Loop Behavior Research Articles

Dynamic Analysis of Current Loops Behavior in a Wind Turbine Based Doubly-fed Induction Generator

Recently, the doubly-fed induction machine is commonly utilized in wind generation system. A doubly-fed induction generator (DFIG) has been an extensively known machine compared to other types of the wind energy system. This paper presents, a detailed model that comprises a wind turbine (WT), DFIG, rotor side converter (RSC), power electronic components, and grid side converter (GSC) which are used to investigate the dynamic performance of a wind turbine based on DFIG. Vector control approach has been implemented to design the whole system. There are different control strategies for controlling the machines. However, in this paper, indirect speed control strategy has been performed and the dynamic characteristics of current loops in a wind turbine based on DFIG are analyzed. The entire system has been confirmed by MATLAB/Simulink software and detailed results are discussed.

Comparative study on (Na0.47Bi0.47Ba0.06)0.95A0.05TiO3 (A = Sr2+/Ca2+) lead-free ceramics: Scaling behavior of ferroelectric hysteresis loop

Scaling behavior of dynamic hysteresis of (Na0.47Bi0.47Ba0.06)0.95A0.05TiO3 (A = Sr2+/Ca2+) (expressed as BNBT-Sr and BNBT-Ca, respectively) lead-free ceramics was comparatively studied. BNBT-Ca exhibits typical ferroelectric hysteresis (polarization vs electric field, P–E) loops, while BNBT-Sr shows pinched P–E loops. The two samples' electric field and frequency-dependent dynamic hysteresis behavior were systematically investigated. The dopants difference (Sr2+/Ca2+) produces different scaling behavior of dynamic hysteresis, which is related to the electric field-induced phase transition and domain size between BNBT-Sr and BNBT-Ca.

Стійкість систем векторного керування напругою асинхронного генератора

The paper presents an analysis of the stability properties of typical structures of induction generators-based vector control systems with linear proportional-integral currents and DC-link voltage controllers. The study is based on the mathematical model of an induction machine taking into account the magnetization curve. It provides the modification of the typical voltage-flux vector control algorithm by considering the saturation of the magnetic system. The stability proof problem of an induction generator-based generation system is that its model is nonlinear and nonminimal-phase, and that the dynamics of the DC-link voltage is nonlinear even for a constant flux linkage and speed due to the presence of nonlinear components which are proportional to active losses. The conditions which provide consideration of the reduced-order system dynamics are formulated and properties of local asymptotic stability of the generation system with typical vector control algorithms are proven based on the singular perturbation theory. It is shown that the local asymptotic stability is ensured when the regulation processes of the DC-link voltage and the torque-forming stator current component are decoupled, which is achieved due to the proposed special adjustment of the voltage and current controllers. A modified vector control algorithm of induction generator is studied in simulation and experimentally. At the first stage, the system dynamics is investigated when the flux subsystem is in equilibrium point. As a result, the possibility of the reduced-order system consideration for the design and analysis of the voltage regulation subsystem was confirmed. At the second stage, the dynamic behavior of the voltage control loop for different settings of the controllers was experimentally investigated. It is shown that the configuration of the voltage control algorithm proposed in the work provides the timescale separation of the current and DC-link voltage regulation processes, as well as their quasi-decoupling.

Automatic track guidance of industrial trucks with time-variant vehicle parameters using AI-based controllers

This paper presents an extension of a self-learning control concept for automatic track guidance of industrial trucks in intralogistic systems. The presented approach is based on Reinforcement Learning (RL), a method of Artificial Intelligence (AI) and is able to adapt itself to different industrial truck variants and the associated specific vehicle parameters. Moreover, time-variant parameters during operation, such as the vehicle's velocity are taken into account. In order to consider the existing a priori knowledge of the controlled system and to avoid starting the whole training process of the controller for each truck variant from scratch, the training process is divided into two steps. In the first step, the controller is trained on a model using parameters of a nominal vehicle variant. Based on this, the control parameters are only fine-tuned in the second step. In this way the controller is adapted to the actual truck variant and the corresponding parameter values. In order to take into account the time-variant vehicle parameters during operation, the Artificial Neural Networks (ANN) of the RL controller and the observation vector are suitably extended. In this way, the varying speed can be considered in both training steps and the control parameters can be optimized accordingly. Thus, in case of the investigated scenarios a stable control loop behavior can be guaranteed for the entire speed range of industrial trucks. In order to demonstrate this, the new approach is compared with a RL control concept, not considering time-variant parameters.

