Davide Poli

Bio: Davide Poli is an academic researcher from University of Pisa. The author has contributed to research in topics: Electric power system & Grid. The author has an hindex of 17, co-authored 117 publications receiving 1403 citations.

Control techniques of Dispersed Generators to improve the continuity of electricity supply

Abstract: It is expected that dispersed generation (DG) will play an increasing role in electric power systems in the near future. Among the benefits that DG can give to the power system operators and to the electricity customers, one of the most attractive is the possibility of improving the continuity of power supply. DG plants can be designed to supply portions of the distribution grid in the event of an upstream supply outage. Techniques for controlling DG plants that use feedback of only locally measurable variables are presented. This solution allows correct system operation and switching between parallel and isolated modes without needing online communication of control signals between the generators. The control technique is described with particular reference to inverter-interfaced systems (micro-turbines, fuel cells). Simulations of sample cases including different size and type of generators are presented.

Optimized Thermal and Electrical Scheduling of a Large Scale Virtual Power Plant in the Presence of Energy Storages

Abstract: Smart grids are often analyzed using a top-down approach, i.e., starting from communication and control technologies evolution, to then focus on their effects on active and passive users, in terms of new services, higher efficiency and quality of supply. However, with their bottom-up approach, virtual power plants (VPP) are very promising instruments for promoting an effective integration of distributed generation (DG) and energy storage devices as well as valid means for enabling consumers to respond to load management signals, when operated under the supervision of a scheduling coordinator. These aggregation factors can be very profitable for the distributed energy resources (DERs) economy and for the energy network itself. This paper presents a new algorithm to optimize the day-ahead thermal and electrical scheduling of a large scale VPP (LSVPP) which contains: a) many small-scale producers and consumers (“prosumers”) distributed over a large territory and b) energy storage and cogeneration processes. The algorithm also takes into account the actual location of each DER in the public network and their specific capability. Thermal and electrical generator models, load and storage devices are very detailed and flexible, as are the rates and incentives framework. Several novelties, with respect to the previous literature, are proposed. Case study results are also described and discussed.

Challenges in energy systems for the smart-cities of the future

Abstract: In the last years the European Union has actively promoted the renewable energies and the Combined Heat and Power (CHP) also for residential and tertiary buildings. The exploitation of renewable sources and cogeneration seems hampered by the regulatory wall that prohibit for residential, tertiary and commercial buildings the constitution of users clusters. In fact, the unification up to a threshold value of some tens of kVA, at least, can facilitate the installation of renewable energy power plants as solar PV modules or CHP systems (cogeneration) or CCHP systems (tri-generation), overcoming technical and economical barriers and combining several load profiles. The actual distribution system for low voltage LV customers appears inadequate to comply with these goals. At this aim the authors propose the design of a Sustainable Energy Microsystem (SEM) for the integration of different subsystems, currently independent, as final users and high efficiency buildings, dispersed generation from renewable and Combined Heat and Power (CHP) units and subsystems for the urban mobility: metro-transit, trams and recharging of plug-in hybrid and electric vehicles (PHEV) for the surface mobility. The integration is analyzed in the direction of a “smart city” concept, with the optimized and integrated management of many services. These activities are about the general topic of design and construction of nearly zero energy buildings with the use of innovative technologies as home and building automation. The buildings integrated in “energy hub” with dispersed generation and urban mobility systems, constitute the “energy islands” of the future smart grid.

State-Of-Charge Evaluation Of Supercapacitors

Abstract: In the last years, energy storage systems are increasingly involved in applications in which they are required to deliver or adsorb significant charging or discharging currents in short intervals of time, typically a few seconds. Thanks to their high specific power, supercapacitors may represent one of the most promising technologies for this kind of applications. However, one of the main concerns regarding their operation is the accurate estimation of their state of charge; the most common technique, based on ampere-hour counting, typically requires some correction mechanisms, since it implies a significant loss of accuracy over time, due to the accumulation of measuring errors. In the present paper, a novel algorithm to assess the state of charge of supercapacitors is described and implemented. The algorithm is based on the evaluation of the parameters of an equivalent electric circuit of the supercapacitor, and on the consequent use of a Luenberger-style technique for the runtime evaluation of its state of charge, based on the measure of current and voltage at supercapacitor's terminals. The algorithm estimates the cell open circuit voltage while the current is highly variable, as typical in power-oriented applications, hence the corresponding state of charge.

