Percorrer por autor "Monteiro, Joaquim"
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- Backstepping sliding mode controller for MPPT in DC microgrid connected Quadratic Boost converters fed from PV systemsPublication . Monteiro, Joaquim; Silva, J. Fernando; Cordeiro, Armando; Pinto, Sónia; Pires, V. Fernão; Monteiro, Joaquim; Cordeiro, Armando; IEEEPhotovoltaic (PV) systems are crucial for harnessing solar energy; however, environmental factors and the variability of the connected load significantly influence their energy generation capacity. In this context, the effectiveness of the controller used for maximum power point tracking (MPPT) to enhance efficiency relies on a thorough analysis of the nonlinear models of PV systems. Over these last decades, many control techniques have been developed to enhance the energy extraction from PV cells and improve system efficiency. Since real-world systems have real-time variations, it is difficult to continuously update both the system and the controller. The changes can produce steady state errors in the output and reduce the efficiency of the controller. As a solution to this issue, in this work a nonlinear backstepping sliding mode controller (BSMC) is proposed to improve the performance of the MPPT system. The BSMC MPPT, coupled to a DC-DC quadratic boost converter (QBC), is used as the interface between a PV array and a microgrid. Backstepping control ensures global asymptotic stability of the system by achieving the optimal power point, following Lyapunov stability criteria. Simulation and experimental results of the proposed MPPT solution are presented confirming that the system operates as expected.
- 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.
- A DC DC converter with extended voltage static gain input output continuous current and reduced switch voltage stressPublication . Monteiro, Joaquim; Monteiro, Joaquim; Pires, V. Fernão; Foito, Daniel; Silva, J. Fernando; Pinto, Sónia
- DC-DC converter with Buck-Boost characteristics and high voltage gain based on the differential conceptPublication . Pires, V. Fernão; Foito, Daniel; Cordeiro, Armando; Monteiro, Joaquim; Pinto, Sónia; Silva, J. Fernando; Monteiro, Joaquim; Cordeiro, Armando; IEEEThis paper introduces a novel DC-DC converter based on the differential concept. This topology can operate in interleaved mode, which, together with the differential concept, allows for a reduction in the size of the inductors. This converter is also characterized by their continuous input current. Moreover, it is also characterized by an extended voltage range when compared with the classical Buck-Boost converter. Another aspect, is that the voltage stress across the switches is reduced when compared with the output voltage. The same regarding the voltage stress across the capacitors. The proposed converter will be tested through the one of the most used simulation tools, as well as, by a laboratory prototype.
- Decoupled Direct Power Compensators for a Dual-Inverter Based UPFCPublication . Monteiro, Joaquim; Silva, J. Fernando; Pinto, Sónia; Pires, V. Fernão; Monteiro, Joaquim; IEEEIn recent decades, Unified Power Flow Controllers (UPFCs) have become essential devices for enhancing the flexibility and controllability of modern electrical transmission networks. These devices facilitate the simultaneous control of local bus voltage and the optimization of power flow within electrical power transmission systems. The multilevel converter capability to operate with high voltage levels while generating low-distortion AC voltages, makes multilevel topologies suitable for UPFCs. Within this framework, this paper presents a novel multilevel converter topology and control strategy specifically designed for UPFC applications. The proposed solution employs a dual inverter topology driven by sliding mode direct power controllers, which are controlled via decoupled Proportional-Integral (PI) compensators. The characteristics, capabilities, and resulting flexibility of the proposed UPFC and control subsystem is validated through a series of simulation tests.
- Diagnosing Power Transistor Faults in Multilevel T-Type Based Nine Switch Inverter Using Center of Mass IndexesPublication . Monteiro, Joaquim; Amaral, Tito; Silva, J. Fernando; Pinto, Sonia; Fernao Pires, VitorNine-switch voltage source inverters (NSVSI) are DC-AC converters that utilize a reduced number of switches, making them advantageous for dual or six-phase motors. To enhance the quality of the output voltage and provide fault tolerant capability, NSVSI topologies, like the T-Type-based NSVSI, have been modified to operate as multilevel converters. However, to ensure fault-tolerant capability, a fault diagnosis algorithm for power transistors must be developed. Therefore, this paper proposes a novel fault detection and diagnosis algorithm to identify faulty transistors in a multilevel T-Type-based NSVSI. This method is based on the development of specific indices derived from the center of mass of the output currents. The proposed technique offers a fast and reliable solution, demonstrating robustness under various load conditions. The effectiveness of this method will be validated through a series of simulation tests.
- Direct Power Control of Matrix Converter Based Unified Power Flow ControllersPublication . Monteiro, Joaquim; Silva, J. Fernando; Pinto, S. F.; Palma, João Carlos Pires daThis paper presents the Direct Power Control of Three-Phase Matrix Converters (DPC-MC) operating as Unified Power Flow Controllers (UPFC). Since matrix converters allow direct AC/AC power conversion without intermediate energy storage link, the resulting UPFC has reduced volume and cost, together with higher reliability. Theoretical principles of DPC-MC method are established based on an UPFC model, together with a new direct power control approach based on sliding mode control techniques. As a result, active and reactive power can be directly controlled by selection of an appropriate switching state of matrix converter. This new direct power control approach associated to matrix converters technology guarantees decoupled active and reactive power control, zero error tracking, fast response times and timely control actions. Simulation results show good performance of the proposed system.
- Dual 3-phase bridge multilevel inverters for AC drives with voltage sag ride-through capabilityPublication . Fernao Pires, Vitor; Monteiro, Joaquim; Silva, José FernandoOne of the main power quality issues that can affect variable speed drives (VSDs) is the occurrence of voltage sags on their AC power supply. Voltage sags can affect the inverter nominal operation, leading to a malfunction of the AC motor. This paper presents an inverter with resilient capability to voltage sags. The topology consists of two conventional three-phase bridge inverters arranged to require just a single DC source. This inverter is also characterized by a voltage multilevel operation, providing the full advantages of multilevel converters without the need for level balancing. Associated with this AC motor driver, a control system based on a field-oriented controller with a vector voltage modulator that will enable voltage sag ride-through capability is proposed. The proposed control system does not require any changes in the occurrence of voltage sags. To verify the characteristics of the proposed drive and control system, simulation tests are provided. Simulation results confirm the voltage sag resilient capability of the proposed multilevel converter.
- 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.
- A dual-output NPC-type converter with a model predictive controller with compensation of DC capacitor voltage imbalancePublication . Monteiro, Joaquim; Pires, V. Fernão; Silva, J. Fernando; Pinto, Sónia; Monteiro, JoaquimThe dual output three-level converter is now important for several applications namely dual motor drives. The recent dual output nine-switch multilevel three-phase inverter, based on the NPC-Type structure, has been studied in open loop at nominal conditions, without closed loop control. Moreover, the dual output nine-switch multilevel inverter may present issues related to load currents control and to the unbalance of two series capacitor voltages in the dc-link. Thus, in this research work the model predictive controller (MPC) is proposed for closed loop current control, as well as for mitigation of the capacitor voltages imbalance. The MPC approach allows the minimization of a cost functional weighing two criteria, the tracking errors of the three-phase AC currents of each inverter output, as well as the two capacitors voltage imbalance. Several simulations showing the performance of the proposed control strategy are presented and discussed.
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