DSpace Communidade:
http://www.repositorio.ufc.br/handle/riufc/464
2020-01-26T21:12:29ZSistema de proteção adaptativa aplicado a redes de distribuição e microrredes em média tensão
http://www.repositorio.ufc.br/handle/riufc/48581
Título: Sistema de proteção adaptativa aplicado a redes de distribuição e microrredes em média tensão
Autor(es): Sampaio, Felipe Carvalho
Abstract: The demand for renewable and clean energy sources rose new electrical systems concepts, as
distributed generation and microgrids. Although they bring many benefits for the electrical
system, distributed generation and microgrids cause huge impacts in the operation of electrical
distribution systems, being the impact on protection system one of the most relevant. This work
presents an adaptive protection system to mitigate the microgrid operation impact on protection
system. The system is applied to directional overcurrent protection relays and propose a new
metaheuristic for optimal settings calculation, the Fuzzy-Adaptive Directional Bat Algorithm
(FDBA). The algorithm is validated using the data of three benchmark grids: 3-bus, 9-bus and
30-bus grids. The proposed algorithm performance is compared against the performance of
Genetic Algorithm, Particle Swarm Optimization, Differential Evolution, Bat Algorithm and
Directional Bat Algorithm. The results demonstrate that FDBA presented high convergence
speed, low discoordination, high robustness and acceptable computational burden. The adaptive
protection system was tested in a microgrid under different scenarios of grid topology, distributed
generation connection and grid connection: grid-connected and island. The proposed system
performance was compared against a fixed optimal settings protection system performance. The
results showed that the proposed system presented better performance, allowing more speed and
lower risk of discoordination for the protection system.2019-11-22T00:00:00ZDensidade de corrente de Maxwell no modelo do circuito elétrico global: nova modelagem da origem e da trajetória das descargas atmosféricas
http://www.repositorio.ufc.br/handle/riufc/48466
Título: Densidade de corrente de Maxwell no modelo do circuito elétrico global: nova modelagem da origem e da trajetória das descargas atmosféricas
Autor(es): Rodrigues, Ednardo Moreira
Abstract: Lightning present risks to human and animal life and to power grids. This natural phenomenon
stems, mostly, from Cumulonimbus storm clouds, which function as generators in the global
electric circuit model (GECM). The GECM is described by means of Maxwell’s current density.
In the atmosphere, Maxwell’s current density has four terms, two of which are still subject of
discussion in academia: the convection current density and the lightning current density. The
convection current density model is proposed in three stages: (i) auto-ionization, (ii) diffusion
and (iii) precipitation. At auto-ionization, the availability of charges is estimated through the
water auto-ionization. At step ii, the rate of charging of a cloud particle is established as a
function of its growing rate related to its size and physical state. At stage iii, a separation of
charges occur due to different precipitation rates of the cloud particles responsible for the typical
three or four-pole structure in storm clouds. Analytically, convection current densities of 53
nA.m ́2
can be reached in a storm, while the value accepted by the global electric circuit model
is 56 nA.m ́2
. A simulation was carried out in three dimensions of a simplified storm cloud.
The variation of the electric conductivity of air in function of the altitude was taken into account.
This time-domain simulation was carried out through a Finite Element Method modeling using
COMSOL Multiphysics
R software. The air current density inside of the cylinder makes the
potential and electric field increase with time. The air’s dielectric strength of 111 kV.m ́1
at a
5 km height was overcome in 1 min and 15 s, and the difference of potential stabilized at 230
MV, exceeding the GECM’s value of 200 MV in 15 %. These results indicate that the cloud’s
electrification model proposed provides an adequate description of the storm cloud’s charging
process. In this work it is also proposed a model for the lightning trajectory, which is important
for the elaboration of lightning incidence models for . The proposed incidence model is based on
the deflection of the electric field due to the ionization of the medium, and is therefore named
EFD. This deflection can be found through a numerical solution to Poisson’s equation using
Finite Element Method.
