOF measurement. The non linear action of SMES is realized by controlling the converter firing angles by a smooth four-zone operation, thus determining the voltage applied across the superconducting inductor. While preserving the dynamics of the DC link and supervising the state of charge (SoC) of the inductor, the effectiveness of the aforementioned control strategy is authenticated by performing non-linear simulations in MATLAB/Simulink. In addition, the dominant modes are also tracked and it is found that the percentage increase in aggregate damping ratio is around 133% using the proposed ROCOF-SMES control. [ABSTRACT FROM AUTHOR]

Coupled nonlinear oscillators, e.g., Kuramoto models, are commonly used to analyze electrical power systems. The cage model from statistical mechanics has also been used to describe the dynamics of synchronously connected generation stations. Whereas the Kuramoto model is good for describing high inertia grid systems, the cage one allows both high and low inertia grids to be modelled. This is illustrated by comparing both the synchronization time and relaxation towards synchronization of each model by treating their equations of motion in a common framework rooted in the dynamics of many coupled phase oscillators. A solution of these equations via matrix continued fractions is implemented rendering the characteristic relaxation times of a grid-generator system over a wide range of inertia and damping. Following an abrupt change in the dynamical system, the power output and both generator and grid frequencies all exhibit damped oscillations now depending on the (finite) grid inertia. In practical applications, it appears that for a small inertia system the cage model is preferable. [ABSTRACT FROM AUTHOR]

With increase of practical power system complexity, power system online stability assessment and control is more and more important. Application of the traditional model-driven methods is always limited by contradiction between accuracy and efficiency, while data-driven methods demonstrate strong abilities for the online decision-making support with advancement of various data mining techniques. Instead of direct application of data-driven methods in the power system, this paper first discusses feasible integration approaches for the model-driven and data-driven methods based on the existing achievements, and then, proposes to integrate both methods for the power system online frequency stability assessment and control. The integrated method consists of frequency dynamics prediction and load shedding procedure. In frequency dynamics prediction procedure, integration of system frequency response (SFR) model and the extreme learning machine (ELM)-based learning model is applied, where basic physical causality is kept in the SFR model and ELM is used to fit and correct error of the SFR. The ELM also plays a part in load shedding prediction model construction by digging out mapping relationship from samples. Finally, the proposed prediction and control scheme for the frequency stability is verified by simulations on WSCC 9-bus, New England 39-bus, and NPCC 140-bus system. Results show that the reliability, time efficiency, and accuracy are enhanced with the proposed method. [ABSTRACT FROM AUTHOR]

The absolute requirement to increase the amount of energy generation from renewable sources e.g., predominantly asynchronously connected wind turbines and photovoltaic installations, may in practice during transient events (where frequency changes are examined) excite oscillatory response of the power output of large grid connected synchronous generators. The response of such generators must be controlled either by varying the applied torque of a turbine or by altering the electromagnetic torque in the airgap. Choosing the latter, the adequacy of a voltage regulator, particularly that of the embedded power system stabilizer (PSS) circuit, is investigated using the IEEE PSS1A model for the automatic voltage regulator of a synchronous generator driven by a gas turbine. The response is obtained via closed form analytic solutions for both small (linear) and large (nonlinear) scale transient events in the energy grid system. In tandem with the analytical study, the behavior simulated with a computer model from MATLAB-SimPowerSystems is reviewed. [ABSTRACT FROM AUTHOR]

Transmission faults caused by recent wildfires in California have induced the disconnection of utility-scale converters in photovoltaic (PV) power plants. Postmortem investigations reported that tripping commands were caused by phase-locked loops (PLLs) and dc-side dynamics, which are typically unmodeled in classical transient stability studies. Since existing simulation packages rely on simplified models that neglect these dynamics, they have a limited capability to predict converter behavior during faults. To address this shortcoming, we set forth a positive-sequence model for PV power plants that is derived from physics and controls first principles. As seen on utility-scale three-phase converters, the model includes PLLs, dc-side dynamics, and closed-loop controllers. Instances of the developed model are integrated into illustrative power systems containing conventional generators. Numerical simulations of the obtained multi-machine multi-converter power systems are assessed via a suitable set of stability and performance metrics. [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]