FORC-Diagram Analysis for a Step-like Magnetization Reversal in Nanopatterned Stripe Array.

The fabrication approach of a magnonic crystal with a step-like hysteresis behavior based on a uniform non-monotonous iron layer made by shadow deposition on a preconfigured substrate is reported. The origin of the step-like hysteresis loop behavior is studied with local and integral magnetometry methods, including First-Order Reversal Curves (FORC) diagram analysis, accompanied with magnetic microstructure dynamics measurements. The results are validated with macroscopic magnetic properties and micromagnetic simulations using the intrinsic switching field distribution model. The proposed fabrication method can be used to produce magnonic structures with the controllable hysteresis plateau region’s field position and width that can be used to control the magnonic crystal’s band structure by changing of an external magnetic field.

Control of capillary driven fluid flows for safe operation of spacecraft fluid supply systems using artificial porous media

In weightlessness, capillary forces become the main driving forces in the flow of liquids. Fuel supply of engines being started in weightlessness, water supply to life support systems in habitable modules, heat exchange using capillary pumps – all those processes rely heavily on capillary forces. Thus, safety and reliability of Space mission strongly depends on our skills in controlling capillary driven fluid flows. Adequate mathematical models for predicting capillary driven imbibition in artificial porous specimens are needed. The paper discusses the features of the flow of liquids through a porous medium under the action of capillary forces under microgravity conditions. An important feature of such flows is the hysteresis effect: in the case of multiple imbibition of a porous medium, the liquid flows in different ways through the dry medium and through the medium moistened in the process of previous imbibitions. This effect is observed during experiments on repeated imbibition of an artificial porous medium during parabolic flights of an Airbus A300-ZeroG aircraft organized by the European Space Agency. With each subsequent parabola, the liquid rises to a greater height. Modeling such processes requires special mathematical models described in this work. Comparison of the results of numerical modeling and experimental data provides a unique opportunity to choose empirical constants on an experimental basis thus developing a robust tool for predicting fluid behavior in hydraulic loops of Space vehicles.

Viscous magnetization decrease in first-order reversal curves induced by rotatable magnetic anisotropy in polycrystalline exchange-biased bilayers

A prototypical polycrystalline in-plane exchange bias system exhibited a viscous decrease of the ferromagnetic magnetization upon increasing external magnetic field when measuring first-order reversal curves. The phenomenon is investigated by means of angular-resolved vectorial magneto-optical Kerr magnetometry complemented by fits of model calculations and by Kerr microscopy. It is found that the viscous magnetization decrease is mediated by a rotatable magnetic anisotropy arising from thermally unstable antiferromagnetic grains coupled to the probed ferromagnet. This additionally manifests itself by a creeping domain wall motion in the ferromagnet due to thermally activated processes in the antiferromagnet. The investigations are in agreement with a generalized description of polycrystalline exchange bias systems and emphasize the relevance of understanding minor loop behavior addressing nonsaturated magnetic states for systems susceptible to dynamic changes on the hysteresis loop timescale.

Eco-evolutionary responses of the microbial loop to surface ocean warming and consequences for primary production.

Predicting the response of ocean primary production to climate warming is a major challenge. One key control of primary production is the microbial loop driven by heterotrophic bacteria, yet how warming alters the microbial loop and its function is poorly understood. Here we develop an eco-evolutionary model to predict the physiological response and adaptation through selection of bacterial populations in the microbial loop and how this will impact ecosystem function such as primary production. We find that the ecophysiological response of primary production to warming is driven by a decrease in regenerated production which depends on nutrient availability. In nutrient-poor environments, the loss of regenerated production to warming is due to decreasing microbial loop activity. However, this ecophysiological response can be opposed or even reversed by bacterial adaptation through selection, especially in cold environments: heterotrophic bacteria with lower bacterial growth efficiency are selected, which strengthens the "link" behavior of the microbial loop, increasing both new and regenerated production. In cold and rich environments such as the Arctic Ocean, the effect of bacterial adaptation on primary production exceeds the ecophysiological response. Accounting for bacterial adaptation through selection is thus critically needed to improve models and projections of the ocean primary production in a warming world.

