Cancellation Of Oscillations Research Articles

An evolutionary intelligent control system for a flexible joints robot

In this paper, we present a model for a serial robotic system with flexible joints (RFJ) using Euler–Lagrange equations, which integrates the oscillatory dynamics generated by the flexible joints at specific operating points, using a pseudo-Ornstein-Uhlenbeck process with reversion to the mean. We also propose a Stochastic Flexible - Adaptive Neural Integrated System (SF-ANFIS) to identify and control the RFJ with two degrees of freedom. For the configuration of the model, we use two adaptive strategies. One strategy is based on the Generalised Delta Rule (GDR). In contrast, a second strategy is based on the EDA-MAGO algorithm (Estimation Distribution Algorithms - Multi-dynamics Algorithm for Global Optimisation), improving online learning. We considered three stages for analysing and validating the proposed SF-ANFIS model: a first identification stage, a second stage defined by the adaptive control process, and a final stage or cancellation of oscillations. Results show that, for the identification stage, the SF-ANFIS model showed better statistical indices than the MADALINE model in control for the second joint, which presents the greatest oscillations; among those that stand out, the IOA (0.9955), VG (1.0012) and UAPC2 (-0.0003). For the control stage, The SF-ANFIS model showed, in a general way, the best behaviour in the system’s control for both joints, thanks to the capacity to identify and cancel oscillations based on the advanced sampling that defines the EDA algorithm. For the cancellation of the oscillations stage, the SF-ANFIS achieved the best behaviour, followed by the MADALINE model, where it is highlighted the UAPC2 (0.9525) value.

Doubly Fed Induction Machine-Based DC Voltage Generator with Reduced Oscillations of Torque and Output Voltage

The doubly fed induction machine (DFIM)-based DC voltage generator is equipped with a stator-connected diode rectifier. The six-pulse diode rectifier as a nonlinear circuit introduces harmonics in the stator and rotor current and distorts the machine stator voltage, as well as the stator flux. This causes electromagnetic torque oscillations and instantaneous power components oscillations. The torque oscillations adversely impact the mechanical parts of the drive-train and oscillations of the p component of instantaneous power influence DC-bus voltage oscillations. The oscillations can be somewhat cancelled by control methods. However, cancellation of electromagnetic torque is not strictly coupled with cancellation of oscillations of the p component of instantaneous power. The paper presents an analysis of influence of the control methods aimed at a reduction of torque oscillations on the output voltage oscillations level in the stand-alone DFIM-based DC voltage generator. Field-oriented control FOC with current controllers and space vector modulation-based direct torque control DTC-SVM with flux module regulation have been compared with control in which electromagnetic torque is one of the commanded variables, whereas the second variable is the dot product of stator flux and rotor current space vectors. The contributions of this paper are the introduction of a new variable in the second control path in the DTC-SVM method instead of flux vector length and the proof that it can reduce torque and DC-bus voltage oscillations in the DFIG-DC system. Additionally, this paper reveals that for proper stator-to-rotor-turns ratio of a doubly fed machine necessary for reduction of the rotor converter power, lower DC-bus voltage can be obtained than is required for full realization rotor side voltage requested by rotor current controllers. This is the reason why, regardless of the control method, torque oscillations cannot be always fully cancelled, and a comparative study of the methods at these conditions has been conducted in simulation and in laboratory tests.

The effect of two distinct fast time scales in the rotating, stratified Boussinesq equations: variations from quasi-geostrophy

Inspired by the use of fast singular limits in time-parallel numerical methods for a single fast frequency, we consider the limiting, nonlinear dynamics for a system of partial differential equations when two fast, distinct time scales are present. First-order slow equations are derived via the method of multiple time scales when the two small parameters are related by a rational power. We find that the resultant system depends only on the relationship of the two fast time scales, i.e. which fast time is fastest? Using the theory of cancellation of fast oscillations, we show that with the appropriate assumptions on the nonlinear operator of the full system, this reduced slow system is exactly that which the solution will converge to if each asymptotic limit is considered sequentially. The same result is also obtained via the method of renormalization. The specific example of the rotating, stratified Boussinesq equations is explored in detail, indicating that the most common distinguished limit of this system—quasi-geostrophy, is not the only limiting asymptotic system.

