Percorrer por autor "Cordeiro, Armando"
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- DC Microgrids: Benefits, Architectures, Perspectives and ChallengesPublication . Pires, Vítor Fernão; Pires, A. J.; Cordeiro, ArmandoOne of the major paradigm shifts that will be predictably observed in the energy mix is related to distribution networks. Until now, this type of electrical grid was characterized by an AC transmission. However, a new concept is emerging, as the electrical distribution networks characterized by DC transmission are beginning to be considered as a promising solution due to technological advances. In fact, we are now witnessing a proliferation of DC equipment associated with renewable energy sources, storage systems and loads. Thus, such equipment is beginning to be considered in different contexts. In this way, taking into consideration the requirement for the fast integration of this equipment into the existing electrical network, DC networks have started to become important. On the other hand, the importance of the development of these DC networks is not only due to the fact that the amount of DC equipment is becoming huge. When compared with the classical AC transmission systems, the DC networks are considered more efficient and reliable, not having any issues regarding the reactive power and frequency control and synchronization. Although much research work has been conducted, several technical aspects have not yet been defined as standard. This uncertainty is still an obstacle to a faster transition to this type of network. There are also other aspects that still need to be a focus of study and research in order to allow this technology to become a day-to-day solution. Finally, there are also many applications in which this kind of DC microgrid can be used, but they have still not been addressed. Thus, all these aspects are considered important challenges that need to be tackled. In this context, this paper presents an overview of the existing and possible solutions for this type of microgrid, as well as the challenges that need to be faced now.
- A DC-DC Converter with Capability to Support the Voltage Balance of DC Bipolar MicrogridsPublication . Pires, Vítor; Foito, Daniel José Medronho; Cordeiro, Armando; Silva, J. FernandoBipolar DC microgrids are now starting to become an interesting solution for power distribution. Although presenting several advantages over DC unipolar microgrids, bipolar DC has the intrinsic problem of voltage unbalance that may appear depending on the converter topology and load sharing. Therefore, this paper presents a new DC-DC converter topology that can be used with renewable energy sources and has the capability to simultaneously ensure the bipolar microgrid voltage balance. The operation of the proposed topology together with its characteristics is described. A theoretical study of this converter will also be presented, complemented by a set of results from computer simulations. To support these simulations, results from a laboratory prototype will also be displayed. The voltage balance capability of the converter will be checked experimentally.
- Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators Connected to DC Bipolar MicrogridsPublication . Pires, Vitor Fernão; Cordeiro, Armando; Foito, Daniel José Medronho; Silva, J. Fernando A.This paper introduces a new topology for a DC-DC converter with bipolar output and high voltage gain. The topology was designed with the aim to use only one active power switch. Besides the bipolar multiport output and high voltage gain this converter has another important feature, namely, it has a continuous input current. Due to the self-balancing bipolar outputs, the proposed topology is suitable for bipolar DC microgrids. Indeed, the topology balancing capability can achieve the two symmetrical voltage poles of bipolar DC microgrids. Furthermore, it is possible to create a midpoint in the output of the converter that can be directly connected to the ground of the DC power supply, avoiding common-mode leakage currents in critical applications such as transformerless grid-connect PV systems. The operating principle of the proposed topology will be supported by mathematical analysis. To validate and verify the characteristics of the presented topology, several experimental results are shown.
- A Fault Diagnosis Scheme Based on the Normalized Indexes of the Images eccentricity for a Multilevel Converter of a Switched Reluctance Motor DrivePublication . Amaral, Tito G.; Pires, Vitor; Foito, Daniel José Medronho; Cordeiro, Armando; Rocha, José Inácio Pinto Rosado; Pires, A. J.; Martins, J. F.This paper addresses the fault detection and diagnosis of a fault in the switches of the Switched Reluctance Machine (SRM) power electronic converter. Due to the advantages of using multilevel converters with these machines, a fault detection and diagnosis algorithm is proposed for this converter. The topology under consideration is the asymmetric Neutral Point Clamped (ANPC), and the algorithm was developed to detect open and short circuit faults. The proposed algorithm is based on an approach that discriminates eccentricity of the images formed by the converter voltages. This discrimination is realized through the development of normalized indexes based on the entropy theory. Besides the different fault type the algorithm is also able to detect the transistor under fault. The possibility to implement the proposed approach will be verified through simulation tests.
- Fault-Tolerant SRM Drive with a Diagnosis Method Based on the Entropy Feature ApproachPublication . Pires, Vitor Fernão; Amaral, Tito G.; Cordeiro, Armando; Foito, Daniel José Medronho; Pires, A. J.; Martins, João F.The power electronic converter design is essential for the operation of the switched reluctance motor (SRM). Thus, a fault-tolerant power converter is fundamental to ensure high reliability and extend the drive operation. To achieve fault tolerance, fault detection and diagnosis methods are critical in order to identify, as soon as possible, the failure mode of the drive. To provide such capability, it is proposed in this paper a new fault-tolerant power converter scheme combined with a fault detection method regarding the most common power semiconductors failures in SRM drives. The fast and reliable proposed diagnosis method is based on the entropy theory. Based on this theory, normalized indexes (diagnostic variables) are created, which are independent from the load and speed of the motor. Through this method, it is possible to identify the faulty leg, as well as the type of power semiconductor fault. To test and evaluate the proposed solution several laboratory experiments were carried out using a 2 kW four-phase 8 / 6 SRM.
