2,348 research outputs found
A comprehensive review on modular multilevel converters, submodule topologies, and modulation techniques
The concept of the modular multilevel converter (MLC) has been raising interest in research in order to improve their performance and applicability. The potential of an MLC is enormous, with a great focus on medium- and high-voltage applications, such as solar photovoltaic and wind farms, electrified railway systems, or power distribution systems. This concept makes it possible to overcome the limitation of the semiconductors blocking voltages, presenting advantageous characteristics. However, the complexity of implementation and control presents added challenges. Thus, this paper aims to contribute with a critical and comparative analysis of the state-of-the-art aspects of this concept in order to maximize its potential. In this paper, different power electronics converter topologies that can be integrated into the MLC concept are presented, highlighting the advantages and disadvantages of each topology. Nevertheless, different modulation techniques used in an MLC are also presented and analyzed. Computational simulations of all the modulation techniques under analysis were developed, based on four cascaded full-bridge topologies. Considering the simulation results, a comparative analysis was possible to make regarding the symmetry of the synthesized waveforms, the harmonic content, and the power distribution in each submodule constituting the MLC.This work has been supported by FCT—Fundação para a Ciência e Tecnologia, within the
R&D Units Project Scope UIDB/00319/2020. Mr. Luis A. M. Barros is supported by the doctoral
scholarship PD/BD/143006/2018, granted by the Portuguese FCT foundation
Balancing the active power of a railway traction power substation with an sp-RPC
The railway system is one of the safest, most efficient, and environmentally friendly means of land transport for people and goods. However, as the demand for mobility has increased, the current railway system has shown some weaknesses, requiring an increase in catenary power in order to be able to supply power to longer trains and faster locomotives, as well as to increase rail traffic. This paper proposes a control algorithm to be implemented in a sectioning post-Rail Power Conditioner (sp-RPC). The sp-RPC is connected to the neutral section between two traction power substations (TPS). With the control algorithm, it is possible to minimize the existing unbalance of the active powers of each TPS. In a regenerative braking condition, this surplus energy can be used to assist the traction of another locomotive on the existing overhead line. In this way, it is possible to increase the capacity of the overhead line. The analysis was performed with computer models using a modular multilevel converter (MMC) topology for the sp-RPC. Quantitative results for different consumption events of the locomotives and the analysis of the response to these variations are presented.This work has been supported by FCT—Fundação para a Ciência e Tecnologia, within
the R&D Units Project Scope UIDB/00319/2020. Luis A. M. Barros is supported by the doctoral
scholarship PD/BD/143006/2018, granted by the Portuguese FCT foundation
A possible origin of superconducting currents in cosmic strings
The scattering and capture of right-handed neutrinos by an Abelian cosmic
string in the SO(10) grand unification model are considered. The scattering
cross-section of neutrinos per unit length due to the interaction with the
gauge and Higgs fields of the string is much larger in its scaling regime than
in the friction one because of the larger infrared cutoff of the former.The
probability of capture in a zero mode of the string accompanied by the emission
of a gauge or Higgs boson shows a resonant peak for neutrino momentum of the
order of its mass. Considering the decrease of number of strings per unit
comoving volume in the scaling epoch the cosmological consequences of the
superconducting strings formed in this regime will be much smaller than those
which could be produced already in the friction one.Comment: 14 pages Latex, 4 figues/ep
Opportunities and challenges of power electronics systems in future railway electrification
With the continuous expansion of the railway power
systems, the integration of high speed locomotives and the need to
increase the overhead catenary line power capacity, the main
shortcomings of the conventional railway feeding system are
becoming more evident. In order to overcome these drawbacks
and to contribute to the technological evolution with innovative
and electrically more efficient systems, several solutions have been
proposed and implemented. In this context, this paper briefly
presents a study of different railway power systems, highlighting
emerging concepts, such as regenerative braking, energy storage
systems, the inclusion of renewable energy sources, bidirectional
power flow and wireless power transfer. Some of these concepts
can be implemented in short to medium term, or in the long term.
Following these concepts, an overview of the power electronics
challenges for the implementation of these emerging concepts is
presented and discussed.This work has been supported by FCT –Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project QUALITY4POWER PTDC/EEI-EEE/28813/2017. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018 granted by the Portuguese FCT foundation. Mr. Mohamed Tanta was supported by FCT PhD grant with a reference PD/BD/127815/2016
Evaluation of static synchronous compensator and rail power conditioner in electrified railway systems using V/V and Scott power transformers
In this paper a comprehensive review of electrified railway systems is carried out, identifying the electric power quality deterioration which may appear due to nonlinear dynamic traction loads. Following this topic, a computational simulation of Static Synchronous Compensator (STATCOM) and Rail Power Conditioner (RPC) are presented, making a comprehensive analysis of each of these solutions regarding the power quality improvement in electrified railway systems. Four case studies are presented: (i) STATCOM evaluation when a traction power system is fed by a V/V power transformer; (ii)STATCOM evaluation when a traction power system is fed by a Scott power transformer; (iii) RPC evaluation when atraction power system is fed by a V/V power transformer; (iv) RPC evaluation when a traction power system is fed by aScott power transformer.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project QUALITY4POWER PTDC/EEI-EEE/28813/2017, and by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018 granted by the Portuguese FCT foundation.
