https://repositorio.ufu.br/handle/123456789/5465 2026-08-19T03:31:33Z https://repositorio.ufu.br/handle/123456789/49315 Title: Novo conversor isolado de múltiplas entradas e múltiplas saídas multidirecional para arquiteturas modernas de distribuição de energia CC de baixa tensão Abstract: This work presents the modelling, analysis, and simulation-based evaluation of a multidirectional, multi-winding, multiport flyback DC-DC converter proposed for the integration, within a single conversion stage, of sources and loads operating at different voltage levels in low-voltage DC architectures. By doing so, the need for intermediate DC-DC converters and the losses inherent to multistage power processing are reduced, thereby favoring higher power density. As a proof of concept, a three-port configuration composed of a photovoltaic source, a DC load, and a battery energy storage system was adopted to develop the analytical formulations, the control strategy, and the validation studies. For converter operation, an operating scheme is adopted in which the magnetization and demagnetization processes of the coupled inductor take place individually for each port, thereby reducing the dynamic coupling among ports, increasing the flexibility of the turns-ratio design, and simplifying control implementation. Energy coordination is performed through a Power Flow Control Strategy (PFCS), in which the voltage of port 2 acts as the global coordination variable and is maintained within a band delimited by four voltage levels, from which the operating modes are selected according to the balance among photovoltaic generation, load demand, and the power-exchange capability of the storage system. Within this framework, port 1, connected to the photovoltaic system, operates either in Maximum Power Point Tracking (MPPT) mode or in voltage-droop-based power-limiting mode, referred to as Voltage Droop Control Mode (VDCM). For this port, a Finite Control Set Model Predictive Control (FCS-MPC) strategy is employed to track the photovoltaic array voltage reference, which is generated either by the MPPT algorithm, featuring an adaptive step size and based on observer-estimated photovoltaic current without the need for a current sensor, or by the VDCM, depending on the system operating mode. Port 3, associated with battery energy storage, is bidirectionally controlled through two voltage-droop strategies, one dedicated to the charging process and the other to the discharging process. Under surplus-energy conditions, the system selects the Battery Voltage Droop Control by Charging Mode (BVDMcha), in which the battery absorbs power; under power-deficit conditions, it selects the Battery Voltage Droop Control by Discharging Mode (BVDMdis), in which the battery supplies power to the system. When no energy exchange is required, port 3 remains in a standby state characterized by the IDLE mode. In a complementary manner, port 2, associated with the DC load, incorporates protection functions that allow the load either to remain connected or to be disconnected. Simulation results under islanded operation and different irradiance and load-demand conditions showed that the voltage of port 4 2 remained within the specified range under both surplus- and deficit-power scenarios, with port 3 transitioning between the BVDMcha and BVDMdis modes to absorb or supply energy as required. In addition, a comparative evaluation of alternative control strategies for port 3 was carried out, highlighting differences in dynamic compatibility with the photovoltaic control loop. In summary, the obtained results indicate that the proposed multiport topology, together with the new operating scheme and the developed control strategy, constitutes a technically viable solution for integrating, within a single conversion stage, elements operating at different voltage levels in DC architectures. 2026-06-12T00:00:00Z https://repositorio.ufu.br/handle/123456789/48761 Title: Uma proposta metodológica não invasiva para o compartilhamento da responsabilidade sobre desequilíbrios de tensão baseada na minimização da correlação das fontes Abstract: Electrical power systems have undergone substantial transformations due to the incorporation of new technologies, bringing significant impacts on power quality, notably the voltage imbalance arising from operational conditions imposed by modern power grids. In fact, this indicator and others associated with the loss of power quality have grown and, for many installations, reach proportions exceeding the limits established by regulatory bodies. Such violations represent sources of harmful impact for the agents involved, who may suffer various losses, such as a decrease in network operational efficiency, reduction in the useful life of installation components, and untimely supply interruptions, among others. In these circumstances, when such regulatory standard violations occur, mitigation alternatives emerge that represent high financial costs; recognizing that connection buses — the Points of Common Coupling — unite two or more agents, this can lead to conflicts between the parties. Focusing on the search for means of responsibility sharing regarding the final effects, the literature presents a vast bibliography that, however, still lacks non-invasive analysis methods with consolidated physical and application properties for practical field use. Considering this fact, this thesis proposes the development of the Correlation Minimization Method, a new non-invasive strategy for the sharing of responsibility over total voltage unbalances measured at the PCC that offers reliability, robustness, and practical applicability. The methodology is based on the statistical independence of the fast-varying components of the agents' current sources and stands out for not requiring physical interventions in the network for the analysis process. Besides establishing the theoretical foundations of this new strategy, the work evaluates its performance comparatively with the main methodologies in literature, such as Least Squares and Complex Independent Component Analysis Method, demonstrating, through computational analysis and experimental validations in a real facility, its superiority in terms of reliability, robustness, and operational practicality. 