ISEL - Eng. Electrotécn. - Artigos
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- Modular nine-level single-phase inverter with quadruple voltage gain using reduced blocking voltage switchesPublication . Pires , V. Fernão; Cordeiro, Armando; Foito, Daniel; Monteiro, Joaquim; Chen, Hao; Silva, J. Fernando; Cordeiro, Armando; Monteiro, JoaquimThis paper presents a novel approach to enhancing modular voltage source inverters, focusing on achieving high-voltage gain and minimizing harmonic distortion. The suggested solution includes a transformerless, single-phase, nine-level voltage source inverter that cuts down on the number of passive parts that are needed while still achieving a high-voltage gain of up to four times the input DC voltage sources. An essential feature of this topology is that all the switches are subjected to a maximum blocking voltage four times lower than the maximum AC voltage that can be applied to the load. Consequently, this leads to a significant reduction in the Total Voltage Blocking, standardization of the power semiconductors, and converter modularity structure. Furthermore, the proposed inverter topology presents voltage self-balancing capability, eliminating any balancing issues for the two floating capacitors of each voltage source inverter. The theoretical assumptions put forward in this study will be tested through experimental results obtained from a laboratory prototype.
- A grid-tied AC drive using a multilevel topology obtained from the nine-switch converterPublication . Monteiro, Joaquim; Pires, V. Fernão; Silva, J. Fernando; Pinto, Sónia; Monteiro, JoaquimNine-switch inverters, has been widely used in several power systems applications, especially for a dual motor or six-phase machine. Due to their interesting features such as the reduced switch number, this structure has been extended to multilevel topologies. Among the several multilevel topologies, the active-neutral-point-clamped (ANPC) based nine-switch multilevel converter (ANPC-NSMC) has been one of the interesting solutions. In this paper, instead of using this topology for a dual motor or six-phase motor, it is proposed a back-to-back application. In this way, one of the outputs is connected to the grid, while the other output is connected to the three-phase motor. However, for drives a closed loop control is needed. Therefore, a field-oriented controller and a model predictive control (MPC) strategy to control this AC drive is also proposed. The MPC will be used for closed loop current control, as well as for mitigation of the capacitor voltages imbalance. This optimal predictive controller allows the minimization of a cost functional weighing three criteria, the tracking errors of the three-phase AC currents of each side, as well as the two capacitors voltage imbalance. The performance of the proposed control strategy will be verified and discussed through several simulations results.
- A fault tolerant model predictive control with self- adaption for the three-phase T-type inverterPublication . Monteiro, Joaquim; Silva, J. Fernando; Pinto, Sónia; Pires, V. Fernão; Monteiro, JoaquimMultilevel inverters with three-level T-Type topology are widely recognized as a highly recommended solution for applications that require reliability and fault tolerance. However, achieving a fault tolerant operation system typically requires the implementation of fault detection algorithms along with modulator or control system. This paper proposes a different approach by introducing a self-adaptive control system designed to ensure fault-tolerant operation under open-switch fault conditions. The proposed control system is based on Model Predictive Control (MPC). The proposed controller intrinsically detects deviations from the desired setpoint and automatically cancels the usage of the faulty voltage vectors. Furthermore, the proposed control ensures capacitor voltage balancing, even under fault-tolerant conditions. The effectiveness of the proposed faulttolerant MPC method is demonstrated through several simulation tests. The results obtained confirm the validity and feasibility of the proposed approach.
- A dual-output NPC-type converter with a model predictive controller with compensation of DC capacitor voltage imbalancePublication . Monteiro, Joaquim; Pires, V. Fernão; Silva, J. Fernando; Pinto, Sónia; Monteiro, JoaquimThe dual output three-level converter is now important for several applications namely dual motor drives. The recent dual output nine-switch multilevel three-phase inverter, based on the NPC-Type structure, has been studied in open loop at nominal conditions, without closed loop control. Moreover, the dual output nine-switch multilevel inverter may present issues related to load currents control and to the unbalance of two series capacitor voltages in the dc-link. Thus, in this research work the model predictive controller (MPC) is proposed for closed loop current control, as well as for mitigation of the capacitor voltages imbalance. The MPC approach allows the minimization of a cost functional weighing two criteria, the tracking errors of the three-phase AC currents of each inverter output, as well as the two capacitors voltage imbalance. Several simulations showing the performance of the proposed control strategy are presented and discussed.
- A DC DC converter with extended voltage static gain input output continuous current and reduced switch voltage stressPublication . Monteiro, Joaquim; Monteiro, Joaquim; Pires, V. Fernão; Foito, Daniel; Silva, J. Fernando; Pinto, SóniaIn recent decades, DC-DC converters have been important to help the penetration of renewable energy sources into the power grid and for use as independent power sources. These power converters are commonly used in many power conversion appliances and portable electronic devices. However, to regulate and convert a photovoltaic (PV) power source voltage to the required output voltage, it is often necessary to use DC-DC converters to provide a stable and adjustable voltage, a feature that most of these converters do not guarantee. Thus, this paper presents a new single-switch DC-DC converter with Boost characteristics. This converter is characterized by extended static voltage gains and input/output currents. Besides, differently to the standard Boost, the voltage stress of the proposed converter switch is lower than the converter output voltage. The proposed converter operating principle and static gain will be examined through theoretical analysis. Some simulation and experimental tests will evaluate its performance and other particularities of this DC-DC converter.