This paper investigates the enactment of battery energy storage system (BESS) and static compensator (STATCOM) in enhancing large-scale power system transient voltage and frequency stability, and improving power export capacity within two interconnected power systems. A PI-lead and lead-lag controlled BESS is proposed for multimachine power system to provide simultaneous voltage and frequency regulation within the defined battery state-of-charge ranges and an equivalent Finnish transmission grid is used to evaluate the system performance. According to Australian National Electricity Market grid requirements, the performances of the proposed control schemes are compared with conventional PI controlled BESS and STATCOM under multiple temporary and permanent fault conditions. In addition, two adjacent disturbance events are also applied to evaluate system performance with BESS and STATCOM. Through simulation results, it is shown that when there is a ${\text{44}\%}$ increase in power export and the STATCOM fails, incorporating BESS improves the performance and justifies the novelty of this study. Moreover, the proposed lead-lag controlled BESS manifests better transient performance than BESS with PI-lead and traditional PI controller, in the event of divergent temporary and permanent faults. [ABSTRACT FROM AUTHOR]

Total transfer capability (TTC) is an effective indicator to evaluate the transmission limit of the interconnected systems. However, due to the large-scale wind power integration, operation conditions of a power system may change rapidly, yielding time-varying characteristics of the TTC. As a result, the traditional time-consuming transient stability constrained TTC model is unable to assess the online transmission margin. In this paper, we propose an online measurement-based TTC estimator using the nonparametric analytics. It consists of three major components: the probabilistic data generation, the composite feature selection, and the group Lasso regression-based training scheme. Specifically, we present a probabilistic data generation approach to take into account the uncertainties of the day-ahead generation scheduling and to reduce the number of redundant or infeasible data. Then, the composite feature selection is used to reduce the dimension of the generated data and identify the features which are highly correlated with TTC. The features are determined by the maximal information coefficients and nonparametric independence screening approach. Finally, these selected features are trained by the group Lasso regression to learn the correlation between the TTC and the online measurements. Once real-time measurements are available, the TTC can be assessed immediately through the learned correlation relationship. Extensive numerical results carried out on the modified New England 39-bus test system demonstrate the feasibility of the proposed TTC estimator for online applications. [ABSTRACT FROM AUTHOR]

A new energy-dissipating hybrid control framework is proposed in this paper. The proposed framework incorporates a plant with continuous dynamics connected in parallel with a hybrid controller that combines logical switches with continuous dynamics. The overall closed-loop system can be described as a hybrid impulsive dynamical system in which the redundant energy preserved in the plant can be damped quickly and continuously due to the enhanced dissipativity of the closed-loop system. The proposed framework is applied to design decentralized nonlinear excitation controllers for synchronous generators in a multimachine system to improve its transient stability, in which the synchronous generators are modeled as port-controlled Hamiltonian systems. Simulation studies on the IEEE 10-generator, 39-bus New England power system are carried out to verify the effectiveness of the proposed energy-dissipating hybrid excitation control to improve the transient stability and dissipativity of the interconnected power system under various fault conditions. [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 presents a comprehensive approach toward the design of primary and secondary controllers in low-inertia power grids with mixed lines and a large amount of inverter-interfaced generation. First, a complete dynamic phasor model is developed that represents the electromagnetic and electromechanic dynamics of lines, inverters, synchronous machines, and constant power loads. The model offers a straightforward way to combine white-, gray- and black-box models, and its structure lends itself well to control design. In a second step, it is shown how a recently developed robust fixed-structure control design method can be applied to the challenging and relevant problem of primary and secondary control in medium-and low-voltage grids. A comprehensive three-part simulation example demonstrates how frequency and voltage transient stability and performance can be achieved through a methodical design process. It is also shown how nonstandard performance specifications such as proportional power sharing can be directly incorporated in the design. Finally, a distributed secondary controller from the literature is reformulated and designed using the presented framework, and all results are validated in nonlinear simulation. [ABSTRACT FROM AUTHOR]

When solving network algebraic equations during power system transient stability simulations, the nonzero elements in the independent vector and the elements needed in the solution vector are determined by the location of source nodes. Different kinds of source nodes will have a different influence on the solution process of the network equations. According to these features of source nodes, sparsity techniques, more specifically, the node ordering algorithm and sparse vector method, are improved in this paper. A new heuristic ordering algorithm is proposed to enhance the efficiency of the sparse vector method by reducing the number of nodes in the factorization path set of source nodes while maintaining the sparsity of the factorized matrix. A multipath sparse vector method is proposed to avoid the unnecessary computation in the iterative solution process of the network equations, whereby the idea of the method is to form different paths for different types of source nodes. Different paths are used to solve different elements in the solution vector. The correctness and effectiveness of these improvements is proven by the simulation results of three practical power systems (up to 13 490 nodes) and six IEEE examples (up to 162 nodes). [ABSTRACT FROM AUTHOR]

