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22 pages, 4448 KiB

Open AccessFeature PaperArticle

Enlightening Load Modeling by Means of Power Factor Decompositions

by Helmo K. Morales Paredes, Matheus Branco Arcadepani, Alexandre Candido Moreira, Flávio A. Serrão Gonçalves and Fernando Pinhabel Marafão

Energies 2023, 16(10), 4089; https://doi.org/10.3390/en16104089 - 15 May 2023

Viewed by 1234

Abstract

Considering the proliferation of power electronics applications and distributed energy resources, modern power grids are facing a significant increase in harmonic currents circulation and supply voltage deterioration, occasionally associated with small frequency variations. In such a context, the understanding of power phenomena in [...] Read more.

Considering the proliferation of power electronics applications and distributed energy resources, modern power grids are facing a significant increase in harmonic currents circulation and supply voltage deterioration, occasionally associated with small frequency variations. In such a context, the understanding of power phenomena in circuits with linear and non-linear loads under non-sinusoidal voltage conditions is nontrivial and still does not allow for an easy interpretation of harmonic sources, harmonic power flow or the identification of the parameters of a proper equivalent circuit. The main challenge is to develop modern theoretical approaches for load characterization, modeling, and parameter estimation so that new techniques can be formulated to provide adequate guiding for the analysis, compensation, revenue metering, accountability and other applications of power systems. Thus, based on the Conservative Power Theory (CPT) and further decomposition of its apparent power and power factor definitions, this paper proposes a novel methodology for estimating equivalent parameters and for proposing proper equivalent circuits capable of representing/modeling the main characteristics of single-phase generic loads (black boxes) and the related power phenomena in terms of passive dipoles (linear loads) or of harmonic voltage/current sources and their intrinsic transimpedances/transadmittances (non-linear loads). Simulation and experimental results were depicted to support and validate the proposed approach, showing that it might be a powerful modeling technique to represent generic loads in a modern power grid scenario, while being used for complex applications such as reactive power compensation or accountability in circuits with nonlinear loads and distorted voltages. Full article

(This article belongs to the Special Issue Linear and Nonlinear Electric Circuits: Theoretical Analysis and Applications)

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19 pages, 4877 KiB

Open AccessArticle

Solar UAVs—More Aerodynamic Efficiency or More Electrical Power?

by Liviu Dinca, Jenica-Ileana Corcau and Daniel-Gabriel Voinea

Energies 2023, 16(9), 3778; https://doi.org/10.3390/en16093778 - 28 Apr 2023

Cited by 2 | Viewed by 1340

Abstract

Solar UAVs (unmanned aerial vehicles) have experienced important development in recent years. The use of solar free energy is not neglected in the present energy crisis, with the intention to move toward green energies. However, an important problem arises concerning the limited amount [...] Read more.

Solar UAVs (unmanned aerial vehicles) have experienced important development in recent years. The use of solar free energy is not neglected in the present energy crisis, with the intention to move toward green energies. However, an important problem arises concerning the limited amount of solar energy available on board UAVs. Until now, high-aerodynamic-efficiency configurations have been used. These configurations use high-aspect-ratio wings. However, high-aspect-ratio wings have some disadvantages regarding their excessive elasticity and weak bending resistance in the housing section. Additionally, the aircraft maneuverability is reduced. In this work, a study is proposed on a solar UAV configuration that sacrifices high aerodynamic efficiency for a higher surface area available for solar cells. In this manner, the amount of energy available on board the UAV is increased, and the UAV structure becomes more rigid and robust. The presented UAV fits better with more complex evolutions, is more maneuverable and the wingspan is much reduced. This UAV is more compact, can maneuver better in the take-off and landing phases, and the necessary storage space is considerably reduced. This paper highlights the performances that can be achieved using this kind of UAV and explores whether these performances are enough for some applications. Using an on-board energy balance, the possible performances of this new configuration is studied. As this is a preliminary study, the precision level is not very high, but it offers an image concerning the possibilities of this new configuration. Full article

(This article belongs to the Special Issue Linear and Nonlinear Electric Circuits: Theoretical Analysis and Applications)

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26 pages, 13207 KiB

Open AccessArticle

Analytical Investigation of the Properties of Transients in Unbalanced Three-Phase Four-Wire Networks

by Diego Bellan

Energies 2022, 15(23), 9122; https://doi.org/10.3390/en15239122 - 1 Dec 2022

Cited by 4 | Viewed by 1293

Abstract

In this paper, the theoretical properties of transients in three-phase networks, including the fourth wire and unbalanced source, are systematically investigated by resorting to several analytical tools. First, a Cartesian space vector is introduced to provide the geometrical three-dimensional representation of a three-phase [...] Read more.

