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In this work, a phenomenological approach is proposed to analyze the electrical transport through an insulating barrier in insulating/metallic bilayer systems using conductive atomic force microscopy. The influence of the substrate in the electrical properties of ferroelectric/ferromagnetic bilayers was studied in the frame of this model. The substrate roughness was found to increase the barrier height distribution and increase the attenuation length in the material, reducing the barrier quality for the developing of multiferroic tunnel junctions. [ABSTRACT FROM AUTHOR]

This article provides a new methodology for wind turbine-site matching by using a probabilistic approach. The random behavior of the wind speed climate and the uncertainties of wind turbine characteristics are important to take into account in models used to evaluate the performance of the wind turbine. The proposed formulation of the wind turbine-site matching is derived based on the probabilistic reliability assessment approach. It was experimented using different power curve approximation models, for different random conditions, using time series of wind speed in two sites in Morocco: Dakhla and Essaouira. A comparison based on methods used in literature for the estimation of two-parameter of the Weibull function to fit the wind speed distribution is also carried out. The results revealed that the introduced performance indicators are less sensitive to the models used to approximate the wind power curves compared to the deterministic conventional indicator that leads to different rankings and problems of over-sizing or under-sizing. However, those performance indicators are more sensitive to the variation of the wind speed distribution parameter’s and can help on accurately estimate the wind power. Moreover, the proposed formulation allows a global sensitivity analysis using Sobol’s indices to observe the influence of each input parameter on the observed variances of the performance of a wind turbine. A numerical application illustrates the interpretation of sensitivity indices and shows the impact of the wind speed and the rated wind speed on the variance of the wind turbine performance. This method can help wind energy developers and manufacturers to optimally select WTGs for their future project and accurately forecast the performance of their WTGs for monitoring and maintenance scheduling under uncertainty. [ABSTRACT FROM AUTHOR]

This paper presents a new transformer, that is, the custom power active transformer (CPAT)—which integrates shunt and series equivalent circuits within the transformer's magnetic structure. Thus, it provides power system services using a single transformer. The CPAT equipped with a power converter can be utilized in distribution systems to control grid current and load-voltage waveforms while operating as a step-up or step-down transformer between the grid and load. Moreover, it can provide other services that any typical shunt-series compensation arrangement provides. The design and analysis of a single-phase CPAT are presented, showing the effect of coupling between windings and transformer parameters affecting CPAT operation. In this paper, control of the CPAT in a unified power-quality controller application is investigated to attenuate grid-current and load-voltage harmonics as well as compensate for reactive power requirements and mitigate grid inrush current. Through simulation and experimental implementation, the merits and performance of the CPAT were validated. [ABSTRACT FROM PUBLISHER]

This paper proposes a methodology for transient state estimation in power systems. The proposed methodology is formulated using approximation methods for derivatives to relate the state variables to measurements. It does not require knowledge of the steady state to establish the predisturbance operation conditions. The method uses an optimal monitoring system based on topological analysis to obtain full observability. A saving index is introduced to analyze the effectiveness of the instrumentation used. The adverse effect of noisy measurements in the estimation process is mitigated by using an infinite impulse response filter. A transient index is introduced to estimate the fault location. The transient state estimation is assessed using two test systems. The results are validated through direct comparison against those obtained by simulation using SimPowerSystems toolbox of Simulink. With the proposed methodology, the transient state estimation can be obtained with an important saving in the implementation of the measuring system and with considerably less computational effort. [ABSTRACT FROM PUBLISHER]

Analysis of recent blackouts over the past decade has indicated overloads as being responsible for initiation and development of most large area failures. The overload occurrences have also been found to correspond especially with the overcurrent and distance protection, often causing their overfunction under allowable power system operating conditions. It is highly desired to improve the operation of protection relays for the sake of avoiding future blackout occurrences or at least lowering their scale. One of the possibilities to do so is an application of the Dynamic Line Rating algorithms into the standard overcurrent relay with the hope of ensuring safe relay behavior during overloads. The Dynamic Line Rating is usually proposed to be used for increasing the line transfer capacity by monitoring of the overhead conductors temperature and weather conditions. It is clear that one must also take into account the impact of DLR-operated line on the existing protection devices. It is required to adapt their decision-making algorithms to the new conditions, while satisfying arbitrarily established protection principles. This paper presents firstly chosen recent decade blackouts, highlighting the main causes of their formation and development process. Applicable solutions for overcurrent relay improvement are then proposed, which is followed by analyses of the new relay algorithms’ operation during allowable overloads and faults. The enhanced overcurrent relay solution introduced in this paper proved to be an efficient technique also for blackout prevention. [ABSTRACT FROM AUTHOR]