This paper introduces a new approach, based on faster-than-real-time (FTRT) analysis, to predict out-of-step (OOS) condition of a turbine-generator (T-G) unit subsequent to a fault scenario. The proposed FTRT analysis is based on 1) solving a state-space model of the T-G electromechanical system and corresponding controllers without the need for online measurements, and 2) an estimated Thevenin equivalent of the rest of the power system. The measurement-free FTRT analysis is carried out after the Thevenin parameters are estimated subsequent to the fault clearance instant. Equal area criterion is applied on the predicated variables to detect OOS condition. A reliable decision can be made based on this approach, since it does not involve simplifying assumptions contrary to the existing approaches. The FTRT approach accurately considers the impacts of the detailed model of the generator, automatic voltage regulator, prime mover, governor system, and the host power system. This paper provides detailed mathematical formulation for the proposed OOS detection method and verifies its feasibility and accuracy based on single machine and large test systems. The proposed approach is also implemented on an industrial platform and evaluated. The results confirm that the proposed approach can accurately identify OOS conditions, earlier than the rotor angle noticeably increases. [ABSTRACT FROM AUTHOR]

Effective control measures taken on the transient potential energy distribution in power transmission network can not only improve the stability of power system but also reduce the probability of cascading failures occurrence. By researching the distribution variation rules of voltage, phase‐angle difference, potential energy and its margin in the three‐machine system, the relationship is revealed further between transient potential energy distribution and network structure. The potential energy distribution mainly depends on the topology structure and parameter of the network, the potential energy is distributed most easily in the vulnerable links where equivalent reactance is bigger and voltage is lower. Three control measures are proposed to relieve the accumulation of transient potential energy. Changing network structure and parameter in vulnerable links can perfect the internal structure of power network from the root, and then improve the resisting disturbance capacity of the power system. Whereas decreasing the transmission power in the vulnerable links is an emergency control measure for improving the operation stability of power system on‐line. Simulation results on wepri‐36 system testify the validation of the proposed method. [ABSTRACT FROM AUTHOR]

Future shipboard power systems using Medium Voltage Direct (MVDC) technology will be based on a widespread use of power converters for interfacing generating systems and loads with the main DC bus. Such a heavy exploitation makes the voltage control challenging in the presence of tightly controlled converters. By modeling the latter as constant power loads (CPLs), one possibility to ensure the bus voltage stability is offered by the linearizing via state feedback technique, whose aim is to regulate the generating DC-DC power converters to compensate for the destabilizing effect of the CPLs. Although this method has been shown to be effective when system parameters are perfectly known, only a partial linearization can be ensured in case of parameter mismatch, thus, jeopardizing the system stability. In order to improve the linearization, therefore, guaranteeing the voltage stability, an estimation method is proposed in this paper. To this aim, offline tests are performed to provide the input data for the estimation of model parameters. Such estimated values are subsequently used for correctly tuning the linearizing function of the DC-DC converters. Simulation results for bus voltage transients show that in this way converters become sources of stabilizing power. [ABSTRACT FROM PUBLISHER]

Transient rotor angle stability assessment and oscillatory rotor angle stability assessment subsequent to a contingency are integral components of dynamic security assessment (DSA) in power systems. This study proposes a hybrid algorithm to determine whether the post-fault power system is secure due to both transient rotor angle stability and oscillatory rotor angle stability subsequent to a set of known contingencies. The hybrid algorithm first uses a new security measure developed based on the concept of Lyapunov exponents (LEs) to determine the transient security of the post-fault power system. Later, the transient secure power swing curves are analysed using an improved Prony algorithm which extracts the dominant oscillatory modes and estimates their damping ratios. The damping ratio is a security measure about the oscillatory security of the post-fault power system subsequent to the contingency. The suitability of the proposed hybrid algorithm for DSA in power systems is illustrated using different contingencies of a 16-generator 68-bus test system and a 50-generator 470-bus test system. The accuracy of the stability conclusions and the acceptable computational burden indicate that the proposed hybrid algorithm is suitable for real-time security assessment with respect to both transient rotor angle stability and oscillatory rotor angle stability under multiple contingencies of the power system.

