Massimo Brignone

Optimal Control and Operation of Grid-Connected Photovoltaic Production Units for Voltage Support in Medium-Voltage Networks

The strong increase in the number of installed photovoltaic (PV) production plants has slowly changed the assets and the operating conditions of the electricity power system. In this context, the supply and control of the reactive power from the renewable generation plants are becoming an important issue to be exploited that can facilitate the integration of PV and wind power in electricity grids. The aim of this paper is to propose an optimized control strategy to manage the reactive power resource generated by PV plants in order to improve the quality of the low/medium voltage distribution network and meet the latest technical requirements listed by distribution system operators in their grid codes. A methodology to define the optimal reactive power references for each PV unit connected to a generic distribution network is presented for a specified goal (e.g., the achievement of suitable voltage levels at the grid nodes). Such reference signals are then provided to the PV plants regulation systems, which are designed in order to guarantee the decoupling between the active and reactive power channels, due to the use of the Feedback Linearization control technique. The problem is formulated in a generalized way, so that it can be extended to any possible grid configuration.

The linear sampling method without sampling

We present a new implementation of the linear sampling method in which the set of discretized far-field equations for all sampling points is replaced by a single-functional equation formulated in a Hilbert space defined as a direct sum of L2 spaces. The squared norm of the regularized solution of such an equation is used as an indicator function and is analytically determined together with its Fourier transform. This provides some theoretical hints about the spatial resolution achievable by the method.

Application of the No-Sampling Linear Sampling Method to Breast Cancer Detection

In this paper, the no-sampling linear sampling method is applied to microwave imaging of cancerous tissues in realistic models of female breast obtained from magnetic resonance imaging (MRI). The adopted formulation is based on a modified version of the far-field equation, sensitive to anomalies with respect to the healthy breast. The healthy configuration is taken into account through the related Greens function, which is numerically computed. The adopted imaging technique is assessed against the inspection of tumors of several positions and sizes in noisy environments. Moreover, a numerical analysis of the robustness of the method is performed when the model parameters used for evaluating the Greens function are not exactly known.

Metformin Temporal and Localized Effects on Gut Glucose Metabolism Assessed Using 18F-FDG PET in Mice

In the course of metformin treatment, staging abdominal cancer lesions with 18F-FDG PET images is often hindered by the presence of a high bowel radioactivity. The present study aimed to verify the mechanism underlying this phenomenon. Methods: Fifty-three mice were submitted to dynamic acquisitions of 18F-FDG kinetics under fasting conditions. Three small-animal PET scans were obtained over a 4-mo study period. The animals were subdivided into 4 groups according to the following metformin administration protocol: group 1, untreated mice (n = 15); group 2, mice exposed to metformin treatment (750 mg/kg/d) for the 48 h before each PET study (pulsed, n = 10); group 3, mice treated for the whole study period (prolonged, n = 10); and group 4, mice in which prolonged treatment was interrupted 48 h before PET (interrupted, n = 8). The rate constant of 18F-FDG uptake was estimated by Patlak analysis. At the end of the study, the ileum and colon were harvested, washed, and counted ex vivo. Two further groups, of 5 animals each, were included to evaluate the effect of prolonged metformin treatment on phosphorylated adenosine monophosphate (AMP)–activated protein kinase (pAMPK) form and gene expression for thioredoxin-interacting protein (TXNIP). Results: Pulsed treatment did not modify gut tracer retention with respect to the untreated group. Conversely, prolonged treatment induced a progressive increase in 18F-FDG uptake that selectively involved the colonic wall, without any significant contamination of bowel content. This effect persisted after a complete drug washout in the interrupted group. These responses were paralleled by increased pAMPK availability and by reduced expression of TXNIP messenger RNA in colonic enterocytes exposed to prolonged metformin treatment. Conclusion: Metformin causes a selective increase in colonic 18F-FDG uptake. This effect appears after a relatively long period of treatment and persists soon after drug washout. Accordingly, the increased bowel glucose metabolism reflects a biologic response to chronic metformin treatment characterized by increased levels of pAMPK and reduced levels of TXNIP.

A fully no-sampling formulation of the linear sampling method for three-dimensional inverse electromagnetic scattering problems

We describe a very fast and automatic formulation of the linear sampling method for three-dimensional electromagnetic inverse scattering problems. This formulation is an extension of a no-sampling implementation recently proposed for two-dimensional configurations. In this 3D framework, regularization occurs independently not only of the sampling point but even of the polarization of the fundamental solution used as a known term. Furthermore, a very effective automatic procedure for the selection of the optimal surface describing the scatterer is introduced.

An optimization algorithm for the operation planning of the University of Genoa smart polygeneration microgrid

The aim of this paper is to describe the Smart Polygeneration Microgrid (SPM), which is being constructed at the Savona Campus of the Genoa University, also thanks to funding from the Italian Ministry of Education, University and Research (amount 2.4 Million Euros). Specifically, a detailed model of the grid is presented and an optimization problem is defined, in order to achieve suitable goals, like the minimization of the production costs or the maximization of power quality or environmental indices.

A linear sampling approach to crack detection in microwave imaging

In this contribution a new approach for inspecting crack and defects in known structures by using microwaves is presented. The novelty consists in using a new formulation of the linear sampling method called the no sampling linear sampling method to invert the scattered data, which results to be particularly fast and effective. Such a technique belongs to the category of qualitative methods and is able to retrieve position and shape of anomalies inside a known structure, but it does not provide any information on the point values of the dielectric parameters of the defects. In the paper the formulation of the problem and the new version of the linear sampling method are outlined and some numerical results are provided to assess the proposed approach.

Evaluation of Power System Lightning Performance, Part I: Model and Numerical Solution Using the PSCAD-EMTDC Platform

The paper addresses the important issue of evaluating the overvoltages produced on a power system by a lightning event. First, the theoretical formulation of the problem in the time domain is presented. Then its numerical solution together with its implementation is described. Finally, a PSCAD-EMTDC interface and platform is developed, which allows us to model a realistic network, automatically distinguish between direct and indirect strokes and account for power network precontingency conditions. The obtained results are compared with a frequency-domain solution for a simple case in order to validate the finite-difference time-domain method adopted to solve the coupling equations and the interface with PSCAD. The comparison with the well-known LIOV code for a more complex case is used as a general validation of the overall tool. In a companion paper, the developed platform will be used to evaluate the lightning performance of a portion of the Italian MV distribution network.

An Energy Management System for the Savona Campus Smart Polygeneration Microgrid

The paper proposes an Energy Management System (EMS) for the optimal operation of the Savona Campus Smart Polygeneration Microgrid (SPM) to minimize the overall production costs while satisfying all the thermal and electric network constraints. To do this, first an adequate model of all the components installed in the SPM is presented, then a detailed and computationally efficient electric network representation is derived. The experimental validation performed on the SPM shows a good agreement with the energy management already present in the control room of the SPM and highlights the advantages of the proposed approach both in terms of CPU effort and of completeness of the model.

The use of constraints for solving inverse scattering problems: physical optics and the linear sampling method

Physical optics is an asymptotic scattering regime where the wavelength of the incident field is much smaller than the linear dimensions of the scatterer. In such conditions, the inverse scattering problem of determining the object profile from measurements of the far-field pattern can be formulated in terms of a linear integral equation of the first kind. We apply an iterative algorithm with convex projections to scattering data corresponding to different conducting objects and discuss the complementarity between this physical optics approach and the reconstruction algorithm based on the linear sampling method. Finally, the two approaches are combined to increase the reconstruction accuracy.