Decarbonizing the global electricity system is expected to contribute significantly to mitigating climate change. A significant body of research has focused on the development of low-carbon power systems; hence, this bibliometric review is timely. We assess the global scientific research on low-carbon electricity both quantitatively and qualitatively, based on the Science Citation Index Expanded (SCI-Expanded) and Social Sciences Citation Index (SSCI) spanning a quarter century and 13,767 publications. Our analysis illustrates the role of inter-institutional collaboration in successful scientific research on low-carbon power systems. The United States has contributed most to the low-carbon electricity literature with 3074 publications, the highest h-index (58), 8 of the 10 most cited articles, and 4 of the 10 most productive institutions. The Chinese Academy of Science is the most productive institution with 270 publications and notably high levels of international collaboration. Based on an analysis and visualization of author keywords and content analysis, we also characterize three phases of the global transition to low-carbon electricity. The 1990s involved reliance on traditional base-load fuels (coal and nuclear), which spurred the search for cleaner alternatives. These alternatives materialized as the rise of clean coal and wind in the first decade of the 21st century, followed by the growth of solar and natural gas beginning in 2010. Besides this evolution of technologies, we document the transition to more nuanced forms of economic and policy analysis in recent years. [ABSTRACT FROM AUTHOR]

In this paper two mathematical programming models are presented and compared for the solution of the European electricity day-ahead market with adjustable block orders. The concept of “adjustable” products is initially introduced, as products that can be partially cleared; thus, they do not bear the inherent indivisibilities of the classical block orders that are tradable in the European markets. Also, the clearing conditions of these adjustable products are analytically described. Due to their flexibility, the market clearing can adjust their clearing status accordingly, in order to match supply offers with demand bids avoiding non-convexities in the problem solution surface. This leads to the elimination of paradoxically accepted and rejected block orders. These adjustable products are modeled within the context of the European electricity day-ahead market problem, which is formulated as two different mathematical programming models: a Mixed Complementarity Problem (MCP) and a Linear Programming model (LP). The two models are evaluated in terms of computational efficiency using the pan-European zonal power system, by considering an increasing number of adjustable products per product type. The MCP model can formulate more adjustable product types, by efficiently formulating respective non-linear mixed pricing rules, but it is computationally demanding; on the other hand, the LP model is computational efficient, but it is not flexible enough to handle an extended variety of adjustable supply/demand block orders. [ABSTRACT FROM AUTHOR]

This paper proposes a decision tree (DT)-based security dispatch method applied to integrated electric power and natural-gas networks (IPGNs) against credible contingencies that may cause violations. Preventive adjustments to the optimal electric energy generation and gas production are carried out based on the security regions and boundaries of controllable variables determined by the DTs. The easily interpretable DT’s rules that describe the security regions are tractable constraints to be included in the optimization routines of electricity generation and gas production rescheduling. Some specific critical contingencies applied to the IEEE 118-bus test system integrated with the 15-node natural gas network are taken as examples to demonstrate a promising application of the proposed security dispatch method to restore IPGN security. [ABSTRACT FROM AUTHOR]

This short communication introduces vector fitting for mode estimation from ringdown responses of power systems. The performance of the method is evaluated for different power system models and is found to be very accurate. [ABSTRACT FROM AUTHOR]

This paper presents a new method, called multicycle Q-modulation, which can be used in wireless power transmission (WPT) to modulate the quality factor (Q) of the receiver (Rx) coil and dynamically optimize the load impedance to maximize the power transfer efficiency (PTE) in two-coil links. A key advantage of the proposed method is that it can be easily implemented using off-the-shelf components without requiring fast switching at or above the carrier frequency, which is more suitable for integrated circuit design. Moreover, the proposed technique does not need any sophisticated synchronization between the power carrier and Q-modulation switching pulses. The multicycle Q-modulation is analyzed theoretically by a lumped circuit model, and verified in simulation and measurement using an off-the-shelf prototype. Automatic resonance tuning in the Rx, combined with multicycle Q-modulation helped maximizing PTE of the inductive link dynamically in the presence of environmental and loading variations, which can otherwise significantly degrade the PTE in multicoil settings. In the prototype conventional two-coil link, the proposed method increased the power amplifier plus inductive-link efficiency from 4.8% to 16.5% at ( RL = 1\, kW, d23 = 3\,cm), and from 23% to 28.2% at (RL = 100\,{\Omega}, d23 = 3\,cm) after 11% change in the resonance capacitance, while delivering 168.1 mW to the load (PDL). [ABSTRACT FROM PUBLISHER]

This paper deals with the combined least mean square–least mean fourth (LMS–LMF)-based control algorithm for distribution static compensator (DSTATCOM) in three-phase distribution system to alleviate the power quality problems caused by solid-state equipments and devices. The combined LMS–LMF-based algorithm is simulated using Sim Power System (SPS) toolbox in MATLAB for obtaining the corresponding active and reactive weights and supply reference currents. The proposed control algorithm has advantages of both LMF- and LMS-based control algorithms, which helps in fast and accurate response with a robust design. Depending on the value of error signal obtained in any of the phases either of LMS- or LMF-based control is used to minimize the error. The developed combined LMS–LMF-based algorithm is implemented on the prototype of the proposed system and responses obtained are found satisfactory with harmonic spectra of the supply currents meeting the power quality standards. [ABSTRACT FROM PUBLISHER]