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]

Power system operation practices are changing with the addition of renewable energy resources such as photovoltaic (PV) sources. The diverse and intermittent nature of these resources demands new operation strategies to ensure system reliability. As more PV units are added to power systems, the power generated by conventional generation resources should be reduced to accommodate these new resources. The reduction in fossil-fired generation allows realization of benefits in the sustainability of the generation mix. While some of the conventional generating units are retired, some should be retained for system reliability. This paper investigates the impact of generation redispatch or generation displacement in systems with high PV penetration. Comparing various study scenarios, a method based on regression techniques and Chebyshevs inequality is introduced in this paper. This method is used to calculate the dispatch or displacement ratio of the conventional generators for optimal steady state and transient response of the system. Recommendations are formulated based on an actual large-scale power system in the western United States. [ABSTRACT FROM PUBLISHER]

With the increasing penetration of distributed generation, distribution networks are evolving from passive to active. New transient simulation methods are required to study the detailed dynamic characteristics of large‐scale active distribution networks. A model order reduction method based on Krylov subspace theory is introduced in this study to reduce the overall model scale of active distribution networks for transient simulations. A modified state‐space model of linear distribution networks is developed to replace the conventional models for improvement in model reduction efficiency, while guaranteeing the passivity and stability of the reduced models. The proposed model order reduction method is validated with the IEEE 123‐node test network. The results prove that the proposed method is effective for different applications to improve the simulation efficiency of large‐scale active distribution networks. [ABSTRACT FROM AUTHOR]

In general, a smart grid is a modernized electrical grid that uses digital technology for measurement, control, and protection functions to ensure a network security. It tries to solve the problem of weather-dependant fluctuations of renewable energy power supplies (e.g. wind turbines, or photo-voltaic systems) when they are connected to an actual power system. In two papers in this issue, we present some of the challenges raised by Smart Grids in instrumentation and measurement applications, putting emphasis on synchrophasor estimation. In this part 1 article, we describe the problem of identifying a normal condition from a fault condition and between a fault condition and an oscillation using phasor estimations in protective relays. In "Synchrophasor Measurement Challenges in Smart Grids," we discuss a novel synchrophasor- estimation algorithm that improves the accuracy of the estimates under oscillations conditions and serves to identify electromechanical modes in Smart Grids. This algorithm ameliorates protection as well as measurement applications in smart grids. [ABSTRACT FROM PUBLISHER]

A Weierstrass-based numerical method for computing damping torque of a 3-machine power system during transient period is proposed and evaluated. Numerical studies were performed to demonstrate mutual impacts of generators on the damping torque, when one of the generators is presented by a detailed model. The relationship between the averaged self-damping torque coefficient of the detailed model and the damping coefficient of the classical model is numerically studied. One interesting observation from our studies is that the damping torque coefficients tend to become zero at the end of transient stability period if all the generators are represented by the detailed model. This observation can be useful to determine the duration of transient stability period. One application of the proposed Weierstrass-based method is to determine appropriate and accurate damping terms for power system dynamic simulation. [ABSTRACT FROM PUBLISHER]

Intermittent nature of renewable energies and random nature of moving loads negatively influence the power system transient stability. Energy storage can enhance the system response by providing short-term energy sources. However, fast dynamic storage systems require advanced controllers to stabilize the transients. This paper introduces the application of a decentralized overlapping decomposition controller in transient stability of renewable energy penetrated storage-based power systems. In a battery-based power system there exists strongly coupled state variables shared among areas. Large-scale controllers can decouple the system state variables and stabilize the oscillations. Here, the model of battery storage is obtained considering the battery's state of charge and the droop in power electronic interfaces. The overlapping decomposition decentralized controller demonstrates an enhanced transient stability performance under variable state of charge in various capacity of storage devices. [ABSTRACT FROM PUBLISHER]

This paper deals with linear systems under sustained random perturbations. The stochastic perturbation model is given by a bounded Markov diffusion process, as it appears, e.g., in the description of load or generation uncertainties of power systems. For such systems, the Lyapunov exponents describe necessary and sufficient conditions for almost sure asymptotic stability. The present article reviews several numerical methods for the computation of Lyapunov exponents and applies this methodology to international test systems: four machines - ten bus and ten machines -thirty nine bus. [ABSTRACT FROM PUBLISHER]