An Analysis of Minor Hysteresis Loops Behavior under PWM Voltage - Electromagnetic Device at No-Load and Loaded Conditions

This paper addresses the influence of the primary and secondary resistances on the behavior of minor hysteresis loops when the electromagnetic device is fed by three-level PWM (pulse width modulation) voltage. To study the device transferring energy to a load, the experimental approaches are different of traditional procedures to material characterization, where problems inherent to the process are added. Analytical, FEM and experimental analysis are performed on a toroidal transformer equipped with a flux sensing coil. The leakage fluxes related to the primary and secondary currents are shown to cause errors in the measurement of the core magnetization current. A solution to mitigate this problem is employed, consisting in twisting and winding together primary and secondary conductors. Experimental methodologies for obtaining the value of the iron losses when the device is transferring energy to a load are also performed. The study shown showed that supply voltage with three-level PWM waveform causes minor hysteresis loops and the greater the resistance value of the excitation winding, the larger the areas of the minor hysteresis loops. On the other hand, by increasing the energy transferring to a load the minor loops areas tend to decrease.

Rheological behavior of bentonite-water suspension at various temperatures: Effect of solution salinity

Bentonite suspension have been widely used as drilling fluid in drilling engineerings. In this work, a modified thixotropic loop test was conducted on 6 wt% bentonite suspensions with 4 solution salinities, to investigate the influence of salinity on rheological behaviors of Na-bentonite suspensions. Most of flow curves were well fitted with Herschel-Bulkley model except first upward curves, where stress overshoot appeared in the initial stage. It was found that the yield stress and flow index decreased with increasing salinity. The suspensions present shear thinning behavior in the first upward curves but shear thickening or Bingham behavior in the second loops. Besides, at 20 and 14 °C, a notable thixotropic type transition was observed from positive to negative when the second shear loop was applied to the suspensions in case of low salinity. Both the change of flow type and thixotropy mentioned before may be attributed to the further structural evolution resulting from the long-time shearing at low salinities. However, this change was suppressed at 4 g/L due to the effect of high salinity on particle association mode. The test at 7 °C showed interesting results that the twice upward flow curves presented the stress overshoot and the twice loops performed a positive thixotropic behavior, not as same as the cases of the other temperatures. It indicates the structural evolution during shear process may be affected at low enough temperatures.

Electronic structure and unusual magnetic properties of diluted magnetic semiconductors Pb1-x-ySnxScyTe

We synthesize a single-crystal Pb1-x-ySnxScyTe ingot and investigate the magnetic properties (2.0 ≤ T ≤ 300 K, B ≤ 3 T) of alloys cut from it (x = 0.045–0.175, y ≤ 0.04). At low temperatures, all samples exhibit paramagnetic contribution to the magnetization, which contradicts the generally accepted model of doping-induced rearrangement of the electronic structure of alloys and is most likely due to the paramagnetism of electrically neutral Sc2+ ions or their clusters. In p-type samples, a high-temperature ferromagnetic ordering with a Curie temperature as high as TC = 145–150 K is found, presumably due to the RKKY hole-mediated interaction of Sc2+ ions. We obtain dependences of the concentration of paramagnetic ions, of the paramagnetic Curie-Weiss temperature Θ and of the Curie temperature TC on the concentrations of scandium and tin. At temperatures T < 100 K, the spin-glass-like behavior of magnetization and ferromagnetic hysteresis loops in the field dependences of magnetization are detected, indicating the formation of a mixed ferromagnetic–spin glass phase.

Influence of power step on the behavior of an Open Natural Circulation Loop as applied to a Parabolic Trough Collector

This paper investigates the dynamic behaviour of a low pressure open natural circulation loop applied to a parabolic trough collector. An in-house experimental setup is developed to perform the test. The experiments are performed on two distinct modes: H-mode and S-mode, corresponding to single-phase and two-phase flow. Three distinct power amplitude modes viz, 250, 325, and 464.3 W with a power step number of 24, 18 and 12 having a duration of 15, 20 and 30 min are considered. A Fast Fourier Transform analysis revealed that the flow in the loops is stable with a maximum decay ratio of 0.726. Instabilities, including Density Wave Oscillation, geysering and flashing, are observed during the test. Moreover, the thermal inertia of the loop has a significant role in the initial stage of power steps. An increase in the power step size conferred a 9.1%–33.4% increase in the outlet temperature of water in H-mode. In S-mode, an increase in power step size delayed the onset of boiling and reduced the duration of boiling by 2.8–14.32% and 8.03–22.02%. The loop can generate a mass flux of 40–42.5 kgm2s−1 in H-mode and up to 400 kgm2s−1 in S-mode, which is significant.