In this paper, the theoretical properties of transients in three-phase networks, including the fourth wire and unbalanced source, are systematically investigated by resorting to several analytical tools. First, a Cartesian space vector is introduced to provide the geometrical three-dimensional representation of a three-phase voltage/current transient. It is shown that a voltage/current transient can be always represented as a three-dimensional trajectory leaving one plane (corresponding to the previous steady state) towards another plane (corresponding to the new steady state at the end of the transient). The quantity driving the trajectory from one plane to another is the Park/Clarke zero component. Second, the Clarke transformation is used to study the original three-phase circuit as a superposition of two independent transients: the transient of the Clarke space vectors and the transient of the Clarke zero components. Third, the Park transformation is used to evaluate the dq0 components of transient voltages/currents. Since the Park transformation is related to the Clarke transformation through a simple frequency shift, the effects on the frequency content of the steady-state and transient waveforms are put into evidence. Three case studies are presented and solved to prove the theoretical results. Full article

(This article belongs to the Special Issue Linear and Nonlinear Electric Circuits: Theoretical Analysis and Applications)

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29 pages, 7814 KiB

Open AccessArticle

Experimental Study on the Behavior of Aluminum Fuse Element Inside 24 kV, 50 kA High-Voltage Fuses

by Cristian-Eugeniu Sălceanu, Marcel Nicola, Claudiu-Ionel Nicola, Daniel Ocoleanu, Cătălin Dobrea, Daniela Iovan and Sorin Enache

Energies 2022, 15(19), 7171; https://doi.org/10.3390/en15197171 - 29 Sep 2022

Cited by 4 | Viewed by 1562

Abstract

High-voltage fuses are found in most electrical installations, where they are used for overcurrent protection and are the pieces of equipment providing the highest degree of protection for the lowest initial cost. This article focuses on the behavior of high-voltage fuses containing a [...] Read more.

High-voltage fuses are found in most electrical installations, where they are used for overcurrent protection and are the pieces of equipment providing the highest degree of protection for the lowest initial cost. This article focuses on the behavior of high-voltage fuses containing a fuse element entirely made of aluminum. We made high-power linear electrical circuits for experiments on these fuses under the most severe operating conditions. The article presents the construction details of the fuse element and its features, as well as various arc extinguishing media. The heating behavior and time–current characteristics were studied in comparison with fuses made of copper. We obtained the maximum instantaneous value of the current reached during interruption for a 24 kV, 50 kA, 50 A fuse, as well as the value of the minimum breaking current. Full article

(This article belongs to the Special Issue Linear and Nonlinear Electric Circuits: Theoretical Analysis and Applications)

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10 pages, 1412 KiB

Open AccessArticle

Aspects Regarding the Optimization of Cross Geometry in Traction Asynchronous Motors Using the Theory of Nonlinear Circuits

by Sorin Enache, Ion Vlad and Monica Adela Enache

Energies 2022, 15(18), 6648; https://doi.org/10.3390/en15186648 - 11 Sep 2022

Cited by 3 | Viewed by 1442

Abstract

Modern electrical traction uses asynchronous motors for driving railway vehicles because these motors have a lot of advantages in comparison with the classical, direct current motors. Reducing active and reactive electrical energy consumption is a concern in the case of these motors, meaning [...] Read more.

Modern electrical traction uses asynchronous motors for driving railway vehicles because these motors have a lot of advantages in comparison with the classical, direct current motors. Reducing active and reactive electrical energy consumption is a concern in the case of these motors, meaning a decrease in exploitation costs. The research carried out shows, by results and simulations, the effects of the geometry optimization for the stator and rotor lamination and emphasizes how much the total and exploitation costs. Cross geometry optimization means preserving constant electromagnetic stresses, using the same gauge dimensions, preserving the constant ampere-turn for a pole pair, having a maximum torque exceeding the imposed limit, and increasing the air-gap magnetic induction. The results obtained indicatea decrease in the total cost, by 42,600 € (12.31%), for a asynchronous tractionmotor in comparison with the existing variant. Full article

(This article belongs to the Special Issue Linear and Nonlinear Electric Circuits: Theoretical Analysis and Applications)

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13 pages, 5886 KiB

Open AccessArticle

Numerical Simulation for Redundant Electro-Hydrostatic Servo-Actuators under Certain Special Conditions

by Liviu Dinca, Radu Bogateanu, Jenica-Ileana Corcau, Alexandru Dumitrache and Bogdan Suatean

Energies 2022, 15(16), 5906; https://doi.org/10.3390/en15165906 - 15 Aug 2022

Cited by 3 | Viewed by 1277

Abstract

This work presents some numerical simulations, performed using AMESim software, for a system composed by two redundant servo-actuators. Certain operating conditions are taken into account for these two electro-hydrostatic servo-actuators, which are coupled to the command surface (aileron) of a transport aircraft. We [...] Read more.

