ESTGV - DEE - Documentos de congressos (comunicações, posters, actas)
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- Application-Driven design to extend WSN lifetimePublication . Marques, Bruno; Ricardo, Manuelhe lifetime of a WSN depends on the energy of the nodes. As soon as nodes run out of energy, they get disconnected from the WSN. This paper proposes an Application Driven solution that increases the WSN lifetime by limiting the routing and forwarding functions of the network mainly to nodes running the same applications. The solution is evaluated against AODV, and the results obtained show gains of about 30%
- Architecture of Information System for Monitoring of Photovoltaic PlantsPublication . Pereira, António; Tomé, Paulo; Costa, Paulo Moisés; Pascoal, JoséThe monitoring and supervision systems are crucial to the operation of photovoltaic plants (PV), allowing the gathering of data about its operation. This data, after proper processing, allow to obtain performance indicators, the establishment of comparisons, the identification of behavior trends, the detection and location of malfunctions in equipment / systems and the definition of optimized maintenance plans. The most obvious consequence of the use of monitoring and supervision systems is the improvement of the technical and economical performance of PV plants. This article presents an architecture of a system able to provide information about the operation of a PV plant, regardless of its size, in a mobile device. The proposed architecture includes important aspects concerning the design of information systems, namely concerning the system flexibility and security.
- Economic Analysis of Microgrids Including Reliability AspectsPublication . Costa, Paulo Moisés; Manuel, MatosRecently, the new concept of microgrid (muG) has been emerging on distribution networks as a way to ease the integration of micro generation in LV networks and increase reliability. A muG is an association of a low voltage distribution network, small modular generation systems (micro-generators), loads and storage devices having some local coordinated functions. This entity can operate in two different modes: interconnected or emergency. In the first mode, the microgrid is connected with the distribution network, importing or exporting electricity and/or ancillary services. When in emergency mode, the microgrid operates isolated from the distribution network and uses local resources, changing from power control to frequency control and, if necessary, shedding load. A micro grid will only be established if its promoters achieve sufficient advantages that justify the incurred costs, namely the investment, operation and maintenance costs. The main purpose of this paper is to identify all the relevant costs and benefits and build a decision model for the situation, taking into account the regulatory framework, which is essential for the definition of some of the benefits. The paper also shows how to include in the evaluation the risk associated to the uncertainties in data and parameters. An illustrative example is included that shows a possible situation of equilibrium between global costs and benefits
- Flexible Power Control of Photovoltaic Plants Connected to Distribution NetworksPublication . Ribeiro, Susana; Costa, Paulo Moisés; Gouveia, Eduardo; Sousa, Pedro; Albuquerque, DanielThis paper presents a system to control the power injected by a photovoltaic (PV) plant on the receiving network. This control is intended to mitigate some of the negative impacts that these units may produce on such networks, while increasing the installed power of the plant. The controlled parameters are the maximum allowed value of injected active power and the corresponding power factor, whose setpoints values may be fixed or dynamic. The developed system allows a local and a remote control. The injected power and the corresponding power factor may be set by following a predetermined profile or by real time adjustments to fulfill specific operation constraints on the receiving network. The system acts by adjusting the control parameters on the PV inverters. The main goal of the system is, in the end, to control the PV plant, ensuring the accomplishment of technical constraints and, at the same time, maximizing the installed power of the PV plant, which may be an important issue concerning the economic performance of such plants
- High Energy OFDM Pulse Design Algorithm for Acoustic ToF Ranging and LocalizationPublication . Albuquerque, Daniel; Vieira, José; Lopes, Sérgio; Aguilera, Teodoro; Álvarez, FernandoThis paper proposes an algorithm to design band-limited Orthogonal Frequency Division Multiplexing (OFDM) pulses for accurate time-of-flight ranging in acoustic-based localization systems. The proposed algorithm is capable to generate OFDM pulses with higher energy when compared with other common pulse design approaches with similar characteristics. The results attained have shown that it is possible to design OFDM pulses with 17% more energy than a chirp or a BPSK pulse with the same characteristics. The proposed algorithm uses an iterative approach to increase the pulse energy while keeping the same amplitude, bandwidth and duration in each iteration. Two different OFDM pulses are provided and compared with two common pulses, namely chirp and BPSK pulses, with the same characteristics.
