ISEL - Eng. Electrotécn. - Artigos
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- 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.
- Pilot scale continuous pulsed electric fields treatments for vinification and stabilization of Arinto and Moscatel graúdo (Vitis vinifera L.) white grape varieties: effects on sensory and physico-chemical quality of winesPublication . Silva, Filipa V.M.; Borgo, Riccardo; Guanziroli, Andrea; Ricardo-da-Silva, Jorge M.; Aguiar-Macedo, Mafalda; Redondo, LuisPulsed electric field (PEF) processing of white grapes (Arinto, Moscatel Graúdo also known as Moscatel de Setúbal) before pressing for must extraction (1.2 and 1.6 kV/cm) and before bottling for finished wine physical stabilization (10 kV/cm) was implemented in a pilot-scale winery to produce about 540 L of wine for each variety. PEF was applied at these two different stages of wine production, and its effects on the sensory and physico-chemical quality of the wines were investigated. The sensory triangle tests revealed no significant change in both wine varieties’ colour, odour, and taste with PEF extraction and PEF stabilization treatments. However, for colour coordinates assessed with a spectrophotometer, a significant increase in CIE b* colour coordinate was registered for PEF extracted Arinto and Moscatel wine samples, showing a development of a more intense yellow colour. Concerning physico-chemical quality parameters, the PEF extraction increased both wine varieties’ turbidity and pH, although total acidity was not affected. The total phenols also increased in Arinto with extraction. The second PEF treatment applied for wine stabilization did not affect any of the quality parameters, except total phenols, which decreased in Moscatel wine. The results encourage the application of PEF in the wineries at different stages of vinification of white wine grape varieties.
- A buck-boost converter with extended duty-cycle range in the buck voltage region for renewable energy sourcesPublication . Monteiro, Joaquim; Fernao Pires, Vitor; Foito, Daniel; Cordeiro, Armando; J. F. Silva, Fernando Silva, Fernando A Silva, J. Fernando Silva, J F A Silva, Fernando Silva José; Pinto, SoniaBuck-boost DC-DC converters are useful as DC grid interfaces for renewable energy resources. In the classical buck-boost converter, output voltages smaller than the input voltage (the buck region) are observed for duty cycles between 0 and 0.5. Several recent buck-boost converters have been designed to present higher voltage gains. Nevertheless, those topologies show a reduced duty-cycle range, leading to output voltages in the buck region, and thus require the use of very low duty cycles to achieve the lower range of buck output voltages. In this work, we propose a new buck-boost DC-DC converter that privileges the buck region through the extension of the duty-cycle range, enabling buck operation. In fact, the converter proposed here allows output voltages below the input voltage even with duty cycles higher than 0.6. We present the analysis, design, and testing of the extended buck-boost DC-DC converter. Several tests were conducted to illustrate the characteristics of the extended buck-boost DC-DC converter. Test results were obtained using both simulation software and a laboratory prototype.
- SWHORD simulator: A platform to evaluate energy transition targets in future energy systems with increasing renewable generation, electric vehicles, storage technologies, and hydrogen systemsPublication . Sousa, Jorge A. M.; Lagarto, João; Carvalho, Ezequiel; Martins, AnaThis paper presents the simulation platform SWHORD, specially designed for the analysis of future energy systems under energy transition targets. The model is implemented in GAMS as a cost minimization mixed integer programming problem of a hydro-thermal power system, which includes high penetration of non-dispatchable renewable generation, storage technologies, electric vehicles, and hydrogen systems. Simulations are performed on an hourly basis for one year of operation, enabling the evaluation of both short-term dynamics and the seasonal behaviour of the system and including the hourly power generation profile by technology, fuel and emission costs, CO2 emissions and storage levels, as well as the renewable curtailment needed to balance the system. The model was validated by backtesting with historical data of the Portuguese power system and, from a comprehensive statistical analysis of the dispatchable generation, it is concluded that the simulation results present a good fit with the real data. An illustrative use case is presented to evaluate the consistency of the Portuguese targets for 2030. Simulation results put in evidence the advantages of the SWHORD simulator to study the complex interactions among the new drivers of future energy systems, such as electric vehicles, storage technologies, and hydrogen systems.
- Using power electronics and automation to simulate solar PV systemsPublication . Fonte, Pedro M.; Cordeiro, Armando; Barata, Filipe; Pires, V. Fernão; Chaves, Miguel; Foito, Daniel; Gamboa, PauloThis paper presents a solar photovoltaic panel simulator system with the ability to perform automatic tests in different condition according to manufacture parameters. This simulator is based on three buck--boost DC -DC converters controlled by a microcontroller and supported by a AXC 1050 Programmable Logic Controller from Phoenix Contact which is responsible for running the automatic tests. This solution allows to understand the typical operation of solar photovoltaic panels and MPPT algorithms considering suddenly changes in the irradiation, temperature, or load.
