Double Loop Research Articles

Adaptive Supplementary Control of VSG Based on Virtual Impedance for Current Limiting in Grid-Connected and Islanded Microgrids

By applying virtual synchronous generator (VSG) method in high penetration level microgrids, current limiting issue under fault condition has become an important challenge. The main objective of this paper is to propose a novel current limiting strategy which has the capability of voltage tracking error reduction to avoid voltage controller saturation. This purpose is obtained by adaptive virtual impedance-based reference voltage correction during fault condition. Furthermore, positive and negative peak detection-based current limiting method implemented in double loop control system prepares soft transition ability. Moreover, this current limiting method generates the adaptive term of virtual impedance part. In contrast to conventional VSG methods, the proposed approach provides high quality voltage and current for microgrid in both grid-connected and islanded modes during fault conditions. The offline and hardware in the loop (HIL) simulation results confirm that the peak current of the inverter is restricted to the threshold value under symmetrical and asymmetrical faults for two operating modes of microgrid.

The indirect shared steering control under double loop structure of driver and automation

The indirect shared steering control under double loop structure of driver and automation

Nanopore sensitization based on a double loop hybridization chain reaction and G-quadruplex.

The widespread implementation of solid-state nanopores faces challenges such as lower resolution and increased electrical noise when compared to biological nanopores. Incorporating specific nucleic acid reactions can enhance resolution. In this study, we've developed a nucleic acid amplifier to enhance the sensitivity of solid-state nanopores, utilizing a G-rich sequence and hybridization chain reaction. This amplifier improves target concentration and volume amplification, showing promise in nanopore sensitivity tests.

Prevention aid in qualitative analysis of dermatoglyphic patterns in relation to type 2 diabetes mellitus: a pilot study.

The significant differences in the fingerprint pattern frequencies in type 2 diabetes mellitus (T2DM) patients and controls could be a possible way to identify patients with a risk of developing T2DM. The results could be used in the earlier diagnosis and treatment. The study was undertaken to find out the reliability of fingerprint patterns as a possible predictive tool for T2DM diagnosis. A total of 1,260 fingerprints were acquired using the optical contact sensor DactyScan 26i. The results of the qualitative analysis of the fingerprint pattern frequencies have been compared between T2DM patients and controls and also between the fingers to each other. We have detected the frequency of patterns: plain arch (Ap) and tented arch (At), radial loop (Lr), ulnar loop (Lu), double loop (Ld), spiral whorl (W), and plain whorl (concentric) (Wp). Statistical analysis was performed using Pearson's chi-square by Statistica ver. 12. We found statistically significant differences (p < 0.05) in the frequency of individual dermatoglyphic patterns among patients with diabetes and healthy controls as follows: in the left thumb (L1) in a radial loop, double loop and spiral whorl pattern; in the left middle finger (L3) in a tented arch and radial loop; in the right ring finger (R4) in a tented arch, spiral and plain whorl; and in the right little finger (R5) in a tented arch and spiral whorl. Fingerprint pattern frequencies might be used as another screening tool and indicator in T2DM prevention. Qualitative analysis of fingerprint patterns could be useful regarding the additional prevention diagnostics of T2DM in the population.

Existence and Number of Figure-Eight Loops in Planar Sector-Wise Linear Systems with Saddle–Saddle Dynamics

In this paper, we investigate the existence of one type of homoclinic double loops (i.e. figure-eight loops) in a family of planar sector-wise linear systems with saddle–saddle dynamics. We obtain necessary and sufficient conditions for the existence of a figure-eight loop. Moreover, we prove that such systems can have simultaneously three types of invariant sets: a figure-eight loop, a homoclinic loop and three different types of periodic orbits. We also provide an example to show that a crossing limit cycle can bifurcate from this figure-eight loop.

