Maura Musio

A virtual power plant management model based on electric vehicle charging infrastructure distribution

The exploitation of distributed generation based on intermittent renewable energy sources (RES) has increased the load and generation profile variability. The resort to distributed energy storage systems (DESSs) is usually proposed to compensate the volatility introduced by RES. In particular, plug-in electric vehicles (EVs) are considered one of the most interesting solutions for providing DESSs with the aim of exploiting RES production and matching the distributed electrical generation to the local demand. The aim of this paper is to analyze the impact of vehicle-to-grid technology on an weakly interconnected Virtual Power Plant (VPP) in order to evaluate the effects that distribution and availability of EVs charging structures can have on VPP total cost. A novel mathematical modeling of the mobility system is firstly developed to calculate the probabilistic distribution of parking places. Thereafter, the economic impact on a VPP has been evaluated for different plug-in ratio and charging station scenarios.

Optimal management strategy of energy storage systems for RES-based microgrids

An optimal control strategy devoted to manage the daily charging/discharging profiles of Energy Storage Systems (ESSs) is described in the present paper. The proposed approach aims to minimize Microgrids (MGs) daily electricity costs considering both the real-time price evolution and the effects of intermittent Renewable Energy Sources (RESs). Referring to MGs and electricity market modeling as well as to their main physical and economic constraints, an optimal ESS charging/discharging strategy has been developed. The effectiveness of the proposed ESS management is verified on a MG case study. Particularly, the electricity demand and RES production measured on a small-scale MG are used to compare the daily MG electricity costs and energy balances with and without the proposed optimal control strategy of ESS.

Optimal Electric Vehicle charging strategy for energy management in microgrids

In the present paper a novel approach for determining the charging profile of Electric Vehicles (EVs) suitable for their integration into microgrids is presented. The main goal of the proposed control strategy is to define the optimal daily charging profile of each EV in order to increase microgrid autonomy. This goal is achieved by means of the optimal control theory, taking into account all system constraints, such as instantaneous energy productions and consumptions, rated power and capacity of EV batteries as well as their mobility habits and requirements. Thus, the microgrid energy systems considered in this paper are firstly presented and briefly analysed, together with their mathematical modelling. Subsequently, the optimal control problem is formulated, leading to the achievement of optimal charging/discharging strategies for each EV in order to optimize microgrid operations. The effectiveness of the proposed optimal EV control strategy is then verified through a simulation case study, which refers to a cluster of two microgrids, which are connected in unconventional manner by means of an EV, operating in Vehicle-to-Grid (V2G) mode. The comparison with a dumb charging strategy is finally reported in order to highlight the worth of the proposed approach.

A non-linear dynamic electrical model of Sodium-Nickel Chloride Batteries

In this paper a non-linear second order circuit model of high temperature Sodium-Nickel Chloride batteries (SNBs) is presented. The aim is the development of an accurate model easily implementable in microgrids Energy Management System and suitable for their real-time control. The proposed model is based on the analysis of the experimental performance of a commercial 23.5 kWh SNB. In particular, the mathematical description of the used algorithm, the model parameters identification method as well as the measurement tests carried out for their evaluation are reported and discussed in detail. Then, the model is validated using a measured current-voltage profile, developed in order to trigger the whole battery operative range. The comparison between the experimental data and simulations has confirmed the good accuracy of the proposed model in a defined SOC range. However, due to the particular chemical composition of the battery positive electrode, a novel modelling approach specific for the SNB technology has been finally demonstrated to be necessary.

An agent based approach for the development of EV fleet Charging Strategies in Smart Cities

In the present paper an agent based approach, addressed to simulate the behaviour of a Plug-in Electric Vehicles (PEV) fleet into a Smart City, is presented. Considering the traffic data-set available from mobility plans, a spatial and time model, representing the evolution of travel patterns, can be developed considering each vehicle as an agent. The following statistical analysis in space and time of the agent behaviours is used to plan the PEV charging infrastructure of municipalities. The proposed planning methodology has been tested on an European city in order to evaluate the effectiveness of the proposed procedure. Such charging infrastructure, defined according to the mobility needs, has been tested and used to evaluate the customer satisfaction of PEV users in term of charging demand. The proposed charging system has been implemented to estimate the average daily energy profiles for charging the smart city PEV fleet during a typical workday. This has been finally used as one day ahead energy reference profile to develop a market-oriented EV charging strategies. The performance of the proposed smart charging strategies has been finally simulated and compared.

