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- 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.
- New backstepping controllers with enhanced stability for neutral point clamped converters interfacing photovoltaics and AC microgridsPublication . Barros, J. Dionísio; Silva, J. Fernando A.; Rocha, Luis LamyThis work presents a new approach to obtain pulse width modulation (PWM) backstepping controllers with enhanced stability for neutral point clamped (NPC) multilevel converters to deliver energy from photovoltaic (PV) panels into AC microgrids. Stability enhanced backstepping non-linear controllers are obtained from the equations of the dq frame converter model to regulate the PV voltage to track the power point, and to balance the capacitor voltages through DC biasing of the PWM carriers, using a novel dynamic equation of the capacitors incremental unbalance voltage, while controlling the grid injected AC currents. Besides, the proposed controllers can change the PV panels operating point to curtail inject power for AC voltage / frequency regulation. The NPC converter and AC microgrid are simulated in MATLAB / Simulink and implemented in the laboratory to evaluate the performance of the PV energy conversion using the new stability enhanced backstepping PWM control. Simulation and experimental results show that, regarding predictive controllers, the novel stability enhanced backstepping requires lower microprocessor power than predictive controllers while presenting a similar behavior in PV voltage and power point tracking regulation, or for voltage / frequency regulation of the microgrid. AC injected currents show low levels of total harmonic distortion similar to predictive controllers and can operate at near unity power factor.
- Impact of the new electricity remuneration scheme on the waste-to-energy recovery activity in PortugalPublication . Silva, Mário; Lagarto, João; Sousa, Jorge A. M.; Santos, Feliz; Viveiros, Carla; Barata, FilipeThe remuneration scheme for the electricity produced by Waste-to-Energy (WtE) recovery plants has changed recently in Portugal according to 2020 legislation. The new model, linking the electricity remuneration from WtE plants to the spot electricity prices, is expected to bring greater uncertainty in the waste activity, which is a novelty for the sector. In Portugal, Valorsul is the municipal waste treatment entity responsible for the recovery and treatment of municipal solid waste (MSW) produced in 19 municipalities in the Lisbon area. This paper highlights the impact of the new Portuguese electricity remuneration scheme for electricity from waste on Valorsul’s WtE plant. For this purpose, the new remuneration scheme is modeled and simulated based on electricity spot market price scenarios, which are compared with the base case scenario of the former remuneration scheme. Considering different electricity prices for the electricity produced by the WtE plant, the present study anticipates the consequences of the gate-fee of such regulatory changes. Results show that any price changes in the electricity remuneration scheme are offset by equivalent changes in the waste gate-fee. Consequently, the change in the remuneration of the electricity from the WtE plant is, in fact, neutral for the Valorsul accounts and lower revenues from the electricity generation activity of the WtE will negatively impact the gate-fee prices paid by the waste users.
- High frequency transformers for solid-state transformer applicationsPublication . Santos, Nuno; Chaves, Miguel; Gamboa, Paulo; Cordeiro, Armando; Santos, Nelson; Pinto, Sónia FerreiraThis paper focuses on the study of the high frequency transformer incorporated in solid- state transformers, specifically on the development of the steps that enable the design of an optimized high frequency transformer and its equivalent model based on the desired characteristics. The impact of operating a transformer at high frequency and the respective solutions that allow this impact to be reduced are analyzed, alongside the numerous advantages that the utilization of these transformers has over traditional 50/60 Hz transformers. Furthermore, the power scheme of the solid-state transformer is outlined, focusing on the power converters, which are immediately before and after the high frequency transformer (HFT). We also investigate a control technique that allows for correct operation and the existence of power bidirectionality. In a novel approach, this paper demonstrates the systematic steps for designing an HFT according to the desired specifications of each given project, helping students and engineers achieve their objectives in power-electronic applications. Moreover, this paper aims at increasing the knowledge of this area of power electronics and facilitating the development of new topologies with high power density, which are very important to the integration of renewable power sources and other applications. Finally, a simulation is presented to validate a high frequency transformer and its control technique.
- 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, Ana AlexandraThis 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.
- Renewable energy communities optimal design supported by an optimization model for investment in PV/wind capacity and renewable electricity sharingPublication . Sousa, Jorge A. M.; Lagarto, João; Camus, Cristina Inês; Viveiros, Carla; Barata, Filipe; Silva, Pedro; Paraiba, OrlandoThe EU Renewable Energy Directive 2018/2001 (RED II) has unlocked the participation of local citizens and authorities in collective renewable energy projects through the concept of Renewable Energy Communities (REC). In this context, the present study proposes an optimization model to support REC's investment decisions on the renewable generation portfolio and operational electricity sharing management.The model presented follows an annualized investment optimization approach considering that one REC member can invest in additional renewable generation. A case study of a REC with three members is presented in a framework of four scenarios and results are discussed using the levelized cost of electricity (LCOE) and the marginal realized price concepts. A sensitivity analysis is also performed to address the interannual variability of the solar and wind resources.In the base case scenario, which corresponds to the site-specific conditions of the investing REC member, an overall net revenue of 87 keuro/year was computed. The sensitivity analysis for this scenario showed that the investment is more sensitive to the solar resource, with revenues changing between -3.3% and 0.1% in comparison with the average resource availability.This paper contributes to the existing literature by identifying the main drivers behind the optimal investment decision of a REC, which result from the relationship between the marginal realized price and the levelized cost of the electricity generated by each renewable technology. The results supported by the present model reinforce the benefits of RECs as enablers for the deployment of renewable generation, thus contributing to the decarbonization of the energy systems.