Browsing by Issue Date, starting with "2020-08-07"
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- Three-level NPC dual-buck inverter designed to safety-critical applicationsPublication . Cordeiro, Armando; Fernao Pires, Vitor; Foito, DanielThis paper presents a three-phase three-level NPC (neutral point-clamped) Dual-Buck inverter topology suitable to increase fault-tolerant capability to safety-critical applications. Using the proposed topology, it is possible to achieve energy processing capability in case of several failure modes. The faulttolerant enhancements are a consequence of appropriate modifications in the control strategy and from redundancy of power devices to maintain the correct operation of the converter. The proposed control strategy adopted in the presented solution can also equalize the capacitor voltages automatically. Some simulation results are included in this study to confirm the validity of the theoretical study.
- Fault tolerant operation of three-phase 3 level T-Type qZS inverters using sliding mode current controllersPublication . Fernao Pires, Vitor; Foito, Daniel; Santos, Natalia; Cordeiro, Armando; Roncero Clemente, Carlos; Silva, J. F.Due to the boost characteristic and the several possible outputs of quasi-Z-source inverters (qZSI), these topologies can be valuable options to operate under fault conditions, provided the controller is able to take advantage of the available output states. Thus, the development of control systems to take advantage of the available outputs is needed. Hence, this paper focuses on the development of a control system to operate a three-phase three-level T-Type qZSI under fault tolerant conditions. The controller is based on a sliding mode current controller associated to a vectorial modulator selecting the available outputs. The proposed strategy for the controller and modulator is presented taking into consideration the normal and fault-tolerant requirements. The strategy also considers the balance of the capacitors under fault tolerant condition. The converter operating in both modes is tested through several simulation studies.
- Bridging the gap between academic and industrial hydrocracking: on catalyst and operating conditions' effectsPublication . Mendes, Pedro S. F.; Silva, João M; Ribeiro, M Filipa; Daudin, Antoine; Bouchy, ChristopheThis work aims at bridging the knowledge gap between the well-studied Pt/zeolite catalysts and the industrially-employed NiMoS/(Al2O3+ zeolite) ones. To do so, catalyst series based on HUSY zeolite were evaluated in the hydroconversion of n-hexadecane under similar operating conditions, but the industrially-relevant H2S and NH(3)contaminants were added when evaluating the latter. The intrinsic performance of Pt/HUSY and NiMoS/(Al2O3+ HUSY) catalysts was noticeably similar, when well-balanced, with the catalytic activity being however much lower in the latter (temperature gap of 125 K). Ammonia inhibition of more than 99% of the protonic sites was revealed to be the origin of such low activity. On the other hand, the metal-acid balance was only reached at sufficiently low reaction temperatures (ca.593 K),i.e.when the NH(3)inhibiting effect increased the metal to acid site ratio in NiMoS/(Al2O3+ HUSY) to values five orders of magnitude larger than those in the Pt/HUSY one. In addition to the understanding achieved on the role of metal-acid balance in industrial-like catalysts and its key controlling parameters, these findings also point to the need to develop better hydrogenating functions to improve the efficiency, and consequently the sustainability of liquid fuel production.
- An 8/6 SRM drive with a multilevel topology based on a cross-switched configurationPublication . Fernao Pires, Vitor; Foito, Daniel; Pires, Armando J.; Cordeiro, Armando; Martins, J. F.SRM drives based on multilevel power electronic converter presents several advantages, like reducing the switching frequency and improve the operation of the motor under high speed. In this way, several multilevel power converter topologies have been developed for the SRM drives. In line with this, this paper proposes a new multilevel power converter topology for the 8/6 SRM drive. The topology was developed with the purpose to reduce the number of power semiconductors, without reducing the performance of the motor. The proposed topology was designed in a way that uses crossover switches. The operation of the power converter topology in all of their modes is analyzed in a detailed way. The verification of the global system performance (drive and motor) is realized by the implementation of simulation studies. Indeed, through these studies it is verified that at low speed operation the switching frequency is reduced, but maintaining the application of the maximum voltage during the magnetization and demagnetization process.
- Intelligent systems applied to buildings' managementPublication . Pereira, Rita; Barata, Filipe; Viveiros, CarlaEnergy efficiency in buildings are an important domain regarding its impact in the global energy consumption. Several efficiency measures are currently available, using different methodologies. In this paper an approach using intelligent systems is implemented through a smart controller able to automatically and efficiently manage building’s energy. This smart controller uses Fuzzy Logic Control (FLC) as a decision maker and is supported by Artificial Neural Networks (ANN) used to forecast the building outside temperature. In addition, and in order to increase overall energy efficiency, renewable energies associated with a storage system are considered. For the designed smart controller implementation, a thermal house model is simulated using a MATLAB toolbox. In this paper emphasis is given to the building´s Heating Ventilation and Air Conditioning (HVAC) control and a rough economic analysis is drawn, allowing to infer about the adopted efficiency measures impact.
- Effects of broken skirts and pollution on voltage distribution for cap and pin glass insulatorsPublication . Mateus, C.; Barata, Filipe; Luís, RicardoCap and Pin insulators are key elements on aerial electric power transmission lines in which their performance is subject to the environmental elements, like pollution and/or humidity. Furthermore, a broken insulator (stub) on an insulator string may change the voltage distribution along the chain. This paper goal is to study the effects of the voltage distribution along with tempered glass cap and pin insulator string in the presence of broken skirts as well contamination by pollution, using for that purpose a finite element software. This paper presents the voltage distribution profile across single and fourteen units of glass insulator string with stubs at distinct locations as well for the presence of contamination by pollution. It is concluded that the presence of pollution on a string with stubs will alter and exacerbate the increase of electrical potential effect due to the presence of stubs.