J. Boaventura Cunha

Fractional order electromagnetics

The Maxwell equations constitute a formalism for the development of models describing electromagnetic phenomena. The four Maxwell laws have been adopted successfully in many applications and involve only the integer order differential calculus. Recently, a closer look for the cases of transmission lines, electrical motors and transformers, that reveal the so-called skin effect, motivated a new perspective towards the replacement of classical models by fractional-order mathematical descriptions. Bearing these facts in mind this paper addresses the concept of static fractional electric potential. The fractional potential was suggested some years ago. However, the idea was not fully explored and practical methods of implementation were not proposed. In this line of thought, this paper develops a new approximation algorithm for establishing the fractional order electrical potential and analyzes its characteristics.

Real-time parameter estimation of dynamic temperature models for greenhouse environmental control

Abstract For a greenhouse located at UTAD-University, the methods used to estimate (in real-time) the parameters of the inside air temperature model will be described. The structure and the parameters of the climate discrete-time dynamic model were previously identified using data acquired during two different periods of the year. Several experiments showed that the second-order models identified achieve a close agreement between simulated and experimental data. Later, it was found that parameters change with varying operational conditions. Thus, for an efficient use of these models in real-time control, a recursive identification technique was implemented for the estimation of the parameters.

A networked platform for agricultural management systems

Greenhouse control computers are an essential part of modern greenhouse operation. Climate, irrigation and nutrient supply must be controlled, in an economical way, to produce the best crop conditions. Current research on CO 2 enrichment and optimal growth strategies implies the use of powerful tools, either based on hardware or software. This paper describes the design and implementation of a distributed data acquisition and control system for computerised agricultural management systems that is being developed at Universidade of Tras-os-Montes and Alto Douro, Vila Real. Different communications platform concepts, such as Controller Area Network (CAN), Wireless Technologies, Ethernet and Internet tools supported by Transfer Control Protocol/Internet Protocol (TCP/IP) and e-mail tools supported by Simple Mail Transfer Protocol (SMTP) were used to achieve a network with a low-cost, flexible, and functional characteristics. The system management and maintenance tasks are divided into two types of performance levels. At a lower supervision level, a Local Controller placed in the greenhouses performs the monitoring/control and communications actions. The management decisions are performed at the higher level. The techniques and tools, which provide to the user a transparent, friendly and intuitive Graphical User Interface (GUI) will be presented.

Solar data acquisition wireless network for agricultural applications

This paper describes the implementation of a wireless data acquisition network for agricultural applications based on the Microchip PIC16C71, and the Intel 87C592 microcontrollers. The system uses a set of solar powered wireless data-acquisition stations (SPWAS) linked by radio frequency to a base station (BS). The base station has as main functions the control of the data-acquisition stations and the storage of the data collected by them. The network has been applied to collect outdoor and indoor climate data from a set of greenhouses located at Universidade de Tras-os-Montes e Alto Douro (UTAD), in the northwest of Portugal. Experimental tests have been done since mid June 1996, and the results obtained show that the communications to the BS were performed without errors or loss of data.

Greenhouse air temperature control using the particle swarm optimisation algorithm

Abstract The particle swarm optimisation algorithm is proposed as a new method to design a model based predictive controller subject to restrictions. Its performance is compared with the one obtained by using a genetic algorithm for the environmental temperature control of a greenhouse. Controller outputs are computed in order to optimise future behaviour of the greenhouse environment, regarding set-point tracking and minimisation of the control effort over a prediction horizon of one hour with a one-minute sampling period.

FRACTIONAL ELECTRICAL DYNAMICS IN FRUITS AND VEGETABLES

Abstract Fractional calculus (FC) was originally developed in a pure mathematical viewpoint. However, nowadays FC is applied in many emerging fields of physics and engineering. This paper studies the fractional electrical impedance of vegetables and fruits having FC modelling in mind. In this line of thought, are developed several experiments for measuring the impedance of botanical elements, based in the Bode and polar diagrams. An electrical circuit that models these systems is presented and conclusions are drawn.

Teaching particle swarm optimization through an open-loop system identification project

The particle swarm optimization (PSO), one of the most successful natural inspired algorithms, is revisited in the context of a proposal for a new teaching experiment. The problem considered is the open‐loop step identification procedure, which is studied as an optimization problem. The PSO canonical algorithm main issues addressed within the proposed open‐loop step identification experience are: the swarm random initialization methodology, the population size variation, and the inertia weight selection. The teaching experience learning outcomes are stated, simulation results presented, and feedback results from students analyzed.

Soil moisture sensor with built-in fault-detection capabilities

A soil moisture sensor (SMS) was built around a RISC-like microcontroller and common peripherals to perform data acquisition, signal processing, configuration, fault-detection and data communication with control/management systems. The SMS employs capacitance and heat-pulse techniques to determine the soil water content. The sensor uses the capacitance technique as the main method while the heat-pulse readings, acquired at a lower rate, are used for calibration and fault detection purposes. The temperature sensors and the heater were assembled in a four-needle probe. Several experiments were conducted for different types of soil. The results showed that this sensor could be applied in an effective way to measure the soil water content. Several tests are being performed to conclude about the sensor dependence with soil temperature and chemical composition as well about its long-term stability.

Multi-Objective Particle Swarm Optimization Design of PID Controllers

A novel variant of a multi-objective particle swarm optimization algorithm is reported. The proposed multi-objective particle swarm optimization algorithm is based on the maximin technique previously proposed for a multi-objective genetic algorithm. The technique is applied to optimize two types of problems: firth to a set of benchmark functions and second to the design of PID controllers regarding the classical design objectives of set-point tracking and output disturbance rejection.

Real-Time Parameter Estimation of Dynamic Temperature and Humidity Models for Greenhouse Adaptive Climate Control

Abstract A real-time parameter estimator for the climate discrete-time dynamic models of a greenhouse located at the North of Portugal are presented. The experiments showed that the second-order models identified for the air temperature and humidity achieve a close agreement between simulated and experimental data. The real-time data acquisition and the recursive identification techniques implemented are used in the simulation and design of an adaptive climate controller to achieve set-point accuracy and minimisation of the energy inputs.