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Rising power demands in more electrical aircraft (MEA) put power converters for commercial airplanes under increasing pressure to fulfill current harmonic distortion regulations as specified, for example, in DO-160G. Today, the implementation of filters is seen as an effective tool for dealing with harmonics; however, their increased weight and volume are not welcomed in the aerospace industry. This paper proposes a circuit, named forced commutation controlled series capacitor (FCSC-rectifier), which is able to maintain low individual harmonic current levels without the need for filter components. The FCSC-rectifier includes a variable capacitive line reactance that interacts in a controlled manner with the inductive line impedance. The result is that the converter input current is nearly purely sinusoidal with a power factor of almost unity. The FCSC-rectifier is to be used for stand-alone variable-voltage, variable-frequency generation systems and can, therefore, power the full authority digital electronic control system (FADEC) in an MEA. This paper shows that the FCSC-rectifier can maintain a high power factor and acceptable current harmonic levels without the use of filters, despite large voltage and frequency variations. A full description of the circuit modes of operation is presented in this paper together with simulation results showing circuit performance characteristics over a range of voltages and frequencies. Results are experimentally verified using a 1-kW test circuit. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive optimization control scheme to improve efficiency and dynamic response of dual-active-bridge (DAB) dc–dc converters. Unified-phase-shift (UPS) control is widely used to increase the efficiency of DAB dc–dc converters by minimizing the peak current, but dynamic performance of the converters needs to be further enhanced. In this paper, to gain superior dynamic performance of DAB dc–dc converters, an equivalent power-balancing (PB) model is employed, which is capable of predicting dynamic behavior of converter output voltages due to input voltage fluctuation and load disturbance. And then, combining the UPS control and the PB control, a comprehensive UPS and PB (UPS-PB) scheme is proposed to improve the efficiency and dynamic performance simultaneously. This work also includes the detailed inductance parameter sensitivity of the proposed UPS-PB scheme and a zonal voltage control strategy to further improve dynamic responses of the output voltage under the start-up process or a large step change of the output voltage reference. Moreover, the variant of UPS-PB scheme for constant power load is analyzed in the experimental part. Finally, experimental results have verified the excellent performance of the proposed UPS-PB scheme and correctness of theoretical analysis in this work. [ABSTRACT FROM AUTHOR]

In the event of a single line to ground (SLG) fault in a non-effectively grounded distribution network, the faulted current is weak (only a few amperes or less) and the existing devices cannot accurately judge the faulted feeder. In this paper, we proposed algorithms that combine complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and Hilbert transform to construct a multi-criteria comprehensive voting method. First, CEEMDAN algorithm is used to decompose the zero-sequence current to obtain the IMF1(the first intrinsic mode function) component and the Hilbert transform is used to calculate the instantaneous amplitude and instantaneous phase. Then, according to the three largest instantaneous amplitudes information, we constructed the characteristic instantaneous phase, characteristic instantaneous energy relative entropy and characteristic instantaneous zero sequence current polarity criteria from the phase, energy and polarity, respectively. Finally, we proposed a comprehensive voting method, which is specifically shown as follows: when two or more criteria show that one feeder or the bus has an SLG fault, it is voted that the feeder or the bus has an SLG fault. In contrast, if the judgment results of the three criteria are inconsistent, then we would return to recalculation and then vote. Compared with existing method, simulation tests and field experiments show that the method proposed in this paper has higher accuracy and a faster calculation speed. [ABSTRACT FROM AUTHOR]

A novel traveling-wave-based fault-location algorithm for multiterminal transmission lines is introduced in this paper. Existing traveling-wave fault-location methods that based on the data measured at line terminals lack reliability and accuracy because time synchronization is needed, which brings error. To solve this problem, the complex structure of multiterminal power system is divided into several fault identification branches, current at the midpoint of each branched is measured, a novel fault-location algorithm is proposed, and the time synchronization error is eliminated. A line-based device is designed to measure the current at the midpoint of each branch. An accurate value of the traveling wave speed can be obtained by merely applying the data record in one measuring device. Thus, the fault-location accuracy is improved. The system model applied in this paper comprises one transmission line and two tapped lines, and the proposed method applies to networks with more terminals. Performance of this method is tested by different cases by PSCAD. The hardware platform has been tested in Sichuan Province, China. [ABSTRACT FROM AUTHOR]

DC ice melting is an effective technical method against ice disaster on transmission lines. To satisfy the demand for simultaneous de-icing and reactive power compensation for substations, this paper proposed a large-capacity low-cost DC deicer with reactive power compensation, which is mainly composed of rectifier transformer, Static Var Generator (SVG) and diode rectifier. In the proposed topology, SVG and diode rectifier share the rectifier transformer, but rectifier transformer capacity is not increased compared with a single deicer. This paper firstly presents the proposed topology and analyzes its advantages. Then, the rectifier transformer design is introduced, and the SVG control strategy is presented. Simulation results for the proposed device are presented, and an engineering devices with a capacity of 21.8 MVA developed for the 220 kV Fuchong substation is described. The simulation and application results indicate that the proposed devices work well. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for voltage dip classification using deep convolutional neural networks. The main contributions of this paper include: 1) to propose a new effective deep convolutional neural network architecture for automatically learning voltage dip features, rather than extracting hand-crafted features; 2) to employ the deep learning in an effective two-dimensional (2-D) transform domain, under space-phasor model (SPM), for efficient learning of dip features; 3) to characterize voltage dips by 2-D SPM-based deep learning, which leads to voltage dip features independent of the duration and sampling frequency of dip recordings; and 4) to develop robust automatically-extracted features that are insensitive to training and test datasets measured from different countries/regions. Experiments were conducted on datasets containing about 6000 measured voltage dips spread over seven classes measured from several different countries. Results have shown good performance of the proposed method: average classification rate is about 97% and false alarm rate is about 0.50%. The test results from the proposed method are compared with the results from two existing dip classification methods. The proposed method is shown to outperform these existing methods. [ABSTRACT FROM AUTHOR]

