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Publications

Publications by CPES

1996

Phasor visualizer for investigation, teaching and control of induction motor

Authors
Araujo, RE; Goncalves, JJ; Tavares, A; Freitas, DS;

Publication
MELECON '96 - 8TH MEDITERRANEAN ELECTROTECHNICAL CONFERENCE, PROCEEDINGS, VOLS I-III: INDUSTRIAL APPLICATIONS IN POWER SYSTEMS, COMPUTER SCIENCE AND TELECOMMUNICATIONS

Abstract
The phasor visualizer presented in this paper is performs real time calculation in steady-state and transient conditions of simultaneous electromagnetic torque, magnetic flux, voltages and currents of an induction motor supplied with sinusoidal voltages or through frequency converters and provide an oscillographic display. The phasor visualizer is an instrument for analysis, investigations and teaching of AC machine drives. The instruments needs no shaft position or speed sensor, it uses exclusively the acquired stator currents and voltages. The main fields of application are: element of a monitoring system, integration in a control unit, research tool for induction motor drives, and test shop. Practical results of the implementation are be presented and discussed.

1996

Conditions for equivalence between the compositional rule of inference and the compatibility modification inference

Authors
Villar, J;

Publication
IEEE International Conference on Fuzzy Systems

Abstract
This paper shows that the compositional rule of inference reduces to the compatibility modification inference, when the antecedent of a fuzzy rule and its input fulfil some properties. Two main types of implications are investigated, those generalizing the classical material conditional (residuated and strong implications), called in this paper m-implications, and those generalizing the classical Cartesian product (t-norms and pseudo-conjunctions), called t-implications. For m-implications, when their maximum modus ponens generating function is used, the compatibility measure depends obviously on the relationship between input and antecedent, but also on the t-norm the implication comes from. Similarly, for t-implications, also used as their own modus ponens generating function, the compatibility measure depends again on the input and antecedent, but also on the t-norm they come from. As it could be expected, in the first case the compatibility measure is a degree of the inclusion of the input into the antecedent, while in the second one it is a degree of the intersection of both.

1995

REAL-TIME PREVENTIVE ACTIONS FOR TRANSIENT STABILITY ENHANCEMENT WITH A HYBRID NEURAL-NETWORK - OPTIMIZATION APPROACH

Authors
MIRANDA, V; FIDALGO, JN; LOPES, JAP; ALMEIDA, LB;

Publication
IEEE TRANSACTIONS ON POWER SYSTEMS

Abstract
This paper reports a new approach in defining preventive control measures to assure transient stability relatively to one or several contingencies that may occur separately in a power system. Generation dispatch is driven not only by economic functions but also with the derivatives of the transient energy margin value; these derivatives are obtained directly from a trained Artificial Neural Network (ANN), using ri:al time monitorable system values. Results obtained from computer simulations, for several contingencies in the CIGRE test system, confirm the validity of the developed approach.

1995

Generation transmission power system reliability evaluation by Monte-Carlo simulation assuming a fuzzy load description

Authors
SARAIVA, JT; MIRANDA, V; PINTO, LMVG;

Publication
1995 IEEE POWER INDUSTRY COMPUTER APPLICATION CONFERENCE, CONFERENCE PROCEEDINGS

Abstract
This paper presents a Monte-Carlo algorithm considering loads defined by fuzzy numbers. In this methodology states are sampled according to the probabilistic models governing the life cycle of system components while fuzzy concepts are used to model uncertainty related to future load behavior. This model can be used to evaluate generation/transmission power system reliability for long term planning studies as one uses the more adequate uncertainty models for each type of data. For each sampled state a Fuzzy Optimal Power Flow is run so that one builds its power not supplied membership function. The paper proposes new indices reflecting the integration of probabilistic models and fuzzy concepts and discusses the application of variance reduction techniques if loads are defined by fuzzy numbers. A case-study based on the IEEE 30 bus system illustrates this methodology.

1995

Electric distribution systems planning with fuzzy loads

Authors
Matos M.A.; Ponce de Leão M.T.;

Publication
International Transactions in Operational Research

Abstract
Distribution systems planning heavily depends on the predicted future consumptions in the service area. When statistical data exist about past consumptions, probabilistic forecasting methods may be applied, and expected cost/benifit and risk analysis are used to decide between different solutions. In most cases, however, this strategy is not applicable, due mainly to the lack of significant data (new developing areas, rapidly changing situations) and uncertainty of economic and social factors. In the latter case, the use of fuzzy models is an interesting alternative, accommodating expert planner's qualitative judgments about future loads and allowing us to use 'typical' load diagrams in new areas. The paper discusses the main concepts of electric distribution system planning when loads are fuzzy modeled, and presents an illustrative application example. © 1995.

1995

On-line decoupled algorithm for state estimation and bad data processing using hypothesis tests

Authors
Ferreira Isabel, M; Barbosa, FPM;

Publication
Proceedings of the Universities Power Engineering Conference

Abstract
This paper presents an approach to the Dynamic State Estimation (DSE) problem to determine the real-time state of an electric power system under quasi-static operating conditions. Bearing in mind the large dimension of power systems, a new DSE algorithm is proposed in order to give a satisfactory solution from the computational point of view for the following steps of the DSE procedure: state forecasting, state filtering and detection and identification of bad data. Simulation results show the performance of the proposed algorithm under different operational conditions: normal, sudden change in the system operating point and occurrence of bad data.

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