Provision of reactive power services by energy communities in MV distribution networks

The 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

An ADMM approach for day-ahead scheduling of a local energy community

The paper deals with the day-ahead operational planning of a grid-connected local energy community (LEC) consisting of several prosumers each equipped with generating units, loads and battery energy storage units. The prosumers are connected to the same low-voltage distribution network. In order to preserve, as much as possible, the confidentiality of the features and forecast of prosumers' equipment, the problem is addressed by designing a specific distributed procedure based on the alternating direction method of multipliers (ADMM). The distributed procedure provides the scheduling of the batteries to limit the balancing action of the external grid. Results obtained for various case studies are compared with those obtained by a centralized approach. The values of the objective function, the profiles of the power exchanged with the utility grid and the profile of the energy stored in the batteries provided by the distributed approach are in close agreement with those calculated by the centralized one

Comparison between Multistage Stochastic Optimization Programming and Monte Carlo Simulations for the Operation of Local Energy Systems

The paper deals with the day-ahead optimization of the operation of a local energy system consisting of photovoltaic units, energy storage systems and loads aimed to minimize the electricity procurement cost. The local energy system may refer either to a small industrial site or to a residential neighborhood. Two mixed integer linear programming models are adopted, each for a different representation of the battery: A simple energy balance constraint and the Kinetic Battery Model. The paper describes the generation of the scenarios, the construction of the scenario tree and the intraday decision-making procedure based on the solution of the multistage stochastic programming. Moreover, the daily energy procurement costs calculated by using the stochastic programming approach are compared with those calculated by using the Monte Carlo method. The comparison is repeated for two different sizes of the battery and for two load profiles

The impact of psychological distress on weight regain in post-bariatric patients during the COVID-19 pandemic: A latent profile analysis

Objective: The COVID-19 pandemic has caused a global health crisis disrupting healthcare delivery for people with severe obesity who have undergone bariatric surgery. This study examined the role of psychological distress during the first Italian COVID-19 lockdown in predicting post-operative outcomes in post-bariatric patients reaching the end of the 12-18 months follow-up during the lockdown. By using a person-centered approach, groups of patients with different psychological distress profiles were identified. We hypothesized that compared to post-bariatric patients with low psychological distress, post-bariatric patients with high psychological distress will be more at risk of weight regain. Methods: A total of 67 patients (71.6% female, Mage = 45.9) participated in this observational retrospective cohort study. Patients' anthropometric data were gathered from medical records while the weight at the end of the lockdown through phone interviews. Psychological distress, operationalized with anxiety symptoms, depressive symptoms, and sleep disturbances, was assessed by an online self-report questionnaire. Results: Significant differences were highlighted in the high and low psychological distressed group in weight changes, F(1,58) = 5.2, p < 0.001, η2 = 0.3. Specifically, compared to post-bariatric patients in the low psychological distress group, those in the high psychological distressed group reported weight regained (95% CI = 1.0, 2.6). Conclusion: Results highlight the need to target post-bariatric patients with high psychological distress who are at risk for weight regain during the COVID-19 pandemic. Interventions mitigating psychological distress and obesogenic behaviors during future pandemics or in post-COVID times are needed in vulnerable post-bariatric patients reporting high psychological distress

Inverse Laplace Transform of Sunde's Formula for the Ground Impedance of Buried Cables

The time-domain calculation of electromagnetic transients in multi-conductor lossy overhead lines and buried cables requires the evaluation of the transient ground resistance matrix. For the case of overhead lines, analytical expressions for the transient ground resistance obtained by solving the inverse Laplace transform of Sunde's formula have been recently presented. This paper presents the expressions obtained by the analytical inverse Laplace transform of Sunde's formula for the case of buried cables. The results provided by the proposed analytical expressions agree with those given by the numerical inverse transform of Sunde's formula. The new expressions are adopted for the calculation of the per-unit-length voltage drop in a multiconductor underground line. The voltage drop waveforms are compared with those given by recently proposed time-domain analytical expressions that neglect displacement currents