In this paper, an experimental validation of three-dimension multiconductor cell analysis (MCA) is presented: a measurement campaign has been performed on Capri–Torre Annunziata three-core 29.5 km long submarine cable link. All the theoretical conclusions derived by the authors in a previous paper are now experimentally confirmed and the model is, therefore, validated. Based on the example in this paper, the maximum difference between MCA results and measurements is 7% on the positive sequence resistance at power frequency. A 10% difference occurs in the evaluation of positive sequence reactance. The agreement between MCA and real measurements in zero sequence impedance is very good with differences lower than 5% in real and imaginary parts. [ABSTRACT FROM AUTHOR]

A comprehensive time series power flow (TSPF) framework is proposed for the analysis of fault-induced delayed voltage recovery (FIDVR). TSPF bridges the gap between static power flow simulations and time-domain simulations for FIDVR analysis. FIDVR events can be simulated faster with TSPF, while transient simulations normally require much longer time. In the TSPF framework, a random model for the disconnection of the induction motors is proposed to determine the load for different “snapshots” during FIDVR events. Regression analysis is used to predict the parameters needed in the simulations. There is no need to simplify the network topology or aggregate loads into clusters as in measurement-based load modeling approaches. The techniques presented in this paper successfully reproduced two FIDVR events recorded in heavily meshed distribution networks in New York City in 2010 and 2015. The paper uncovers that the proper modeling of motor protections (thermal and under-voltage) is key to properly predict FIDVR events. [ABSTRACT FROM AUTHOR]

A novel approach to synchronization of shore and ship power systems is presented in this paper, providing a blackout-free supply from the shore. An application of the shore-to-ship synchronization strategy, proposed in the paper, instead of the commonly used ship-to-shore synchronization, enables a fuller exploitation of the high dynamic offered by power electronic converters. Converters are increasingly being used in shore-to-ship supply arrangements in order to ensure the required levels of voltages and frequencies, specified in shore-supply related standards. Simulation results, supported by preliminary tests in small-scale experimental arrangements, have confirmed that shore-to-ship applications might significantly improve the dynamics of the synchronization as well as the parameters of the load transferring process, especially under distorted ship voltage conditions. [ABSTRACT FROM AUTHOR]

Due to the anticipated proliferation of HVDC links up to and beyond 2020 into transmission systems, it is expected that in some locations, two or more HVDC links will be installed with a short electrical distance between them and will form a multiinfeed (MI)-HVDC scenario for the system. The control and operation of MI-HVDC systems are of particular concern for weak grids such as that likely to be found in the North of Scotland network. It is shown that the ac voltage regulation in the VSC-HVDC link may adversely affect the dynamic performance of the host weak ac system under the MI-HVDC scenario. To overcome this identified limitation associated with the ac voltage controller in the VSC-HVDC link, a new controller modification conforming to the grid code is proposed in this paper. Furthermore, this paper presents a robust control design method for ac voltage control using the fractional order (FO) control design theory. The influences of the proposed FO-based ac voltage controller are assessed alongside various voltage controllers for the representative North Scotland system. It is shown that the FO-based ac voltage controller has favorable effects on the dynamic behavior of weak ac systems with MI-HVDC. [ABSTRACT FROM AUTHOR]

The control of reactive power exchange between grids of different voltage levels has always been a concern for system operators. With production moving from the transmission to the distribution level, its importance increases. This paper proposes a novel approach to estimate reactive power capability of the grid as a whole. A linearized analytical model for an estimation of available reactive power exchange at the interface between two grids has been developed. The maximum estimation error for the scenarios we tested was only 2%. The model gives the relation between important grid parameters and the supported reactive power. The conclusions drawn from the model are confirmed on typical Swedish distribution network with scattered wind power and small industry consumers. Common scenarios in development of distribution grids are applied to show relevant parameters influence. One studied scenario is replacement of overhead lines with cables. It is shown that this particular change enhances the reactive power capability of the grid which is directly seen from the analytical analysis without running any optimal power flow. The analytical model proposed in this paper gives fundamental understanding of the reactive power capability of radial distribution grids. [ABSTRACT FROM AUTHOR]

DC electric power systems, including HVDC, HVDC light, dc distribution systems, and dc microgrids, have a significant position in present and, especially, future electric power systems, namely, smart grids. One of the most significant issues of electric power systems, including dc electric power systems, is the calculation of accurate and fair energy costs of the consumers. In this paper, novel, simple, practical, and precise relations between economic and electrical variables in dc electric power systems are extracted. The novel relations prove that there are interesting relations between voltages of nodes, as electrical variables, and prices of nodes, as economic variables, in dc electric power systems. Applying the extracted novel relations in this paper, a new, fair, precise, practical nodal price, i.e., the fair nodal price, is determined to calculate the energy costs of consumers in dc electric power systems, including dc distribution systems and microgrids. Moreover, as an application of the extracted novel relations, a practical method to determine the fair nodal prices of all nodes and, as a result, the real energy cost of each consumer at each node of dc electric power systems is presented. The analyses results demonstrate the mentioned significant characteristics. [ABSTRACT FROM AUTHOR]

