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- Aplicação de técnicas de identificação paramétrica ao motor de indução trifásicoPublication . Leite, VicenteCom o desenvolvimento das teorias de controlo e das tecnologias de aquisição e processamento de dados, nomeadamente, processadores digitais de sinal (DSP), o motor de indução trifísico tem vindo a substituir o tradicional motor de corrente contínua, como principal meio de accionamento nas aplicações de controlo industriais. Se associarmos a este desenvolvimento, as características mais importantes do motor de indução trifásico, como a robustez, a ausência de manutenção e o preço, compreendemos as razões pelas quais é hoje, o motor mais utilizado na indústria.
- Overvoltage protection for grid-connected picohydro generation using photovoltaic invertersPublication . Scotta, Isabella Cristina; Maidana, Wellington; Leite, VicenteVery small-scale hydropower plants are environmentally friendly and renewable resource-based innovative solutions. The interest in pico-hydro systems (up to 5 kW) has increased significantly from the first stand-alone applications, at remote sites, to the distributed generation, with the injection of generated energy into the grid. Recently, there have been advances in the grid connection of these systems using off-the-shelf components, namely photovoltaic inverters. Therefore, pico-hydro systems have gained an enormous potential in distributed generation, particularly in the context of microgrids. However, in situations of over-power, or whenever the generator is under no load, e.g. when the grid fails, there is a need for effective over-voltage protection, as in small wind turbines. This paper proposes two over-voltage protection circuits, designed to ensure the integration of pico-hydro turbines connected to the grid using conventional photovoltaic microinverters and string inverters, for power ranges of 300 W and some kW, respectively. Extensive tests were performed on an emulation platform and a workbench using these two different over-voltage protection circuits. One is designed to connect the generators of water wheels to the grid and the other to connect 1,500 W generators of water turbines. The experimental results demonstrated the performance of the proposed over-voltage protection circuits in four different situations. Both avoid irreversible damages of generators, photovoltaic microinverters and string inverters in the context of the above-described grid connection approach.
- An integrated test bench for research, study or demonstration of variable speed drives of induction motorsPublication . Teixeira, Henrique José Alves; Leite, Vicente; Batista, José; Araújo, Rui Esteves; Freitas, Diamantino SilvaThis paper presents an integrated and low cost test bench for teaching and R&D purposes in variable speed drives of induction motors. The test bench is composed by different integrated sub-systems and the resulting platform is suitable for control, parameter estimation and condition monitoring of induction machines controlled by electrical drives
- Sliding mode controllers for the regulation of DC-DC power convertersPublication . Araújo, Rui Esteves; Leite, V.; Freitas, Diamantino SilvaSliding mode controllers are derived for the control of the average output voltage in DC/DC power converters. The controller design is carried out on the basis of well-known bilinear models of such circuits. A cascaded control structure is chosen for ease of control realization and to exploit the motion separation property of this power converter. The performance of the proposed sliding mode controllers is tested for the buck and boost converter type. The numerical simulations will demonstrate the efficiency of sliding mode techniques in this field as a powerful alterative to other existing methods.
- A real-time estimator of electrical parameters for vector controlled induction motor using a reduced order extended Kalman filterPublication . Leite, V.; Araújo, Rui Esteves; Freitas, Diamantino Silva
- Assessment of energy use and energy efficiency in two portuguese slaughterhousesPublication . Feliciano, Manuel; Rodrigues, Filipe; Gonçalves, Artur; Santos, José M.R.C.A.; Leite, VicenteWith the objective of characterizing the profile and performance of energy use by slaughterhouses, surveys and audits were performed in two different facilities located in the northeastern region of Portugal. Energy consumption from multiple energy sources was assessed monthly, along with production and costs, for the same reference year. Gathered data was analyzed to identify and quantify the main consuming processes and to estimate energy efficiency indicators for benchmarking purposes. Main results show differences between the two slaughterhouses concerning energy sources, consumption by source and sector, and global energy efficiency. Electricity is the most used source in both slaughterhouses with a contribution of around 50%, being essentially used for meat processing and refrigeration. Natural gas, in slaughterhouse A, and pellets, in slaughterhouse B, used for heating water take the second place, with a mean contribution of about 45%. On average, a 62 kgoe/t specific energy consumption (SEC) was found, although with differences between slaughterhouses. A prominent negative correlation between SEC and carcass production was found specially in slaughterhouse A. Estimated Specific Energy Cost and Greenhouse Gases Intensity (GHGI) show mean values of about 50 €/t and 1.8 tCO2e/toe, respectively. Main results show that there is a significant margin for improving energy efficiency and therefore lowering costs in this type of non-energy intensive industries.