Non-Destructive Testing Using Transmission Line-Based Microwave Sensors

In this study, some types of antennas and metamaterial structures have been designed and produced with the aim of determining and detecting ionized chlorine of sea sand in concrete. The first structure has a Loop-like resonator with the sample, the second structure has a Bowtie-shaped resonator with the sample and the third structure has double loop resonators on both sides of concrete samples also non-destructive method is applied for all structures. Different samples of concrete are produced with different proportions of ionized sea sand. Electrical properties of concrete samples for all structures are investigated in the frequency range of 1-9 GHz. The structures are designed in the CST Microwave Studio program. Also, the simulation study of the designed structures shows that the most important resonance frequency changes, considering the dielectric constant of concrete samples, for the Loop-like structure occur in the 1-8 GHz, Bowtie-shaped structure in 1-4 GHz and double Loop structure in 1-9 GHz of frequency band. The important point in this study is the changes of the waveform at the resonance frequency. The output waveform (reflection coefficient S11/ transmission coefficient S12) should change in linear form by considering the dielectric coefficient. We have used copper for the resonators and also the material with ℇ value of 3 as the substrate layers of the structures. We have simulated three types of designed structures with CST Microwave Software and then achieve the results and evaluate them. Both numerical and experimental tests have given approximately same results and are in good agreement with each other. These proposed structures can be used in many applications where it is necessary to determine the rate of ionized sea sand in cement-based composites such as concrete.

Double homoclinic bifurcations by perturbing a class of cubic Z2-equivariant polynomial systems with nilpotent singular points

This paper focuses on the study of the limit cycle bifurcation of a general cubic Z2-equivariant Hamiltonian differential system with two nilpotent singular points. Initially, the necessary and sufficient conditions for the occurrence of two nilpotent singularities are provided in the unperturbed system, along with a complete description of all possible phase portraits on the plane. Subsequently, using a combination of the Melnikov function method and various analytical techniques, we derive the approximate expansion of the first order Melnikov function at the interval endpoint, as well as formula for its coefficients. These results can be utilized to analyze double homoclinic loop bifurcation of the perturbed system, finding the lower bound of limit cycles.

Control Strategy of Three-level Active Neutral Point Clamped Grid Connected Inverters in Unbalanced Power Grid

Traditional phase-locked loops in three-level active neutral point-clamped inverter grid-connected systems for photovoltaic power generation exhibit a deficiency in the decoupling of positive and negative sequences under unbalanced power grid conditions. To address this issue, this study proposes the implementation of the fourth-order generalized integrator into the phase-locked loop to facilitate positive and negative sequence decoupling. Initially, a 3L-ANPC inverter grid connection system is established. However, under unbalanced grid voltage conditions, the PLL effect of the Decoupled Double Synchronous Reference Frame Phase-Locked Loop is found to be suboptimal, leading to considerable fluctuations and distortions in the output frequency signal. To address these complications, we propose an optimized phase-locked loop structure. In this improved design, the PLL first utilizes the FOGI to filter out multiple harmonics in the grid voltage prior to decoupling the positive and negative sequence voltage. This process effectively mitigates the effect on the PLL, thereby enabling rapid and precise tracking of the grid voltage. Simulation analysis is conducted by using Matlab/Simulink to substantiate the effectiveness of the proposed PLL, demonstrating its ability to reliably lock onto the frequency and phase of the fundamental voltage under conditions of unbalanced power grid voltage.

High energy storage density in NaNbO3 antiferroelectrics with double hysteresis loop

Antiferroelectrics (AFEs) possess great potential for high performance dielectric capacitors, due to their distinct double hysteresis loop with high maximum polarization and low remnant polarization. However, the well-known NaNbO3 lead-free antiferroelectric (AFE) ceramic usually exhibits square-like P–E loop related to the irreversible AFE P phase to ferroelectric (FE) Q phase transition, yielding low recoverable energy storage density (Wrec). Herein, significantly improved Wrec up to 3.3 J/cm3 with good energy storage efficiency (η) of 42.4% was achieved in Na0.7Ag0.3Nb0.7Ta0.3O3 (30Ag30Ta) ceramic with well-defined double P–E loop, by tailoring the A-site electronegativity with Ag+ and B-site polarizability with Ta5+. The Transmission Electron Microscope, Piezoresponse Force Microscope and in-situ Raman spectra results verified a good reversibility between AFE P phase and high-field-induced FE Q phase. The improved stability of AFE P phase, being responsible for the double P–E loop and improved Wrec, was attributed to the decreased octahedral tilting angles and cation displacements. This mechanism was revealed by synchrotron X-ray diffraction and Scanning Transmission Electron microscope. This work provides a good paradigm for achieving double P–E loop and high energy storage density in NaNbO3-based ceramics.

