Daniele Mestriner

A simplified first harmonic model for the Savona Campus Smart Polygeneration Microgrid

Microgrids (MGs) may represent a new answer to many old problems in energy and electric world, such as pollution, high reliability, efficiency and so on. The MG rapid increase implies a fast transformation of the electric power systems that are now characterized by new energy sources requiring dedicated control architectures and simulation tools. Unfortunately, the majority of such new sources are connected to the MG by means of power electronic converters that often make it impossible to replicate some of the concepts, tools and control philosophies commonly used in traditional networks. For this reason, there is a strong need of developing models for MG structures that can be reliable but sufficiently simple to be used for the control system design. In this framework, this paper presents a simplified first harmonic model for the Smart Polygeneration Microgrid (SPM) located in the Savona Campus of the University of Genoa that allows the interface with many controllers. The developed simplified model is validated comparing it with a complete simulation performed in the PSCAD-EMTDC environment that allows to represent each component with a high level of detail.

A new method to evaluate the stability of a droop controlled micro grid

The increasing interest in Microgrids (MGs) leads to the research of more efficient control methods and claims for new methods to assess the obtained working points stability. As the majority of renewable sources are connected to the MG by means of power electronic converters, it is often impossible to replicate some of the concepts, tools and control philosophies commonly used in traditional networks. One of the more frequent control methods in literature is the droop philosophy, whose stability issues have been deeply investigated. In order to evaluate the stability of a droop controlled MG, the present paper presents a new method, whose main advantage is the reduction of the computational effort that reflects in benefits for PLC and control hardware implementation. Simulation tests for validating the suggested technique are provided highlighting its good performances.

Approximate characterization of large Photovoltaic power plants at the Point of Interconnection

The aim of the present article is that of proposing a calculation procedure to assess electric quantities at the Point of Interconnection (POI) of large PhotoVoltaic (PV) power plants on the basis of rated data and main design elements of the plant itself. The quantities of inters are active and reactive power available at the POI in order to extrapolate the power plant capability starting from the capabilities of PWM inverters. The procedure also allows evaluating the POI voltage variations, an important element due to the increasing requirements for renewable generation units to participate in voltage regulation. The main interest in such a methodology lays in its simplicity of application, that allows avoiding the usage of dedicated software for load flow calculations, and flexibility, that makes it suitable for the support of the bidding and pre-design phase of large photovoltaic power plants.

Evaluation of the Mitigation Effect of the Shield Wires on Lightning Induced Overvoltages in MV Distribution Systems Using Statistical Analysis

Lightning overvoltages are one of the most dangerous factors affecting the power quality of a distribution grid. In medium voltage (MV) overhead distribution systems, lightning transients can be caused by either direct or indirect strikes. Indirect strikes are much more frequent than direct strikes and can cause flashovers, especially when the line insulation level is low. The most widely employed protection measures against lightning overvoltages are the use of the shield wires, and/or surge arresters, and increasing the line insulation level. In particular, many studies have shown a significant reduction in the induced voltage magnitudes, thanks to the use of the shield wires in both transmission and distribution systems. This paper deals with the possibility of adopting the shield wires to mitigate lightning induced overvoltages in MV networks, and proposes an analysis on the main parameters that influence their performances. This aim is pursued by means of a probabilistic and statistical analysis based on the response surface method (RSM), which permits to obtain the equation of the surface that best approximates a given model. The application and efficiency of the proposed RSM-based approach have been illustrated by applying it to a realistic situation of a rural distribution line.

Evaluation of lightning-induced overvoltages on a distribution system: Validation of a dedicated code using experimental results on a reduced-scale model

The present paper presents the results of the comparison between a recently developed code for the evaluation of lightning-induced overvoltages in the PSCAD-EMTDC environment and the measurements on an experimental facility developed at the University of São Paulo, São Paulo, Brazil. The extensive validation campaign is performed considering different cases, from a single line to a typical distribution system with one main feeder and many laterals containing both linear and non non-linear elements, such as surge arresters.