- Photovoltaic water pumping system for small power conventional AC pumpsPublication . Tangerino, Bruno Henrique Boschetti; Roman, Dionizio José Vargas; Leite, V.; Goedtel, Alessandro; Ferreira, Ângela P.; Batista, José; Maidana, WellingtonThe interest of photovoltaic (PV) water pumping systems with standard components is increasing as a low cost and independent solution over dedicated systems. However, one of the challenges of this alternative is the fact that small power systems to drive power pumps require a small number of PV modules and the PV string voltage is, usually, not enough to feed the frequency converter. This paper presents an approach to the drive, using a DC/DC converter with maximum power point tracking (MPPT). The overall system has been tested on a real experimental platform.
- Grid-connection approaches for pico-hydro systemsPublication . Leite, V.; Ferreira, Ângela P.; Couto, José; Batista, JoséSmall hydropower systems are considered an environmentally friendly energy option. They have a huge untapped potential which allow it to make a more significant contribution to future energy demand with many advantages. Grid-connected pico-hydro systems are an emerging solution for application in a huge number of applications such as in household water supply, wastewater treatment facilities and to improve control systems and optimize generation as a part of integrated water management systems. They are also very promising for integration in microgrids in many developing countries. This paper presents and discusses the main three grid-connection approaches for pico-hydro systems: using specifically designed power converters; using standard wind inverters; and using standard photovoltaic inverters. These latest approaches based on conventional inverters are practical solutions able to explore a large amount of feasible sites with low-head and very low-head. Moreover, photovoltaic micro inverters, recently launched in the market, are propose for very low power generators (250-300 W). These approaches improve efficiencies, reduce costs and environmental impacts and improve reliability. Experimental evaluation of the performance in steady-state and in dynamic conditions proves the feasibility of these innovative approaches.
- Analyses of MPPT algorithms in real test conditionsPublication . Guimarães, Thiago Fialho; Leite, VicenteMaximum Power Point Tracking (MPPT) algorithms are of major importance for optimized yield in gridconnected PV systems. Many algorithms have been investigated. However, most of the works compare these algorithms based on a literature review or on simulation. This paper presents an experimental analysis of MPPT techniques: two of the simplest (Perturb & Observe and Incremental Conductance) and two of the most complex (Fuzzy Logic Controller and Particle Swarm Optimization). The results are carried out in real test conditions, with and without shadow. The power converter is based on a boost converter and a voltage source inverter. The control is implemented using Simulink® and dSPACE 1103 real-time controller board. Moreover, the MPPT techniques of three commercial string inverters are also analysed.