EXPERIMENTAL STUDY ON SEISMIC PERFORMANCE OF ENERGY DISSIPATION AND POSITION LIMITATION STEEL BRACE AND STRUCTURE SEISMIC VULNERABILITY ANALYSIS

A kind of energy dissipation and position limitation type steel brace is proposed to improve the seismic performance of a building structure. Five steel braces are designed, and the limitation displacement, limitation block number, steel core section size and length are chosen as the design parameters. Based on the test study, the characteristics including the failure mode, hysteresis loops behavior, skeleton curves, and stiffness are demonstrated. The seismic collapse resistance of steel braced frame structures is evaluated through IDA analysis. The results show that: the steel brace structure is reasonable with stable hysteretic performance, and the position limitation block could play a limiting role and provide greater additional stiffness. The number and section size of the position limitation block and the weld stiffness of the joint surface with the steel core affect the lifting degree of the additional stiffness. The calculation results of the stiffness formulas presented are in a good agreement with the experimental values, which can provide a reference for the practical design of steel braces. The collapse reserve coefficient of this type of steel braces with position limitation blocks is increased, beneficial to improve the collapse resistance of soft first storey building.

Temperature-dependent structure and magnetization of YCrO3 compound

We have grown a YCrO3 single crystal by the floating-zone method and studied its temperature-dependent crystalline structure and magnetization by x-ray powder diffraction and PPMS DynaCool measurements. All diffraction patterns were well indexed by an orthorhombic structure with space group of Pbnm (No. 62). From 36 K to 300 K, no structural phase transition occurs in the pulverized YCrO3 single crystal. The antiferromagnetic phase transition temperature was determined as T N = 141.58(5) K by the magnetization versus temperature measurements. We found weak ferromagnetic behavior in the magnetic hysteresis loops below T N. Especially, we demonstrated that the antiferromagnetism and weak ferromagnetism appear simultaneously upon cooling. The lattice parameters (a, b, c, and V) deviate downward from the Grüneisen law, displaying an anisotropic magnetostriction effect. We extracted temperature variation of the local distortion parameter Δ. Compared to the Δ value of Cr ions, Y, O1, and O2 ions show one order of magnitude larger Δ values indicative of much stronger local lattice distortions. Moreover, the calculated bond valence states of Y and O2 ions have obvious subduction charges.

Lightning Surge Analysis for Overhead Lines Considering Corona Effect

Corona discharge characteristics are measured in a corona cage. The difference is found between the q–u curves under double exponential and damped oscillation surges. The behavior of the minor loops is revealed for the q–u curves under positive and negative damped oscillation surges. An extended improvement is made on the traditional approach for modeling of the q–u curves under damped oscillation surges. The extended approach has the capability of describing the complicated trajectory feature of the minor loops. On the basis of the extended approach, an efficient method is proposed for performing lightning surge analysis of overhead lines considering the corona effect. In the proposed method, an overhead line with corona is divided into a certain number of line segments. Each segment is converted into a circuit unit consisting of a non-linear branch and a linear circuit. With these circuit units connected in sequence, a complete equivalent circuit is constructed for the overhead line with corona. The transient responses can be obtained from the solution to the equivalent circuit. Then, the calculated results are compared with the field test results on a test overhead line.

An Improved Robust Adaptive Controller for a Fed-Batch Bioreactor with Input Saturation and Unknown Varying Control Gain via Dead-Zone Quadratic Forms

In this work, a new adaptive controller is designed for substrate control of a fed-batch bioreactor in the presence of input saturation and unknown varying control gain with unknown upper and lower bounds. The output measurement noise and the unknown varying nature of reaction rate and biomass concentration and water volume are also handled. The design is based on dead zone quadratic forms. The designed controller ensures the convergence of the modified tracking error and the boundedness of the updated parameters. As the first distinctive feature, a new robust adaptive auxiliary system is proposed in order to tackle input saturation and control gain uncertainty. As the second distinctive feature, the modified tracking error converges to a compact region whose bound is user-defined, in contrast to related studies where the convergence region depends on upper bounds of either external disturbances, system states, model parameters or terms and model parameter values. Simulations confirm the properties of the closed loop behavior.

