High-gain Feedback Research Articles

Study on the Control of Shunt Active DC Filter for HVDC Systems

A shunt active dc filter (ADF) has been applied in high-voltage dc transmission systems for harmonic suppression. Some key problems in the design of ADF control systems have not been investigated thoroughly due to high harmonic frequency and the complexity of system modeling. In this paper, a high-gain feedback control strategy is proposed, which is independent of circuit parameters. The authors draw a comparison between the harmonic suppression effects of ADF and that of a passive filter and prove that the former can increase the series impedance of the hybrid filter, while the latter can decrease the equivalent voltage. Based on circuit analyses, solutions, such as selection of the dc-side voltage, regulation of the modulation index, system stability conditions, filter design, and switching noise are presented. The consistency between theory analyses and experimental results verifies the feasibility of the proposed control strategy.

Control of Pneumatic Anti-Vibration Apparatus Using Integrated Signal of Relative Acceleration

Precision instrument has maximum permissible vibration in the field of precision positioning. An anti-vibration apparatus has been widely used to restrain floor vibration in this field. In order to avoid the deformation of main body supported by air springs and to eliminate air spring stiffness, the control system of anti-vibration apparatus having the positive feedback using differential signal of relative position was previously proposed. However disturbance suppression characteristic of conventional system is not well because the differential operation increases high frequency sensor noises. Therefore, the positive feedback using integrated signal of relative acceleration is proposed. This system has the elimination function of air spring stiffness and good disturbance suppression characteristic. Then, this paper firstly explains the elimination function of air spring stiffness in this system. Secondly, the disturbance suppression characteristics of this system are compared with that of conventional system. Finally, the problem of implementation due to the high-gain feedback is explained.

Adaptive control for edge alignment in polyester film processing

AbstractEdge alignment of polyester (PET) films is important for achieving product quality and processing speed in winding, coating, drying, and other processes. The edge alignment can be achieved by lateral deflection control, provided that the film tension and transport speed are even at desired values. This article aims to correct the lateral deflection of films by designing robust controllers to swivel the guiding rollers and to maintain even tension and speed at target levels. The self‐tuning neuro‐proportional integral derivative controller and adaptive high‐gain output feedback controller are adopted to guide the lateral deflection so that the film aligns at the desired position. A control scheme, neuron controller by associative learning, is used for maintaining tension and speed control. These strategies are applied to a simplified PET film processing system. The experimental results demonstrate that in our setup, the control schemes can effectively alleviate not only the lateral deflection but also the tension and speed fluctuation at target levels. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:153–162, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20096

CMOS High-CMRR Current Output Stages

Two CMOS current output stages are presented. Compared to the traditional solution, which exhibits unbalanced operation, the proposed ones exploit an auxiliary high-gain feedback loop which provides differential drive, thereby highly improving the common-mode rejection ratio (CMRR). Prototypes are designed and fabricated in a 0.35-mum technology and experimental results confirm that a CMRR increase greater than 20 dB can be achieved and, for one of the two solutions, without increasing the voltage requirements.

Feedback-Linearized Inverse Feedforward for Creep, Hysteresis, and Vibration Compensation in AFM Piezoactuators

In this brief, we study the design of a feedback and feedforward controller to compensate for creep, hysteresis, and vibration effects in an experimental piezoactuator system. First, we linearize the nonlinear dynamics of the piezoactuator by accounting for the hysteresis (as well as creep) using high-gain feedback control. Next, we model the linear vibrational dynamics and then invert the model to find a feedforward input to account vibration - this process is significantly easier than considering the complete nonlinear dynamics (which combines hysteresis and vibration effects). Afterwards, the feedforward input is augmented to the feedback-linearized system to achieve high-precision highspeed positioning. We apply the method to a piezoscanner used in an experimental atomic force microscope to demonstrate the method's effectiveness and we show significant reduction of both the maximum and root-mean-square tracking error. For example, high-gain feedback control compensates for hysteresis and creep effects, and in our case, it reduces the maximum error (compared to the uncompensated case) by over 90%. Then, at relatively high scan rates, the performance of the feedback controlled system can be improved by over 75% (i.e., reduction of maximum error) when the inversion-based feedforward input is integrated with the high-gain feedback controlled system.

