ISEL - Eng. Electrotécn. - Comunicações
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Percorrer ISEL - Eng. Electrotécn. - Comunicações por Domínios Científicos e Tecnológicos (FOS) "Engenharia e Tecnologia::Engenharia Eletrotécnica, Eletrónica e Informática"
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- Dual three-phase four-leg multilevel inverter with backstepping prediction for unbalanced low-voltage gridsPublication . Monteiro, Joaquim; Pires, V. Fernão; Cordeiro, Armando; Pinto, Sónia; Silva, José Fernando; Monteiro, Joaquim; Cordeiro, ArmandoWind and solar renewable energy sources (RES) have been fundamental in reducing carbon emissions in electrical energy systems. However, when integrated into low voltage grids, some problems can arise due to the high number of single-phase loads. This situation often leads to unbalanced loads, which can result in increased losses or even under- or over-voltages in one of the phases. This issue is even more critical in the context of isolated microgrids. Therefore, this paper introduces a novel control system for a grid-connected photovoltaic (PV) generation with storage setup based on a dual three-phase four-leg multilevel inverter. This power converter topology, comprising two four-leg two-level three-phase inverters, connects two PV arrays to a three-phase transformer with four wires which in turn connects to a grid. This arrangement is designed to inject PV-generated power into the low voltage (LV) grid, providing support for unbalanced loads. A new backstepping method including the delay simplified dynamics is derived to estimate the optimum converter voltage and near optimum vector to control the load currents, while balancing the capacitor DC voltages. As only one voltage estimate is needed, a fast controller is obtained even if the converter has a high number of voltage vectors. The backstepping method increases the speed of choosing the converter vector, allowing the control of the grid currents injected under both balanced and unbalanced conditions, while also maintaining balance of the capacitor DC voltages in RES. Experimental tests were conducted using a laboratory prototype to evaluate the backstepping performance applied to the proposed PV generation system.
- ESS design and management considering solar PV to fed off-grid EV chargerPublication . Santos, Diogo; Fonte, Pedro M; Pereira, Rita Marcos Fontes Murta; Barata, Filipe; Almeida, Paulo; Cordeiro, Armando; Luís, Ricardo Jorge Ferreira; Fernao Pires, VitorThe increase of electric vehicles creates several challenges to the electric grid, mainly in those with weak power or off-grid. DC microgrids are becoming more and more important in the context of renewable energy sources, where solar PV systems are dominant. In this paper is proposed the design of a DC system to charge electric vehicles using PV generation and a battery storage system. A single DC-DC converter is used to operate the solar PV array with maximum power point tracking method and controls power flow from PV to storage battery and to the EV, operating as DC EV charger. The operation under various loading conditions is discussed. The performance of the proposed solution was simulated using MATLAB/Simulink software.
- Improving the FMEA method to failure risk assessment of transformers: a case study in Tehran electric power distribution transformersPublication . Shafei, Atefeh Pour; Rezaei, Alireza; Silva, J. Fernando A.; Monteiro, J.; Monteiro, JoaquimDistribution transformers play a pivotal role in power networks, serving as critical assets whose failure can lead to substantial expenses for replacement or repair. This study employs an improved Failure Modes and Effects Analysis (FMEA) method, utilizing transformer failures within the Tehran Electric Power Distribution Company over a decade. The Risk Priority Number (RPN) criterion assesses the failure probability associated with various failure modes for quantization within the FMEA method. Risk prioritization is determined through the RPN formulation. This paper proposes new improvements in FMEA, including an expert-based weighting method applied to the weighted RPN's sub-parameters to enhance precision and calculate RPN values based on the age group of each transformer. Subsequently, strategic corrective actions are proposed and implemented to mitigate the risk of transformer failures in the upcoming year. The culmination of this case study results in improved prediction capabilities and more effective failure prevention strategies for the company's transformers, facilitating purposeful asset management.
- Model predictive control of dual three-phase four-leg multilevel inverter supplying photovoltaic energy to low-voltage unbalanced gridsPublication . Monteiro, Joaquim; Pires, V. Fernão; Silva, J.; Fernando et al.; Monteiro, JoaquimIn this paper, a new control system is proposed for a grid-connected photovoltaic (PV) generation system based on a dual three-phase four leg multilevel inverter. This power converter topology, built using two four-leg two-level three-phase inverters, connects two PV arrays in the DC side to three open-end-windings of a three-phase transformer on the AC side. This arrangement is controlled to inject the PV generated power into the low voltage (LV) grid allowing support for unbalanced loads. The proposed control system is based in the model predictive control (MPC). It allows the control of the injected grid currents in balanced/unbalanced conditions while ensuring the balance of the capacitor DC voltages. Several simulation tests are made to validate the effectiveness of the control strategy applied to the proposed PV generation system.
- Particle swarm optimization-based algorithm for optimal reactive power dispatchPublication . Menezes, R.; Fonte, Pedro M; Pestana, RuiOptimal Reactive Power Dispatch (ORPD) is very important for the security and economy of power systems. It is a mixed integer nonlinear optimization problem for which metaheuristic methods have proven to be effective in its solution. This paper presents an implementation of the particle swarm optimization algorithm (PSO) for the solution of the ORPD. Another approach, called Fitness-Distance Ratio PSO (FDR-PSO), is implemented to improve the results of the basic PSO. One other version called Second Order PSO (SO-PSO) is implemented for the same purpose. This second-order principle was combined with the FDR-PSO, making it the SO-FDR-PSO. These versions were tested on the IEEE 14 bus and IEEE 39 bus systems. The results show that the tested PSO algorithm and its improved versions can converge to good global optimal solutions (the best optimal solution the PSO could find), effectively solving the ORPD, with increasing degrees of success.