Day-ahead scheduling has played a significant role in the operation of distribution systems, aiming at minimizing the total operation cost. With the excessive integration of information and communication technologies and intelligent electronic devices, distribution system operators may seek to optimally control the active management elements to increase the economic and technical performance of future smart distribution systems. This paper focuses on an integrated day-ahead scheduling scheme that is formulated as a mixed integer second-order cone programming problem to obtain the optimal solution by means of the relaxed power flow model (RPFM). The detailed technical constraints for all the elements are accommodated based on the RPFM-based optimization method. Meanwhile, active management cost and punishment cost of wind power curtailed and customer energy not supplied are also considered in the design objectives of this paper. In order to address the uncertainties, a stochastic robust optimization method is first introduced to decide the active management elements (including capacitor bank, electrical storage system, controllable load, and switch) as the robust decision scheme. Afterwards, the column-and-constraint generation algorithm is applied to solve the proposed stochastic robust two-stage optimization model. Numerical results based on the IEEE 33-bus, PG&E 69-bus, and practical 152-bus systems are obtained to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Independent system operators (ISOs) are responsible for the secure and economic operation of the power systems. Accordingly, ISOs should solve an optimal power flow to minimize the operating cost of a system while meeting the system's security constraints. However, transmission congestion could drastically limit more economical generating units from being dispatched in the power system operation. In this paper, a decentralized transmission switching is introduced in the operation of multi-area power systems to manage the congestion both on regional transmission lines and tie lines while considering credible contingencies. Our proposed methodology relies on a decentralized optimization methodology. Thus, regional control centers in areas would be able to locally manage the congestion within their regional networks as well as tie lines connecting them to their neighboring areas. Several testing systems are studied in this paper to test the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a method for harmoniously coordinating roles between generators and faster-acting energy storage systems (ESSs), e.g., batteries, to improve their frequency response and regulation services to the grid, particularly at the high wind penetration. This paper theoretically demonstrates that the proposed droop with the state of charge (SOC) feedback (DaSOF) provides a unified frequency control framework for distributed and energy-constrained ESS, seamlessly fitting the conventional primary and secondary frequency control practice. The ESS autonomously takes charge of high-frequency components of a frequency deviation and thus complements the frequency controls of the incumbent generators. By securing the SOC of the ESS at the desired level, the method provides the capability to provide other ancillary services from the energy-constrained ESS. These coordinated roles are represented and validated through time- and frequency-domain analyses. Rigorous case studies using DIgSILENT/PowerFactory demonstrate the efficacy of the proposed method to support the high level of variable renewable energy, which should help in improving the value of operating the ESS and scale up renewable energy. [ABSTRACT FROM AUTHOR]

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

This paper presents parameter values and ranges of static load models used in a power system analysis for the representation of both individual electrical devices and aggregate system loads. The paper discusses and correlates load models and their parameters following statistical processing of the responses of around 100 transmission system operators and utilities around the world, who participated in a survey initiated by CIGRE Working Group C4.605, with the corresponding information on load models and their parameter values from the existing literature. According to the survey, the most frequently used static load models are voltage dependent, and voltage and frequency dependent exponential load models. The identified typical parameter values and ranges of these static load models, both for low voltage devices and for aggregate loads at higher voltage levels, are results of the analysis of a large number of data. Based on these results, the paper provides recommendations for their further use in power system studies and also introduces a novel method for obtaining the mean values and ranges of parameters of the aggregate system load models. [ABSTRACT FROM AUTHOR]

This paper focuses on economic dispatch (ED) in power systems with intermittent wind power, which is a very critical issue in future power systems. A stochastic ED problem is formed based on the recently proposed versatile probability distribution of wind power. The problem is then analyzed and proved to be strictly convex. Although such convex optimization is tractable in many cases, it may take a long time to solve due to its large scale. This paper proposes a dual decomposition method to decompose the large problem. Then, two methods are employed to solve the decomposed problem, namely, the subgradient method and a faster method, limited-memory BFGS with box constraints (L-BFGS-B, a quasi-Newton method). Case studies were conducted to verify the efficiency of the dual decomposition and L-BFGS-B method for solving the stochastic ED problem. [ABSTRACT FROM AUTHOR]

The introduction of an equivalent model for a regional power area in a large-scale power system with complex loads is essential for reducing the computation burden in real-time dynamic analyses. In this paper, we propose a generalized discrete-time equivalent model (GDEM) with specific relations among model parameters for simulating the physical characteristics of a regional power area. The GDEM facilitates the interconnection of equivalent models representing regional power areas and improving the simulation accuracy and speed in large-scale dynamic power systems. This paper first investigates the inherent relations among GDEM parameters in the discrete-time models of synchronous generators and composite loads so as to guide the GDEM parameter estimation in regional power areas. This paper then develops relations among GDEM parameters for a regional power area. Numerical experiments are conducted by simulating ground faults in the China Electric Power Research Institute system and the accuracy of the proposed GDEM is verified by analyzing the dynamic simulation results. In addition, this paper has applied the GDEM to study the regional power area of Central China, which validates the use of GDEM in practical power system analyses. [ABSTRACT FROM AUTHOR]