Feedback Cooling of a Cantilever’s Fundamental Mode below 5 mK

We cool the fundamental mechanical mode of an ultrasoft silicon cantilever from a base temperature of 2.2 K down to 2.9+/-0.3 mK using active optomechanical feedback. The lowest observed mode temperature is consistent with limits determined by the properties of the cantilever and by the measurement noise. For high feedback gain, the driven cantilever motion is found to suppress or "squash" the optical interferometer intensity noise below the shot noise level.

Investigations into the stability of a PID-controlled micropositioning and vibrationattenuation system

This paper describes a theoretical and experimental investigation into the stability andperformance of an active micropositioning and vibration attenuation system, based onpiezoelectric actuators incorporated into a very stiff base structure and controlled throughdecentralized PID feedback of the equipment position. Vibration attenuation of up to−35 dB over a bandwidth of several hundred hertz was demonstrated through experiments.However, high integral feedback gain is required to achieve a sufficient vibrationattenuation performance, thus inevitably creating an inherently unstable activesystem. Establishing guidelines concerning the design of active systems based on thedescribed approach and identifying parameters that affect the system stability is themotivation of this research. An analytical model of a test rig was set up and validatedagainst measurements so that the effect of structural changes on the stability ofthe control system could be assessed. Stiff mounts, little mass of the controlledequipment and sufficient passive damping of mounts and base were found to beessential for the stability and functionality of the active system. Based on thedeveloped guidelines, a prototype of a fully functional micropositioning and vibrationattenuation system was manufactured as part of a project aimed at building a novelmagnetic resonance imaging (MRI) scanner. The maximum stable PID gains wereused to assess the relative system stability since an analytical model that reliablypredicted the stability margins was not available. Experiments conducted on theprototype identified and quantified the influence of various parameters on thesystem stability, such as the control scheme utilized, the number of controlleddegrees-of-freedom, signal conditioning, the passive damping and the control loopfrequency. Passive damping was considered the single most important parameter ofinfluence.

High gain feedback, tolerance, and stabilization of linear systems

The problem of stabilizing linear continuous-time systems is revisited with the objective of investigating the tolerance allowed in the implementation of stabilizing feedback controllers. It is shown that, for high gain feedback, this tolerance can be described by a cone in the feedback parameter space, called the “tolerance cone”. The tolerance cone describes fractional (percentage) errors the feedback controller can tolerate without jeopardizing the internal stability of the controlled system. The larger the vertex angle of this cone, the more tolerance is available when implementing the controller. The vertex angle of the tolerance cone is determined by the proximity to singularity of a certain matrix derived from the controlled system.

Dynamic Nonlinear Control for Fast Seek-Settling Performance in Hard Disk Drives

This paper proposes a dynamic nonlinear control scheme to improve the seek-settling performance in hard disk drive servo system by a combination of a novel designed reference generator and a nonlinear feedback controller. The feedback controller consists of a linear one for short rise time and an associated nonlinear one for small overshoot. In order to improve the settling performance and system stability due to actuator saturation, reference trajectory is designed based on the performance of feedback loop so that the position error signal in the tracking stage is decreased greatly, which effectively avoids the actuator saturation with a high gain feedback control design. A parameterized second-order system is proposed to generate such desired reference trajectory. The stability of the proposed control scheme is proved through appropriate Lyapunov functions. The results in simulation and implementation show that the proposed control design performs better as compared with linear and optimal control laws for both short and long tracking lengths

지능판에 동위치화된 압전 센서-액추에이터의 응답특성 연구

A smart panel with structural sensors and actuators for minimizing noise radiation or transmission is described in the paper with the concept of active structural acoustical control. The sensors and actuators are both quadratically shaped piezoelectric polyvinylidene fluoride(PVDF) Polymer films to implement a volume velocity sensor and uniform force actuator respectively. They are collocated on either side of the panel to take advantage of direct velocity feedback(DVFB) strategy, which can guarantee a robust stability and high performance as long as the sensor-actuator response is strictly positive real(SPR). However, the measured sensor-actuator response of the panel showed unexpected result with non-SPR property. In the paper, the reason of the non-SPR property is investigated by theoretical analysis, computer simulation and experimental verification. The investigation reveals that the arrangement of collocated piezoelectric PVDF sensor and actuator pair on a panel is not relevant to get a high feedback gain and good performance with DVFB strategy.

