Browsing by Author "Cunha, J. Boaventura"
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- Adaptable control for electrical generation at irregural wind speedsPublication . Puga, Ricardo; Ferreira, Judite; Cunha, J. Boaventura; Vale, ZitaThe main aims of this work are the development and the validation of one generic algorithm to provide the optimal control of small power wind generators. That means up to 40 kW and blades with fixed pitch angle. This algorithm allows the development of controllers to fetch the wind generators at the desired operational point in variable operating conditions. The problems posed by the variable wind intensity are solved using the proposed algorithm. This is done with no explicit measure of the wind velocity, and so no special equipment or anemometer is required to compute or measure the wind velocity.
- An evolutionary hybrid Approach in the design of combinational digital circuitsPublication . Reis, Cecília; Tenreiro Machado, J. A.; Cunha, J. BoaventuraThis paper presents a hybrid genetic algorithm, also know as memetic Algorithm (MA), applied to the design of combinational logic circuits. In view of the fact that hybrid algorithms have shown to be very effective in solving many hard combinatorial optimization approaches, The main idea is to apply a local refinement to an evolutary Algorithm (EA) in order to improve the fitness of the individuals in the population. The results show an improvement of the final fitness function followed by a reduction of the average number of generations required to reach the solutions and its standard deviation, for all the tested circuits.
- Analysis of Two Arms Working in CooperationPublication . Ferreira, N. M. Fonseca; Machado, J. A. Tenreiro; Cunha, J. BoaventuraThis paper analyzes the performance of two cooperative robot manipulators. In order to capture the working performancewe formulated several performance indices that measure the manipulability, the effort reduction and the equilibrium between the two robots. In this perspective the proposed indices we determined the optimal values for the system parameters. Furthermore, it is studied the implementation of fractional-order algorithms in the position/force control of two cooperative robotic manipulators holding an object.
- Application of Genetic Algorithms to the Implementation of Fractional Electromagnetic PotentialsPublication . Jesus, Isabel S.; Tenreiro Machado, J. A.; Cunha, J. BoaventuraA genetic algorithm (GA) is a search technique based on the natural selection process. The GAs provide further flexibility and robustness that are unique for signal process. Recently, a closer look of some phenomena present in electrical systems, such as motors, transformers and lines, and the motivation towards the development of comprehensive models, seem to point out the requirement for a fractional calculus approach. Bearing these ideas in mind, we address the analysis and the synthesis of fractional-order multipoles, based in a GA optimization scheme.
- Circuit Synthesis Using Particle Swarm OptimizationPublication . Reis, Cecília; Tenreiro Machado, J. A.; Galhano, Alexandra; Cunha, J. BoaventuraParticle Swarm Optimization (PSO) is a population-based search algorithm that is initialized with a population of random solutions, called particles. In a PSO scheme each particle flies through the search space with a velocity that is adjusted dynamically according with its historical behavior. Therefore, the particles have a tendency to fly towards the best search area along the search process. PSO is also an evolutionary computation technique well adapted to the automatic design of electronic devices. In this line of thought, this paper proposes a PSO based algorithm for logic circuit synthesis. The results show the statistical characteristics of this algorithm with respect to number of generations required to achieve the solutions. The results are compared with other two Evolutionary Algorithms (EAs), namely Genetic and Memetic Algorithms (GA and MA).
- Digital Circuit Design Using Dynamic Fitness FunctionsPublication . Reis, Cecília; Tenreiro Machado, J. A.; Cunha, J. BoaventuraThis paper proposes and analyses the performance of a Genetic Algorithm using two new concepts, namely a static fitness function including a discontinuity measure and a fractional-order dynamic fitness function, for the synthesis of combinational logic circuits. In both cases, experiments reveal superior results in terms of speed and convergence to achieve a solution.
- Electrical Skin Phenomena: A Fractional Calculus AnalysisPublication . Machado, J. A. Tenreiro; Jesus, Isabel; Galhano, Alexandra; Cunha, J. Boaventura; Tar, J. K.The internal impedance of a wire is the function of the frequency. In a conductor, where the conductivity is sufficiently high, the displacement current density can be neglected. In this case, the conduction current density is given by the product of the electric field and the conductance. One of the aspects the high-frequency effects is the skin effect (SE). The fundamental problem with SE is it attenuates the higher frequency components of a signal. The SE was first verified by Kelvin in 1887. Since then many researchers developed work on the subject and presently a comprehensive physical model, based on the Maxwell equations, is well established. The Maxwell formalism plays a fundamental role in the electromagnetic theory. These equations lead to the derivation of mathematical descriptions useful in many applications in physics and engineering. Maxwell is generally regarded as the 19th century scientist who had the greatest influence on 20th century physics, making contributions to the fundamental models of nature. The Maxwell equations involve only the integer-order calculus and, therefore, it is natural that the resulting classical models adopted in electrical engineering reflect this perspective. Recently, a closer look of some phenomas present in electrical systems and the motivation towards the development of precise models, seem to point out the requirement for a fractional calculus approach. Bearing these ideas in mind, in this study we address the SE and we re-evaluate the results demonstrating its fractional-order nature.
- Electrical skin phenomena: a fractional calculus analysisPublication . Machado, J. A. Tenreiro; Jesus, Isabel S.; Galhano, Alexandra; Cunha, J. Boaventura; Tar, József K.The internal impedance of a wire is the function of the frequency. In a conductor, where the conductivity is sufficiently high, the displacement current density can be neglected. In this case, the conduction current density is given by the product of the electric field and the conductance. One of the aspects of the high-frequency effects is the skin effect (SE). The fundamental problem with SE is it attenuates the higher frequency components of a signal.
- Evolutionary Computation in the Design of Logic CircuitsPublication . Reis, Cecília; Tenreiro Machado, J. A.; Cunha, J. Boaventura; Pires, E. J. SolteiroThis paper presents two evolutionary schemes and a swarm intelligence algorithm for the design of combinational logic circuits. A Genetic and a Memetic schemes as the evolutionary algorithms. The Particle Swarm Optimization as the swarm algorithm. The fitness function used in these three algorithms is sequential, that is, divided in two parts. The first part of the fitness function f1 evaluates the circuit functionality, while the second part f2 deals with the circuit complexity. The experiments consist in applying the algorithms in the design of two arithmetic circuits: the one-bit full adder and the one-bit full subtractor. We also present a scalability analysis using the parity checker family of circuits.
- Evolutionary design of combinational circuits using fractional-order fitness functionsPublication . Reis, Cecília; Tenreiro Machado, J. A.; Cunha, J. BoaventuraThis paper analyses the performance of a genetic algorithm using the new concept of fractional-order dynamic fitness function, for the synthesis of combinational logic circuits. The experiments reveal superior results in terms of speed and convergence to achieve a solution.