A fast reliability calculation method based on the fault incidence matrix (FIM) for the complex distribution system is proposed in this paper. First, the M-segment-N-tie-switch (MSNT) reliability calculation unit for the complex distribution network is established and the power supply path matrix is obtained by inversing the node branch incidence matrix of the MSNT unit. Then, three types of FIMs are constructed considering the influence type of each fault event on the load points. Finally, the system reliability indexes are calculated through the algebraic operation between the FIMs and the fault event parameter vectors. The accuracy and the efficiency of this method are verified using the IEEE RBTS bus-6 system. The reliability evaluation method proposed in this paper avoids complicated fault event enumeration and repetitive fault influence range searching, thus, saves the computation time greatly. And more importantly, the analytical expression of the reliability indexes in the matrix form can clearly show the influence of each fault event on each load interruption. So, it is convenient for the reliability sensitivity analysis and helpful for the operator with the reliability improvement planning. [ABSTRACT FROM AUTHOR]

Optimal placement and sizing of distributed energy resources (DERs) can be performed from various points of view. In this paper, a multiobjective function is employed to determine optimal place and size of DERs including combination of photovoltaic resources and a small-scale synchronous generator (SSSG) with an internal combustion engine as its prime mover. As the objective function, not only minimization of investment costs, operation costs, and system losses are used, but also the voltage of microgrid (μG) busses and current of lines are considered as constraints. In addition, this paper shows mechanical stresses can be imposed on the SSSG caused by generator swings after short circuit fault clearing. Furthermore, it may lead to mechanical fatigue in its associated shaft and prime mover. Meanwhile, it is revealed that the mechanical stresses depend on the DERs placement and size. Thus, a novel index representing the stresses on the SSSG shaft is applied in the multiobjective goal function. This decreases SSSG loss of life in a μG with overhead lines which has high rate of short circuit faults. Optimization studies are performed in a six-bus and four-DER μG using time-based simulations. [ABSTRACT FROM AUTHOR]

This paper presents an online event location estimating process in a wide-area power system using the phasor measurement unit (PMU). For real-world applications of PMU-based event location estimation (ELE), it is necessary to consider the insufficiency of PMU data caused by a lack of PMUs, communication failure, PMU malfunction, etc., because insufficient PMU data cannot guarantee event observability over the entire network. To ensure possible event locations in a real-world system, an estimation method is developed by combining offline zonal analysis and an online ELE algorithm. The K-mean clustering method is utilized for electrical-bus clustering, which enables us to recognize separate electrical zones (EZs). Then, we propose a two-stage ELE algorithm by estimating the event EZ and localizing the specified event section within the estimated EZ. Proposed ELE algorithm is applied to a real-world PMU data collected from southwestern part of the United States. Finally, successful results from a real-world PMU data application are presented at the end of this paper. [ABSTRACT FROM AUTHOR]

This paper analyzes different models for evaluating investments in energy storage systems (ESS) in power systems with high penetration of renewable energy sources. First of all, two methodologies proposed in the literature are extended to consider ESS investment: a unit commitment model that uses the “system states” (SS) method of representing time; and another one that uses a “representative periods” (RP) method. Besides, this paper proposes two new models that improve the previous ones without a significant increase of computation time. The enhanced models are the “system states reduced frequency matrix” model which addresses short-term energy storage more approximately than the SS method to reduce the number of constraints in the problem, and the “representative periods with transition matrix and cluster indices” (RP-TM&CI) model which guarantees some continuity between representative periods, e.g., days, and introduces long-term storage into a model originally designed only for the short term. All these models are compared using an hourly unit commitment model as benchmark. While both system state models provide an excellent representation of long-term storage, their representation of short-term storage is frequently unrealistic. The RP-TM&CI model, on the other hand, succeeds in approximating both short- and long-term storage, which leads to almost 10 times lower error in storage investment results in comparison to the other models analyzed. [ABSTRACT FROM AUTHOR]

To encourage and support innovation, synthetic electric grids are fictional, designed systems that mimic the complexity of actual electric grids but contain no confidential information. Synthetic grid design is driven by the requirement to match wide variety of metrics derived from statistics of actual grids. In order to scale these systems to 10,000 buses or more, robust reactive power planning is needed, accounting for power flow convergence issues. This paper addresses reactive power planning and power flow convergence in the context of large synthetic power grids. The iterative algorithm presented by this paper supplements a synthetic transmission network that has been validated by a dc power flow with a realistic set of voltage control devices to meet a specified voltage profile, even with the constraints of difficult power flow convergence for large systems. The algorithm is illustrated with an example new synthetic 10,000 bus system, geographically situated in the western United States, which is publicly available and useful for a variety of research studies. An analysis is shown validating the synthetic system with actual grid characteristics. [ABSTRACT FROM AUTHOR]

