ISEL - Eng. Electrotécn. - Artigos
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Browsing ISEL - Eng. Electrotécn. - Artigos by Field of Science and Technology (FOS) "Engenharia e Tecnologia::Engenharia Eletrotécnica, Eletrónica e Informática"
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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.
- 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.
- 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.
- 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.