A Modified Active Power Control Scheme for Enhanced Operation of PMSG-Based WGs

This paper emphasizes the development of a simplified active power control scheme for enhanced operation of grid integrated permanent magnet synchronous generator based wind-driven generators (WGs). An active power reference generation scheme is proposed for the machine side converter (MSC) to inject active power into the grid even under grid disturbances, without violating system components rating. In this scheme, the controller employed for MSC adjusts the active power captured proportionate to the drop in the grid voltage upon considering wind speed and rotor speed. Furthermore, unlike dual vector control scheme, the grid side converter controller is implemented in a positive synchronous frame with the proposed current oscillation cancellation scheme to suppress the oscillations in dc-link voltage, active and reactive power of the grid and to obtain symmetrical sinusoidal grid current. Extensive analytical simulation has been carried out in PSCAD/ EMTDC to validate the superiority of proposed control scheme over the conventional schemes when WG is subjected to various grid disturbances. The reduced percentage of oscillation in the system parameters such as dc-link voltage and grid active power confirms the efficacy of the proposed method when compared with the conventional control techniques.

Relationship Between Two Direct Power Control Methods for PWM Rectifiers Under Unbalanced Network

Active power control plays an important role in a pulse width modulation (PWM) rectifier under both balanced and unbalanced network conditions. The prior methods to achieve active power oscillation cancellation (APOC) under unbalanced grid voltages are usually implemented by forcing the grid current to track appropriate current references. They require fine tuning work of a current controller and positive-/negative-sequence extraction of grid voltage/currents and/or converter voltage, which complicates the design of the controller. This paper presents two APOC methods in the frame of direct power control (DPC) for the PWM rectifier and reveals their inherent relationship. In the first method, an appropriate power compensation is added to the original power references without modifying the internal control structure. In the second method, a novel definition of reactive power is employed to replace conventional reactive power, which achieves the aim of APOC automatically. Both methods can be easily integrated with existing DPC schemes with a slight modification. The sequence extraction required in prior methods is eliminated. The inherent relationship between these two methods is investigated, and it is found that they are completely equivalent. The two APOC methods are comparatively studied and implemented in the basic table-based DPC. Simulation and experimental results confirm the theoretical study and the effectiveness of the two methods.

An implementation of double-frequency oscillation cancellation technique in control of DSTATCOM

SUMMARY This paper presents an implementation of double-frequency oscillation cancellation (DFOC) technique in phase locked loop less synchronous reference frame theory for control of a distribution static compensator (DSTATCOM). This control algorithm on DSTATCOM is used for improvement of power quality under linear and nonlinear loads. The DFOC technique is used for cancellation of double-frequency component from the load fundamental active and reactive power components of currents which are used for deriving the reference supply currents without time delay. A DSTATCOM is developed, and its performance is tested using a digital signal processor. The performance of DSTATCOM is found satisfactory for different types of loads in transient and steady state conditions. Copyright © 2013 John Wiley & Sons, Ltd.

Unitarity of scattering and edge spin accumulation

We consider a 2D ballistic and quasi-ballistic structures with spin-orbit-related splitting of the electron spectrum. The ballistic region is attached to the leads with a voltage applied between them. We calculate the edge spin density which arises in the presence of a charge current through the structure. We solve the problem with the use of the method of scattering states and clarify the important role of the unitarity of scattering. In the case of a straight boundary it leads to exact cancellation of long-wavelength oscillations of the spin density. In general, however, the smooth spin oscillations with the spin precession length may arise, as it happens, e.g., for the wiggly boundary. Moreover, we show that the result crucially depends on the form of the spin-orbit Hamiltonian.

