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- DC Microgrids: Benefits, Architectures, Perspectives and ChallengesPublication . Pires, Vítor Fernão; Pires, A. J.; Cordeiro, ArmandoOne of the major paradigm shifts that will be predictably observed in the energy mix is related to distribution networks. Until now, this type of electrical grid was characterized by an AC transmission. However, a new concept is emerging, as the electrical distribution networks characterized by DC transmission are beginning to be considered as a promising solution due to technological advances. In fact, we are now witnessing a proliferation of DC equipment associated with renewable energy sources, storage systems and loads. Thus, such equipment is beginning to be considered in different contexts. In this way, taking into consideration the requirement for the fast integration of this equipment into the existing electrical network, DC networks have started to become important. On the other hand, the importance of the development of these DC networks is not only due to the fact that the amount of DC equipment is becoming huge. When compared with the classical AC transmission systems, the DC networks are considered more efficient and reliable, not having any issues regarding the reactive power and frequency control and synchronization. Although much research work has been conducted, several technical aspects have not yet been defined as standard. This uncertainty is still an obstacle to a faster transition to this type of network. There are also other aspects that still need to be a focus of study and research in order to allow this technology to become a day-to-day solution. Finally, there are also many applications in which this kind of DC microgrid can be used, but they have still not been addressed. Thus, all these aspects are considered important challenges that need to be tackled. In this context, this paper presents an overview of the existing and possible solutions for this type of microgrid, as well as the challenges that need to be faced now.
- Modelo da característica magnética do gerador eléctrico de relutância comutado aplicado a conversores de energia eólicaPublication . Lobato, Pedro; Rafael, Silviano; Pires, A. J.
- An Adaptive PID Speed Controller for an 8/6 Switched Reluctance MachinePublication . Rafael, Silviano; Santos, P. J.; Pires, A. J.This paper presents a classical controller with parameters adaptation capability, in an automatic way. This controller is based on a PID where a parameters adaptation algorithm is used and applied to the switched reluctance motor (SRM) speed control. This PID design do not require any kind of adjustment or calibration from the operator. The parameters adaptation algorithm implemented is based on one fuzzy system with a Takagi-Sugeno inference mechanism with some simplifications. These simplifications had the goal to select the parameters adaptation algorithm contributing for a fast controller response. The developed adaptive PID algorithm was modelled and simulated.
- Multi-machine topology versus monolithic switched reluctance machine in low speed applicationsPublication . Lobato, Pedro; Dente, J. A.; Martins, J. F.; Pires, A. J.In regards to SR machines design, there are a multiplicity of feasible topologies, differentiated by the properties of the electrical and magnetic circuits, and their relative location. A feasible SRG topology for an energy converter can comprise a series of n-SR machines assembled on a common axis. Comparing with a monolithic SR machine, that mono-axial multi-machine topology shows a higher fault tolerance and a simpler maintenance. The proposed scale models methodology makes it easy to incorporate in comparison of SR topologies other physical phenomena such as thermal effect and magnetic saturation by introducing some constraints. With the comparison of topologies, the issues surrounding the design of low speed SR multi-machine topology are discussed, leading into consideration monolithic topologies. The monolithic topology can optimize the efficiency taking benefits from the gain of power per unit of copper mass and lower losses.
- Field-Based Model for Switched Reluctance Generators in Direct Drive Wind Energy ConvertersPublication . Lobato, Pedro; Dente, J. A.; Pires, A. J.This work is motivated by the application of Switched Reluctance Generator (SRG) to direct-drive wind turbines and other low speed renewable energy systems. Direct drive energy converters take important benefits from the elimination of the gearbox, which has traditionally been used to interface a slowly prime mover shaft with the generator shaft. Moreover, the actual trend of exploiting the offshore wind resources makes robustness and reliability vital to the economic operation of wind turbines in that specific environment. The proposed field-based model with a triangular approach of the characteristics of flux-linkage makes it easy to incorporate magnetic saturation by introducing some constraints. With a specific aid of finite element analysis, the triangular approach of magnetic characteristics is used to make the comparison of SRG topologies a less time-consuming task. This work underlines dimensional and similarity arguments to extend previous discussions about SRG modeling into a more general context.
- A ZigBee Wireless Domotic System with Bluetooth InterfacePublication . Leite, Eurico; Varela, Luís; Fernão Pires, Vítor; Pires, A. J.; Cardoso, Filipe; Martins, João F.In this paper a wireless home automation system is presented. The proposed system allows controlling devices in a home environment by using a simple Bluetooth equipped mobile phone. The mobile phone communicates with a main Bluetooth/ZigBee module that communicates with the different ZigBee modules acting as the coordinator of the ZigBee network established between all nodes where electrical devices are connected. The identification of each device is made through DomoML strings by using the KNX home automation standard protocol.