Mr. Mohamed Tanta was supported by FCT PhD grant with a reference PD/BD/127815/2016
Submodule topologies and PWM techniques applied in modular multilevel converters: review and analysis
Nowadays electrical energy presents itself as the most promising solution to satisfy the energy needs of smart cities. For electrical energy to be managed efficiently and sustainably, the use of power electronic converters is essential. The evolution of semiconductors, in terms of blocking voltages, conduted current and switching frequencies, led to the emergence of new topologies for more robust and compact power electronics converters with high-frequency galvanic isolation. However, for high and medium voltage applications, such as electric railways, wind turbines, solar photovoltaic, or energy distribution systems, the semiconductor blocking voltages are still below the values in demand. In order to solve this problem, modular multilevel converters (MMC) has been implemented, requiring more sophisticated control algorithms and complex pulse width modulation (PWM) techniques, such as space vector modulation. In this paper, different topologies to be integrated into an MMC are presented, as well as PWM techniques for MMC, making a comparative analysis based on computer simulations of different PWM techniques developed in PSIM software. An MMC consisting of 4 full-bridge DC-AC power converters connected in series was considered as the study basis for the analysis of the PWM techniques.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project QUALITY4POWER PTDC/EEI-EEE/28813/2017. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018 granted by the Portuguese FCT foundation. Dr. Mohamed Tanta was supported by FCT PhD grant with a reference PD/BD/127815/2016
Development of a Modular Multilevel Cascade Converter based on full-bridge submodules with a common DC Bus
The Modular Multilevel Cascade Converters (MMCC) present themselves as one of the solutions for high power and high voltage applications. Modularity and low voltage stress in each semiconductor are some of the features of this solution. This paper presents a study with experimental results concerning an MMCC composed by three full-bridge submodules with a common DC-bus and with low frequency cascaded transformers. Sharing the DC bus for each submodule al-lows for a simpler control algorithm as well as a simpler interface point with renewable energy sources or energy storage systems. Along the paper, it is presented the step-by-step methodology to obtain the main parameters of the elements that constitute the MMCC, namely the transformers equivalents model. Thus, it was possible to develop a more realistic simulation model, whose results obtained are very similar to the experimental results.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project QUALITY4POWER PTDC/EEI-EEE/28813/2017, and by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018 granted by the Portuguese FCT foundation
Baryogenesis through gradual collapse of vortons
We evaluate the matter-antimatter asymmetry produced by emission of fermionic
carriers from vortons which are assumed to be destabilized at the electroweak
phase transition.The velocity of contraction of the vorton, calculated through
the decrease of its magnetic energy, originates a chemical potential which
allows a baryogenesis of the order of the observed value. This asymmetry is not
diluted by reheating if the collapse of vortons is distributed along an
interval of ~ 10^-9 sec.Comment: 14 pages, Latex, no figure
The role of emotional intelligence and self-care in the stress perception during COVID-19 outbreak: An intercultural moderated mediation analysis
Background: The relationship between emotional intelligence (EI) and stress has been widely studied, as well as
the beneficial role of self-care to maintain health and wellbeing. However, the joint contribution of EI and self-
care in predicting stress has not been examined during COVID-19 lockdown. This study aimed to examine the
mediating role of self-care in the relationship between EI and stress and the potential moderator role of gender.
Methods: A sample of 1082 participants from four Hispanic countries completed measures related to socio-
demographic, trait emotional intelligence (Trait Meta-Mood Scale), self-care activities (Self-care Activities
Screening Scale) and stress (Perceived Stress Scale).
Results: Mediation analyses revealed that self-care increased the explained variance of the prediction of stress by EI dimensions after controlling gender and age. However, gender only moderated the relationship between selfcare and stress in the mediation model corresponding to emotional attention.
Conclusions: Data supported a general model for the interaction of EI and self-care as contributing factors of
stress. Further research is needed to replicate it in more culturally distant samples and to fully explore the po-
tential role of gender differences. Future intervention programs should include a balanced combination of EI and
self-care to increase their benefits on people’s healt
Experimental validation of a reduced-scale rail power conditioner based on modular multilevel converter for AC railway power grids
Rail power conditioner (RPC) has the ability to improve the power quality in AC railway power grids. This power conditioner can increase the loading capacity of traction substations, balance the active power between the feeder load sections, and compensate for reactive power and current harmonics. At present, there is increasing use of multilevel converter topologies, which provide scalability and robust performance under different conditions. In this framework, modular multilevel converter (MMC) is emerging as a prominent solution for medium-voltage applications. Serving that purpose, this paper focuses on the implementation, testing, and validation of a reduced-scale laboratory prototype of a proposed RPC based on an MMC. The developed laboratory prototype, designed to be compact, reliable, and adaptable to multipurpose applications, is presented, highlighting the main control and power circuit boards of the MMC. In addition, MMC parameter design of the filter inductor and submodule capacitor is also explained. Experimental analysis and validation of a reduced-scale prototype RPC based on MMC topology, are provided to verify the power quality improvement in electrified railway power grids. Thus, two experimental case studies are presented: (1) when both of the load sections are unequally loaded; (2) when only one load section is loaded. Experimental results confirm the RPC based on MMC is effective in reducing the harmonic contents, solving the problem of three-phase current imbalance and compensating reactive power.This work has been supported by the Portuguese Foundation of Science and Technology
(FCT), in Portuguese, Fundação para a Ciência e Tecnologia within the R&D Units Project Scope:
UIDB/00319/2020. Mohamed Tanta was supported by FCT grant with a reference PD/BD/127815/2016.
Jose Cunha is supported by FCT grant with a reference PB/BD/143005/2018. Luis A. M. Barros is
supported by FCT grant with a reference PD/BD/143006/2018
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