Magnetic, Antiferroelectric-like Behavior and Resistance Switching Properties in BiFeO3-CaMnO3 Polycrystalline Thin Films

The effect of ferromagnetic CaMnO3 (CMO) addition to structural, magnetic, dielectric, and ferroelectric properties of BiFeO3 is presented. X-ray diffraction and Raman investigation allowed the identification of a single pseudocubic perovskite structure. The magnetic measurement showed that the prepared films exhibit a ferromagnetic behavior at a low temperature with both coercive field and remnant magnetization increased with increasing CMO content. However, a deterioration of magnetization was observed at room temperature. Ferroelectric study revealed an antiferroelectric-like behavior with a pinched P–E hysteresis loop for 5% CMO doping BFO, resulting in low remnant polarization and double hysteresis loops. Whereas, high remnant polarization and coercive field with a likely square hysteresis loop are obtained for 10% CMO addition. Furthermore, a bipolar resistive switching behavior with a threshold voltage of about 1.8 V is observed for high doped film that can be linked to the ferroelectric polarization switching.

Deeper student-teacher partnership in 5 steps

Students as Partners initiatives have the potential to enable students and staff to collaborate on improving the teaching and learning experience (Mercer-Mapstone et al., 2017). Following two iterations of a students as partners initiative applied across different disciplines to enhance student-teacher partnership, an implementation strategy was established through a 5-steps process of recruitment, active listening, review, co-design, and evaluation. The proposed model established deeper partnership during the learning process, delivering significant changes that enhanced students’ learning instead of the typical iterative design at the end of the learning period (course). The partnership contributed to student partners’ development through an experiential learning process. Integrating learning theories and practices with human-centered design, we explore the research question: How do we nurture a deep student and teacher partnership for positive impact? Underpinned by Argyris &amp; Schön’s (1974) double loop learning and design thinking the 5-steps approach resulted in greater student experience and satisfaction, enabled the development of a sense of community and personal development for student partners and course convenors.

Pengaruh Model Pembelajaran Kooperatif Tipe Double Loop Problem Solving terhadap Kemampuan Penalaran Adaptif dan Disposisi Matematis pada Materi Trigonometri

This study was motivated by the low quality of education in Indonesia based on the results of PISA 2018, the implementation of the 2013 Curriculum which did not follow the use of appropriate learning models, as well as the low adaptive mathematical reasoning abilities and mathematical disposition of students. This research aims to determine the influence of the Double Loop Problem-Solving cooperative learning model on the adaptive reasoning abilities and mathematical disposition of class X students at SMA Negeri 1 Karangan on Trigonometry material. This research was conducted using a quantitative approach with a Quasi-Experimental research type and a Nonequivalent Posttest-Only Control Group Design. As for sampling, non-probability sampling was used with the Purposive Sampling technique with class X MIPA 3, totaling 35 students, as the experimental class and X MIPA 4, totaling 36 students, as the control class. Data collection techniques using tests, questionnaires, and documentation. The data analysis technique in this research uses the Manova test. The research results show that there is a significant influence due to the application of the Double Loop problem-solving cooperative learning model on students' adaptive reasoning abilities and mathematical disposition.

Influence of nitrogen content on the pit formation and pit propagation in the welded joints of X5CrNi18‐10 stainless steel

AbstractThe influence of welding current and nitrogen content in argon shielding gas on the resistance of the welded joint (weld metal and heat‐affected zone [HAZ]) of the stainless steel X5CrNi18‐10 to the formation and growth of pits was investigated. Also, the susceptibility of the welded joint to intergranular corrosion was examined. Pitting corrosion resistance indicators were determined based on anodic potentiodynamic polarization measurements in NaCl + Na2SO4 solution, while susceptibility to intergranular corrosion was determined by the potentiokinetic method with a double loop (DL EPR). SEM/EDS was used to analyze the microstructure. It has been shown that higher nitrogen content in shielding gas leads to an increase in the resistance of welded joints (weld metal and HAZ) to the pit formation. However, an improvement in the resistance to the pit formation leads to a decline in the resistance of the welded joint to pit growth. An explanation of this phenomenon is proposed. Also, it was shown that the increase of the welding current increases the susceptibility of the welded joint to intergranular corrosion, while the higher nitrogen content has no effect.

