Paulo Moisés Costa

Loss allocation in distribution networks with embedded generation

This 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.

Economic Analysis of Microgrids Including Reliability Aspects

Recently, 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

Reliability of distribution networks with microgrids

The 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.

A Regulatory Framework for Microgeneration and Microgrids

The concept of microgrid (mugrid) has been emerging as a way to integrate microgeneration (muG) in LV networks and simultaneously improve its potential benefits. Technical requirements to connect mugrids to LV networks have been studied in order to make this concept technologically feasible and safe to operate. However, the regulatory framework for economic integration of muG and mugrids on distribution systems, despite being crucial, is still an open issue. The main purpose of this paper is to contribute for the development of an appropriate economic regulation framework that removes the barriers to muG and mugrid development. To do so, the relevant costs and benefits resulting from the establishment of muG and mugrid are identified and a methodology for sharing those costs and benefits among the involved economic agents is presented. The only pre-requisite of such a methodology is that a net benefit to all economic agents exists, which is the case most of the times. An illustrative example is included.

Issues on performance of wind systems derived from exploitation data

Modern wind systems generate electrical energy running at variable rotational speed. Operating as energy generation plants they present a stochastic behavior dependent on random wind speed. So operation performance becomes an issue when it is approached integration into the grid either in terms of quality of delivered power or in terms of generated power available to the transmission system operator. The communication deals with real performance of two types of wind systems integrated into a wind farm. Both the systems are modern ones, running at variable rotational speed, being one based on synchronous electrical generator, another one on asynchronous electrical generator. Approaching a wind system as a production unity whose output is dependent on a stochastic input the authors analyze behavior of the wind systems with the method ¿data envelopment analysis¿. The performed analysis allows at concluding on optimization methods not only driven by theoretical analysis of the wind system but by real operation of the systems. According to global behavior in terms of energy generation the authors discuss some of the reasons for the results found. They conclude pointing out needs of integrating control actions for the wind turbine and the electrical generator based on getting knowledge on the system through data preprocessing and pos-processing allowing at improving global operation.

Architecture of information system for monitoring of photovoltaic plants

The 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.

Progress in Identifying High Nature Value Montados: Impacts of Grazing on Hardwood Rangeland Biodiversity

ABSTRACT Due to their complex structure and traditional low-intensity management, Portuguese oak woodland rangelands known as montados are often considered high nature value (HNV) farming systems, and as such, they may be deemed eligible for subsidies and incentives by governmental and nongovernmental agencies. Too little is known about how the HNV concept might be applied to conserve complex silvopastoral systems. These systems, due to their structural and functional complexity at multiple scales, tend to support high levels of biodiversity. Montados are in sharp decline as a result of the rapid specialization of land management that, through simplification, undermines multifunctionality. Understanding how changes in management influence these systems and their biodiversity is needed for prioritizing conservation efforts and for ensuring they remain HNV systems. On the basis of a field survey in 58 plots distributed among 29 paddocks on 17 farms, we conducted an integrated analysis of the relationship between grazing intensity and biodiversity in montados of similar biophysical and structural characteristics. Data on management were obtained through interviews, and biodiversity data (vegetation, macrofungi, birds, herpetofauna) were obtained through specific field protocols. Additional spatial data, such as soil characteristics, slope, land cover, and linear landscape elements, were also analyzed. The results show no overall biodiversity variation as a result of different management practices. However, different groups of species react differently to specific management practices, and within a pasture, grazing impacts are heterogenous. In low grazing intensity plots, macrofungi species richness was found to be higher, while bird species richness was lower. Using tree regeneration as proxy for montado sustainability, results show less tree regeneration in areas with higher forage quality and more intense grazing. Pathways for future progress are proposed, including creating areas within a paddock that attract grazing away from where regeneration is desired.

Safe operation of transmission system considering EV at distribution level

In this paper, the IEEE 14 bus test system is used in order to perform adequacy assessment of a transmission system when large scale integration of electric vehicles is considered at distribution levels. In this framework, the symmetric/constr ained fuzzy power flow (SFPF/CFPF) was proposed. The SFPF/CFPF models are suitable to quantify the adequacy of transmission network to satisfy “reasonable demands for the transmission of electricity” as defined, for instance, in the European Directive 2009/72/EC. In this framework, electric vehicles of different types will be treated as fuzzy loads configuring part of the “reasonable demands”. With this study, it is also intended to show how to evaluate the amount of EVs that can be safely accommodated to the grid meeting a certain adequacy level.

Flexible power control of photovoltaic plants connected to distribution networks

This 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.

Probabilistic security constrained fuzzy power flow models

In 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 components 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.