DC Microgrids: Benefits, Architectures, Perspectives and Challenges

One 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.info:eu-repo/semantics/publishedVersio

A High-Voltage Gain Non-Isolated DC–DC Converter Designed for Bipolar DC Microgrids

Publisher Copyright: © 2023 Taylor & Francis Group, LLC.DC microgrids are now starting to attract huge attention from researches and engineers. Among the several DC microgrid architectures, bipolar DC microgrids are advantageous to accommodate a wider range of DC loads. However, due to mismatched loads connected to the two poles, bipolar DC microgrids may show voltage balancing issues. In this context, this article presents a new high input-to-output voltage gain, non-isolated DC–DC converter specifically designed for bipolar DC Microgrids. The proposed converter supports the balance of voltages at both bipolar DC microgrid poles, as the converter can transfer energy between the two poles in an unbalanced way. The description, theoretical support, and operation of the proposed converter will be presented. The theoretical assumptions will be complemented with several results obtained from computer simulation tests. The simulation tests will be compared to laboratory results from an experimental prototype. The obtained results confirm the theoretical properties of the proposed converter.publishersversionpublishe

A Review of the Power Converter Interfaces for Switched Reluctance Machines

The 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.info:eu-repo/semantics/publishedVersio

Superconductivity and their applications

Trabalho apresentado em International Conference on Renewable Energies and Power Quality (ICREPQ’17), 4 a 6 de Abril de 2017, Málaga, EspanhaThe research in the field of superconductivity has led to the synthesis of superconducting materials with features that allow you to expand the applicability of this kind of materials. Among the superconducting materials characteristics, the critical temperature of the superconductor is framing the range and type of industrial applications that can benefit from them. Some examples of industrial applications incorporating superconducting materials stand out in this paper. Among other possibilities, the nuclear magnetic resonance, the magnetic levitation train, the transport processing of electrical energy (motors, generators, transformers and power lines) and superconducting magnetic energy storage (SMES) systems are already solutions contributing to the nowadays daily life, but more than that, are solutions that will contribute to improve the quality of life of many human beings in the near future. In addition to these solutions, in this paper are presented and discussed the pros and cons of a solution designed for the fast field cycling nuclear magnetic resonance technique that benefits of the usage of superconducting blocks.N/

Development of a System for the Usability of Forest Residuesfor Electric Energy Production

Trabalho apresentado em International Conference on Renewable Energies and Power Quality, 4-6 maio 2016, Madrid, SpainN/

Bidirectional DC-DC Converter with High Voltage Gain for the Charge/Discharge Control of Storage Systems

Trabalho apresentado em 10th Electric Power Quality and Supply Reliability Conference, 29-31 de agosto, Tallin, EstóniaThis paper presents a study of a bidirectional dc-dc converter with high voltage gain to regulate the charge and discharge of electrochemical storage systems. The converter is characterized by quadratic voltage gain characteristics in both directions. In this context it can be used to regulate a dc interface between the storage system and a dc/ac converter connected to the electrical grid. It will be analysed the converter in ideal and non-ideal conditions. A control system to regulate the output voltages and currents are also proposed. Simulation results are presented in order to validate the control system associated to the converter for the charge/discharge of the storage system.N/

Testing System for PV Grid-Connected Power Condition Systems with Support for Ancillary Services

Funding Information: This work was supported by national funds through FCT—Fundação para a Ciência e a Tecnologia with reference UID/CEC/50021/2020 and UID/EEA/00066/2020. Publisher Copyright: © 2023 by the authors.Due to the high spread of photovoltaic (PV) systems in the low voltage distribution grids there is a substantial number of requirements for the connection of these systems. Therefore, several tests should be performed before the integration of the PV systems into the grid. Moreover, new requirements have been established that are most likely to be implemented in the near future. To provide these tests and verify if PV systems are in accordance with requirements and recommendations, a testing setup for the PV systems was developed. This testing system consists of a controllable power source prepared to receive energy and to inject it into the grid. In fact, that system imposes a controllable voltage, in amplitude and frequency, to the PV system to simulate the perturbations of the grid. Since the system under test must inject energy in accordance with the standards’ specifications, then the controllable power source that emulates the grid must receive that energy. Moreover, it should also be prepared for PV systems that are able to provide ancillary services, including new ones that support imbalanced networks. A fast and robust control system will be used for this controllable power source. Several experimental tests from the developed prototype are presented.publishersversionpublishe