Multivariable control of hybrid powertrain dynamics at GM

AbstractThis article illustrates the control design process, from the requirements determination phase to the vehicle validation phase, as applied to GM's first two‐mode hybrid electric powertrains. Customer requirements are first translated into metrics that must be met with the closed loop control design. Physics‐based modeling tools developed in‐house are utilized to simplify the development of control design and simulation models for the multi‐input multi‐output hybrid driveline system. Frequency sweep methods and tools are then employed to validate the models and later to verify the control implementation with vehicle tests. Modern control tools are used to develop a multi‐input multi‐output feedback control design. Finally, vehicle test results show how this design approach is successful in dramatically changing the open loop behavior of the dynamic driveline response, turning an unsalable product into a world class leader in drive quality.

The effect of wavy surface on boundary layer instabilities of an airfoil

PurposeThe purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability analyses.Design/methodology/approachFlow field calculations over smooth and wavy-surface NACA 0012 airfoils at 2° angle of attack and at Reynolds number of 200,000 are performed using the large eddy simulation (LES) approach. Three geometrical configurations are considered: a smooth NACA 0012 airfoil, wavy surface on the suction side (SS) and wavy surface on the pressure side (PS). The spatial stability analyses using the LES-generated flow fields are conducted and validated against the Orr-Sommerfeld stability analysis for the smooth airfoil configuration.FindingsThe spatial stability analyses show that inclusion of the wavy-type modification on the SS of the airfoil does not lead to altering of the acoustic feedback loop mechanism, with respect to the mechanism observed for the smooth airfoil configuration. In contrast, applying the surface modifications to the airfoil PS leads to a significant reduction of the amplification range of disturbances in the vicinity of the trailing edge for the frequency of the acoustic feedback loop mechanism.Practical implicationsThe spatial analyses using, for example, LES-generated flow fields can be widely used to determine acoustic sources and associated distributions of amplifications for a wide range of applications in the aeroacoustics.Originality/valueThe spatial stability analysis approach based on flow fields computed a priori using the LES method has been introduced, validated and used to determine behaviour of the acoustic feedback loop when accurate reconstruction of geometry effects is required.

Experimental and Simulation-Based Performance Analysis of a Computed Torque Control (CTC) Method Running on a Double Rotor Aeromechanical Testbed

Concept of closed loop control appears in many fields of engineering sciences, where the output quantity of some physical system must be forced to follow some prescribed function over time, e.g., when a robotic arm endpoint must track a desired trajectory or path given as timed series of spatial coordinates. The classic approach for solving this kind of problem involves a PID compensation block, and the necessary input signal for keeping the controlled process in the vicinity of the desired trajectory is calculated as the weighted sum of momentary deviation, deviation integral, and deviation derivative relative to the reference path. However, despite the obvious advantages, practical usability, and simplicity of the PID controllers, their performance is limited when they are utilized for controlling nonlinear systems. Even with linear systems, their proper operation requires an accurate system model and precise tuning process for finding the best weight values for the proportional, integral, and derivative effects, and the planned closed loop behavior might change significantly as the parameters of the controlled plant change over time. In this article, a computed torque-based controller is presented, which has only one adjustable parameter ensuring precise trajectory tracking even with significantly alternated model constants. The practical usability of the offered algorithm is evaluated and verified by simulations and experiments performed on a simple mechanical bi-rotor testbed playing the role of controlled plant.

A modified curve-approximated hysteretic model for partially concrete-filled steel tube bridge piers

A modified curve-approximated hysteretic model for partially concrete-filled steel tube (PCFST) bridge piers is developed based on the previous research work. The proposed model, which consists of a series of quadratic and cubic curves and takes into account the P-Δ effect, pinching behavior in unloading-reloading hysteretic loops, and deterioration of strength and stiffness, can be used to precisely describe complicated hysteretic behavior of cantilever-type PCFST bridge piers. Parameters of this model are calibrated on the basis of quasi-static cyclic test results. To verify the validity of the proposed model, a total of 12 pseudo-dynamic tests were carried out. The detailed comparisons of different seismic performance indices between experimental and numerical results, such as the maximum response displacement, the residual displacement, and the amount of energy dissipation, indicated that the proposed model can be an acceptable complementary and assisting tool for the nonlinear seismic response assessment of PCFST piers.