Experimental investigation of microstructural, mechanical and corrosion properties of 316L and 202 austenitic stainless steel joints using cold metal transfer welding

The objective of the current experimental study is to investigate influence of dissimilar welding between 316 L Austenitic and 202 Austenitic Stainless Steel. This is achieved through the utilization of Cold Metal Transfer (CMT) Welding in conjunction with the GTAW mode. Various welding approaches are employed, including the use of ER316L and ER309L fillers, as well as a no-filler (autogenous) welding technique. Microstructural observation shows martensitic formation in the interface region. The tensile test was conducted by using Universal Testing Machine for the weldment and found that ER316L filler (721 MPa) has higher strength than ER309L (672 MPa) and autogenous weld (528 MPa). Charpy impact test was used to determine toughness of the weldment and found that ER309L Filler weld has toughness (87 J) which is higher than ER316L filler weld (5 4 J) and autogenous weld (23 J). Vicker's hardness test shows that autogenous weld hardness (avg. 193.34 HV) which is highest than ER309L filler (avg.188 HV) and ER316L filler weld (avg. 184.67 HV). The intergranular corrosion test by double loop electrochemical potentiokinetic reactivation (DLEPR) test shows sensitization at highest degree for autogenous weld (18.25 %) than ER316L filler weld (9.22 %) and ER309L filler weld (7.28 %).

A Polynomial Synthesis Approach to Design and Control an LCL-Filter-Based PWM Rectifier with Extended Functions Validated by SIL Simulations

Controlling a PWM rectifier can be challenging due to the bilinear nature of its averaged model. This paper introduces the use of the Butterworth approach to design and control an LCL-filter-based PWM rectifier with power quality functions. By leveraging the linear part of the system, this approach reduces the number of variables involved in the control scheme. The rectifier is designed and controlled in a concatenated manner to ensure proper performance even during demanding power-quality events. The uniqueness of this approach lies in the fact that a fourth-order model can be regulated by using solely three-state variables and linear techniques founded on Butterworth polynomial synthesis. This approach differs from previous methods in that it does not employ nonlinear controllers, dq transformations, or double control loops. Hence, this divergent approach contributes to the simplification of power converter design and control through the application of the same polynomial synthesis, besides enhancing system operation in demanding scenarios. Extensive SIL simulations of a 1 kW, 220 Vrms PWM rectifier using the OPAL-RT-1400 platform were conducted to demonstrate the feasibility of the proposed controller. The selected tests reveal the validity of this proposal even when the PWM rectifier faces multiple power quality events simultaneously.

Proportional-Derivative Plus Integral Controller Tuning for Led Lighting Based on the Mathematical Model

The depletion of energy resources have made saving energy a challenge in recent decades. One of the main components of energy consumption is lighting, it represents up to 20% of total energy consumption in the world; the largest amount consumed in residential and commercial buildings. Led technology, due to its characteristics of long life, high efficiency, low consumption and dimming capacity, has become an alternative to illuminate spaces. This work proposes a control scheme for LED lamp lighting with a double control loop, proportional- derivative in the internal loop and integral in the external one, based on the mathematical model in the absence of external lighting. In addition, the tuning strategy for the controller gains is proposed based on the design parameters of the standard second-order system. Through simulation it is shown that the tuning of the control strategy is adequate.

Relaxor Ferroelectric AgNbO3 Film Fabricated on (110) SrTiO3 Substrates via Pulsed Laser Deposition

AgNbO3-based materials have attracted extensive attention in energy storage due to their double hysteresis loops, but they suffer from low breakdown strength (Eb). AgNbO3 films with few defects and small thickness exhibit high Eb, which helps to improve the energy storage performance. In this work, we successfully prepared AgNbO3 thin films on (110) SrTiO3 substrate using pulsed laser deposition technology. The AgNbO3 film shows good crystalline and relaxor ferroelectric behavior. A high Eb up to 1200 kV/cm is obtained in AgNbO3 film, which contributes to good recoverable energy storage density Wrec up to 10.9 J/cm3 and energy efficiency η of 75.3%. Furthermore, the Wrec remains above 2.9 J/cm3 and the η varies between 72.5% and 82.5% in a wide temperature range of 30–150 °C. This work reveals the great potential of relaxor ferroelectric AgNbO3 film for energy storage.