- Estimação de estados, parâmetros e velocidade do motor de indução trifásico com metodologias de identificação em tempo realPublication . Leite, VicenteAs leis de controlo dos sistemas electrónicos de accionamento do motor de indução trifásico, em aplicações de velocidade variável, utilizando técnicas de controlo recentes e de elevado desempenho, designadamente, o controlo vectorial, requerem o conhecimento preciso dos parâmetros eléctricos do motor. A variação destes parâmetros, ao longo do tempo, afecta o desempenho das leis de controlo, sendo necessário proceder à sua estimação durante o funcionamento normal do motor. Neste contexto, são estudados procedimentos de modelação e identificação paramétricas, com o objectivo de obter modelos descritos directamente pelos parâmetros físicos do motor, ou por outros, a partir dos quais aqueles possam ser obtidos. Nesta dissertação, são desenvolvidos novos procedimentos de modelação, na representação de espaço de estados, que permitem estimar, conjuntamente, estados e parâmetros eléctricos do motor de indução. A estimação, em tempo real, é realizada utilizando o algoritmo do filtro de Kalman estendido (EKF – Extended Kalman Filter), dada a sua natureza recursiva e sua adequação a modelos não lineares e variantes no tempo, sob a forma de espaço de estados. Tendo em conta a elevada dimensão dos modelos e esforço computacional do EKF, para aplicações em tempo real, são introduzidos, nesta dissertação, procedimentos inovadores para a redução da ordem e uma nova forma de discretização dos modelos de espaço de estados no tempo contínuo. Aos modelos de ordem reduzida obtidos, é aplicado o EKF, para a estimação conjunta das componentes do fluxo do rotor e dos parâmetros eléctricos. Os mesmos modelos são também utilizados para a estimação conjunta do fluxo do rotor e da velocidade angular do motor de indução. Atendendo ao peso computacional do EKF e às dificuldades específicas da estimação de grandezas associadas ao motor de indução, é desenvolvido um conjunto de modelos lineares simples, para a estimação dos parâmetros do estator, utilizando métodos recursivos de erro de predição, nomeadamente, o algoritmo do gradiente, o método recursivo de mínimos quadrados e o filtro de Kalman. Estes algoritmos, são então interligados com o EKF, com base no princípio de estimadores de estado adaptativos, tendo em vista a estimação conjunta, mas autónoma, dos parâmetros do estator, por um lado, e das componentes do fluxo do rotor e parâmetros do rotor, por outro, depois de identificadas as potenciais vantagens da utilização desta metodologia de identificação. Deste modo, às estruturas de modelos desenvolvidas, são associados algoritmos recursivos, de modo a construir uma base de procedimentos de identificação suficientemente genérica, flexível e configurável, para estimação das diferentes variáveis associadas ao controlo do motor de indução. Com esta metodologia, é possível ter em conta o regime dinâmico do motor e o seu ponto de funcionamento, de modo a garantir a correcta estimação de todos os parâmetros eléctricos, com base na informação dos sinais da tensão e corrente do estator e da velocidade angular do motor. A estimação da velocidade, requer apenas as componentes da tensão e corrente do estator. As diferentes metodologias de identificação, adequadas à estimação de estados, parâmetros eléctricos e velocidade do motor de indução trifásico, foram validadas experimentalmente, em tempo diferido e em tempo real, utilizando o sistema de desenvolvimento da dSPACE, baseado na carta de controlo DS1103, no programa Simulink e outros programas específicos. The control of modern and high-performance electrical drives for induction motors, in variable speed applications, like vector control, requires the accurate knowledge of the induction motor electrical parameters. Since these parameters are time-varying and variations affect the performance of the control laws, their on-line estimation is needed during the normal operation of the motor. In this context, parametric modeling and identification procedures are investigated with the objective of obtaining models described by a set of either directly the physical parameters of the induction motor, or other parameters from which those could be obtained. In this thesis, new modeling procedures are developed, in the state-space representation, in order to enable the joint estimation of states and electrical parameters of the induction motor. Since the extended Kalman filter (EKF) is suitable for time-varying and non-linear state-space models and considering its recursive nature, this algorithm was used for the joint and on-line estimation of those variables. Taking into account the relatively high order of the models and the computational effort of the EKF for real time applications, new procedures are introduced in this thesis so as to reduce the order of the models and an innovative strategy is proposed for the discretization of the continuous time state-space models. The EKF is then applied to the reduced order models, obtained in this way, for joint estimation of the rotor flux components and the electrical parameters. The same models are also used for the joint estimation of the rotor flux and angular speed of the induction motor. Considering the