The potential of corticomuscular and intermuscular coherence for research on human motor control

The potential of corticomuscular and intermuscular coherence for research on human motor control

Perfect wave oscillation suppression with reflection coefficients adaptation in PWM motor drives with long feeding cables

A perfect wave oscillation cancellation scheme is a proposed method for suppressing overvoltage in adjustable speed PWM motor drives through long feeding cables. It is a new solution to the overvoltage problem, which cascades the proposed filter with the transmission line achieving a pure delay transfer between inverter and motor, completely removing the pulse reflection that causes the overvoltage problem. Simple voltage transfer function with time delay is derived under a distortionless transmission assumption, which is valid in practice. The proposed PWM input voltage form is calculated by inverting the voltage transfer function. Also, the unknown reflection coefficients are identified through a simple adaptive algorithm. The simulation results verify the performance of the proposed method, which is compared with a previous method.

PREFACTOR-FREE FORWARD-BACKWARD SEMICLASSICAL DYNAMICS

Within a differential expression of the Heisenberg operator, the forward and backward evolution can be joined together along a closed time contour. This manipulation leads to a dramatic cancellation of oscillations due to the two individual propagators in the Heisenberg operator and the resulting forward-backward propagator is more tractable to semiclassical approximations. This article gives a detailed description of the forward-backward semiclassical dynamics (FBSD) formalism. The semiclassical propagators, especially those of the initial value representations (IVRs), are briefly discussed. The derivation of the FBSD based on the Herman–Kluk propagator is reviewed. Different FBSD formulations with other semiclassical IVRs are worked out and numerical calculations show that they are also capable of describing quantum dynamics semiquantitatively and all display accuracy similar to the classical Wigner method.

A CMOS feedforward neural-network chip with on-chip parallel learning for oscillation cancellation

The paper presents a mixed signal CMOS feedforward neural-network chip with on-chip error-reduction hardware for real-time adaptation. The chip has compact on-chip weighs capable of high-speed parallel learning; the implemented learning algorithm is a genetic random search algorithm: the random weight change (RWC) algorithm. The algorithm does not require a known desired neural network output for error calculation and is suitable for direct feedback control. With hardware experiments, we demonstrate that the RWC chip, as a direct feedback controller, successfully suppresses unstable oscillations modeling combustion engine instability in real time.

Coherent control of precessional dynamics in thin film permalloy

We demonstrate a method of eliminating overshoot and ringing in magnetization dynamics when the system bandwidth includes the intrinsic ferromagnetic resonance (FMR). The method employs staggered step excitation for the cancellation of FMR oscillations while maximizing the risetime of the magnetization response. The second-harmonic magneto-optic Kerr effect is used to measure the magnetic response at a localized spot on the sample. The measured response is adequately modeled with the Landau–Lifshitz–Gilbert differential equation. We explain the observed behavior in terms of destructive interference.

Experimental investigation of flow-induced acoustic oscillations in a piping system with closed branches

An experimental study of flow-excited acoustic oscillations in piping systems with closed branches is presented in this paper. An influence of acoustic interactions between branches on a generated sound was investigated in arrangements with two and three branches. Significant changes of frequency and level of oscillation in terms of branch lengths were observed. In the system with three branches, at the specified lengths of one branch, a cancellation of oscillations was noticed.

Simulations of layer-by-layer sputtering during epitaxy

We have performed computer simulations of simultaneous and sequential ion bombardment and epitaxial growth. In agreement with recent reflection high-energy electron diffraction (RHEED) measurements on Si, we observe ion-induced RHEED oscillations, a cancellation of RHEED oscillations during simultaneous equal-rate ion bombardment and growth, and a reversal of growth-induced roughening by subsequent ion bombardment. Comparison between simulations and measurements indicate that a model of the ion/surface interaction characterized by the creation of mobile vacancies with minimal preferential sputtering is sufficient to simulate all the RHEED measurements.

