Fault-tolerant multilevel converter to feed a switched reluctance machine

The switched reluctance machine (SRM) is one of the most interesting machines, being adopted for many applications. However, this machine requires a power electronic converter that usually is the most fragile element of the system. Thus, in order to ensure high reliability for this system, it is fundamental to design a power electronic converter with fault-tolerant capability. In this context, a new solution is proposed to give this capability to the system. This converter was designed with the purpose to ensure fault-tolerant capability to two types of switch faults, namely open- and short-circuit. Moreover, apart from this feature, the proposed topology is characterized by a multilevel operation that allows improvement of the performance of the SRM, taking into consideration a wide speed range. Although the proposed solution is presented for an 8/6 SRM, it can be used for other configurations. The operation of the proposed topology will be described for the two modes, fault-tolerant and normal operation. Another aspect that is addressed in this paper is the proposal of fault detection and diagnosis method for this fault-tolerant inverter. It was specifically developed for a multilevel SRM drive. The theoretical assumptions will be verified through two different types of tests, firstly by simulation and secondly by experiments with a laboratory prototype.info:eu-repo/semantics/publishedVersio

The choice of transport technology in the presence of exports and FDI

In a set-up with intermediate production, we analyze how a shipper's choice of transport technology, traditional versus modern, interacts with the mode of foreign expansion by an service firm, export versus foreign direct investment (FDI). In terms of the mode of foreign expansion by the service firm, we obtain that: due to trade in intermediate goods, trade and FDI can be complements; the export strategy dominates when the economies of scale at plant level are high and trade costs are low; the FDI strategy is preferable when market size is large and trade costs are intermediate. In what concerns the choice of transport technology by the shipper, we find that: the modern technology tends to be implemented in larger markets; economic integration can encourage the adoption of modern technology vis-à-vis the traditional one; the modern technology adoption is more likely for intermediate levels of transport costs. We then have that modern technology adoption usually occurs under the FDI strategy, since both emerge when trade costs are intermediate and market size is large.Transport Technology, Foreign Direct Investment, Trade, Service Sector, Firm Location.

Media bias, news customization and competition

The media bias literature has focused its attention on single-ideology media firms. We analyze the incentives for media firms to adopt a multi-ideology strategy. A multi-ideology strategy occurs when a media firm adapts news to consumers’ political preferences. In this sense, news customization can reduce media bias, since media firms can cover a larger variety of political opinions. We show that although the incentives to customize are larger under duopoly than under monopoly, a monopolist might also end up offering customized news to consumers. In this sense, we argue that the competition policy for the media sector should take into consideration not only media concentration issues, but also the plurality of political opinions embraced inside a media firm

Should governments help winners or losers?

One central result in the strategic trade literature is that governments should not support domestic ”losers” but domestic ”winners”. We show that when first-mover advantages are taken into account, the reverse holds, governments have stronger incentives to support domestic ”losers” that face foreign ”winners”. Accordingly, governments can play Stackelberg against foreign Stackelberg leaders to prevent them from playing Stackelberg against domestic Stackelberg followers

Migration policy, illegal migrants, self-selection and brain drain

We compare two migration policies: an open migration policy, where all migrants can migrate legally; and a selective migration policy, where migrants are selected according to skills. We show that since the selective migration policy can create illegal migration, it has the following effects relatively to the open migration policy: (1) it weakens the chances of a positive self-selection of skilled migrants; (2) it reduces the possibility of a beneficial brain gain; and (3) it dampens the effectiveness of education policies. Accordingly, since illegal migration can conduce to brain waste (i.e.: skilled workers working as unskilled), the selective migration policy reduces the incentives of individuals to acquire education and of skilled workers to migrate

PV generator-fed water pumping system based on a SRM with a multilevel fault-tolerant converter

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.info:eu-repo/semantics/publishedVersio

Media bias and news customization

In this paper we analyze the effects of news customization (tailoring news to consumers’ political preferences) on media bias. In particular, we extend Hotelling’s duopoly location model to include news customization. Customization occurs when a media firm supplies the market with a continuous line segment of political opinions (i.e.: multi-ideology firm), instead of just a single point on the line (i.e.: single-ideology firm) as in the standard Hotelling model. The customization strategy has some costs related to the adaptation of news to consumers’ political preferences, however, the advantage arises from the possibility to price discriminate between different consumers. In this set up, we show that the possibility to customize news by media firms does not reduce media bias. Accordingly, in order to avoid fierce price competition in the standard segment (which also reduces the revenues from price discrimination in the customized segment), firms decide not to cover a larger variety of political options

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

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