computational effort of the EKF and the specific difficulties in the estimation of the variables related to the induction motor, a set of simple and linear models is developed for the state parameters estimation, using recursive prediction error methods, namely, the gradient algorithm, the recursive least squares method and the Kalman filter. These algorithms are connected with the EKF in a bootstrap manner based on the concept of adaptive state estimators in view of the joint, but autonomous, estimation of the stator parameters, on the one hand, and the rotor flux and rotor parameters, on the other hand, following the observation of the potentialities of using these identification methodologies. By this way, the recursive algorithms are associated to the developed model structures in order to build a sufficiently generic, flexible and configurable base of identification procedures for the estimation of the different variables related to the induction motor control. Using this methodology, it is possible to take into account the dynamics of the motor as well as its operating point, for the suitable estimation of all electrical parameters considering only the information provided by the stator voltage and current signals and the rotor speed. In the speed estimation algorithm only the stator voltage and current components are required. The different identification methodologies, as well as the speed estimation, were validated with experimental data, in off-line and real time operation, using the dSPACE development system, based on the DS1103 controller board, Simulink and other specific software. Les lois de contrôle des systèmes électroniques d’actionnement du moteur d’induction triphasé sur des applications de vitesse variable, utilisant des techniques de contrôle moderne de performance élevée, spécialement le contrôle vectoriel, exigent la connaissance assez précise des paramètres électriques du moteur. La variation temporelle de ces paramètres, affecte la performance des lois de contrôle. Il est donc nécessaire de procéder à son estimation pendant le fonctionnement du moteur. Dans ce contexte, des procédés de modélisation et d’identification paramétriques sont étudiés, avec l’objectif d’obtenir des modèles décrits directement par les paramètres physiques du moteur d’induction, ou d’ autres, qui peuvent être utilisés pour obtenir ces paramètres physiques. Dans cette dissertation de nouveaux procédés de modélisation sont développés, dans la représentation d’espace d’état, qui permettent d’estimer conjointement, états et paramètres électriques du moteur d’induction. L’estimation en-ligne, de ces paramètres, est réalisée à travers l’utilisation du filtre de Kalman étendu (Extended Kalman Filter), pour sa nature récursive et parce que cet algorithme est adapté aux modèles d’espace d’état variables dans le temps et non-linéaires. En considérant la dimension élevée des modèles et le temps de computation du EKF, pour les applications en temps réel, dans cette dissertation des procédés innovatrices pour la réduction de l’ordre des modèles et une nouvelle forme de discrétisation des modèles d’espace d’état dans le temps continu sont introduites. Aux modèles d’espace d’état d’ordre réduite qui sont obtenus est appliqué l’EKF pour estimer conjointement les composantes du flux du rotor et les paramètres électriques. Les mêmes modèles sont aussi utilisés pour estimer conjointement le flux du rotor et la vitesse angulaire du moteur d’induction Considérant l’effort de computation du EKF et les difficultés spécifiques de l’estimation des grandeurs associées au moteur d’induction, un ensemble de modèles linéaires simples, pour l’estimation des paramètres du stator, est développé, en utilisant des méthodes récursives d’erreur de prédiction, spécialement, l’algorithme du gradient, la méthode des moindres carrés récursifs et le filtre de Kalman. Ces algorithmes, sont interliés avec l’algorithme du EKF en considérant le principe des estimateurs d’état adaptatifs, pour effectuer l’estimation simultanée, mais autonome, des paramètres du stator en utilisant une méthode récursive d’erreur de prédiction, et des composantes du flux du rotor et des paramètres du rotor en utilisant l’EKF, après avoir identifiées les potentiels avantages de l’utilisation de cette méthodologie d’identification. Aux structures des modèles développées sont donc associés des algorithmes récursifs, avec l’objectif de construire une base de conduites d’identification suffisamment générique, flexible et configurable, pour l’estimation des différentes variables associées au pilotage du moteur d’induction, en considérant le régime dynamique et le point de fonctionnement, pour garantir une correct estimation des paramètres électriques du moteur. Dans l’estimation des paramètres, des composants de tension et courrant du stator et la vitesse angulaire du moteur sont utilisés. L’estimation de la vitesse utilise seulement des composants de tension et courrant du stator. Les différentes méthodologies d’identification des paramètres électriques, et d’estimation de la vitesse, ont été validées expérimentalement, hors-ligne et en-ligne, en utilisant le système de développement de dSPACE, qui est basé dans la carte de contrôle DS1103, Simulink et autres programmes spécifiques.