NONLINEAR OUTPUT REGULATION AND CROSS-TERMS COMPENSATION1

In this paper we survey the results recently obtained in (Marconi et al., 2006) in the context of output regulation and we frame them in a broader context of set stabilization by output feedback. The peculiarity of the set stabilization framework which is here formulated is given by the presence of non-vanishing cross-terms between zero- and output-dynamics. We show how the mathematical tools developed in (Marconi et al., 2006) allow for the synthesis of a robust control law which is not inspired by certainty equivalence principles. As new application of the tools we show how a problem of output feedback asymptotic stabilization with zero dynamics which are not exponentially stable can be handled by means of high-gain output feedback.

2P1-A11 アクチュエータ束により駆動されるLoosely Coupled Mechanismの角度制御(フレキシブル・メカニズム)

We present a link mechanism with a loosely coupled mechanism (LCM), modeled on a human joint. A viscoelastic object functions as a cartilaginous area and soft actuators as muscles. The link of an LCM has high compliance with soft materials, additionally bends smoothly as a human joint. We made an LCM using shape memory alloy (SMA) actuator bundles to regulate the link angle. Due to large generative force of actuator bundles, we have better response in angle control. Although it is impossible to set a high gain for each SMA, the whole system using actuator bundles can realize high gain feedback in angle control.

Corrective movements in response to displacements in visual feedback are more effective during periods of 13–35 Hz oscillatory synchrony in the human corticospinal system

Oscillatory synchronization in the beta (approximately 20 Hz) band is a common feature of human motor control, manifest at cortical and muscular levels during tonic contraction. Here we test the hypothesis that the influence of visual feedback on performance in a positional hold task is increased during bursts of beta-band synchrony in the corticospinal motor system. Healthy subjects were instructed to extend their forefinger while receiving high-gain visual feedback of finger position on a PC screen. Small step displacements of the feedback signal were triggered either by bursts of beta oscillations in scalp electroencephalogram or randomly with respect to cortical beta activity, and the resulting positional corrections expressed as a percentage of the step displacement. Corrective responses to beta and randomly triggered step changes in visual feedback were 41.7+/-4.9 and 31.5+/-6.8%, respectively (P<0.05). A marked increase in the coherence in the beta band was also found between muscle activity and cortical activity during the beta-triggered condition. The results suggest that phasic elevations of beta activity in the corticospinal motor system are associated with an increase in the gain of the motor response to visual feedback during a tonic hold task. Beta activity may index a motor state in which processing relevant to the control of positional hold tasks is promoted, with behavioural consequences.

Random lasing in weakly scattering systems

We present detailed experimental and numerical studies of random lasing in weakly scattering systems. The interference of scattered light, which is weak in the passive systems, is greatly enhanced in the presence of high gain, providing coherent and resonant feedback for lasing. The lasing modes are confined in the vicinity of the pumped volume due to absorption of emitted light outside it. In the ballistic regime where the size of the gain volume is less than the scattering mean free path, lasing oscillation occurs along the direction in which the gain volume is most extended, producing directional laser output. The feedback for lasing originates mainly from backscattering of particles near the boundaries of the pumped region. It results in nearly constant frequency spacing of lasing modes, which scales inversely with the maximum dimension of the gain volume.

Accurate, Compact, and Power-Efficient Li-Ion Battery Charger Circuit

A novel, accurate, compact, and power-efficient lithium-ion (Li-Ion) battery charger designed to yield maximum capacity, cycle life, and therefore runtime is presented and experimentally verified. The proposed charger uses a diode to smoothly (i.e., continuously) transition between two high-gain linear feedback loops and control a single power MOS device, automatically charging the battery with constant current and then constant voltage. An adaptive power-efficient charging scheme in the form of a cascaded switching regulator supply ensures the voltage across the charging power-intensive pMOS remains low, thereby reducing its power losses and yielding up to 27% better overall power efficiency. An 83% power-efficient printed circuit board prototype was built and used to charge several Li-Ion batteries to within plusmn0.43% of their optimum full-charge voltage and therefore within a negligibly small fraction of their full capacity