Energy Production Analysis and Optimization of Mini-Grid in Remote Areas: The Case Study of Habaswein, Kenya

Abstract: Rural electrification in remote areas of developing countries has several challenges which hinder energy access to the population. For instance, the extension of the national grid to provide electricity in these areas is largely not viable. The Kenyan Government has put a target to achieve universal energy access by the year 2020. To realize this objective, the focus of the program is being shifted to establishing off-grid power stations in rural areas. Among rural areas to be electrified is Habaswein, which is a settlement in Kenya’s northeastern region without connection to the national power grid, and where Kenya Power installed a stand-alone hybrid mini-grid. Based on field observations, power generation data analysis, evaluation of the potential energy resources and simulations, this research intends to evaluate the performance of the Habaswein mini-grid and optimize the existing hybrid generation system to enhance its reliability and reduce the operation costs. The result will be a suggestion of how Kenyan rural areas could be sustainably electrified by using renewable energy based off-grid power stations. It will contribute to bridge the current research gap in this area, and it will be a vital tool to researchers, implementers and the policy makers in energy sector.

Random graphs

Abstract: We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Hierarchical control of droop-controlled DC and AC microgrids — a general approach towards standardization

Abstract: DC and AC Microgrids are key elements to integrate renewable and distributed energy resources as well as distributed energy storage systems. In the last years, efforts toward the standardization of these Microgrids have been made. In this sense, this paper present the hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to microgrids. The hierarchical control proposed consist of three levels: i) the primary control is based on the droop method, including an output impedance virtual loop; ii) the secondary control allows restoring the deviations produced by the primary control; and iii) the tertiary control manage the power flow between the microgrid and the external electrical distribution system. Results from a hierarchical-controlled microgrid are provided to show the feasibility of the proposed approach.

World energy outlook

Abstract: This chapter discusses leading problems linked to energy that the world is now confronting and to propose some ideas concerning possible solutions. Oil deserves special attention among all energy sources. Since the beginning of 1981, it has merely been continuing and enhancing the downward movement in consumption and prices caused by excessive rises, especially for light crudes such as those from Africa, and the slowing down of worldwide economic growth. Densely-populated oil-producing countries need to produce to live, to pay for their food and their equipment. If the economic growth of the industrialized countries were to be 4%, even if investment in the rational use of energy were pushed to the limit and the development of nonpetroleum energy sources were also pursued actively, it would be extremely difficult to prevent a sharp rise in prices. It is evident that it is absolutely necessary to pursue actively the development of coal, natural gas, and nuclear power if a physical shortage of energy is not to block economic growth.

Defining control strategies for MicroGrids islanded operation

Abstract: This paper describes and evaluates the feasibility of control strategies to be adopted for the operation of a microgrid when it becomes isolated. Normally, the microgrid operates in interconnected mode with the medium voltage network; however, scheduled or forced isolation can take place. In such conditions, the microgrid must have the ability to operate stably and autonomously. An evaluation of the need of storage devices and load shedding strategies is included in this paper.

A wireless controller to enhance dynamic performance of parallel inverters in distributed generation systems

Abstract: This paper presents a novel control strategy for parallel inverters of distributed generation units in an AC distribution system. The proposed control technique, based on the droop control method, uses only locally measurable feedback signals. This method is usually applied to achieve good active and reactive power sharing when communication between the inverters is difficult due to its physical location. However, the conventional voltage and frequency droop methods of achieving load sharing have a slow and oscillating transient response. Moreover, there is no possibility to modify the transient response without the loss of power sharing precision or output-voltage and frequency accuracy. In this work, a great improvement in transient response is achieved by introducing power derivative-integral terms into a conventional droop scheme. Hence, better controllability of the system is obtained and, consequently, correct transient performance can be achieved. In addition, an instantaneous current control loop is also included in the novel controller to ensure correct sharing of harmonic components when supplying nonlinear loads. Simulation and experimental results are presented to prove the validity of this approach, which shows excellent performance as opposed to the conventional one.