2026-05-06T00:00:00Z https://repositorio.ufu.br/handle/123456789/48667 Title: Ai-driven lightweight motor assessment embedded in an exergame for post-stroke rehabilitation Abstract: Introduction: Stroke is a leading cause of long-term disability worldwide and frequently results in persistent upper-limb motor impairments. Accurate motor assessment is essential for rehabilitation planning and monitoring recovery. This assessment is traditionally performed using standardized clinical scales, such as the Fugl-Meyer Assessment (FMA), which require trained healthcare professionals, can be time- and resource-intensive, and involve subjectivity, as scores may vary across evaluators. Moreover, they cannot be easily administered remotely, and repeated in-person evaluations can be difficult for individuals with mobility limitations. Faster and more objective assessment approaches could enable more frequent evaluations and improve the tracking of motor recovery. Although recent advances in digital health, exergames, and Artificial Intelligence (AI) have enabled alternative solutions, many existing systems rely on specialized motion capture sensors, time-consuming software, or non-interpretable AI models, limiting accessibility, scalability, and clinical adoption. Objectives: This thesis aims to develop and evaluate a sensor-free, lightweight, and interpretable approach for post-stroke upper-limb motor assessment embedded into a rehabilitation exergame. The proposed system simultaneously provides therapeutic exercises and automatically estimates upper-limb motor performance during gameplay using only a standard camera, enabling supervised remote use. Specifically, the objectives are to (i) review existing automated motor assessment methods and their relationships with kinematic game parameters, and (ii) propose and preliminarily validate a low-cost exergame framework capable of estimating clinical motor impairment using simple and transparent kinematic features. Materials and Methods: A systematic review was conducted to analyze current technologies and computational approaches for automated upper-limb motor assessment after stroke, identifying the most used game parameters. Based on these findings, an experimental study was developed using a Unity-based rehabilitation exergame controlled by arm movements captured with a standard camera and processed using the MediaPipe framework. Sixteen kinematic and spatiotemporal features were extracted from two-dimensional hand and arm trajectories during gameplay. Twelve individuals with chronic stroke (24 upper limbs) participated, with bilateral FMA scores used as the clinical reference. Correlation analyses, exhaustive feature selection, and multiple linear regression modeling were performed to estimate FMA scores, with exploratory comparisons to alternative machine learning models. Results: The systematic review indicated that most existing approaches depend on external sensors or computationally complex methods, often limiting interpretability and real-world applicability. In the experimental study, some gameplay-derived and clinically interpretable features, including average hand aperture, and spatial exploration area, were significantly correlated with FMA scores. A lightweight multiple linear regression model demonstrated strong predictive performance for affected limbs (Spearman ρ = 0.92, R² = 0.89, RMSE = 4.42) and accurately stratified motor impairment severity, achieving accuracies between 86% and 93%. More complex machine learning models did not outperform the interpretable regression approach. Conclusion: This thesis demonstrates that sensor-free, low-cost, interpretable and lightweight computation models for post-stroke motor assessment can be embedded into rehabilitation exergames using kinematic features derived from a standard camera, and be potentially valid for motor function assessment. Further tests with more games and populations are needed to generalize the result. Integrating assessment into gameplay reduces clinical workload, enables high-frequency monitoring, and improves accessibility for telerehabilitation. 2026-03-02T00:00:00Z https://repositorio.ufu.br/handle/123456789/48575 Title: Expressões analíticas aproximadas em forma fechada para a probabilidade média de erro de símbolo da modulação QAM cruzada nos canais de desvanecimento η–μ e κ–μ Abstract: Introduction: Modern communication systems, such as 5G and 6G, require high reliability and low latency, but are heavily affected by channel fading, which compromises signal quality in multipath environments. Although traditional models, such as Rayleigh, Rician, and Nakagami-m, are widely used, they present limitations by assuming specific propagation conditions and failing to accurately represent the diversity of real-world scenarios, especially at millimeter-wave frequencies. To overcome these limitations, generalized models such as the η–μ and κ–μ have been proposed, offering greater flexibility by accounting for multiple dominant components and unbalanced scattering. However, the estimation of error probabilities associated with these models is essential for their practical implementation. Objectives: This work presents the derivation of approximate closed-form analytical expressions for the Average Symbol Error Probability (SEP) and investigates their performance for M-QAM modulation under generalized fading models. Materials and Methods: The adequacy of the derived expressions was analyzed considering standardized millimeter-wave frequency bands of 26, 28, 39, 55, 60, and 65 GHz. These analyses were based on channel modeling results obtained from an extensive measurement campaign in indoor environments under both Line-of-Sight (LoS) and non-Line-of-Sight (nLoS) conditions, as well as varying distances between transmitting and receiving antennas (Tx and Rx) with vertical and horizontal polarizations (VV and HV). Results: The expressions were validated through simulations performed using the MATLAB software, demonstrating strong agreement between the theoretical curves and the simulated results. The analyses revealed that line-of-sight scenarios exhibit significantly superior performance compared to nLoS cases. Furthermore, it was observed that increasing the frequency does not necessarily lead to worse performance, and that higher modulation orders require higher Eb/N0 values to achieve low error rates, highlighting the importance of employing robust coding techniques. The results contribute to a better understanding of the potential and challenges of M-QAM modulation in realistic 5G millimeter-wave communication scenarios. 2026-03-03T00:00:00Z