- Modbus Protocol as Gateway between different Fieldbus devices: a Didactic ApproachPublication . Cordeiro, Armando; Costa, Paulo; Pires, VítorThis paper is dedicated to improve the skills of Electric Engineering students about Industrial Automation. This is done creating a set of practical exercises in the laboratory that allow students to interact with didactic and industrial equipment understanding the compatibility problems and give students the tools, the knowledge and even some creative freedom to solve problems that happens in real situations. In this case, it was focuses in the interconnection of equipment from different manufacturers using the Modbus protocol. To allow to the students this practical study, it was developed a solution with a Modbus RTU protocol directly implemented in program memory of both S7-200 (using the Freeport configuration mode) and S7- 300 PLCs. The solution allows a gateway between Modbus-TCP (over a Master TSX PLC from Schneider-Electric) and Profibus-DP (over a Master S7-300 PLC from Siemens).
- A Multilevel Fault-Tolerant Power Converter for a Switched Reluctance Machine DrivePublication . Pires, Vítor Fernão; Cordeiro, Armando; Foito, Daniel José Medronho; Pires, A. J.; Martins, João; Chen, HaoReliability in the electrical drives is becoming an important issue in many applications. In this context, the reliability associated to the switched reluctance machine (SRM) is also an important area of research. One of the major problems, that strongly affect its operation, are drive power semiconductors faults. Typical power converter topologies used in SRM drives cannot handle faults in their power semiconductors. So, this paper presents a power converter topology that provides fault-tolerant capabilities to the drive under a switch fault. This power converter will be used considering that a change in the direction of the current that flows in the SRM windings does not affect the behavior of the machine. Besides that, the proposed power converter will allow to generate multilevel phase voltages in order to apply different voltage levels as function of the SRM speed. A laboratory power converter was developed to test the SRM drive in normal and faulty conditions. From the obtained results it was possible to verify the fault-tolerant capability of the drive under switch faults in different devices and failure modes. It was also possible to confirm the multilevel operation of the drive.
- PV Generator-Fed Water Pumping System Based on a SRM with a Multilevel Fault-Tolerant ConverterPublication . Pires, Vítor Fernão; Foito, Daniel José Medronho; Cordeiro, Armando; Chaves, Miguel; Pires, A. J.This paper presents a pumping system supplied by a PV generator that is based on a switched reluctance machine (SRM). Water pumping systems are fundamental in many applications. Most of them can be used only during the day; therefore, they are highly recommended for use with PV generators. For the interface between the PV panels and the motor, a new multilevel converter is proposed. This converter is designed in order to ensure fault-tolerant capability for open switch faults. The converter is based on two three-level inverters, with some extra switches. Moreover, to reduce the number of switches, the converter is designed to provide inverse currents in the motor windings. Due to the characteristics of this motor, the inverse currents do not change the torque direction. In this way, it was possible to obtain an SRM drive with fault-tolerant capability for transistor faults; it is also a low-cost solution, due to the reduced number of switches and drives. These characteristics of fault-tolerant capability and low cost are important in applications such as water pumping systems supplied by PV generators. The proposed system was verified by several tests that were carried out by a simulation program. The experimental results, obtained from a laboratory prototype, are also presented, with the purpose of validating the simulation tests.
- A Review of the Power Converter Interfaces for Switched Reluctance MachinesPublication . Pires, Vítor Fernão; Pires, A. J.; Cordeiro, Armando; Foito, Daniel José MedronhoThe use of power electronic converters is essential for the operation of Switched Reluctance Machines (SRMs). Many topologies and structures have been developed over the last years considering several specific applications for this kind of machine, improving the control strategies, performance range, fault-tolerant operation, among other aspects. Thus, due to the great importance of power electronic converters in such applications, this paper is focused on a detailed review of main structures and topologies for SRM drives. The proposed study is not limited to the classic two-level power converters topologies dedicated to the SRMs; it also presents a review about recent approaches, such as multilevel topologies and based on impedance source network. Moreover, this review is also focused on a new class of topologies associated to these machines, namely the ones with fault-tolerant capability. This new category of topologies has been a topic of research in recent years, being currently considered an area of great interest for future research work. An analysis, taking into consideration the main features of each structure and topology, was addressed in this review. A classification and comparison of the several structures and topologies for each kind of converter, considering modularity, boost capability, number of necessary switches and phases, integration in the machine design, control complexity, available voltage levels and fault-tolerant capability to different failure modes, is also presented. In this way, this review also includes a description of the presented solutions taking into consideration the reliability of the SRM drive.
- A Skewness Based Method for Diagnosis in Quasi-Z T-Type Grid-Connected ConvertersPublication . Amaral, Tito; Cordeiro, ArmandoOne of the very interesting converters for transformerless grid-connected PV systems is the multilevel quasi-Z T-Type inverter. Besides their multilevel operation, it presents voltage Boost capability and robustness to instantaneous switching between power semiconductors of the same leg and capability to work in fault tolerant condition. However, to ensure this capability, it is essential to ensure a fast and correct diagnosis of the component under fault. Thus, this paper proposes a new method for the detection of an open switch fault. The proposed approach uses the inverter AC line currents that will be analyzed by a Skewness based method. The method has the capability to distinguish the switch under fault. Besides that, it presents robustness to interferences such as noise, as well is insensible to variations of the injected power into the grid. Several simulation and experimental results will be presented in order to verify the capability of the proposed method.