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Publicações

Publicações por CPES

2007

EPREV - A wind power forecasting tool for Portugal

Autores
Rodrigues, A; Lopes, JA; Miranda, P; Palma, J; Monteiro, C; Sousa, JN; Bessa, RJ; Rodrigues, C; Matos, J;

Publicação
European Wind Energy Conference and Exhibition 2007, EWEC 2007

Abstract
Wind energy experiences in Portugal an increasing interest. Slightly more than 1700 MW were operating by the end of 2006, in a system with a global capacity of about 12 GW (8,5 GW peak demand). Several new wind farms are under construction and a considerable amount of connection points are or will be granted in the coming years. More than 5000 MW are expected to be connected to the grid around 2012, the global generating capacity being then about 16 GW. Clearly, a wind power forecasting system must be implemented that will help to deal with the significant penetration of the technology in the electrical system. A group of wind farm promoters, owning the majority of the capacity installed so far, ordered to a consortium of universities and research institutes the development of a forecasting tool, giving rise of the EPREV project, wholly financed by them. The system will have the following main characteristics: Wind speed and active power forecasting up to 72 hours; Evaluation of the forecasting uncertainty; Possibility of using the predictions of physical models and the information from the wind farm Supervisory Control And Data Acquisition (SCADA); Capacity of predicting only with SCADA information for very short term. The main components of the system are: A human-machine-interface, allowing the control of the system, the selection and aggregation of forecasting models and the visualization of results; A power forecasting model for individual wind turbines and for wind farms. A cascade of models is used, starting in the mesoscale simulation, with up to 2 km resolution. The outputs of the mesoscale models are corrected and statistically adapted to the fine scale conditions. Two models and different boundary conditions are run, in three nested domains (54x54, 18x18 and 6x6 km). The advantage of using a 2x2 km resolution is also tested. The statistical models are fed with recent information from the wind farms, after a learning process that made use of the historical information of its operation. Three different types of statistical models are employed: Power Curve Model (PCM), Auto Regressive (AR) and Neural Network Assembling Model (NNAM). The wind simulation at the wind farm scale is done both by linearized physical models and Computational Fluid Dynamics (CFD) models, namely using VENTOS®, a code developed at the University of Porto. The duration of the project is planned to be 1 year, including off-line tests of the complete system for 3 wind farms, for performance evaluation purposes.

2007

Experimental evaluation on parameter identification of induction motor using continuous-time approaches

Autores
Cerqueira, NM; Soares, JR; de Castro, RP; Oliveira, HS; Araujo, RE;

Publicação
POWERENG2007: INTERNATIONAL CONFERENCE ON POWER ENGINEERING - ENERGY AND ELECTRICAL DRIVES PROCEEDINGS, VOLS 1 & 2

Abstract
This paper evaluates parameter identification of induction motor (IM) using two different methods. The proposed methods provide an accurate estimation on the parameters for the IM steady state model. Both algorithms were tested with real data and then used to estimate the parameters of the motor. The disturbances in the acquired signals were reduced using some signal processing techniques. The processed signals were then applied in both identification procedures. The first method is based on optimization by nonlinear least squares algorithm that permits establishing convergence constrains, avoiding impossible physical results. The second is an indirect method that allows keeping the physical meaning of the continuous time parameters when converting to discrete time domain. The effectiveness of the proposed methods is verified by experimental tests and results of the methods are discussed.

2007

A new FPGA based control system for electrical propulsion with electronic differential

Autores
de Castro, RP; Oliveira, HS; Soares, JR; Cerqueira, NM; Araujo, RE;

Publicação
2007 EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS, VOLS 1-10

Abstract
In this paper we present a new fully integrated control system in a System-on-Chip (SoC) suitable to implement the controller for a Neighbourhood Electric Vehicle (NEV) based on FPGA (Field Programmable Gate Array) technology. A prototype has been designed specifically to meet the requirement of low cost and it contains all of the active functions required to implement the electronic differential. The controller uses Field Oriented Control (FOC) techniques with offline parametric identification of the motors to enhance its performance. A PC based user interface allows easy controller configuration, data acquisition and performance analysis. The functionality of the electronic differential is verified through experiments with a bench test equipment equivalent to the actual system. The experimental results show that the proposed controller is able to follow the reference torque and curvature angle with a good dynamic and relatively low error.

2007

Long-term price range forecast applied to risk management using regression models

Autores
Azevedo, F; Vale, ZA; Oliveira, PBM;

Publicação
2007 INTERNATIONAL CONFERENCE ON INTELLIGENT SYSTEMS APPLICATIONS TO POWER SYSTEMS, VOLS 1 AND 2

Abstract
Long-term contractual decisions are the basis of an efficient risk management. However those types of decisions have to be supported with a robust price forecast methodology. This paper reports a different approach for long-term price forecast which tries to give answers to that need. Making use of regression models, the proposed methodology has as main objective to find the maximum and a minimum Market Clearing Price (MCP) for a specific programming period, and with a desired confidence level a. Due to the problem complexity, the meta-heuristic Particle Swarm Optimization (PSO) was used to find the best regression parameters and the results compared with the obtained by using a Genetic Algorithm (GA). To validate these models, results from realistic data are presented and discussed in detail.

2007

A decision-support system based on particle swarm optimization for multiperiod hedging in electricity markets

Autores
Azevedo, F; Vale, ZA; de Moura Oliveira, PBD;

Publicação
IEEE TRANSACTIONS ON POWER SYSTEMS

Abstract
This paper proposes a particle swarm optimization (PSO) approach to support electricity producers for multiperiod optimal contract allocation. The producer risk preference is stated by a utility function (U) expressing the tradeoff between the expectation and variance of the return. Variance estimation and expected return are based on a forecasted scenario interval determined by a price range forecasting model developed by the authors. A certain confidence level a is associated to each forecasted scenario interval. The proposed model makes use of contracts with physical (spot and forward) and financial (options) settlement. PSO performance was evaluated by comparing it with a genetic algorithm-based approach. This model can be used by producers in deregulated electricity markets but can easily be adapted to load serving entities and retailers. Moreover, it can easily be adapted to the use of other type of contracts.

2007

Connecting the intraday energy and reserve markets by an optimal redispatch

Autores
Garcia Gonzalez, J; Roque, AMS; Campos, FA; Villar, J;

Publicação
IEEE TRANSACTIONS ON POWER SYSTEMS

Abstract
Electricity markets based on simple bids provide a very high degree of transparency and simplicity. However, simple bids fail to capture many well-known characteristics of generating units and, therefore, the responsibility for obtaining feasible schedules is transferred to market participants. The purpose of this paper is to help the generating utility to automatically analyze the last energy program cleared in the market and, in case this program is technically unfeasible, to provide an alternative schedule by redispatching the generating units. This is achieved by formulating an optimization problem where the objective is to find the cheapest and feasible instantaneous power trajectory of each generator, trying to minimize the differences between its hourly average values and the last energy program. As the objectives of the utility can vary during the day, three different models are presented. Two of them are formulated as a joint energy and reserve dispatch in order to take into account possible commitments acquired in the ancillary services market of AGC regulation. In this sense, a novel approach for considering discontinuous ancillary regulation curves is proposed. Some numerical examples are included to illustrate the essential features of the models.

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