Browsing by Author "Santos, Nuno"
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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.
- Material Manipulável Estruturado versus Applet no desenvolvimento do Pensamento Algébrico ao nível do 1º Ciclo do Ensino BásicoPublication . Santos, Nuno; Afonso, Paulo; Gil, H.This investigation was conducted in the framework of the master's degree in Preschool Education and teaching of the first cycle of basic education, with students of a class of third-year elementary schooling in a Castelo Branco elementary school. Through this study, we intend to examine whether digital technology improving the number of success cases and decisionmaking in solving mathematical tasks involving repetition patterns, compared the tasks solved by using the standard blocks. This research, comparative in nature, was based on a mixed approach (quantitative and qualitative) data processing level. Our intervention was structured in 3 phases. In the first phase, the 23 students who made up the class solved 4 tasks with repeating patterns through a work record (repeating Patterns: ABAB, ABCABC, ABBABB e ABBCCABBCC). The responses of students, in the schedule of work, were analyzed through a holistic scale focused adaptation of [1], in which it was ranked each response between 0 to 2 points. From the ratings obtained by students, the class was divided into 2 homogenous groups. On the other hand, in the second phase, the students who were part of the Group (11 students) solved the same tasks using an applet, while students who comprised the Group B (12 students) solved the same tasks through manipulable material (standard blocks). To proceed to correction of the tasks of the group, we ran the ' screenshots ' to computer screens for each task. On the other hand, the answers of the students of Group B were analyzed using not only to work but also the photos of the compositions performed. In the third stage we proposed the same tasks, in which all students in the class, decided the issues through a worksheet. After the data analysis we found that there were no statistically significant differences between the results obtained by the students who worked with the applet compared students who worked with manipulable materials. Although both groups of the 1st to the 3rd stage have improved substantially in terms of decision-making, as well as the number of replies considered assertive, but not so complete that work with the applet was better for the work with manipulable materials.
- Novel design of the converter for an active UPS application based on Marx modulator concept with supercapacitorsPublication . Pestana, Celso; Canacsinh, Hiren; Chaves, Miguel; Gamboa, Paulo; Cordeiro, Armando; Luís, Ricardo; Martins, Ana Alexandra; Encarnação, Luís; Pereira, Fernando; Silva, José Fernando; Santos, NunoA new Marx modulator 4-leg multilevel converter is proposed to replace the well-known 4-leg inverter fed from batteries in Uninterruptible Power Supply (UPS) applications. The novel design concept for the Marx modulator based multilevel converter is presented and described. Each leg uses 2 Marx modulator modules, each one using an Electrochemical Double-Layer Capacitor (EDLC) (also known as supercapacitor (SC)) energy storage bank. The new topology concept enables multilevel operation with five voltage level per phase, allowing high quality voltage and current waveforms, distributed supercapacitor storage and reduction of supercapacitor bank voltage. The proposed converter can operate as UPS or as Active Power Filter (APF), powering non-linear or/and unbalanced loads, while balancing each leg supercapacitor voltage. A control strategy to choose the redundant vector configuration to balance the supercapacitor voltages is explained. Simulation results are presented for a Marx modulator based interactive 40 kVA UPS.