If an interarea oscillatory mode has insufficient damping, generator redispatch can be used to improve its damping. We explain and apply a new analytic formula for the modal sensitivity to rank the best pairs of generators to redispatch. The formula requires some dynamic power system data and we show how to obtain that data from synchrophasor measurements. The application of the formula to damp interarea modes is explained and illustrated with interarea modes of the New England 10-generator power system. [ABSTRACT FROM PUBLISHER]

There is increasing evidence of shortage of ramping resources in the real-time operation of power systems. To explain and remedy this problem systematically, in this paper we take a novel look at the way the day-ahead unit commitment (UC) problem represents the information about load, generation and ramping constraints. We specifically investigate the approximation error made in mapping of the original problem, that would decide the continuous-time generation and ramping trajectories of the committed generating units, onto the discrete-time problem that is solved in practice. We first show that current practice amounts to approximating the trajectories with linear splines. We then offer a different representation through cubic splines that provides physically feasible schedules and increases the accuracy of the continuous-time generation and ramping trajectories by capturing sub-hourly variations and ramping of load in the day-ahead power system operation. The corresponding day-ahead UC model is formulated as an instance of mixed-integer linear programming (MILP), with the same number of binary variables as the traditional UC formulation. Numerical simulation over real load data from the California ISO demonstrate that the proposed UC model reduces the total day-ahead and real-time operation cost, and the number of events of ramping scarcity in the real-time operations. [ABSTRACT FROM PUBLISHER]

Electric power systems can display a range of undesirable dynamic phenomena by which acceptable, stable operation may be lost. Quasi-steady-state operational problems such as the voltage instability phenomena are among these. Ill-conditioning of the power flow, reflected in high sensitivity of bus voltage magnitudes to load variation is an often observed precursor to such quasi-steady state operational problems. Motivated by this insight, work here will propose a voltage stability and conditioning monitor that is model-free in real-time, based solely on phasor measurement unit (PMU) data, arguing that such an approach is well suited to near-real-time application. We review model-dependent singular value analysis in voltage stability assessment, and relate these existing approaches to our proposed model-free method in real-time application. The proposed algorithm is first applied under the idealized assumption of full measurement data at all buses. This work then extends the algorithm to apply in the more practical case for which only subset of buses have available measurement data. The proposed approach is illustrated in IEEE test cases, augmented to include heavy load conditions that stress voltage stability. Algorithms for efficient computation of small numbers of singular values, as well as means to exploit low-rank updates in data, are reviewed to demonstrate opportunities for fast computation that allow these SVD methods to operate in near-real-time in large systems. [ABSTRACT FROM PUBLISHER]

Improved formulations of and solution techniques for the alternating current optimal power flow (ACOPF) problem are critical to improving current market practices in economic dispatch. We introduce the IV-ACOPF formulation that unlike canonical ACOPF formulations–which represent network balancing through nonlinear coupling–is based on a current injections approach that linearly couple the quadratic constraints at each bus; yet, the IV-ACOPF is mathematically equivalent to the canonical ACOPF formulation. We propose a successive linear programming (SLP) approach to solve the IV-ACOPF, which we refer to as the SLP IV-ACOPF algorithm. The SLP IV-ACOPF leverages commercial LP solvers and can be readily extended and integrated into more complex decision processes, e.g., unit commitment and transmission switching. We demonstrate with the standard MATPOWER test suite an acceptable quality of convergence to a best-known solution and linear scaling of computational time in proportion to network size. [ABSTRACT FROM PUBLISHER]

This paper investigates load frequency control (LFC) of power systems with probabilistic interval delays. The LFC design specifically takes the probability distribution characteristic of the communication delays into account. Firstly, by considering the probability distribution characteristic of the communication delays in the modeling, the original power systems with a PI-based LFC are transformed into a stochastic closed-loop time-delay system. Secondly, by using the Lyapunov-Krasovskii functional method, sufficient delay-distribution-dependent stability and stabilization criteria are derived for the power systems with a PI-based LFC. Following this, an algorithm is provided to obtain the gain of PI-based LFC and the allowable upper bound of the communication delay simultaneously while preserving the desired H\infty performance. Finally, a case study is applied to illustrate the effectiveness of the proposed delay-distribution-dependent PI-based LFC design method. [ABSTRACT FROM PUBLISHER]

Voltage problems are challenging in modern power systems with a high penetration of renewables integrated via power electronics. This paper extends the transient time-scale classification to identify voltage dynamics in modern power systems. Voltage dynamics in the current control time-scale is firstly proposed and then the mechanism of terminal voltage change is elaborated. After that the significant influences of the voltage source converter (VSC), current control (CC) loop and voltage feed forward (VFF) on the voltage dynamics in the current control time-scale are discussed. The VSC current control loop provides positive damping on the terminal voltage, while the VFF scheme results in an additional loop that deteriorates terminal voltage dynamic performance and stability. In addition, a sensitivity analysis was carried out to investigate the influence of critical parameters on stability. Finally, simulation results of a current-controlled VSC attached to different strength of AC grids (including a weak grid) are presented to validate the phenomenon and the influencing factors of voltage dynamics in the current control time-scale. [ABSTRACT FROM PUBLISHER]