Financial Analysis of Household Photovoltaic Self-Consumption in the Context of the Vehicle-to-Home (V2H) in Portugal

Publisher Copyright: © 2023 by the authors.This paper focuses on the purpose to see if it is possible to increase the earnings associated to the installation of PV systems in people’s homes. In accordance with this, a different way of thinking was adopted, namely the investment in batteries to maximize the energy earnings. The main problem of this classical approach is that the investment in those batteries is important. In this way, a different perspective was taken into account, namely the use of the electrical vehicles. This kind of vehicles is starting to become a real reality. In fact, the selling of these vehicles start to become a solution for the ordinary people, and it is expected in a very near future to be a reality for most of them. Thus, this study presents the use of a storage system based on the vehicle-to-home (V2H) technology for the people’s homes. The V2H availability varies among prosumers profile regarding the daily routines, weather conditions, and business aspects, besides other aspects. These profiles were combined with different power panels with and without injection into the grid. The costs of each configuration considering a residential consumer located in Portugal, as well as, their peak solar hours in a year were estimated. From this study, it will be possible to verify that the obtained economical results show that the usage of V2H as storage system based on batteries for modern homes is very attractive.publishersversionpublishe

Water Pumping System Supplied by a PV Generator and with a Switched Reluctance Motor Using a Drive Based on a Multilevel Converter with Reduced Switches

Funding Information: This work was supported by national funds through the FCT—Fundação para a Ciência e a Tecnologia with reference UID/CEC/50021/2020 and UID/EEA/00066/2020. Publisher Copyright: © 2023 by the authors.Pumping systems play a fundamental role in many applications. One of the applications in which these systems are very important is to pump water. However, in the real world context, the use of renewable energies to supply this kind of system becomes essential. Thus, this paper proposes a water pumping system powered by a photovoltaic (PV) generator. In addition, due to its interesting characteristics, such low manufacturing cost, free of rare-earth elements, simple design and robustness for pumping systems, a switched reluctance motor (SRM) is used. The power electronic system to be used in the PV generator and to control the SRM consists of a DC/DC converter with a bipolar output and a multilevel converter. The adopted DC/DC converter uses only one switch, so its topology can be considered as a derivation of the combination of a Zeta converter with a buck–boost converter. Another important aspect is that this converter allows continuous input current, which is desirable for PV panels. The topology selected to control the SRM is a multilevel converter. This proposed topology was adopted with the purpose of reducing the number of power semiconductors. A maximum power point algorithm (MPPT) associated with the DC/DC converter to obtain the maximum power of the PV panels is also proposed. This MPPT will be developed based on the concept of the time derivative of the power and voltage. It will be verified that with the increase in solar irradiance, the generated power will also increase. From this particular case study, it will be verified that changes in the irradiance from 1000 W/m2 to 400 W/m2 will correspond to a change in the motor speed from 1220 rpm to 170 rpm. The characteristics and operation of the proposed system will be verified through several simulation and experimental studies.publishersversionpublishe

Incipient Fault Diagnosis of a Grid-Connected T-Type Multilevel Inverter Using Multilayer Perceptron and Walsh Transform

Publisher Copyright: © 2023 by the authors.This article deals with fault detection and the classification of incipient and intermittent open-transistor faults in grid-connected three-level T-type inverters. Normally, open-transistor detection algorithms are developed for permanent faults. Nevertheless, the difficulty to detect incipient and intermittent faults is much greater, and appropriate methods are required. This requirement is due to the fact that over time, its repetition may lead to permanent failures that may lead to irreversible degradation. Therefore, the early detection of these failures is very important to ensure the reliability of the system and avoid unscheduled stops. For diagnosing these incipient and intermittent faults, a novel method based on a Walsh transform combined with a multilayer perceptron (MLP)-based classifier is proposed in this paper. This non-classical approach of using the Walsh transform not only allows accurate detections but is also very fast. This last characteristic is very important in these applications due to their practical implementation. The proposed method includes two main steps. First, the acquired AC currents are used by the control system and processed using the Walsh transform. This results in detailed information used to potentially identify open-transistor faults. Then, such information is processed using the MLP to finally determine whether a fault is present or not. Several experiments are conducted with different types of incipient transistor faults to create a relevant dataset.publishersversionpublishe