An Improved Approach for the Calculation of the Transient Ground Resistance Matrix of Multiconductor Lines

The general integral expressions for the elements of the ground impedance matrix do not have an analytical inverse transform in the time domain. Therefore, the ground transient resistance of a multiconductor line is commonly evaluated in the time domain by means of approximated expressions in order to avoid the numerical inverse fast Fourier transform burden. In this paper, we propose a new analytical approach for calculating the transient ground resistance in the time domain that stands on the very accurate Sunde logarithmic expression for the ground impedance matrix of an overhead multiconductor line. The proposed analytical approach is adopted for calculating lightning induced voltages in a multiconductor overhead line. The results show that the proposed analytical formula is in perfect agreement with the numerical inverse Fourier transform of the general Sunde expression and, therefore, is more accurate than the approximated expressions available in the literature

Optimization Model for the Analysis of Multiple Energy Communities in the Same Distribution Network with Different Providers

The 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

Basics of Power Systems Analysis

This chapter provides the background required to understand the main aspects of power systems analysis and operation under steady-state and transient or dynamic conditions. It is intended for senior undergraduate or graduate students of electrical engineering as well as practitioners, so readers are assumed to have a solid background knowledge of electrical engineering. The main technical issues associated with power systems analysis are addressed, focusing in particular on alternating current (alternating current (AC)) transmission lines, networks, load-flow and short-circuit calculations, stability analysis, frequency control, and electromagnetic transient appraisal. The chapter also references the most important and popular model frameworks and calculation/modeling tools that have been developed by researchers and engineers working within the electric power systems area in the last few decades. It is emphasized in this chapter that an understanding of the issues dealt with here is required to comprehend other chapters of this handbook devoted to distributed generation and smart grids, and this knowledge will also be needed to be able to operate upcoming power systems. The chapter is divided into sections focusing on the following topics: 1.Power systems evolution, from the origins to the traditional structure2.Transmission lines in steady state, transmitted active and reactive power3.Power flow analysis (load-flow equations and resolution methods)4.Short-circuit calculations for unbalanced faults (symmetrical components, fault equations, and sequence networks)5.Stability (states of operation, classification, P-delta curves, rotor angle stability, equal area criterion, multi-machine stabilty and voltage stability)6.Generators reserve and dynamics, frequency dependence of the load, control structure for frequency control7.Traveling waves in a lossless line, reflection and transmission coefficients, multiple reflections in a line of fine length; electromagnetic transients (classification of transients, electromagnetic transient (EMTP))8.Power systems in the future (why we need a smart(er) grid, microgrids and energy communities) Additional information and supplementary exercises for this chapter are available online

The Use of the Diagnostic Criteria for Psychosomatic Research in Substance Use Disorder Patients

Chaturvedi and Goswami have reported on the useful clinical information that may derive from the use of the Diagnostic Criteria for Psychosomatic Research (DCPR) in a psychiatric setting. It has also been widely accepted that DCPR, being based on a clinimetric approach, allows a more sophisticated qualitative assessment of patients than the dimensional DSM checklist of symptoms. This means that DCPR measures symptoms, physical signs, and other clinical phenomena (e.g. type, severity and sequence of symptoms) and, as suggested by macroanalysis, it diagnoses syndromes and/or disorders that can be organized according to a hierarchical configuration on the basis of where treatment should commence in the first place. Recently, macroanalysis has been proposed for the assessment of substance use disorder (SUD) subjects, and DCPR has been hypothesized as possible predictors of cooccurrent psychiatric disorders in such a clinical population. In this framework, we used both DSM-IV and DCPR criteria in a sample of substance abuse outpatients to verify if DCPR might expand the psychological assessment in SUD settings

Estimation of the expected annual number of flashovers in power distribution lines due to negative and positive lightning

The paper deals with the estimation of the expected annual number of flashovers in overhead power distribution lines due to indirect lightning strokes and aims at extending a procedure previously proposed by the authors, limited to negative downward events, in order to include also positive events. The obtained results show that positive flashes need proper consideration for an improved selection of protection means and countermeasures against flashovers