In this paper, we introduce an approach for a fast assessment of the dynamic characteristics of system frequency during the period of cold load pickup following a large-scale blackout. The approach is developed based on a load model and a model of generation control system: the load model considers the unique time-dependent characteristic of inrush power surges during the period of cold load pickup, while the model of generation control system mimics the characteristics of various governors that are crucial to the determination of the key variables including initial rate of frequency change, frequency nadir and settling frequency. With the proposed linearization and estimation methods, the model of generation control system can be quickly constructed to offer a great amount of flexibility and simplicity for the study of the impact of cold load on frequency response. The proposed approach allows system operators to quickly evaluate many different options for system restoration. The application of the proposed approach is demonstrated in a case study based on the IEEE 39-bus system. The differences between the results obtained using the proposed approach and those obtained from complete PSS/E simulation are very small, which suggests that the linearized model of generation control system is fast, and accurate enough to address the major concerns of cold load pickup in system restoration. [ABSTRACT FROM PUBLISHER]

This paper proposes a quasi-steady-state modeling approach for an approximation of long-term frequency dynamics in power systems. A specific phenomenon of concern is an onset of frequency swings during load/generation imbalance scenarios. The effects of system voltage characteristics, system inertia, and, more importantly, damping controllers are explained and quantified using the described quasi-steady-state models. Application of the methodology to a 14-generator benchmark system demonstrates that described models are suitable for simulation of different disturbance scenarios that can trigger frequency instability. Moreover, linearization of the proposed models can provide convenient means for impact assessment and coordinated design of damping controllers. To demonstrate this, coordinated tuning of multiband power system stabilizers to improve frequency dynamics has been performed and validated through nonlinear simulations using a commercial transient stability software. [ABSTRACT FROM PUBLISHER]

This paper presents a novel functional observer based quasi-decentralized load frequency control scheme for power systems. Based on functional observers theory, quasi-decentralized functional observers are designed to implement any given state feedback controller. The designed functional observers are decoupled from each other and have a simpler structure in comparison to the state observer based schemes. The proposed functional observer scheme is applied to a complex nonlinear power system and the proposed design method is based on the entire network topology. [ABSTRACT FROM PUBLISHER]

This paper proposes a new distributed framework for forecasting-aided state estimation in electric power systems, modeled by a nonlinear dynamic system. We first introduce the point-based Gaussian approximation filters that use Gaussian approximation and various quadrature rules for computing the related posteriors. These filters feature higher tracking accuracy for nonlinear systems compared to the conventional method, e.g., the extended Kalman filter (EKF). Then, motivated by the increasing demands for wide-area monitoring, we develop the distributed version of the point-based Gaussian approximation filter, based on statistical linearization. In distributed state estimation, each sub-station can only access their local measurements. In the absence of a control center, the average consensus algorithm is applied such that the sub-stations can maintain the global state through information exchange with neighbors. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a new methodology to formulate storage behavior in medium- and long-term power system models that use a load duration curve. Traditionally in such models, the chronological information among individual hours is lost; information that is necessary to adequately model the operation of a storage facility. Therefore, these models are not fully capable of optimizing the actual operation of storage units, and often use pre-determined data or some sort of peak-shaving algorithm. In a rapidly changing power system, the proper characterization of storage behavior and its optimization becomes an increasingly important issue. This paper proposes a methodology to tackle the shortcomings of existing models. In particular, we employ the so-called system states framework to recover some of the chronological information within the load duration curve. This allows us to introduce a novel formulation for storage in a system states model. In a case study, we show that our method can lead to computational time reductions of over 90% while accurately replicating hourly behavior of storage levels. [ABSTRACT FROM PUBLISHER]

As the number of renewable energy generation units and, consequently, solid-state based converters increases in the power grid, many power electronics concepts should be integrated into power system analysis and design. Thus, a power laboratory course with emphasis on the nexus between power electronics and power system is desired. However, the flexibility of instructors in designing a wide range of educational experiments is limited by the use of specialized educational setups. This problem can be resolved by allowing students to assemble their setups using laboratory scaled-down devices; however, implementation times can limit students to focus on the main concepts of the experiments. In particular, lacking experience with hardware description languages to develop switching patterns and control schemes for solid-state based converters further increases the implementation times. In this paper, a technique for rapidly implementing switching patterns and control schemes for power converters is proposed. This technique provides an easy-to-use laboratory allowing students to focus on reinforcing the theory learned in energy conversion, motor-drive, power electronics, and power system classes while still providing instructors with the flexibility to design a wide range of educational experiments. [ABSTRACT FROM PUBLISHER]

This paper presents a wide-area control approach to improve the transient stability of the power systems while also damping the post-fault inter-area oscillations. The proposed approach employs a nonlinear Kalman filter to estimate the inter-area modes using phasor measurement units (PMUs). The wide-area control system then uses the estimated inter-area dynamics through the developed control algorithms to improve the first swing and damping stability of the system. The performance of the proposed approach is evaluated on the simplified Australian test system with different load models including induction motors and the results show significant improvement in the stability of the system by simply adding the wide-area control signals to the available controllers in the system. The application of the proposed wide-area control system is shown to be feasible on realistic systems by improving the system stability and efficiency. [ABSTRACT FROM PUBLISHER]