An improved hybrid unified power flow controller (IHUPFC) is developed in this paper to control the power flow and increase the utilization rate of the existing transmission lines. The IHUPFC is composed of an improved “Sen” transformer (IST) and a small capacity unified power flow controller (UPFC). After a detailed introduction of the structure and voltage regulation performance of the IST, this paper derives the capacity relationship between the IST and the UPFC. Then, this paper introduces the technology of the IHUPFC in power flow regulation and transmission capability improvement. Besides, the advantages of the IHUPFC in performance and structure are analyzed. The IST has simpler structure and larger power flow control area than a “Sen” transformer, and the IHUPFC provides a continuous active and reactive power flow control. Simulation and experiment studies are used to verify the practicability and superiority of the IHUPFC. [ABSTRACT FROM AUTHOR]

This paper describes the way that white noise (including quantised input section sampling) imparts errors onto frequency and rate-of-change-of-frequency (ROCOF) measurements. The main paper focus concerns the use of filtered heterodyned (i.e., Fourier) analyses for single-phase and three-phase systems, and the filtered Clarke transform for three-phase systems. The rules and equations governing the effect of white noise on frequency and ROCOF are formulated for these techniques, explaining the subtle effects of aliasing, splitting signals and noise into their positive and negative frequency components, and the correlation or decorrelation of noise. It is shown that—as expected—for three-phase ac measurements, averaging three single-phase Fourier measurements produces the same performance against noise as using a method based on Clarke’s transform, if identical filtering is used. Furthermore, by understanding the theory behind the frequency and ROCOF measurement processes, it is shown that to achieve the lowest RMS errors, in the presence of front-end white noise (alone, ignoring other dynamic signal and power quality aspects), a filter which provides ~40 dB/decade attenuation (i.e., a two-boxcar cascade) is recommended for a frequency measurement, but a filter which rolls off at ~60 dB/decade (i.e., a three-boxcar cascade) is recommended for a ROCOF measurement. [ABSTRACT FROM AUTHOR]

Voltage-controlled voltage-source converters (VSCs) are widely applied in islanded microgrids, dynamic voltage restorers, and uninterruptible power supplies, etc. Typically, an LC filter with a large filter capacitance is employed to improve the quality of output voltage and system robustness against external disturbances. Nevertheless, a large capacitance may lead to a low LC-resonant-frequency and cause unstable voltage control of VSCs when a single-loop proportional-resonant (PR) or resonant controller is used. This paper proposes a novel design of single-loop voltage control, where a negative proportional gain is adopted in the PR voltage controller, and it is revealed that the voltage control can be stable even with a low LC -resonant-frequency, e.g., lower than one-third of the system sampling frequency. To tackle the poor dynamic issue introduced by the negative proportional gain, this paper further proposes a closed-loop zeros configuration-based control method, which can flexibly tune the system dynamic response without affecting its stability. Finally, simulation and experimental results are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

As the muzzle energy in the electromagnetic launch increases, it becomes necessary to use a modular pulsed alternator power system composed of multiple pairs of machines connected in parallel. In practical situations, however, parameter variations between two machines are inevitable, and it has uncertain effects on the system performance. Furthermore, due to pulsed alternators driving railgun through a rectifier, the system connection scheme has two options: 1) two machines are connected in parallel before connecting them to the rectifier and 2) two machines are connected in parallel after connecting them to the rectifier. The sensitivity of two topologies to the parameter variations is also uncertain. To make sense of this uncertainty, the impact of machine parameter variations on the system performance is investigated. This paper is performed on the simulation of a pair of pulsed alternators driving a railgun, using one-factor-at-a-time method to observe the system performance in the parameter variations. The sensitivity of two topologies is analyzed taking into account small variations in machine manufacturing parameters—rotor inertia, field winding, and armature winding and in machine control parameters—rotor speed and rotor angle. The results reveal that the system performance is more sensitive to the machine control parameters compared with the machine manufacturing parameters, especially the initial offset in the rotor angle. Furthermore, the connection scheme in which two machines connected in parallel before connecting them to the rectifier is the more robust and is less sensitivity to parameter variations compared with the other topology. This paper is aimed at the identification of the most sensitive parameter and the more robust topology to provide support for the further application. [ABSTRACT FROM AUTHOR]

This paper addresses signal processing aspects of dynamic power quality monitoring in ac energy systems. The widespread use of high-bandwidth sensors enables a characterization of both steady-state and transient operation. However, the volume of so generated data is such that it necessitates extensive preprocessing and extraction of events of interest in estimation and control. We review approaches based on single (vector) samples, and compare them with methods that require full-period information, such as standard dynamic phasors. In this paper, we propose a sparse alternative to the standard (fast Fourier transform based) evaluation of dynamic phasors, thus bridging the gap between the two classes of techniques. We also outline the computational cost tradeoffs among different variants of sparse Fourier transform customized for electric energy system data. [ABSTRACT FROM AUTHOR]

This paper comprehensively analyzes the stability of a grid-interfacing inverter with the LCL -filter in the discrete domain, where the LCL-filter, along with the controller, is modeled in a polar coordinate. System open-loop and closed-loop poles are analytically studied and expressed in the z -domain. Through the poles movement and distribution analysis, the relationship between system stability and the ratio of resonance frequency over sampling frequency is mathematically revealed and calculated as well as the system control gain limit. Moreover, this paper demonstrates that a grid-voltage feedforward regulator would significantly alter the inverter stability in a weak power system. By means of Jury stability criterion, the stability status under different filter resonance frequency is given. The selection of resonance frequency and filter parameters makes a considerable difference on system behavior. Finally, to improve the robustness against grid inductance variation, a conservative design recommendation of filter parameters and control gain is given. Through the tests on a laboratory-scale prototype, the theoretical analysis is validated by experimental results. [ABSTRACT FROM AUTHOR]