Simulations of Low-Energy Ion Bombardment and Epitaxial Growth

ABSTRACTWe have performed computer simulations of epitaxial growth and low-energy ion bombardment for comparison with reflection high-energy electron diffraction (RHEED) mesurements. The simulations are based on a hybrid Monte Carlo/rate equation approach which includes the processes of defect creation (adatom and surface vacancy), surface diffusion, and attachment and detachment from steps and islands. In this work, we focus on simulating the experimental observations of ion-induced RHEED oscillations and cancellation of RHEED oscillations during simultaneous ion bombardment and growth. For the interaction of the low-energy ion with the surface, we consider two mechanisms: preferential sputtering (where the sputtering cross section depends on the atomic coordination) and mobile vacancies. Our results indicate that the primary interaction of the ion beam with the surface is probably through the creation of mobile vacancies, and that the degree of preferential sputtering is not large.

Hyperbolic systems of conservation laws with a symmetry

Hyperbolic systems of conservaiton laws with a symmetry are studied. Some peculiar phenomena for such systems are shown. Admissibility criteria for solutions to such systems are discussed. propagation and cancellation of initial oscillations for the systems are classified. As a byproduct of this study, an existence theorem of global solutions for the Cauchy of the systems is established.

Simulations of Low-Energy Ion Bombardment and Epitaxial Growth

AbstractWe have performed computer simulations of epitaxial growth and low-energy ion bombardment for comparison with reflection high-energy electron diffraction (RHEED) mesurements. The simulations are based on a hybrid Monte Carlo/rate equation approach which includes the processes of defect creation (adatom and surface vacancy), surface diffusion, and attachment and detachment from steps and islands. In this work, we focus on simulating the experimental observations of ion-induced RHEED oscillations and cancellation of RHEED oscillations during simultaneous ion bombardment and growth. For the interaction of the low-energy ion with the surface, we consider two mechanisms: preferential sputtering (where the sputtering cross section depends on the atomic coordination) and mobile vacancies. Our results indicate that the primary interaction of the ion beam with the surface is probably through the creation of mobile vacancies, and that the degree of preferential sputtering is not large.

Propagation and cancellation of oscillations for hyperbolic systems of conservation laws

Propagation and cancellation of oscillations for hyperbolic systems of conservation laws

On the Control and Stability of Grid Connected Photovoltaic Sources

A methodology is proposed for the effective integration of photovoltaic (PV) devices into the electric utility distribution network operations. The dispersed PV generator is viewed as an active device used to improve system stability by appropriately modulating the power conditioning unit's output power. Disturbances on the utility system can be damped out by injecting this power into the grid in such a way so that the net effect is a cancellation of undesirable oscillations. The approach is implemented by monitoring the oscillating power and generating control signals which shape accordingly the interface unit's output power. Successful implementation of the scheme relies heavily on the speed and flexibility with which the electronic inverter moves power from the primary source/storage facility to the utility lines. Simulation studies, using the proposed control approach, indicate that application of these policies may result in reduced load following requirements for conventional power generating units, increase the value and acceptability of new energy technologies, and improve power quality and stability of the interconnected system.

Modification of muscle responses by spinal circuitry

Recently, we developed a model based on experimental data, which includes a pair of antagonistic muscles, a general load against which the muscles act, feedback pathways from muscle sense organs and spinal inhibitory circuits involving 1A interneurons and Renshaw cells. Descending inputs can activate the model through combinations of inputs to α-motoneurons, γ-motoneurons (via intrafusal muscles and their feedback pathways) or the 1A interneurons. The role of each of these connections is analysed here in terms of its effect on the response of the muscles to impulse inputs, with particular interest in the effects on the overall stability of the systems. Increasing muscle stiffness or feedback from muscle receptors tends to produce high frequency oscillations. Coactivation of α- and γ-motoneurons can lead to cancellation of oscillations, because of delays in the effects of γ-motoneurons on contraction. Connections of 1A inhibitory interneurons onto antagonist motoneurons accentuate the oscillations. Inhibitory connections from Renshaw cells onto α-motoneurons tend to prevent oscillations, whereas the concentrations onto γ-motoneurons may produce them.