The paper focuses on the small-signal stability analysis of large power systems with inclusion of multiple delayed signals. The following four techniques are compared: 1) a Chebyshev discretization scheme of an equivalent partial differential equations that resembles the original delay differential-algebraic equations (DDAEs); 2) an approximation of the time integration operator; 3) a linear multistep discretization of the DDAEs based on an high-order implicit time-integration scheme; and 4) the well-known Padé approximants. These techniques are compared using a GPU-based parallel implementation of the Shur method and QR factorization and tested through a real-world transmission system. [ABSTRACT FROM PUBLISHER]

This paper proposes a two-stage methodology for online identification of power system dynamic signature using phasor measurement unit (PMU) measurements and data mining. Only transient stability status is usually predicted in the literature to assist with corrective control, without the dynamic behavior of generators in the event of instability. This paper uses traditional binary classification to identify transient stability in the first stage, and then develops a novel methodology to predict the nature of unstable dynamic behavior in the second stage. The method firstly applies hierarchical clustering to define patterns of unstable dynamic behavior of generators, and then applies different multiclass classification techniques, including decision tree, ensemble decision tree and multiclass support vector machine to identify characterized unstable responses. The proposed methodology is demonstrated on a multi-area transmission test system. High prediction accuracy at both stages of identification is demonstrated. [ABSTRACT FROM AUTHOR]

This article presents a new design of robust finite-time controller which replaces the traditional automatic voltage regulator for excitation control of the third-order model synchronous generator connected to an infinite bus. The effects of system uncertainties and external noises are fully taken into account. Then a single input robust controller is proposed to regulate the system states to reach the origin in a given finite time. The designed robust finite-time excitation controller can refine the system behaviors in convergence and robustness against model uncertainties and external disturbances. The robustness and finite-time stability of the closed-loop system are analytically proved using the finite-time control idea and Lyapunov stability theorem. The suitability and robustness of the designed controller are shown in contrast with two other strong nonlinear control strategies. The main advantages of the proposed controller are as follows: a) robustness against system uncertainties and external noises; b) convergence to the equilibrium point in a given finite time; and c) the use of a single control input. © 2015 Wiley Periodicals, Inc. Complexity 21: 203-213, 2016 [ABSTRACT FROM AUTHOR]

The paper analyses the performance results of the recently developed short-term forecasting suit for the Latvian power system. The system load and wind power are forecasted using ANN and ARIMA models, respectively, and the forecasting accuracy is evaluated in terms of errors, mean absolute errors and mean absolute percentage errors. The investigation of influence of additional input variables on load forecasting errors is performed. The interplay of hourly loads and wind power forecasting errors is also evaluated for the Latvian power system with historical loads (the year 2011) and planned wind power capacities (the year 2023). [ABSTRACT FROM AUTHOR]

Mitigating and minimizing the impact of the sub-synchronous resonance-related phenomena in wind power plants has become the focus of power system research. This paper is a review of these phenomena, such as SSR, SSCI and SSTI, in various types of wind power plants. The analysis and mitigation techniques are also presented. This review will help researchers in dealing with sub-synchronous resonance related issues in wind power plants. [ABSTRACT FROM AUTHOR]

Natural disasters can cause large blackouts. Research into natural disaster impacts on electric power systems is emerging to understand the causes of the blackouts, explore ways to prepare and harden the grid, and increase the resilience of the power grid under such events. At the same time, new technologies such as smart grid, micro grid, and wide area monitoring applications could increase situational awareness as well as enable faster restoration of the system. This paper aims to consolidate and review the progress of the research field towards methods and tools of forecasting natural disaster related power system disturbances, hardening and pre-storm operations, and restoration models. Challenges and future research opportunities are also presented in the paper. [ABSTRACT FROM AUTHOR]

This paper describes an online small signal stability (SSS) analysis method based on relationships exploration (RE) in a large data set for power systems. The proposed method can explore the relationships between operation variables and the SSS and find the optimal variables as input parameters for SSS analysis. Every relationship will be given score by maximal information coefficient (MIC) and Pearson correlation coefficient (PCC). The high ranked variables are selected to estimate the SSS. The SSS can be estimated online based on explored relationships if the selected variables can be obtained online from the wide area measurement system (WAMS). The method is examined on a 39-bus test system and a 1648-bus system provided by PSS/E, and the result is acceptable. Also the impacts of selected types of relationships, training data size, total number and ranks on estimation accuracy are analyzed. The robustness of the scheme to measurement errors and topology variation are studied. [ABSTRACT FROM AUTHOR]