The unit commitment is still a widely studied problem, especially when more renewable energy of stochastic character is being added to power systems. This paper proposes a model for weekly planning of systems involving hydro, wind, and thermal energy under a stochastic perspective. The proposed model follows the endogenous reserve determination criterion to achieve a simultaneous optimization of energy and reserves considering wind uncertainty, forced outages of equipment, a dc Flow model of the network, and cascaded head sensitive hydro systems, among others. The paper also develops a practical solution methodology based on outer approximation and benders decomposition. Testing has been conducted over four systems, and computational results demonstrate that the proposed model and solution are useful and effective. [ABSTRACT FROM AUTHOR]

Time delay is prejudicial to power system stability and generally worsens the performance of a control system. In this paper, the approaches for stability analysis and stabilization of a power system consisting of time-varying delay are established. The paper starts with the modeling of the power system according to time-delay differential algebraic equations. An integral quadratic constraints (IQC) method is constructed to guarantee the stability of the proposed feedback controller. The frequency-domain IQC and time-domain dissipation inequality are effectively combined to perform stability analysis and stabilization of the power system considering time delays, without complex numerical computation. A two-area four-machine system, an IEEE 10-machine 39-bus system, and a WECC 179-bus system are employed to support the stability criteria and the IQC method. The simulation results indicate that the combined methods effectively damp the oscillation and improve the performance. [ABSTRACT FROM AUTHOR]

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

Centralized electricity markets currently do not optimize reactive power and voltage in the market clearing software. Voltage and local reliability (VLR) commitment requirements are mostly identified through out of market operational procedures. Failure to maintain VLR may incur voltage collapse, generation, transformer loss, or even blackout. Midcontinent Independent System Operator (MISO) employs binary constraints, minimum/maximum generation constraints, interface constraints, and manual commitments to address VLR requirement in the market clearing process and ensure adequate commitment for reliability. This paper integrates binary VLR constraints in day-ahead security constrained unit commitment to improve market efficiency. However, VLR constraints may cause uplift cost, and sometimes the associated uplift cost can be significant. An uplift cost allocation method with the consideration of resources commitment reasons is developed in this paper. The proposed approach is considered for implementation in MISO market clearing process and a MISO test case is used to validate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Day-Ahead Unit Commitment (UC) is an important problem faced by Independent System Operators (ISOs). Midcontinent ISO as the largest ISO in US, solves a complicated UC problem involving over 45,000 buses and 1,400 generation resources. With the increasing number of combined cycle units (CCs) represented by configuration-based modeling, solving the problem becomes more challenging. The state-of-the-practice branch-and-cut method suffers from poor performance when there are a large number of CCs. The goal of this paper is to solve such large UC problems with near-optimal solutions within time limits. In this paper, our recently developed Surrogate Lagrangian Relaxation, which overcomes major difficulties of Lagrangian Relaxation by not requiring dual optimal costs, is significantly enhanced through adding quadratic penalties on constraint violations to accelerate convergence. Quadratic penalty terms are linearized through a novel use of absolute value functions. Therefore, resource-level subproblems can be formulated and solved by branch-and-cut. Complicated constraints within a CC unit are thus handled within a subproblem. Subproblem solutions are then effectively coordinated. Computational improvements on key aspects are also incorporated to fine tune the algorithm. As demonstrated by MISO cases, the method provides near-optimal solutions within a time limit, and significantly outperforms branch-and-cut. [ABSTRACT FROM AUTHOR]

Deployment of renewable energy sources in power grid causes an undesirable characteristic in the voltage profile due to its stochastic nature. Such electrical perturbations may impact the performance of equipment or machines connected to the grid, especially large rated machines (e.g., 250 MW). This paper investigates the electrical, thermal, and mechanical stresses on large rated doubly fed synchronous (fixed speed) and doubly fed asynchronous (variable speed) machines used in pumped storage power plants under voltage unbalance. Also, the lifespan of the drive train considering thermal stress is estimated. In this paper, considering the medium voltage distribution system (15.75 kV), the magnitude of voltage unbalance is opted as 2.5% and 5% to test the performance of doubly fed machines. With respect to these considerations, the impacts on machine parameters such as rotor current, stator current, input power, torque, and losses are comprehensively investigated. To observe the performance of large rated doubly fed machine drive system under voltage unbalances, the MATLAB/Simulink environment is adopted. Also, to realize the real-time impact on doubly fed machines, a prototype rig (with 2.2-kW synchronous and asynchronous machines) are experimented. The practical significance of this relative analysis is to minimize voltage collapse in the system and for developing the robust system with countermeasures. [ABSTRACT FROM AUTHOR]

This paper proposes a novel control method for an asymmetrical-cascaded-multilevel-converter-based hybrid energy storage system (HESS), which includes one battery and several electrical double-layer capacitors (EDLCs). Traditionally, it is challenging to control the power distribution between different cascaded H-bridges by using different energy storage components as dc sources. In this paper, a feedforward space-vector-modulation (FFSVM) technique is used to distribute the active power between the battery and EDLCs. With the proposed voltage feedforward mechanism, the HESS can flexibly operate in the normal operation mode, the high-power output mode, and the reverse power absorption mode. The principle and effectiveness of the improved FFSVM technique are analyzed. Meanwhile, the state-of-charge-balancing mechanisms are introduced. The simulation results obtained in MATLAB/Simulink as well as the experimental results of a hybrid energy storage test bed based on the proposed system are presented to verify its performance. [ABSTRACT FROM PUBLISHER]

