ISEL - Eng. Electrotécn. - Artigos
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- 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.
- Multilevel inverter based on a dual two-level nine-switch converter for a dual three-phase or six-phase motor drive systemPublication . Pires, V. Fernão; Cordeiro, Armando; Foito, Daniel; Pires, A. J.; Silva, J. Fernando A.; Chen, HaoThe nine-switch inverter is considered as a very interesting solution for three-phase dual output applications, such as dual three-phase or six-phase motor drive systems. The main advantage of this approach is a converter topology with a reduced number of power semiconductors. However, the AC output voltages are limited to only two levels. This work proposes a new inverter topology for dual three-phase or six-phase motor drive systems with multilevel output characteristics. The proposed topology is based on two isolated inverters, but the number of legs is reduced from six to three. This structure creates a modular multilevel inverter with a high number of voltage levels while using a comparatively smaller number of power semiconductors. A modulation strategy, associated with the proposed topology, is presented to ensure multilevel operation. The proposed topology and modulation strategy will be tested first through a simulation in Matlab/Simulink and then by laboratory tests using an experimental prototype. The obtained results show a good agreement between simulations and experiments, both confirming the theoretical studies.
- Optimal investment and sharing decisions in renewable energy communities with multiple investing membersPublication . Barbosa, Inês; Sousa, Jorge A. M.; Villar, José; Lagarto, João; Viveiros, Carla; Barata, FilipeThe Renewable Energy Communities (RECs) and self-consumption frameworks defined in Directive (EU) 2023/2413 and Directive (EU) 2024/1711 are currently being integrated into national regulations across EU member states, adapting legislation to incorporate these new entities. These regulations establish key principles for individual and collective self-consumption, outlining operational rules such as proximity constraints, electricity sharing mechanisms, surplus electricity management, grid tariffs, and various organizational aspects, including asset sizing, licensing, metering, data exchange, and role definitions. This study introduces a model tailored to optimize investment and energy-sharing decisions within RECs, enabling multiple members to invest in solar photovoltaic (PV) and wind generation assets. The model determines the optimal generation capacity each REC member should install for each technology and calculates the energy shared between members in each period, considering site-specific constraints on renewable deployment. A case study with a four-member REC is used to showcase the model’s functionality, with simulation results underscoring the benefits of CSC over ISC.
- 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.