1,721,007 research outputs found
Computational Aspects of the Dynamic Response of a Microgrid: A Comparative Analysis
No full textThe paper presents the analysis of the dynamic response of a microgrid, obtained by means of two different simulation environments, i.e. EMTP-RV and Simulink. The aim of the study is to investigate on some differences that could arise between the two environments and to explore when such differences could become meaningful, in particular for the analysis of microgrids. The system under study is a medium voltage microgrid coupled to an external network and containing stationary and rotating loads and a battery energy storage system. The considered case studies are: i) a step load change in order to compare the responses in both grid-following and grid-forming control modes for the battery energy storage system; ii) voltage and frequency step changes to compare two types of loads, namely exponential load and induction motor and iii) the islanding transition of the microgrid
Provision of reactive power services by energy communities in MV distribution networks
Full text linkThe paper presents a procedure for the optimal operation of a community of prosumers connected to a medium voltage distribution network equipped with generation and storage units that considers
the penalization for low power factor operation, the exploitation of direct exchanges of both active and reactive power between the prosumers and the provision of reactive power services by the
community to the local distribution system operator and the transmission system operator. The proposed procedure calculates the maximum and minimum reactive power deviations that each community participant can provide with respect to the reference profile. A deterministic day-ahead scheduling problem is considered assuming the forecast of load and photovoltaic production known without uncertainties. The formulation of the optimization problems and the solution computational requirements are suitable for the inclusion in a stochastic approach. The effectiveness of the approach is supported by numerical simulations of the daily scheduling for different test cases
Day-ahead Multistage Stochastic Optimization of a Group of Electric Vehicle Charging Stations
No full textThis paper deals with the day-ahead optimal scheduling of a parking lot with several bidirectional charging stations for plug-in electric vehicles (EVs), part of a grid-connected system including also a photovoltaic (PV) generating unit and local loads. In the proposed approach, a central dispatching unit implements a multistage stochastic optimization to obtain the day-ahead scheduling of the charging stations considering the uncertainties associated with PV generation, non-dispatchable loads and the connected electric vehicles. The scenario tree is built by means of a reduction technique based on k-medoids so that all the representative scenarios included in the tree are feasible. The objective is the minimization of the expected daily procurement costs, exploiting the Vehicle-to-Grid (V2G) services provided by the parking lot. The performance of the procedure is assessed by using different case studies
Relation of Lightning Induced Flashovers with Stroke Distance and Current Peak
No full textLightning current peak amplitudes and stroke locations are data provided by lightning location systems, albeit with some approximation. We argue that a minimum threshold/value of the ratio between current peak and distance of the stroke location from the line must be reached for an insulation flashover to occur. Equations and/or models providing a relation among induced voltage values, distance and current peak are available: the paper compares the results predicted by Rusck's formula and Darveniza's formula, with those provided by the more detailed model implemented in the LIOV code. The assessment of the accuracy of such a relation is important also for the estimation of the minimum collecting area around the line that includes all dangerous events, which is needed for the calculation of the lightning performance of a power distribution line with a Monte Carlo-based approach. The paper proposes a method for estimating the probability of flashover based on the current peak to distance ratio within the limits of the lightning location systems accuracy
Optimization Model for the Analysis of Multiple Energy Communities in the Same Distribution Network with Different Providers
No full textThe current regulatory framework allows the presence of more than one community in the same distribution network. Participation in a community allows direct power exchanges with the other members. Users are free to take part in a community or not and they can also choose a different energy provider from those of the other participants. By means of a specifically developed optimization model, the paper analyzes the effects of the presence of multiple communities and of different providers. The model defines the price of the transactions among the community participants as shadow prices of the relevant balance constraints. The day-ahead scheduling for different numbers and configurations of energy communities are presented for the IEEE 123-bus feeder test system. The results show that procurement costs increase as the number of communities increases. Scheduling of transactions among participants in the same community is affected by the tariffs set by different providers
Flexibility modeling for parking lots with multiple EV charging stations