This paper proposes an online detection method for power system voltage instability, which considers the internal impedances of generators and the voltage-dependent and recovery characteristics of the electric loads. First, a novel voltage stability analysis method based on the concept of short circuit capacity (SCC) is established. Based on it, a SCC-based voltage stability index (VSI) is defined as the ratio of the SCC supplied by the combined generation-transmission system and the SCC required by load bus to maintain voltage stability. Then, for the calculation of SCC-based VSI, a two-step equivalent method of power system is presented to obtain the SCC supplied by the system side, in which the generator is modeled as a time-varying internal voltage behind constant internal impedance. Meanwhile, a modification method of load power is proposed to deal with the voltage-dependent characteristics and the restoration dynamics of system loads. As a result, the SCC required by loads can be precisely calculated. At last, the 5-bus system and the New England 39-bus system are used to validate the effectiveness of the proposed voltage instability detection method. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Synchronous static compensators (STATCOMs) have been introduced as a member of flexible alternating current transmission systems devices family in both distribution and transmission levels, namely distribution STATCOM and transmission STATCOM, respectively. These compensators have an important role in increasing the power quality in power systems because of having features investigated in various studies and because of the proper implementation of power functions, especially in compensating the voltage flicker. Studies on STATCOM can be categorized in two different parts. The first part is about the various topologies of the electronic converters used in the compensator and different arrangements of the coupling transformers with the network, which can be named as the power part. The second part is about theorizing at the control level, which eventually ends in producing the proper gate signals to control the switching of the electronic power switches in the power part. Considering the fact that two comprehensive reviews on STATCOM have been published in 2002 and 2009, this paper based on the aforementioned categorization reviews the studies fulfilled in the field of synchronous static compensator, especially the relevant studies in recent years published in creditable journals. The paper makes connections among the control methods and compares the ideas about power stage from different perspectives, so that conducted studies will be organized in a systematic order. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents the results obtained from measurements and analyses of acoustic emission (AE) signals generated by partial discharges (PD) in a model of power capacitors during experiments carried out under laboratory conditions. A remotely-controlled mobile unit (RCMU) has been used in experimental tests, allowing the safe execution of measurements in hazardous conditions. The measurement set-up and construction of the RCMU is presented. The study confirmed that it is possible to use a remotely-controlled mobile unit for carrying out measurements under high voltage. The most significant contribution of the paper lies in the idea that the PD of a condenser for electric power is detected using a mobile system, which can also be applied for other purposes related to the non-destructive diagnosis of power equipment systems working under difficult operating conditions. [ABSTRACT FROM AUTHOR]

This paper presents three dynamic linear state-space models of the modular multilevel converter (MMC) which are suitable for small-signal dynamic studies and controller design. The three models differ by the number of states (two, six, and ten) and, therefore, are suitable for different applications based on the required accuracy. The 2nd- and 6th-order models ignore dynamics of the second harmonics and circulating current suppression control (CCSC). The main challenges of dynamic analytical modelling of MMC are the nonlinear multiplication terms in ABC frame equations for modulating oscillating signals. The multiplication nonlinear terms are therefore considered directly in the rotating DQ frame. This requires simultaneous modeling in zero sequence, fundamental frequency DQ and double fundamental frequency DQ2 frames. The proposed linear analytical models are implemented in state space in MATLAB. The validity and accuracy of the models are verified against a detailed 401-level MMC model in PSCAD/EMTDC in both time and frequency domains. The results show very good accuracy for the 10th-order model and decreasing accuracy for the lower order models. The influence of phase-locked loop and CCSC gains on the MMC dynamic is also studied using the proposed 10th model, and the results verify the suitability of the model for this purpose. [ABSTRACT FROM PUBLISHER]

This paper utilizes data measured by phasor measurement units (PMUs) to extract a low-order dynamic equivalent model for power system stability studies. The estimated model is a 2-order model for synchronous machines. This model has the advantage of simplicity of classical model and considerably reduces the oversimplifying error of classical model. This method offers an alternative approach to analytical model reduction techniques based on the detailed system models. The proposed method uses the synchronized bus voltage and current phasors measured by PMUs. Using post disturbance data, electrical and mechanical parameters of the equivalent generator are estimated sequentially. Furthermore, a new approach for estimation of two-machine and single machine infinite bus (SMIB) equivalent systems are presented for analysis of electromechanical oscillations. To evaluate the performance of the proposed approach, simulations are performed on a two area 13-bus test system and real measured PMU data. Simulation results show that the estimated model can represent the dynamic behavior of the studied system with good approximation. [ABSTRACT FROM AUTHOR]

This study provides a new algorithm for grouping coherent generators in power systems using robust principal component analysis. In coherency identification of generators based on measurements by a phasor measurement unit (PMU), PMU measurements can become unavailable because of unexpected failure of data acquisition or communication links. However, the proposed algorithm is robust to missing PMU measurements and is demonstrated on an IEEE 16-generator 68-bus system. This effective identification of coherent clusters with missing PMU measurements is validated and compared with results obtained using the principal component analysis and independent component analysis methods. [ABSTRACT FROM AUTHOR]