- Didactic simulator for water treatment systemsPublication . Cordeiro, Armando; Almeida, Miguel C. L.; Vieira De Brito Almeida, Maria Da GraçaThis paper presents the implementation of a didactic simulator for industrial automation supported by a Human-Machine Interface system. As a result of this work, a solution based on a system of six reservoirs was developed, together with a supervision system that allows the simulator to be controlled and monitored through a Raspberry Pi with a touch screen display and an android application. The aim of this work is to develop a system that can be used by other undergraduate and master’s students of the electrical engineering course at ISEL.
- Dual output and high voltage gain DC-DC Converter for PV and fuel cell generators connected to DC bipolar microgridsPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Silva, José FernandoThis paper introduces a new topology for a DC-DC converter with bipolar output and high voltage gain. The topology was designed with the aim to use only one active power switch. Besides the bipolar multiport output and high voltage gain this converter has another important feature, namely, it has a continuous input current. Due to the self-balancing bipolar outputs, the proposed topology is suitable for bipolar DC microgrids. Indeed, the topology balancing capability can achieve the two symmetrical voltage poles of bipolar DC microgrids. Furthermore, it is possible to create a midpoint in the output of the converter that can be directly connected to the ground of the DC power supply, avoiding common-mode leakage currents in critical applications such as transformerless grid-connect PV systems. The operating principle of the proposed topology will be supported by mathematical analysis. To validate and verify the characteristics of the presented topology, several experimental results are shown.
- A multilevel converter topology for a STATCOM system based on four-leg two-level inverters and cascaded Scott TransformersPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Silva, José FernandoThis paper presents a new power electronic topology for a STATCOM allowing the generation of multilevel AC voltages. This topology is characterized by a modular configuration since it uses two well known four-leg two-level voltage source inverters. A Scott transformer with multiple secondary windings connects the two four-leg inverters to the grid. One of the important features of the proposed power topology is the capability to generate AC voltages with high number of levels, in spite of using only two four-leg two-level voltage source inverters. To maximize the number of voltage levels a geometric progression ratio of 3 between the windings of the transformers connected in cascade is proposed. However, to reduce the turns-ratio span, alternatively a fractional geometric ratio of 1.5 is also proposed and analyzed. A control strategy adapted to the proposed power converter topology is also presented. Besides the control of the reactive power the regulation of the four-leg inverter DC voltage will also be considered. To support the theoretical studies and assumptions, simulations and experiments are presented. Experimental results were obtained using a low power laboratory prototype. The results shown give evidence to the characteristics and features of the proposed power converter topology and control system.
- Control transition mode from voltage control to MPPT for PV generators in isolated DC microgridsPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Silva, J. FernandoThe integration of photovoltaic (PV) power sources on a large scale into grid-tied and islanded solutions is now a reality. Despite the fluctuating characteristics of solar energy, the direct current (DC) nature of PV sources is highly compatible with DC microgrids compared with AC solutions. However, as more PV sources are being installed, challenges related to the control of DC microgrids are also increasing, especially for islanded applications. To ensure an appropriate transition from the maximum power point to DC bus voltage regulation of DC microgrids, novel control strategies must be designed, and this aspect is particularly critical when these grids operate without energy storage systems. We therefore propose a new control strategy for a PV generator for islanded DC microgrids without storage systems. Our approach allows for smooth switching from the maximum power point mode to the voltage control regulation mode (V control) when the available PV power is excessive, thus limiting the generated PV power and returning to maximum power point operation when all the available power is required. This allows us to control a DC microgrid without a storage system and provides a new alternative that offers a cost-effective solution for rural and deprived regions. Our solution combines the maximum power point tracking algorithm with a proportional integral compensator for V control and minimises undervoltage/overvoltage problems in the DC bus. The behaviour of the isolated DC microgrid under different conditions, for example in the case of transitions, perturbations, and different types of loads, is also studied and verified. The performance of the proposed control strategy is confirmed by several simulation and experimental tests.
- Fault-tolerant multilevel converter to feed a switched reluctance machinePublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Pires, Armando J.The switched reluctance machine (SRM) is one of the most interesting machines, being adopted for many applications. However, this machine requires a power electronic converter that usually is the most fragile element of the system. Thus, in order to ensure high reliability for this system, it is fundamental to design a power electronic converter with fault-tolerant capability. In this context, a new solution is proposed to give this capability to the system. This converter was designed with the purpose to ensure fault-tolerant capability to two types of switch faults, namely open- and short-circuit. Moreover, apart from this feature, the proposed topology is characterized by a multilevel operation that allows improvement of the performance of the SRM, taking into consideration a wide speed range. Although the proposed solution is presented for an 8/6 SRM, it can be used for other configurations. The operation of the proposed topology will be described for the two modes, fault-tolerant and normal operation. Another aspect that is addressed in this paper is the proposal of fault detection and diagnosis method for this fault-tolerant inverter. It was specifically developed for a multilevel SRM drive. The theoretical assumptions will be verified through two different types of tests, firstly by simulation and secondly by experiments with a laboratory prototype.