Control system design for VSC transmission

This paper investigates a suitable control system for a DC transmission system based on voltage source converters (VSC). Each of the two VSC converters has two control inputs and the four control channels on a VSC transmission system offer potential for a versatile control. However, the main challenge is the dynamic interaction among the control loops. It is proposed in this study that the overall system stability and good robustness should be achieved with two high-gain feedback loops, one at each converter. Eigenvalue and robustness analysis with MATLAB software shows that the best fast feedback signals are inverter DC voltage and rectifier AC voltage q component. The slow controller consists of three PI controllers that regulate: rectifier AC voltage, inverter AC voltage and the DC power. The VSC transmission control under fault conditions is achieved with a separate controller that takes over system control for fault-level currents. The fault controller regulates the local DC currents at each converter. The proposed controller is tested using PSCAD/EMTDC for a wide range of small-signal step inputs and the design performance is confirmed. The design is also tested for typical fault scenarios on AC and DC side to verify the fault controller operation.

Asymptotic stabilization by PID control: Stability analysis based on minimum phase and high-gain feedback

This paper is concerned with the regulator problem for an SISO system using a PID controller. The controlled object is an SISO system which is controllable. Our purpose is to analyze the stability of the PID control system and to determine the PID parameters so that the closed system is asymptotically stable. The main idea is based on the minimum phase property and Lyapunov's stability theorem. The quasi pole-placement method is used to asymptotically stabilize zero dynamics whose poles depend on the PID parameters. The effectiveness of the proposed method is confirmed by simulation results for various plants. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 44–53, 2006; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/eej.20336

Global chassis control based on inverse vehicle dynamics models

This work proposes to approach global chassis control (GCC) by means of model inversion-based feedforward with allocation directly on the actuator commands. The available degrees of freedom are used to execute the desired vehicle motion while minimizing the utilization of the tyre’s grip potential. This is done by sampled constrained least-squares optimization of the linearized problem. To compensate for model errors and external disturbances, high-gain feedback is applied by means of an inverse disturbance observer. The presented method is applied in a comparison of eight vehicles with different actuator configurations for steer, drive, brake and load distribution. The approach shows a transparent and effective method to deal with the complex issue of GCC in a unitized way. It gives both a base for controller design and a structured way to compare different configurations. In practice, the transparency supports automatic on-board reconfiguration in the case of actuator hardware failure.

High-Gain State Feedback Analysis Based on Singular System Theory

We consider linear, time-invariant state-space systems under high-gain state feedback. The analysis is couched in terms of singular system theory and Grassman manifolds. Our work is distinguished from that of other authors by the fact that we do not allow a gain-dependent state coordinate change. Simple necessary and sufficient conditions are proven under which a singular system is a high-gain limit of a given state-space system. It is shown that the feedback matrix achieves a limit on an appropriate Grassmanian, so infinite gains constitute well-defined mathematical objects. The special cases of minimum-order stable and zeroth-order limits are studied in depth, including an analysis of solution behavior. Finally, the classical cheap control problem is interpreted within the context of our results.

Rigid Body Dynamics, Constraints, and Inverses

Rigid body dynamics are traditionally formulated by Lagrangian or Newton-Euler methods. A particular state space form using Euler angles and angular velocities expressed in the body coordinate system is employed here to address constrained rigid body dynamics. We study gliding and rolling, and we develop inverse systems for estimation of internal and contact forces of constraint. A primitive approximation of biped locomotion serves as a motivation for this work. A class of constraints is formulated in this state space. Rolling and gliding are common in contact sports, in interaction of humans and robots with their environment where one surface makes contact with another surface, and at skeletal joints in living systems. This formulation of constraints is important for control purposes. The estimation of applied and constraint forces and torques at the joints of natural and robotic systems is a challenge. Direct and indirect measurement methods involving a combination of kinematic data and computation are discussed. The basic methodology is developed for one single rigid body for simplicity, brevity, and precision. Computer simulations are presented to demonstrate the feasibility and effectiveness of the approaches presented. The methodology can be applied to a multilink model of bipedal systems where natural and/or artificial connectors and actuators are modeled. Estimation of the forces is accomplished by the inverse of the nonlinear plant designed by using a robust high gain feedback system. The inverse is shown to be stable, and bounds on the tracking error are developed. Lyapunov stability methods are used to establish global stability of the inverse system.