Quadruple-circuit lines with different self-impedances have been applied in power system with the development of power industry. However, the different self-impedances in quadruple-circuit lines will cause problems in fault analysis and related relay protection in the lines. The impedance matrix of these lines is different from that of symmetrical lines, and existing methods cannot completely eliminate all mutual impedance. A new method is proposed to decouple these asymmetrical quadruple-circuits lines in this paper. The phase-to-phase mutual impedance is eliminated first, and then the line-to-line mutual impedance is eliminated according to the circulating current method. The mathematical deduction is formulated to ensure the complete decoupling of the impedance matrix. The fault conditions can be used to obtain the relationship between the independent sequence networks, which can be used to calculate the fault current. Power Systems Computer Aided Design (PSCAD) simulations indicate that the decoupling method is suitable for fault analysis of the quadruple-circuit lines with different self-impedances. The related fault analysis method is quite accurate and easy to be applied. The fault analysis accuracy is not affected by the fault resistance, fault type, fault location, or length of lines. [ABSTRACT FROM AUTHOR]

Small-signal and transient stability of a power system can be improved by installing power system stabilizers (PSSs) inside the excitation controls of the generators. Nonetheless, designing and tuning the PSSs' parameters to suit all operating conditions is a complex and difficult task. Therefore, a new control scheme integrating the principles of the energy function and the functional sensitivity is proposed in this paper. The performance of this control scheme in terms of critical clearing time, simulated dynamic responses, and power oscillation damping was examined using the IEEJ West 10-machine test system. Test results reveal that the proposed scheme can improve both small-signal and transient stability performances under various operating conditions and contingencies. [ABSTRACT FROM AUTHOR]

SUMMARY Some low frequency oscillations (LFOs) with constant amplitude in power systems cannot be explained by the mechanisms such as negative damping, forced oscillation, autoparametric resonance, and bifurcation. In this paper, the concept of transformed periodic orbits is introduced to describe the earlier unexplained periodic steady-state phenomena in power systems. The algorithm of calculating the transformed periodic orbit is presented based on the trapezoidal integration method. Then, a novel mechanism of LFOs is proposed; that is, a transformed periodic orbit emerges when bifurcations or large disturbances occur in power systems. This kind of LFOs can be eliminated by decreasing the generator output power greatly. Simulations on a single-machine infinite-bus system and the IEEE 9-bus system have demonstrated the rationality of the proposed mechanism. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A recent approach to mitigate the adverse effects of photovoltaic (PV) arrays operating under mismatching conditions is the dynamic electrical reconfiguration of the PV panels. This paper introduces a procedure to determine the best configuration of a PV array connected in a series-parallel structure without using complex mathematical models. Such a procedure uses the experimental current vs. voltage curves of the PV panels, which are composed of multiple PV modules, to construct the power vs. voltage curves of all of the possible configurations to identify the optimal one. The main advantage of this method is the low computational effort required to reconstruct the power vs. voltage curves of the array. This characteristic enables one to implement the proposed solution using inexpensive embedded devices, which are widely adopted in industrial applications. The proposed method, and its embedded implementation, were tested using a hardware-in-the-loop simulation of the PV system. Finally, the real-time operation and benefits of the proposed solution are illustrated using a practical example based on commercial devices. [ABSTRACT FROM AUTHOR]

Nowadays, FACTS devices are among the most promising electrical network technologies. The typical representatives of parallel FACTS devices are a static synchronous compensator (STATCOM) and a state var compensator (SVC). The paper deals with the issues of modeling SVC and STATCOM when solving the problem of power system state estimation. The algorithms developed by the authors for embedding the SVC and STATCOM models in the state estimation problem are presented. The paper considers the results of calculations using the algorithms devised for a section of the 500 kV network of the Irkutsk electric power system. A comparative analysis of the obtained results is made. [ABSTRACT FROM AUTHOR]

Conventionally, the frequency of the power system is controlled by matching the electric supply to the varying demand. Some recent studies demonstrated that demand response (DR) can also contribute to the frequency control. However, most of the research works focus on the overall control strategy of DR, whereas the DR parameters are usually randomised rather than carefully designed. In this study, a hybrid hierarchical DR control scheme is designed to support frequency control. The parameters settings are discussed in detail. Instead of randomising the parameters for individual DR controllers, this study proposes a systematic way to design the parameters such as frequency threshold and minimum off-time for individual controllers, so that aggregation of DR can provide primary frequency control smoothly just like thermal generators. Furthermore, the control system is formulated as a multi- objective optimisation problem. The parameters such as the recovery rate of DR and the integral gain of secondary frequency control is optimised so that the maximum deviation, overshoot and oscillations of the frequency can be properly minimised. The proposed method is verified on numerical examples. [ABSTRACT FROM AUTHOR]

This study presents an approach for developing the dynamic equivalent model of an active distribution network (ADN), consisting of several micro-grids, for frequency stability studies. The proposed grey-box equivalent model relies on Prony analysis to establish stop time and load damping as the required modelling parameters. Support vector clustering (SVC) and grouping procedure are employed for aggregation and order-reduction of ADN. This significantly decreases the sensitivity of the estimated parameters to operating point changes which, in turn, guarantees the model robustness. This is done through representing the SVC output, that is, clusters, by cluster substitutes. The final ADN dynamic equivalent model is represented by several groups, in which their mutual interactions are taken into account by a new developed mathematical-based criterion. Simulation results reveal that the proposed model is robust which could successfully take into account the continuous and discontinuous uncertainties. [ABSTRACT FROM AUTHOR]

