This document is a summary of a report prepared by the IEEE PES Task Force (TF) on Microgrid Stability Definitions, Analysis, and Modeling, IEEE Power and Energy Society, Piscataway, NJ, USA, Tech. ...Rep. PES-TR66, Apr. 2018, which defines concepts and identifies relevant issues related to stability in microgrids. In this paper, definitions and classification of microgrid stability are presented and discussed, considering pertinent microgrid features such as voltage-frequency dependence, unbalancing, low inertia, and generation intermittency. A few examples are also presented, highlighting some of the stability classes defined in this paper. Further examples, along with discussions on microgrid components modeling and stability analysis tools can be found in the TF report.
The method of symmetrical components is not effective for fault location in the case of untransposed lines, due to potential couplings between the sequence circuits. This paper proposes a ...non-iterative algorithm in the phase-coordinates for wide-area fault location on untransposed transmission networks. In doing so, first, an improved two-terminal method is suggested to accurately locate faults on untransposed lines. Next, an algorithm is proposed to infer voltage and current phasors at the faulted line ends without direct measurements, by taking advantage of the data provided by phasor measurement units (PMUs). Accordingly, the adverse effect of close instrument transformers transients on the estimation accuracy is minimized. Being highly nonlinear in terms of fault distance and impedance, the fault equations are derived and made linear in this paper by defining six suitable auxiliary variables. The resulting system of equations is solved using the least-squares method to obtain three-phase voltages and currents at the faulted line ends. A main feature of the proposed algorithm is that it only requires a limited number of current and voltage synchrophasors. An additional advantage of the proposed algorithm is that the faulted line is not required to be known a-priori. The proposed algorithm is validated using extensive simulation studies on the New England 39-bus test system, accounting for different fault locations, types and resistances.
This paper deals with the assessment of the lightning performance of distribution lines, namely the estimation of the annual number of lightning-induced flashovers versus the critical flashover ...voltage of the line insulators. The procedure proposed by the authors is compared with the one described in IEEE Std. 1410-2004 Guide for improving the lightning performance of electric power overhead distribution lines. The two methods differ: 1) for the models adopted to evaluate the induced voltages and 2) for the adopted statistical approach. The reasons for differences in the results predicted by the two methods are discussed and the parameters playing the major role in the achievement of the results are identified. The proposed method represents an improvement compared to IEEE Std. 1410 because it takes into account more realistic line configurations and the effect of the finite ground conductivity
•Quantify the link between Hyperloop operation and the capsule’s propulsion system.•Assess the operations of a Hyperloop tube to minimize its global consumption.•Understand whether a magnetic ...levitation system affects the capsule’s propulsion.•Assess the achievable minimal energy consumption of a Hyperloop system.
We present an operational-driven optimal-design framework of a Hyperloop system. The novelty of the proposed framework is in the problem formulation that links the operation of a network of Hyperloop capsules, the model of the Hyperloop infrastructure, and the model of the capsule’s propulsion and kinematics. The objective of the optimisation is to minimize the energy consumption of the whole Hyperloop system for different operational strategies. By considering a network of energy-autonomous capsules and various depressurization control strategies of the Hyperloop infrastructure, the constraints of the optimisation problem represent the capsule’s battery energy storage system response, the capsule’s propulsion system and its kinematic model linked with the model of the depressurization system of the Hyperloop infrastructure. Depending on the operational scheme and lengths of the trajectories, the proposed framework determines optimal operating pressures of the Hyperloop infrastructure between 1.5−80mbar along with the maximum capsules cruising speeds. Furthermore, the proposed framework determines maximum operational power of the capsule’s propulsion system in the range between 1.7−5MW with a minimum energy need of 25Wh/passenger/km.
The literature on the subject of synchrophasor estimation (SE) algorithms has discussed the use of interpolated discrete Fourier transform (IpDFT) as an approach capable to find an optimal tradeoff ...between SE accuracy, response time, and computational complexity. Within this category of algorithms, this paper proposes three contributions: the formulation of an enhanced-IpDFT (e-IpDFT) algorithm that iteratively compensates the effects of the spectral interference produced by the negative image of the main spectrum tone; the assessment of the influence of the e-IpDFT parameters on the SE accuracy; and the discussion of the deployment of IpDFT-based SE algorithms into field programmable gate arrays, with particular reference to the compensation of the error introduced by the free-running clock of A/D converters with respect to the global positioning system (GPS) time reference. The paper finally presents the experimental validation of the proposed approach where the e-IpDFT performances are compared with those of a classical IpDFT approach and to the accuracy requirements of both P and M-class phasor measurement units defined in the IEEE Std. C37.118-2011.