Model-free robust decentralised control of multi-input-multi-output nonlinear interconnected dynamic systems

This study presents a generalised framework for model-free robust decentralised control (MFRDC) of interconnected MIMO dynamic systems, with the goal of significantly reducing complexity in model-based design. A model-free robust sliding mode control, by Lyapunov differential inequality, is presented to achieve simultaneous nonlinear, dynamic, interaction/coupling inversion/cancellation (NDII) for such MIMO systems, which treats the plant/process as a total uncertainty from input to output. The U-control platform is presented, to integrate separately independently designed NDII and an invariant controller (IC) into a complete double loop control system. The associated robust stability and other properties are analysed to provide reference for applications. Two simulated tracking control tests are presented for functionally numerical demonstration, validation of the analytical results and illustration of the transparent procedure for general expansion/applications. These are: a coupled inverted pendulum and a two-input and two-output (TITO) non-affine nonlinear dynamic plant.

Tensile Effect on Sensitization and Corrosion Resistance of Stainless Steels

The purpose of this research is to investigate cold work effect on corrosion behavior of stainless steels of type AISI 304, AISI 316L and AISI 2101. The specimen were processed through cold work simulated by the tensile test at various percentages elongation and then tempered at 600°C for different time intervals. Two electrochemical techniques and hardness test were utilized in this investigation. The first technique was the double loop electrochemical potentiokinetic reactivation (DL-EPR) that yields the values of degrees of sensitization (DOS). The second one was the cyclic potentiodynamic polarization (CPP) to study the ability of the metals to build or repair the damaged films under localized corrosion. The DOS values from the DL-EPR tests of the samples under the same heating conditions suggested that specimens drawn at higher percentage elongation tend to have more chromium depleted areas. Also, the test specimens with more exposure time to heat were more prone to chromium deficiencies. As for the ability of the metal to create or repair damaged film after corrosion has occurred, it was found that AISI 316L had hihger corrosion resistance than AISI 304. However, AISI 2101 stainless steel had highest corrosion resistance. In this study, it was also found that AISI 2101 did not exhibit pitting corrosion, but the crevice corrosion. This could be due the fact that AISI 2101 which is a duplex stainless steel has high corrosion resistance and could trigger the crevice corrosion take place before the pitting initiation.

Superior Energy Storage Performance in Antiferroelectric Epitaxial Thin Films via Structural Heterogeneity and Orientation Control

AbstractDielectric capacitors are desired for electronics and electrical power systems because of their fast charge–discharge speed and high‐power density. Nevertheless, dielectric capacitors typically exhibit lower energy densities in comparison to other energy storage systems like batteries or fuel cells. Among dielectrics, antiferroelectrics have shown great promise for high energy density because of their characteristic double hysteresis loops. However, current antiferroelectric capacitors still face challenges of low efficiency and low breakdown strength due to their large hysteresis, which is harmful to energy efficiency and reliability of the system. Herein, by engineering the nanoscale heterogeneity to mitigate hysteresis and controlling orientation to enhance the polarization, the exceptional energy storage performance of antiferroelectric (Pb0.97La0.02)(Zr0.55Sn0.45)O3 epitaxial thin films is demonstrated. Atomic‐resolution transmission electron microscopy and X‐ray reciprocal space mapping confirm the presence of nanoscale structural heterogeneity, characterized by fragmented antipolar nanodomains. These films exhibit remarkable energy densities, reaching up to ≈84.5 J cm−3, coupled with ultrahigh efficiencies of up to ≈98.5% and superior stability, maintaining efficiencies above 92% across a wide field range of ≈5 MV cm−1. Notably, these findings surpass the capabilities of previously reported dielectric materials, opening new avenues for advanced energy storage applications.