Essential imbalance and fluctuation of the mobile train load draw some problems, e.g., three-phase unbalance, reactive power, voltage and load fluctuation, harmonics, etc. in both public and train supply networks (TSNs). Railway power flow controller (RPFC)'s good performance on dealing with those problems has been convinced in practice these years. However, as the primary task in commercialization, how to qualitatively determine RPFC's design capacity with high cost efficiency and how to comprehensively assess its performance in the design stage have perplexed engineers for many years. To solve those problems in both planning and real-time executing processes, this paper focuses on an RPFC design capacity optimization strategy for grid-connection compatibility and operating performance improvement in terms of both the utility and the TSN. The strategy not only makes a railway substation satisfy the grid-connection standards with high calculating efficiency, but also renders the RPFC to have the minimum design capacity, the excellent feeder voltage control ability, the good fixed capacitor installing prospect, and the high operating efficiency on the targets of reducing the investment and enhancing the transportation ability. The generic models, the industry-oriented design and the quantitative analysis, discussed in this paper give an insight for those concerned based on a balance transformer. Future RPFC projects on serviced railway power systems will benefit from the proposed methodology. [ABSTRACT FROM PUBLISHER]

This paper presents a uniform control strategy for the bidirectional ac/dc interlinking converter (BIC) in hierarchical controlled hybrid microgrid. The uniform control strategy unifies different control structures for multifunctional BIC in terms of power management, ac and dc voltage support. With the unified control structure, various triggering mechanisms for BIC mode-switch are not compulsory in response to the relevant scenario changes in the power network. Therefore, the negative consequences, such as unsmooth transition and system collapse due to the inaccurate or slower mode switch, can be avoided. Moreover, the uniform control strategy is also applicable for the hierarchical controlled hybrid microgrid, whose control architecture is typically comprised of the centralized and decentralized levels. This enables the communication fault ride-through capability and the impact from the communication failures can thus be mitigated. To sum up the above two features, the proposed control strategy is able to provide a smooth operation for the BIC without control mode switch in the event of unintentional scenario changes in power or communication network. To verify the validity of the proposed uniform control strategy, the controller hardware-in-the-loop experimental results have been provided in this paper. [ABSTRACT FROM PUBLISHER]

This paper proposes a new filter design method that can smooth the wind power generation output while keeping the energy capacity and power rating of the energy storage system (ESS) small. Wind power generation causes frequency fluctuations in power systems. Therefore, in many cases, the ESS is needed for smoothing the fluctuations of wind generator output. In order to improve the performance of the ESS controlled with the conventional low-pass filter (LPF), this paper investigates other types of filters. First, the relations between filter and energy capacity/power rating of the ESS are disclosed through the worst-case study. Then, the frequency fluctuation analysis of the power system with respect to the wind power generation is carried out in order to realize a pin-point smoothing. Finally, a metaheuristic optimization method is proposed for the multiobjective design of the filter based on these relations so as to achieve an optimal tradeoff between the output smoothing and energy capacity/power rating of the ESS. It is shown via simulation analysis with real wind data that the proposed method can suppress the frequency fluctuation of the power system effectively with the ESS having smaller energy capacity and power rating. [ABSTRACT FROM PUBLISHER]

An efficient power battery thermal management strategy under low-temperature conditions can effectively alleviate mileage anxiety associated with electric vehicles and improve environmental adaptability. This paper aims to propose a novel coupled thermal management strategy for range extended electric vehicles (REEVs) power systems containing a range extender and a power battery. First, a novel coupled thermal management structure for REEVs power system is designed. Sequentially, a fuzzy controller is developed based on analysis of control rules for different working conditions on the basis of the structure. Furthermore, the stability of the proposed strategy is strictly proven by Lyapunov’s stability theory and phase plane analysis. Finally, a coupled thermal management model is built in AMEsim, and co-simulation between MATLAB/Simulink and AMEsim is developed. The results show that the proposed coupled thermal management strategy efficiently reduces the warm-up time and the steady-state temperature error of the engine and power battery and improves the energy utilization efficiency. [ABSTRACT FROM AUTHOR]

This paper investigates the modal repulsion happened in the sub-synchronous resonance between a synchronous generator and series-compensated transmission line. The investigation is based on the closed-loop model of the series-compensated power system consisted of the torsional and electrical open-loop subsystems. Analytical explanation is presented to show how the SSO modal repulsion is formed as the result of moving close and apart between two open-loop SSO modes. Analysis is carried out to indicate that the peak of the SSO modal repulsion occurs when the two open-loop SSO modes from the torsional and electrical subsystem are closest to each other on the complex plane, which is referred to as the open-loop modal coupling. Estimation on the peak, i.e., the maximum damping degradation of the SSO modes, is derived in the paper. Subsequently, a method of open-loop modal analysis is proposed. Applications of the proposed method of open-loop modal analysis to study the SSOs caused by the DFIGs under the condition of the modal repulsion in the power system are demonstrated and evaluated by example power systems. The concept of modal repulsion explains why the grid connection of the DFIGs may bring about the SSO instability risk in the power system. [ABSTRACT FROM AUTHOR]