Full text linkThe paper proposes an aggregated model that represents the flexibility potential of car parks equipped with multiple electric vehicle (EV) charging stations. The model is used in a stochastic optimization procedure to estimate in advance the maximum flexibility margins of the parking lot. The EV aggregator responsible for the charging stations offers intra-day ancillary services to the grid by specifying the possible margins within which the absorbed power can be varied, either up or down. These adjustments are made at the request of the distribution system operator, ensuring an appropriate level of EV charging. The effectiveness of the model is evaluated for parking lots with different numbers of charging stations and different daily profile forecasts of the number of EV arrivals and departures
Influence of the Radial Electric Field Appraisal on Lightning-Induced Overvoltages Statistical Assessment
No full textThis paper analyzes the influence of the radial electric field radiated by return strokes on the lightning performance of an overhead distribution line. The calculation of the lightning electromagnetic pulse (LEMP) over a finitely conducting ground is performed by solving the Sommerfeld integral for the radial component of the electric field. The proposed method uses a trapezoidal scheme in which nodes are equidistant in logarithmic scale. The method is implemented in the LIOV-EMTP (lightning induced overvoltages-electromagnetic transient program) code that solves the field-to-multiconductor line coupling equations and calculates the lightning induced voltages in distribution networks having complex and realistic configuration. The results obtained by the proposed method for the LEMP calculation are compared with those obtained by using the Cooray-Rubinstein formula, which is the most commonly adopted approximation. Finally, the peak-amplitude probability distributions of the induced voltages obtained by using the two approaches are presented. It is shown that for ground conductivity values larger than 0.001 S/m, the Cooray-Rubinstein formula provides results in agreement with the accurate solution, while it significantly underestimates the lightning performance for lower conductivities and for lines with a high insulation level
Application of the Monte Carlo method to lightning protection and insulation coordination practices
No full textLightning insulation coordination is based on statistical approaches. This allows to correlate the electrical stress caused by lightning and the electrical strength of the insulations, both having probabilistic nature. This chapter provides an example of lightning insulation coordination. Specifically, it deals with the statistical appraisal of the so-called lightning performance of distribution systems, carried out by means of Monte Carlo (MC) simulations. The relevant application to both the cases of direct and indirect lightning events, considering the correlation between the probability distributions of the lightning current parameters, is described and discussed. In particular, the application to the indirect events is based on the definition of a surface around the power line and on the calculation of the induced voltages along the line caused by indirect events having stroke location uniformly distributed within such a surface. The result obtained through the MC simulations is fmally scaled taking into account the annual number of fl ashes per square kilometer expected in the region of interest. In order to obtain significant results, two aspects need to be considered: the surface around the power line should be large enough in order to collect all the events that may endanger the insulation, and the density of the stroke locations should be sufficiently high. Therefore, for medium voltage systems, or even more for the case of low voltage ones, the area can reach a large value indeed, and the number of events to be considered can be consequently huge. The chapter also describes the application of the stratified sampling technique able to reduce the computation effort typical to this type of calculation
Power loss reduction in the energy resource scheduling of a local energy community
Full text linkThe paper focuses on the minimization of the energy procurement cost in the day-ahead optimization of the operation of a local energy community. The community is a set of prosumers, each of them equipped with local generation, energy storage systems and loads. The procedure is based on the classical second order cone programming (SOCP) formulation of the distribution optimal power flow and distinguishes between the power exchanged with the external grid and the power exchanges between the prosumers in order to prioritize the use of local energy resources. The performance of the proposed procedure is shown for various operating conditions of a distribution network in which direct transactions between prosumers connected to different feeders of the same substation are allowed
Procurement Cost Minimization of an Energy Community with Biogas, Photovoltaic and Storage Units
No full textThe paper presents a day-ahead scheduling procedure of a local energy community (LEC) that includes one or more producers equipped with a biogas power plant. The other participants may own photovoltaic units, battery energy systems (BESs), and loads. The aim of the scheduling, which essentially concerns biogas units and BESs, is the minimization of the daily energy procurement cost of the LEC, including the fuel cost. The scheduling procedure also provides the prices of the internal transactions. In particular, the paper shows the impact of the biogas power production and analyzes how it affects the prices of the transactions between the LEC participants. Several case studies are presented, characterized by different scenarios of LEC self-consumption, number of dispatchable units, and fuel consumption. Both a centralized and a distributed optimization model, based on the alternating direction method of multipliers (ADMM), have been implemented and compared
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