- Wide voltage gain range bidirectional DC-DC converter with reduced switches count and buck-boost characteristic in both power flow directionsPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Amaral, Tito; Silva, FernandoSeveral applications require bidirectional power converters with high-voltage gain. While several topologies have been proposed, none of them exhibit Buck-Boost characteristics in both forward and reverse power transfer. Most proposals behave as a Boost converter in forward direction and as a Buck converter in the reverse direction. Therefore, this paper proposes a novel DC-DC bidirectional power converter that exhibits Buck-Boost characteristics in both power flow directions while providing very high wide voltage gain range. The proposed converter has, in addition, the ability to maintain continuous currents in the input and output. The theoretical analysis of the converter under bidirectional power flow conditions will be presented and examined, along with the design of its components. The validation of the characteristics and behavior of the proposed bidirectional power converter were tested in several laboratory experiments. The experimental results obtained from both power flow directions show agreement with the theoretical considerations.
- Artificial vision in renewable photovoltaic systems: a review and vision of specific applications and technologiesPublication . Amaral, Tito G.; Cordeiro, Armando; Fernao Pires, VitorRenewable energy resources have become extremely important in the current context of air pollution and the production of significant amounts of greenhouse gas emissions that contribute to global warming. One of the most important renewable energy sources that has shown the highest growth in recent years is photovoltaic (PV) systems. Due to their significance, this research presents a review of the applications in which artificial computer vision can be used in photovoltaic systems. From the results presented in this review, it will be evident that artificial vision can be applied for several different purposes. The advantages of using this technique will also be highlighted. Additionally, a systematic literature review is presented on the research associated with this topic. Through this review, it will be evident that many advanced algorithms related to image acquisition equipment have been proposed to ensure high reliability and fast results. This review does not merely focus on a specific topic or algorithms associated with image processing applied to photovoltaic systems. Rather, this work presents a broad and comprehensive review detailing all viable applications and associated computer vision technologies that can be deployed within these systems. Besides that, the review will clearly specify which work one is based on public datasets. To allow future reproducibility or research, the links to all public datasets utilized in the works based on them are included.
- PEF priming of seeds for microgreen production: a comparative studyPublication . Aguiar-Macedo, Mafalda; Dulyanska, Yuliya; Guiné, Raquel P. F.; Costa, Daniela V. T. A.; Redondo, LuisSeed priming with Pulsed Electric Fields (PEF) is a promising strategy to enhance early plant development and crop quality. This study evaluated PEF priming effects on Beetroot (Beta vulgaris L.), Arugula (Eruca vesicaria), and Basil (Ocimum basilicum L.) microgreens by assessing the effects of three distinct monopolar PEF protocols (PEFA: 2 kV/cm; PEFB: 3 kV/cm; PEFC: 4 kV/cm). PEFB and PEFC treatments significantly influenced imbibition. Germination Indexes (DGI, CGI, and SVI) were positively and significantly affected, with radicle length increasing up to 33% and DGI improving from 40 to 66 on the 1st day (Beetroot, PEFC). Chlorophylls and the Total Carotenoid concentration increased in Basil but decreased in Beetroot and Arugula. Fat and Protein increased in Beetroot (Fat: +41%; Protein: +34%) and Arugula (Fat: +91%; Protein: +11%) treated with PEFC. PEFB led to an increase in Starch in all species. Crude Fibre and Neutral Detergent Fibre decreased amongst all species. Methionine rose by 100% in Beetroot treated with PEFC. Sensory analysis showed slight increases in Sweet (Beetroot) and Aroma Intensity (Basil and Arugula), although these changes were not statistically significant. Species-specific responses to different PEF protocols were observed: optimal protocols seem to be PEFC for Beetroot, PEFB for Arugula, and PEFA/B for Basil.
- FFC-NMR power supply with hybrid controlo of the semiconductor devicesPublication . Roque, Antonio; Sousa, Duarte M.; Oliveira Sebastião, Pedro José; Vaz da Silva, Vitor; Margato, ElmanoThe performance of FFC-NMR power supplies is evaluated not only considering the technique requirements but also comparing efficiencies and power consumption. Since the characteristics of FFC-NMR power supplies depend on the power circuit topology and on the control solutions, the control design is a core aspect for the development of new FFC systems. A new hybrid solution is described that allows controlling the power of semiconductors by switches (ON/OFF mode) or as a linear device. The approach avoids over-design of the power supply and makes it possible to implement new low power solutions constituting a novel design by joining a continuous match between the ON/OFF mode and the linear control of the power semiconductor devices.
- Decarbonizing hard-to-abate sectors with renewable hydrogen: a real case application to the ceramics industryPublication . Sousa, Jorge A. M.; Azevedo, Inês; Camus, Cristina Inês; Mendes, Luís; Viveiros, Carla; Barata, FilipeHydrogen produced from renewable energy sources is a valuable energy carrier for linking growing renewable electricity generation with the hard-to-abate sectors, such as cement, steel, glass, chemical, and ceramics industries. In this context, this paper presents a new model of hydrogen production based on solar photovoltaics and wind energy with application to a real-world ceramics factory. For this task, a novel multipurpose profit-maximizing model is implemented using GAMS. The developed model explores hydrogen production with multiple value streams that enable technical and economical informed decisions under specific scenarios. Our results show that it is profitable to sell the hydrogen produced to the gas grid rather than using it for self-consumption for low-gas-price scenarios. On the other hand, when the price of gas is significantly high, it is more profitable to use as much hydrogen as possible for self-consumption to supply the factory and reduce the internal use of natural gas. The role of electricity self-consumption has proven to be key for the project's profitability as, without this revenue stream, the project would not be profitable in any analysed scenario.