Outdoor characterization of a Cassegrain-type concentrator photovoltaic receiver

In this study, the characterization of a concentrator photovoltaic (CPV) system based on a Cassegrain-type optic is presented. The indoor and outdoor electrical parameters have been measured and analyzed. On the basis of the IEC 60891 standard, the acquired I-V characteristics have been reported under the CSTC defined in the CEI 82-25 and the electrical parameters deviations have been determined. The correlations among temperature, direct normal irradiance (DNI) and power have been discussed. The results of the absolute power test based on the ASTM E2527 standard and the values of power deviation are reported. Finally the rating power comparison between the two standard test procedures is performed.

A simplified charging battery model for smart electric vehicles applications

This paper proposes a simple and generalized battery model dedicated to lithium rechargeable batteries of electric vehicles, oriented to the energy management of off-board charging stations. In particular, the mathematical description of the used algorithm, the identification of model parameters and the validation of its use for time emulation of fast charging processes are reported and discussed in detail. The comparison between the emulated charging battery behaviours of a Lithium Iron Phosphate battery and the experimental results is reported in order to confirm the accuracy of the model. Finally, an application control scheme for the coordination and energy management of off-board charging stations within the smart grid paradigm is described.

Analysis of Vehicle to Grid and energy storage integration in a virtual power plant

In this paper the integration between the Vehicle to Grid technology and a stationary energy storage system in a Virtual Power Plant (VPP) has been investigated. In order to evaluate the effects of such energy storage systems in an autonomous VPP, an Energy Management System (EMS), oriented to improve the local matching between electrical energy demand and production, has been proposed. To achieve this target and optimize the local energy production exploitation, an energy system design procedure, based on the minimization of the VPP total cost through an annual emulation of the VPPs EMS strategy, has been applied. The proposed methodology, tested on a benchmark VPP, considers the contribution of both electric vehicles and stationary battery in different possible configurations. The comparison among three different cases of study has finally presented at the aim of pointing out the technical and economic benefits.

Concentrator photovoltaic standards: Experimental analyses of technical requirements

The continuing development and the increasing diffusion of concentrator photovoltaic (CPV) systems highlight the lack of specific international standards in the CPV power rating and characterization field. Presently, the only reference standard for CPV cells and modules is the IEC 62108, which does not impose minimum requirements for solar trackers and simulators used in the qualification process of CPV modules. Nevertheless, the overall quality of CPV tests is strictly associated to the technical specifications of these devices. The aim of this paper is to define optical and radiometric properties of solar simulators and the pointing accuracy of solar trackers, required for testing CPV devices and rating their performance. The results of experimental analyses on real CPV systems have been reported, highlighting the criticalities of indoor and outdoor CPV characterization. Finally an outdoor light soaking test, executed under MPPT conditions, has been proposed for the qualification process of high concentrating photovoltaic devices.

Characterization of a CPV module prototype for design and performance improvement

The purpose of this paper is to highlight that a detailed electrical and optical characterization is a basic step to improve the design of a concentrating photovoltaic (CPV) module and enhance its overall performance. The complete characterization of the preliminary CPV module prototype, designed according the state of art, has been carried out revealing lower performances than expected. The reasons of the energy losses have been determined by an accurate optical and electrical analysis. The results of these tests permitted to introduce upgrades into the design of a second version of the CPV module in order to overcome the main defects previously identified. The full characterization of this new version revealed significantly higher performances. Overall, the obtained outcomes demonstrate the benefits of an accurate characterization, allowing both the identification of the system problems design and the evaluation of the effects of the adopted solutions.