This paper presents a new method for analysis of frequency synchronization of lossless power networks whose sources are frequency-droop controlled inverters. Unlike most existing approaches, our method focuses on the interaction between inverters and the network to provide new physical insight into how those interactions create frequency synchronization. We introduce two structure-preserving models of such a network (one bus-oriented and one line-oriented), and show that frequency synchronization corresponds to convergence to an equilibrium of these models. We derive a necessary condition for existence of such equilibria, and determine a simple test for their local stability. Finally, we introduce a sufficient condition for frequency synchronization of such networks, and show that it consists of a set of local criteria which can each be determined from local measurements. [ABSTRACT FROM PUBLISHER]

This paper describes two wide-area protection schemes for controlled islanding of the Uruguayan electrical power system. The first scheme relies only on local signals available for distance protection relays, whereas the second scheme is based both on local and remote synchrophasor measurements. The paper compares results in terms of load shedding amount necessary to maintain system integrity, with and without the proposed protection schemes. The investigation is based on comprehensive transient stability studies using actual dynamical models. Past occurrences that led the system to widespread blackouts have motivated the investigations presented in this paper. [ABSTRACT FROM PUBLISHER]

Electromagnetic Transients Program (EMTP) is widely used in power system dynamics studies. However, in most cases EMTP is found inadequate for dealing with the realistic size power systems due to the small time step resulting in relatively slow simulation speeds. To accelerate the EMTP simulations of power system dynamics, a novel frequency-adaptive methodology is proposed. In this method, a new transformation is presented. The properties of the transformation and the numerical solutions based on the transformation are discussed. The component models obtained by discretizing the differential equations at the branch level are also given which are convenient for EMTP implementation. The proposed method allows using large time steps without sacrificing accuracy, which greatly improves the simulation speed. To validate the proposed methodology, a general program has been developed. Furthermore, various case studies substantiate the claims and demonstrate the application of the method. [ABSTRACT FROM PUBLISHER]

There has been continuous development of techniques for assessing the transient stability of power systems in the uncertain environment. In this paper, a novel framework for stochastic transient stability assessment is proposed. The basic theory of stochastic calculus is first introduced to form the mathematical basis of the proposed approach. A stochastic power system model based on stochastic differential equations (SDEs) is proposed to take into account the uncertain factors such as load levels and system faults. We then present a detailed discussion on the numerical methods for solving SDEs. The stochastic Euler and Milstein schemes are introduced. The concept of strong convergence is also introduced to evaluate their accuracy. The proposed approach is tested with comprehensive case studies to validate its effectiveness. [ABSTRACT FROM PUBLISHER]

This paper focuses on the education aspect of potential functions and presents the concept as a general approach for formulation of dynamic processes in different areas of engineering, e.g., dynamics of motion, electrical fields, power systems, control, and robotics. In power systems, the potential functions have been used in transient stability analysis in capacities such as 1) transient energy function and 2) the theoretical backbone of the equal-area criterion. The unified representation introduced in this paper is to help students (especially global learners by providing them with the big picture of the subject) discover similarities between different disciplines, which facilitates inter-application of the analytical methods. Recognizing the importance of digital computer based simulation techniques in education, the paper also introduces a software tool for assisting students/researchers in experimenting with different forms of potential functions and their application to a dynamic environment consisting of mobile robots, targets, and obstacles. [ABSTRACT FROM PUBLISHER]

This paper studies real-time estimation of stability margin of a power system under disturbances by continuous measurement data. The paper presents a ball-on-concave-surface (BOCS) mechanics system as a power system's adaptive equivalent representing its real-time status and the stability region about a monitored variable. The parameters of the equivalent are adaptive to the operating condition and can online be identified from the phase-plane trajectories of the monitored variable. Accordingly, the stability margin and risk of instability can be estimated. Case studies on a two-generator system and a 179-bus system show that the BOCS system can be applied either locally or for wide-area stability monitoring in real-time calculation of stability margin. This paper proposes a new idea for using real-time measurements to develop and identify a power system's adaptive equivalent as a basis for online prediction of instability. [ABSTRACT FROM PUBLISHER]