This paper presents a decentralized solution algorithm for network-constrained unit commitment (NCUC) in multiregional power systems. The proposed algorithm is based on our previous work in which a local NCUC was formulated for each control entity (i.e., region) and an analytical target cascading (ATC) based distributed but partially parallelized algorithm requiring a central coordinator was presented. The primary objective of this paper is to present a decentralized approach that relaxes the need for any form of central coordinator in ATC and allows fully parallelized solutions of the local NCUCs. To achieve this objective, we formulate a bilevel optimization problem for each control entity. While the upper level solves the NCUC problem of the control entity, the lower level seeks to coordinate the control entity with its neighboring regions. The lower level is a convex optimization, which can be further replaced in the upper level problem by the Karush–Kuhn–Tucker conditions. The control entities communicate directly with each other and synchronously solve their local NCUCs. Having no need for any form of central coordinator, the proposed algorithm is potentially less vulnerable to cyber-attacks and communication failures than the distributed methods utilizing a coordinator. [ABSTRACT FROM AUTHOR]

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

This paper proposes a fundamental model for continuous-time scheduling and marginal pricing of energy generation and storage in day-ahead power systems operation. The paper begins with formulating the economic operation problem of power systems with generating units and energy storage (ES) devices as a continuous-time optimal control problem, where the Lagrange multiplier trajectory associated with the continuous-time power balance constraint is proven to be the marginal price of energy generation and storage. The marginal price is calculated in closed-form, which reveals that in addition to the incremental cost rates of generating units, the marginal price embeds the financial ES charging offers and discharging bids that are defined as incremental charging utility and incremental discharging cost rates. This paper shows that the adjoint function associated with the ES state equation establishes a temporal dependence between the marginal prices during the ES charge and discharge states. A function space-based method is developed to solve the proposed model, which converts the continuous-time problem into a mixed-integer linear programming problem with finite dimensional decision space. The features of the proposed scheduling and pricing models are demonstrated using numerical studies conducted on the IEEE Reliability Test System. [ABSTRACT FROM AUTHOR]

Wide-area damping controller (WADC) is a very effective tool to damp out the low-frequency oscillation in wide-area power systems. However, the WADC needs communication networks to transmit remote signals; hence, the network-induced delay and packet dropout are inevitably introduced in the communication of wide-area measurement systems (WAMS). In order to effectively compensate delay and packet dropout, in this paper, a new wide-area dynamic damping controller (WADDC) is designed. Firstl the discrete-time model of power system with random delay, packet dropout, and external disturbance is established. Then, the WADDC based on robust H∞ control is designed and the sufficient condition about stability of the closed-loop system is given. Finally, the controller designed in this paper is tested on the two-area four-machine power system and the 16-machine 68-bus system. Simulation results demonstrate the effectiveness the proposed methods for damping out the low-frequency oscillation and compensating the network-induced delay and packet dropout. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method to analyze impacts of uncertain variability on power system dynamics. There is considerable interest in integrating intermittent renewable energy and plug-in electric vehicles into power systems. Therefore, power systems are in an environment with increasing uncertain variability. In this paper, the uncertain variability is described as a continuous-time stochastic process, and thus, the power system under uncertain variability is modeled by stochastic differential equations. To quantify impacts of uncertain variability on power system dynamics, an intra-region probability index is presented. Based on the stochastic averaging method, an analytical method is proposed to calculate the intra-region probability. Compared to Monte Carlo simulation, the proposed method is many orders of magnitude faster without sacrificing the result accuracy. Furthermore, several insights are given to improve the power system dynamics under uncertain variability. [ABSTRACT FROM AUTHOR]

The development of platforms and methods for test and calibration of phasor measurement units (PMUs) has drawn attention from the power systems community, especially due to the wide range of specific tests that must be performed. Aiming at reducing labor-intensive processes and the complexity of such tests, this paper presents an automated platform for test, calibration, and performance assessment of PMUs following the IEEE Std C37.118.1. The platform is composed of signal-generation hardware and software running on a personal computer. The test signals are synthesized in software, allowing different waveform configurations for automated testing. Also, the software receives information from the PMU under test and compares it to reference data, displaying results and statistics in real time. Because most of the functions of the system are performed in software, easy inclusion of additional tests or migration to other signal-generation hardware platforms is possible. The resulting test system allows tracing the behavior of the hardware and corresponding embedded software used in the PMU architecture under test through thousands of measurements collected in just a few minutes. The simple and versatile low-cost system presented in this paper enables accurate, flexible, and versatile automated testing of PMU devices with real-time visualization of results. [ABSTRACT FROM AUTHOR]

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

Critical process loads need to be safeguarded against power system disturbances and erroneous operations caused by human factors. During such events, a fast synchronism-supervised transfer scheme is required to ensure continuous operation. This paper discusses the implementation of a fast motor bus transfer scheme using existing protective relays. The scheme is designed to respond to local and remote (upstream) events in the substation. This makes possible an attempt to initiate a fast transfer for events that are remote to the motor bus. On a failure to achieve a fast transfer, the scheme resorts to an in-phase transfer and, if that fails, finally a residual transfer. Real-time dynamic modeling was performed to simulate motor bus decay and reacceleration. This paper provides the results of the simulations and the response of the transfer scheme. [ABSTRACT FROM AUTHOR]