- Load forecasting, the importance of the probability “tails” in the definition of the input vectorPublication . Santos, P. J.; Rafael, Silviano; Pires, A. J.The load forecast is part of the global management of the electrical networks, namely at the transport and distribution levels. This type of methodologies allows to the system operator, to establish and take some important decisions concerning to the mix production and network management, with the minimum of discretionarity. The load forecast in particularly the peak load forecast, represents an important economic improvement in the global electrical systems. Also in certain circumstances, allow reducing the contribution of the non-renewable units, in the daily mixing production. The regressive methodologies specially the artificial neural networks, are normally used in this type of approaches, with satisfactory results. In this paper is proposed a careful analysis in order to define the best-input vector in order to feed the regressive methodology. It was establish careful analyses of the load consumption series. It makes use of a procedural sequence for the pre-processing phase that allows capturing certain predominant relations among certain different sets of available data, providing a more solid basis to decisions regarding the composition of the input vector to ANN. The methodological approach is discussed and a real life case study is used for illustrating the defined steps, the ANN and the quality level of the results.
- Fault Detection in PV Tracking Systems Using an Image Processing Algorithm Based on PCAPublication . Amaral, Tito G.; Pires, Vitor Fernão; Pires, A. J.Photovoltaic power plants nowadays play an important role in the context of energy generation based on renewable sources. With the purpose of obtaining maximum efficiency, the PV modules of these power plants are installed in trackers. However, the mobile structure of the trackers is subject to faults, which can compromise the desired perpendicular position between the PV modules and the brightest point in the sky. So, the diagnosis of a fault in the trackers is fundamental to ensure the maximum energy production. Approaches based on sensors and statistical methods have been researched but they are expensive and time consuming. To overcome these problems, a new method is proposed for the fault diagnosis in the trackers of the PV systems based on a machine learning approach. In this type of approach the developed method can be classified into two major categories: supervised and unsupervised. In accordance with this, to implement the desired fault diagnosis, an unsupervised method based on a new image processing algorithm to determine the PV slopes is proposed. The fault detection is obtained comparing the slopes of several modules. This algorithm is based on a new image processing approach in which principal component analysis (PCA) is used. Instead of using the PCA to reduce the data dimension, as is usual, it is proposed to use it to determine the slope of an object. The use of the proposed approach presents several benefits, namely, avoiding the use of a wide range of data and specific sensors, fast detection and reliability even with incomplete images due to reflections and other problems. Based on this algorithm, a deviation index is also proposed that will be used to discriminate the panel(s) under fault. Several test cases are used to test and validate the proposed approach. From the obtained results, it is possible to verify that the PCA can successfully be adapted and used in image processing algorithms to determine the slope of the PV modules and so effectively detect a fault in the tracker, even when there are incomplete parts of an object in the image.
- PV Generator-Fed Water Pumping System Based on a SRM with a Multilevel Fault-Tolerant ConverterPublication . Pires, Vítor Fernão; Foito, Daniel José Medronho; Cordeiro, Armando; Chaves, Miguel; Pires, A. J.This paper presents a pumping system supplied by a PV generator that is based on a switched reluctance machine (SRM). Water pumping systems are fundamental in many applications. Most of them can be used only during the day; therefore, they are highly recommended for use with PV generators. For the interface between the PV panels and the motor, a new multilevel converter is proposed. This converter is designed in order to ensure fault-tolerant capability for open switch faults. The converter is based on two three-level inverters, with some extra switches. Moreover, to reduce the number of switches, the converter is designed to provide inverse currents in the motor windings. Due to the characteristics of this motor, the inverse currents do not change the torque direction. In this way, it was possible to obtain an SRM drive with fault-tolerant capability for transistor faults; it is also a low-cost solution, due to the reduced number of switches and drives. These characteristics of fault-tolerant capability and low cost are important in applications such as water pumping systems supplied by PV generators. The proposed system was verified by several tests that were carried out by a simulation program. The experimental results, obtained from a laboratory prototype, are also presented, with the purpose of validating the simulation tests.
- Scale Models Formulation of Switched Reluctance Generators for Low Speed Energy ConvertersPublication . Lobato, Pedro; Dente, J. A.; Martins, J.; Pires, A. J.
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