A system of underground distribution cables is usually used to carry electrical energy inside the populated areas. Under loading and faulty conditions backfill soils lose their moisture content around underground distribution cables. This phenomenon forms dry area around the underground cables and leads to the increase of thermal resistance of backfill soil and sequentially decreases in the cable rating. One aim of this study is to determine the most appropriate of the artificial soil that can be used to fill the blanks around the underground distribution cables to minimise the effect of dry zones that cause thermal failure to the cable insulation. The results of the experimental works conducted in this study showed that some soils lose moisture faster than the other; hence in these types of the soil the dry area will be formed around the underground cable faster than the others. [ABSTRACT FROM AUTHOR]

Stochastic subspace identification (SSI) methods have been widely employed for oscillatory mode identification on probing and ambient data and are reported to have good performances. This work proposes a novel SSI-based approach for identifying dominant oscillatory mode from measurement data and extends the application of SSI to ringdown condition. The proposed approach first constructs an initial cluster of eigenvalues from SSI with repetitive calculations and then utilises a novel hierarchical clustering method to extract the dominant modes from the initial cluster. The repetitive calculations within the SSI are performed through varying the model order over a range defined by a novel initial order determination process. By doing so the challenge of model order determination for SSI-based methods is resolved. Moreover, benefiting from the repetitive calculations and the clustering process, the proposed approach is highly immune to prevalent noises in the measurements. Finally, the proposed approach is applied and validated on the field-measurement data from the phasor measurement units of China Southern Power Grid (CSG) through comparisons with Prony, ARMAX, and Monte Carlo methods. Test results demonstrate that the proposed approach performs with high accuracy, robustness, and efficiency in CSG. [ABSTRACT FROM AUTHOR]

Static compensators (STATCOMs) are able to provide rapid and dynamic reactive power support within a power system for voltage stability enhancement. While most of previous research focuses on only an either static or dynamic (short-term) voltage stability criterion, this study proposes a multi-objective programming (MOP) model to simultaneously minimise (i) investment cost, (ii) unacceptable transient voltage performance, and (iii) proximity to steady-state voltage collapse. The model aims to find Pareto optimal solutions for flexible and multi-objective decision- making. To account for multiple contingencies and their probabilities, corresponding risk-based metrics are proposed based on respective voltage stability measures. Given the two different voltage stability criteria, a strategy based on Pareto frontier is designed to identify critical contingencies and candidate buses for STATCOM connection. Finally, to solve the MOP model, an improved decomposition-based multi-objective evolutionary algorithm is developed. The proposed model and algorithm are demonstrated on the New England 39-bus test system, and compared with state-of-the-art solution algorithms. [ABSTRACT FROM AUTHOR]

This study considers the stabilisation of power systems subject to random jumps. Transient, permanent faults of power lines, and the consequent switching of the associated circuit breakers are represented as a discrete-time Markov chain. The controller is designed for Markov jump linear systems based on transition probabilities obtained from statistical data of the faults. The linear matrix inequalities framework is used as a tool for designing the proposed controller. The controller provides desired performance swiftness via regional pole placement with the constraint of system load variations and random variations in the topology. The effectiveness of the power system stabiliser is studied on a single-machine infinite-bus and multi-machine systems. [ABSTRACT FROM AUTHOR]

The power theory, which can be applied to a power system with transmission/distribution lines with unequal resistances, has useful properties of universality and partitioning/augmentation. Its definitions for apparent power and power factor are consistent from a sinusoidal single-phase system to a non-sinusoidal multi-line system. This study shows that a power system can be partitioned into sub-power systems if some conditions are satisfied and further, it is shown that the sub-power systems can be combined into a large power system. The application area of the concept of apparent power and power factor can be extended with consistency from a single system to a large combined system. The usefulness of the properties in analysing and designing combined power systems is illustrated using examples. [ABSTRACT FROM AUTHOR]

Power restoration schemes incorporated into Distribution Automation (DA) system helps in quickly restoring the power during emergency situations like faults. Due to the numerous advancements made in the distribution system operation in recent times, power restoration analysis needs to be done in a look-ahead manner based on system wide operational & monitored data apart from just fault data processing during the outages. With the evolution of Advanced Metering Infrastructure (AMI) during recent times, it is now possible to design the look-ahead restoration schemes by integrating the operation of DA with AMI system using internet protocol based communications, preferably. In this paper, we propose a novel method for power restoration analysis which execute all pre-defined restoration schemes in a look-ahead manner by representing distribution system as a weighted graph and computing graph weights based on representation of DA & AMI system's current operational/ measured/constraint data from each distribution load segment. Computed graph weights are converted to restoration indices with associated ranking based mechanism to indicate criticality & considerations for each power restoration scheme in case of fault occurrence in real-time. A case study on the standard RBTS test system has been demonstrated for the proposed method. [ABSTRACT FROM AUTHOR]