Rita A. Ribeiro

Fuzzy multiple attribute decision making: a review and new preference elicitation techniques

Abstract This paper reviews the main theories and methods used for multiple attribute decision making in a fuzzy environment. Fuzzy multiple attribute decisions involve two processes, the rating and the ranking of alternatives. If the rating results are crisp then the ranking procedure becomes straightforward; hence, the emphasis of this paper is on obtaining crisp ratings for alternatives. In order to aid the decision maker to express his/her attribute preferences, new elicitation techniques to determine attributes importance are proposed. These techniques range from statistical to scaling methods based on linguistic variables, and so enable a more versatile elicitation procedure as well as providing crisp preferences.

A framework for dynamic multiple-criteria decision making

The classic multiple-criteria decision making (MCDM) model assumes that, when taking a decision, the decision maker has defined a fixed set of criteria and is presented with a clear picture of all available alternatives. The task then reduces to computing the score of each alternative, thus producing a ranking, and choosing the one that maximizes this value. However, most real-world decisions take place in a dynamic environment, where the final decision is only taken at the end of some exploratory process. Exploration of the problem is often beneficial, in that it may unveil previously unconsidered alternatives or criteria, as well as render some of them unnecessary. In this paper we introduce a flexible framework for dynamic MCDM, based on the classic model, that can be applied to any dynamic decision process and which is illustrated by means of a small helicopter landing example. In addition, we outline a number of possible applications in very diverse fields, to highlight its versatility.

Vector and scalar control of a four switch three phase inverter

This paper investigates the PWM operation of a four switch three phase inverter (FSTPI), in the case of digital implementation. Different switching sequence strategies for vector control are described and a digital scaler method is also presented. The influence of different switching patterns on the output voltage symmetry, current waveform and switching frequency are examined. The results obtained by employing the vector and scalar strategies are compared and a relationship between them is established. This comparison is based on analytical study and is corroborated by the computer simulations and by the experimental results. The vector approach makes it easy to understand and analyse the FSTPI, as well the choice of a PWM pattern. However, similar results may be obtained through the scalar approach, which has a simpler implementation. The experimental results of the use of the FSTPI and digital PWM to control an induction motor are presented.

Aggregation with generalized mixture operators using weighting functions

This paper regards weighted aggregation operators in multiple attribute decision making and its main goal is to investigate ways in which weights can depend on the satisfaction degrees of the various attributes (criteria). We propose and discuss two types of weighting functions that penalize poorly satisfied attributes and reward well-satisfied attributes. We discuss in detail the characteristics and properties of both functions. Moreover, we present an illustrative example to clarify the use and behaviour of such weighting functions, comparing the results with those of standard weighted averaging operators.

Composition of plastics from waste electrical and electronic equipment (WEEE) by direct sampling.

This paper describes a direct analysis study carried out in a recycling unit for waste electrical and electronic equipment (WEEE) in Portugal to characterize the plastic constituents of WEEE. Approximately 3400 items, including cooling appliances, small WEEE, printers, copying equipment, central processing units, cathode ray tube (CRT) monitors and CRT televisions were characterized, with the analysis finding around 6000 kg of plastics with several polymer types. The most common polymers are polystyrene, acrylonitrile-butadiene-styrene, polycarbonate blends, high-impact polystyrene and polypropylene. Additives to darken color are common contaminants in these plastics when used in CRT televisions and small WEEE. These additives can make plastic identification difficult, along with missing polymer identification and flame retardant identification marks. These drawbacks contribute to the inefficiency of manual dismantling of WEEE, which is the typical recycling process in Portugal. The information found here can be used to set a baseline for the plastics recycling industry and provide information for ecodesign in electrical and electronic equipment production.

Generalized mixture operators using weighting functions: A comparative study with WA and OWA

Abstract In the context of multiple attribute decision making, we present an aggregation scheme based on generalized mixture operators using weighting functions and we compare it with two standard aggregation methods: weighted averaging and ordered weighted averaging. Specifically, we consider linear and quadratic weight generating functions that penalize bad attribute performances and reward good attribute performances. An illustrative example, borrowed from the literature, is used to perform the operators’ comparison. We believe that this comparative study will highlight the potential and flexibility of generalized mixture operators using weighting functions that depend on attribute performances.

Reduced Switch Count DC-Link AC–AC Five-Leg Converter

This paper investigates a reduced switch count dc-link ac-ac five-leg converter for three-phase power conversion. The converter provides both an input rectifier and an output inverter by sharing a leg in order to reduce the number of power switches. Scalar and vector pulsewidth modulation techniques are presented and the concepts of local and global apportioning factors are introduced. A control technique that aims at maximizing the utilization of the dc-link voltage is proposed. A hysteresis current controller that allows operating with one leg being shared by the load and grid sides is developed. In addition, several relevant characteristics of the converter are addressed, such as voltage capability, harmonic distortion, shared-leg and capacitor currents, and power rating. The features of such a converter are compared to those of the six-leg and four-leg converters. Selected experimental results are presented

A fault tolerant induction motor drive system by using a compensation strategy on the PWM-VSI topology

This paper proposes the possibility of developing fault diagnosis and remedial operating strategies, which enable a fault tolerant induction motor drive system. The fault mode investigated is the case in which a misfiring does occur in one of the power switches. The fault diagnosis is achieved by using a strategy that permits both identification and isolation of the faulty components. The fault tolerance is obtained by reconfiguration of the inverter topology. This allows for continuous free operation of the drive even with complete loss of one of the legs of the inverter. Experimental results demonstrate the validity of the system proposed.

Fault detection in voltage-fed PWM motor drive systems

This paper investigates the use of different techniques for fault detection in voltage-fed asynchronous machine drive systems. With the proposed techniques it is possible to detect and to identify in which power switch the failure has occurred. The detection of the fault condition requires the measurement of voltages and currents and is based on analytical models of both the voltage source inverter and the asynchronous machine. Simulation and experimental results are presented to demonstrate the correctness of the proposed techniques. The results obtained indicate that it is possible to embed some fault-tolerant properties for the voltage-fed asynchronous machine drive system.

Handling conflicts in aspectual requirements compositions

Composing aspectual concerns with base concerns may raise conflicting situations that need to be identified and resolved. A conflict is detected whenever two or more concerns that contribute negatively to each other and have the same importance need to be composed together. This paper discusses the use of Multiple Criteria Decision Making (MCDM) methods to support aspectual conflict management in the context of Aspect-Oriented Requirements Engineering. The final solution relies on the use of the obtained concern rankings to handle unresolved conflicts. An illustrative example is presented to discuss how MCDM methods can be used for aspectual conflict handling.