This work presents some numerical simulations, performed using AMESim software, for a system composed by two redundant servo-actuators. Certain operating conditions are taken into account for these two electro-hydrostatic servo-actuators, which are coupled to the command surface (aileron) of a transport aircraft. We first considered the situation of slight asymmetries in the construction of the servo-actuators, then a situation in which one servo-actuator fails at maximum flight speed, and then at a medium flight speed, and finally we considered the effect of gusts upon the system. Small differences in the construction of the servo-actuators were taken into consideration by modifying each of the pump displacements, one by +2% and one by −2%, from the nominal value. It is possible that many other asymmetries exist in the construction of servo-actuators, such as different liquid leakages in the cylinders or pumps, small differences in the controller coefficients, and so on. These differences should be taken into account in future works. Our results provide evidence that, under some operation situations of redundant servo-actuators, significant overstresses can appear in one servo-actuator, leading to a decrease in the time for which the system operates correctly. Full article

(This article belongs to the Special Issue Linear and Nonlinear Electric Circuits: Theoretical Analysis and Applications)

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24 pages, 4687 KiB

Open AccessArticle

Applying Artificial Neural Networks and Nonlinear Optimization Techniques to Fault Location in Transmission Lines—Statistical Analysis

by Simone A. Rocha, Thiago G. Mattos, Rodrigo T. N. Cardoso and Eduardo G. Silveira

Energies 2022, 15(11), 4095; https://doi.org/10.3390/en15114095 - 2 Jun 2022

Cited by 5 | Viewed by 1691

Abstract

This study presents applications of artificial neural networks and nonlinear optimization techniques for fault location in transmission lines using simulated data in an electromagnetic transient program and actual data occurring in transmission lines. The localization is performed by a modular structure of 4 [...] Read more.

This study presents applications of artificial neural networks and nonlinear optimization techniques for fault location in transmission lines using simulated data in an electromagnetic transient program and actual data occurring in transmission lines. The localization is performed by a modular structure of 4 neural networks and by the minimization of objective functions descriptive of the problem, defined according to the parameters of the line and the type of short circuit, submitted to the methods Quasi-Newton, Ellipsoidal, and Real Polarized Genetic Algorithm. The results obtained are compared statistically with those of a classical analytical method. The analysis of the variance of location errors presented by the methods revealed, with 5% significance, statistical evidence that allowed the conclusion that the type of method used affects fault location indication. In simulated scenarios, minor errors were obtained with the neural network and larger with the analytical method. For field oscillographic, the largest errors were in the neural network; there is no evidence to reject the equality between the results of the analytical method and the nonlinear optimization techniques. The Tukey test identified no differences between the nonlinear optimization methods applied to the proposed objective functions, but the low computational cost associated with the Quasi-newton method highlights it. The nonlinear optimization methods used for the localization function proved to be promising for application in companies that operate electrical systems, providing localization errors similar to those presented by the classical analytical method. Full article

(This article belongs to the Special Issue Linear and Nonlinear Electric Circuits: Theoretical Analysis and Applications)

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17 pages, 2204 KiB

Open AccessArticle

An Impedance Matching Solution to Increase the Harvested Power and Efficiency of Nonlinear Piezoelectric Energy Harvesters

by Michele Bonnin, Fabio L. Traversa and Fabrizio Bonani

Energies 2022, 15(8), 2764; https://doi.org/10.3390/en15082764 - 9 Apr 2022

Cited by 21 | Viewed by 1832

Abstract

Circuit theory and nonlinear dynamics are instrumental to design efficient energy harvesters for ambient mechanical vibrations. In this work, we show that an impedance matching networks can be designed that maximizes the harvested power, and improves the power efficiency. The proposed matching network [...] Read more.

Circuit theory and nonlinear dynamics are instrumental to design efficient energy harvesters for ambient mechanical vibrations. In this work, we show that an impedance matching networks can be designed that maximizes the harvested power, and improves the power efficiency. The proposed matching network achieves impedance matching at a single frequency, that can be chosen at will by the designer, and does not need to coincide with the resonant frequency of the harvester. Moreover, the matching network also increases the harvested power over a wide frequency bandwidth. According to our numerical simulations, the matching network increases the maximum harvested power by a factor greater than 3, and the power harvested over the whole frequency spectrum by a factor of 6. The frequency bandwidth can be further extended considering nonlinear energy harvesters. Even using the matching network designed for the linear case, performance is significantly nonetheless improved for the nonlinear harvester. Full article

(This article belongs to the Special Issue Linear and Nonlinear Electric Circuits: Theoretical Analysis and Applications)

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