- Improving the energy efficiency of WSN by using application-layer topologies to constrain RPL-defined routing treesPublication . Marques, Bruno F.; Ricardo, Manuel P.The deployment of thousands of tiny devices inter-networked together and accessible through the Internet is the result of the increasing trend towards enabling the concepts of Internet-of-Things. As these devices may be scattered in a unplanned way, a routing protocol is needed. The RPL protocol is the IETF proposed standard protocol for IPv6-based multi-hop Wireless Sensor Networks (WSN). RPL requires that communication paths go through a central router which may provide suboptimal paths, making no distinction of the applications the nodes run. To address these issues, an Application-Driven extension to RPL is proposed which enables the increase of the WSN lifetime by limiting the routing and forwarding functions of the network mainly to nodes running the same application. This paper evaluates the proposed solution coded in ContikiOS by means of Cooja simulations, and compares it against regular RPL. Simulation results confirm that the proposed solution provides lower energy consumption, lower end-to-end delays, and lower total number of packets transmitted and received.
- Loss allocation in distribution networks with embedded generationPublication . Costa, Paulo Moisés; Matos, ManuelThis paper addresses the allocation of electrical losses in distribution networks with embedded generation, in a liberalized environment. The nonlinear nature of the issue, the loss changes due to voltage variation and, specially, the contribution of embedded generation to loss variation are considered. The proposed method is based on tracing the real and imaginary parts of the currents and has two steps. First, the losses in the distribution network, in the absence of embedded generation, are allocated to the consumers (or their providers). Second, the variations in the losses that result from the influence of embedded generation are allocated to the generators. These variations are a measure of the avoided or added costs related to losses. In the allocation process, made in a branch basis, both real and reactive powers are considered. The methodology presented in this paper can be used to evaluate embedded generation incentives or to design tariffs for the use of the distribution network.
- Monitoring system for small sized photovoltaic power plantsPublication . Correia, Daniel; Tomé, Paulo; Costa, Paulo Moisés; Marques, LuísThis paper presents a monitoring system devoted to small sized photovoltaic (PV) power plants. The system is characterized by: a high level of integration; a low cost, when compared to the cost of the PV system to be monitored; and an easy installation in the majority of the PV plants with installed power of some kW. The system is able to collect, store, process and display electrical and meteorological parameters that are crucial when monitoring PV facilities. The identification of failures in the PV system and the elaboration of performance analysis of such facilities are other important characteristics of the developed system. The access to the information about the monitored facilities is achieved by using a web application, which was developed with a focus on the mobile devices. In addition, there is the possibility of an integration between the developed monitoring system and the central supervision system of Martifer Solar (a company focused on the development, operation and maintenance of PV systems).
- Probabilistic Security Constrained Fuzzy Power Flow ModelsPublication . Gouveia, Eduardo; Costa, Paulo Moisés; Sagredo, Jesus; Soroudi, AlirezaIn restructured power systems, generation and commercialization activities became market activities, while transmission and distribution activities continue as regulated monopolies. As a result, the adequacy of transmission network should be evaluated independent of generation system. After introducing the constrained fuzzy power flow (CFPF) as a suitable tool to quantify the adequacy of transmission network to satisfy 'reasonable demands for the transmission of electricity' (as stated, for instance, at European Directive 2009/72/EC), the aim is now showing how this approach can be used in conjunction with probabilistic criteria in security analysis. In classical security analysis models of power systems are considered the composite system (generation plus transmission). The state of system components is usually modeled with probabilities and loads (and generation) are modeled by crisp numbers, probability distributions or fuzzy numbers. In the case of CFPF the component’s failure of the transmission network have been investigated. In this framework, probabilistic methods are used for failures modeling of the transmission system components and possibility models are used to deal with 'reasonable demands'. The enhanced version of the CFPF model is applied to an illustrative case.
- Reliability of distribution networks with microgridsPublication . Costa, Paulo Moisés; Matos, ManuelThe emergence of micro-generation as a technically sound alternative has lead, in recent times, to the concept of micro grid, a network of LV consumers and producers able to export electric energy in some circumstances and also to work in a isolated way in emergency situations. Research work about the organization of micro grids, control devices, functionalities and other technical and economic aspects is presently being carried out, in order to establish a consistent technical framework to support the concept. Among other aspects, the effect of micro grids in the reliability of the distribution network has been pointed out as an important advantage, due to the ability of isolated operation in emergency situations. In order to address this topic, the present paper identifies the situations where the existence of a micro grid may reduce the interruption rate and time and thus improve the reliability indices of the distribution network. The relevant expressions necessary to quantify the reliability are also presented. An illustrative example is included, where the global influence of the micro grid in reliability is commented.