The results obtained through EFD simulations are similar to MEG for structures with symmetric
distribution of electric potential, such as a high- voltage three-phase transmission line. However,
for a HVDC line, the electrogeometric model does not take into account the different potentials
at each pole of this line. That explains the importance of a physical model, like EFD, and not
simply geometrical. Four lightning current levels (3 kA, 5 kA, 10 kA e 16 kA) are used according
to Associação Brasileira de Normas Técnicas (2015) NBR 5419.
The EFD analysis showed that the classic positioning of the arrestor cables on a HVDC line
present considerable shielding failure, especially on the positive pole, as 90 % of cloud-ground
lightning are of negative polarity.
Thus, a horizontal shifting of the arrestor cables was proposed, reducing SFW in 50 % for
lightning with current peak of 3 kA. For the other current levels, SFW was under 1 m, which can
be negligible in comparison to the altitude between 2 to 5 km at which lightning originate. The
simple EFD proved itself efficient in comparison to classical incidence models.
In order to make the trajectories generated by the model closer to the real phenomenon, however,
distributions (textures) of electric permittivity of air were created by means of the fBm technique.
Many textures were created to represent different storms and, at each one, 73 lightning were
simulated for the four current levels previously presented. The air-termination system for a
three-phase transmission line was assessed in two transverse planes: (i) the tower plane and (ii)
in the middle of the span region. The analysis for the tower plane indicate that the air-termination
system intercepted 96.94 % of lightning with current peak of 2.9 kA. In the span region the
efficiency of the air-termination dropped to 84.46 % for this same current level.2019-02-27T00:00:00ZA Family of high-frequency isolated single-phase AC-AC converters
http://www.repositorio.ufc.br/handle/riufc/48291
Título: A Family of high-frequency isolated single-phase AC-AC converters
Autor(es): Silva Filho, Olympio Cipriano da
Abstract: A family of single-phase AC-AC converters isolated at high frequency is proposed.
A set of common active and passive elements is shared by all topologies of the family and is
based on the interleaved inductors and the DAB (Dual Active Bridge) converter. This enables
high power density and current capacity, as well as smooth switching in part of the
semiconductors. The family consists of nine topologies being three symmetrical and six
asymmetrical. All topologies are described, modeled and simulated. The dynamic performance
is checked against voltage sag and load step. Mathematical analysis and simulations showed
that differences between the switching functions applied to the switches, which define the
primary and secondary voltages of the transformer, increase the circulation current and,
consequently, the losses. This problem is minimized in part of the converters of the family that
can use the proposed partial actuator scheme. In addition, the currents in the transformer were
minimized in some asymmetrical converters through two new modulation schemes. In order to
reduce the total magnetic volume and losses, methods for magnetic integration and modeling
were studied. As a result, two integrated magnets were developed and tested for the Symmetric
Full-bridge converter. At the University of Kassel, an experimental platform was developed
with which results were obtained for five topologies. The results showed a good dynamic
response of all evaluated converters. In addition, the integration brought a reduction in the total
volume of the magnets and an increase in the efficiency of the tested converter.2019-11-08T00:00:00ZModelagem e controle LVP de um helicóptero com 6DOF
http://www.repositorio.ufc.br/handle/riufc/47471
Título: Modelagem e controle LVP de um helicóptero com 6DOF
Autor(es): Muniz, Saulo Guillermo D'Eduard Araripe Sobreira
Abstract: This work seeks to produce, with the aid of matrix inequalities, a stability control for a six degree
of freedom nonlinear helicopter model. The objective is to define a gain capable of ensuring
model stability and reducing disturbance regardless of the condition in which the aircraft is
involved. A study is performed around the linearized equilibrium conditions for the Lynx ZD559
model, in which the independent controlled variable is the speed ahead of the aircraft. The tests
obtained from a stationary controller and one with linear variation aim to elucidate their ability,
and especially related to the last controller, to act on the full spectrum of velocity variation by
presenting an acceptable transient dynamics and disturbance rejection. The results indicate that
under more restricted operating conditions, the linear control of variable parameters was the
only one capable of stabilizing the plant in the established limits, besides presenting a favorable
transient across the speed spectrum when compared to the other control techniques.2019-09-13T00:00:00Z