This paper deals with scale models of power distribution systems for the study of lightning induced voltages on overhead lines. The scale model technique is useful for the investigation of situations ...which are prohibitively complex to be treated theoretically. For instance, urban distribution networks are usually characterized not only by complex topologies but also by the presence of nearby buildings, whose influence on the lightning induced effects can be successfully evaluated by means of reduced models. The paper first describes the scale model implemented for such a purpose at the University of Sao Paulo, Sao Paulo, Brazil. It then presents a comparison between the experimental data obtained with the scale model and the computer simulations obtained by using the LIOV-EMTP code, a software tool able of calculating lightning-induced electromagnetic transients in distribution systems having complex configurations. Finally, the paper shows an application of the scale model in the evaluation of lightning induced voltages on distribution networks considering the presence of nearby buildings
In this paper, we present a performance analysis of the European Cooperation for Lightning Detection (EUCLID) lightning detection network using data obtained on lightning currents measured at the ...Säntis Tower (located in northeastern of Switzerland) from June 2010 to December 2013. In the considered period of analysis, a total number of 269 upward negative flashes were recorded at the Säntis Tower. The performance of the EUCLID lightning detection network is evaluated in terms of detection efficiency, location accuracy, and peak current estimates for upward flashes. Excluding flashes containing only an initial continuous current with no superimposed pulses exceeding 2 kA, the flash detection efficiency for upward flashes is estimated to be 97%. The recorded flashes contained a total of 2795 pulses (including return strokes and International Conference on Communications pulses characterized by risetimes lower than 8 µs and peaks greater than 2 kA). The overall pulse detection efficiency was found to be 73%. For pulses with peak values higher than 5 kA, the pulse detection efficiency was found to be about 83%. Peak current estimates provided by the EUCLID network were found to be significantly larger than their directly measured counterparts. This overestimation might be attributed to the enhancement of the radiated electromagnetic fields associated with the presence of the tower and the mountain. The median of the absolute distance error, defined as the median distance between the Säntis Tower location and the EUCLID's stroke locations, was found to be 186 m, the majority of large location errors being associated with measured current peaks lower than 10 kA. The analysis revealed also that the location accuracy of the EUCLID network improved significantly in 2013 as a result of an upgrade in the location algorithms to take into account propagation effects.
Key Points
The overall pulse detection efficiency for upward flashes was found to be 73%
The detection efficiency for upward flashes with pulses larger than 2 kA was estimated to be 97%
The median of the absolute distance location error for upward flashes was found to be 186 m
Demand response (DR) has traditionally targeted peak shaving for the optimal allocation of electricity consumption on a time scale that ranges from minutes to hours. However, with the availability of ...advanced monitoring and communication infrastructure, the potential of real-time DR for providing ancillary services to the grid has not yet been adequately explored. In this work, we propose a low-overhead decentralized DR control mechanism, henceforth called Grid Explicit Congestion Notification (GECN), intended for deployment by distribution network operators (DNOs) to provide ancillary services to the grid by a seamless control of a large population of elastic appliances. Contrary to classic DR approaches, the proposed scheme aims to continuously support the grid needs in terms of voltage control by broadcasting low-bit rate control signals on a fast time scale (i.e., every few seconds). Overall, the proposed DR mechanism is designed to i) indirectly reveal storage capabilities of end-customers and ii) have a negligible impact on the end-customer. In order to estimate the benefits of the proposed mechanism, the evaluation of the algorithm is carried out by using the IEEE 13 nodes test feeder in combination with realistic load profiles mixed with non-controllable demand and non-dispatchable generation from photovoltaic distributed generation.
In this paper, we present a theoretical analysis of the propagation effects of lightning electromagnetic fields over a mountainous terrain. The analysis is supported by experimental observations ...consisting of simultaneous records of lightning currents and electric fields associated with upward negative lightning flashes to the instrumented Säntis tower in Switzerland. The propagation of lightning electromagnetic fields along the mountainous region around the Säntis tower is simulated using a full-wave approach based on the finite-difference time-domain method and using the two-dimensional topographic map along the direct path between the tower and the field measurement station located at about 15 km from the tower. We show that, considering the real irregular terrain between the Säntis tower and the field measurement station, both the waveshape and amplitude of the simulated electric fields associated with return strokes and fast initial continuous current pulses are in excellent agreement with the measured waveforms. On the other hand, the assumption of a flat ground results in a significant underestimation of the peak electric field. Finally, we discuss the sensitivity of the obtained results to the assumed values for the return stroke speed and the ground conductivity, the adopted return stroke model, as well as the presence of the building on which the sensors were located.
This paper proposes a generic and unified model of the power flow (PF) problem for multiterminal hybrid AC/DC networks. The proposed model is an extension of the standard AC-PF. The DC network is ...treated as an AC one and, in addition to the Slack, PV and PQ nodes, four new node types are introduced to model the DC buses and the buses connecting the AC/DC interfacing converters (IC). The unified model is solved using the Newton-Raphson method. The extended PF equations can be used in the presence of multiple ICs operating under different control modes. Compared to other recent works, the proposed method allows multiple ICs to regulate the DC voltage simultaneously. This corresponds to more realistic operational conditions that ensure redundancy and allow for more flexible control of the hybrid grid. The proposed model can be used for networks under unbalanced conditions and allows for an intentionally negative sequence power injection. In addition to the operational advantages of this method, it is shown that the computational performance of the proposed method is one order of magnitude better than that of other methods presented in the existing recent literature while having the same accuracy.
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