Constant Gain Coefficient Research Articles

Envelope-Based Variable-Gain Control Strategy for Vibration Suppression of Solar Array Using Reaction Wheel Actuator

The orbital operation of spacecraft can excite the long-drawn and low-frequency vibration of the solar array, which is prone to affecting the task execution of the system. To address this issue, an envelope-based variable-gain control strategy is proposed to suppress vibration of the solar array using the reaction wheel (RW) actuator. The RW actuator is individually mounted on the solar array to provide reaction torque through the speed change of its rotor. The governing equation of motion of the solar array actuated by a RW actuator is deduced with the state space representation. The control relation between the measured bending moment and the rotational speed of the RW actuator with the constant-gain coefficient is firstly developed and demonstrated in numerical simulation. Changing the gain coefficient to be inversely proportional to the envelope function of vibration, a variable-gain control strategy is proposed to improve the damping effect of the RW actuator. Simulation results show that the vibration suppression performance of the RW actuator is improved compared to the constant-gain control. As the actual on-orbit natural frequency of the solar array is not always exactly known, the robustness of the control system is analyzed for the deviation between the estimated and the actual natural frequency values. The proposed variable-gain control is also experimentally verified using a simplified elastic plate model. Experimental results indicate that the vibration attenuation time is decreased to 29.1% and 50.22% compared to the uncontrolled and the constant-gain controlled states, respectively.

Quasi-Synchronization and Quasi-Uniform Synchronization of Caputo Fractional Variable-Parameter Neural Networks with Probabilistic Time-Varying Delays

Owing to the symmetry between drive–response systems, the discussions of synchronization performance are greatly significant while exploring the dynamics of neural network systems. This paper investigates the quasi-synchronization (QS) and quasi-uniform synchronization (QUS) issues between the drive–response systems on fractional-order variable-parameter neural networks (VPNNs) including probabilistic time-varying delays. The effects of system parameters, probability distributions and the order on QS and QUS are considered. By applying the Lyapunov–Krasovskii functional approach, Hölder’s inequality and Jensen’s inequality, the synchronization criteria of fractional-order VPNNs under controller designs with constant gain coefficients and time-varying gain coefficients are derived. The obtained criteria are related to the probability distributions and the order of the Caputo derivative, which can greatly avoid the situation in which the upper bound of an interval with time delay is too large yet the probability of occurrence is very small, and information such as the size of time delay and probability of occurrence is fully considered. Finally, two examples are presented to further confirm the effectiveness of the algebraic criteria under different probability distributions.

A velocity field level set method for topology optimization of piezoelectric layer on the plate with active vibration control

Vibration control has significant applications in many engineering areas to achieve designed vibration performances or suppress structural fatigue and failure. This paper presents a velocity field level set method for topology optimization of the piezoelectric layer on a plate with active vibration control. The material distribution of the piezoelectric layer and the topology optimization model for this problem is formulated in the level set framework, which can precisely track the layout (topology/shape) of piezoelectric layers with clear/smooth boundaries. Compared with the density-based method, the level set method can avoid the difficulties in the definition of material distributions and piezoelectric material properties for intermediate densities, which also leads to more accurate vibration control. We employ the constant gain velocity feedback as the vibration control algorithm. The dynamic compliance is set as the objective function and treated as the index representing the plate’s vibration level. Using the velocity field level set method can map the original variational boundary shape optimization problem into the finite dimensional space and solve the optimization problem efficiently by general optimizers. We also show that the self-adjoint scheme can be used in the sensitivity analysis, which avoids solving additional adjoint problems. To verify the validity and efficiency of the proposed method, we give three numerical examples, in which the influence of the external frequency and the constant gain coefficient on optimization results are also discussed.

Exponential Stabilization of Linear Time-Varying Differential Equations with Uncertain Coefficients by Linear Stationary Feedback

We consider a control system defined by a linear time-varying differential equation of n-th order with uncertain bounded coefficients. The problem of exponential stabilization of the system with an arbitrary given decay rate by linear static state or output feedback with constant gain coefficients is studied. We prove that every system is exponentially stabilizable with any pregiven decay rate by linear time-invariant static state feedback. The proof is based on the Levin’s theorem on sufficient conditions for absolute non-oscillatory stability of solutions to a linear differential equation. We obtain sufficient conditions of exponential stabilization with any pregiven decay rate for a linear differential equation with uncertain bounded coefficients by linear time-invariant static output feedback. Illustrative examples are considered.

Influence of saturable absorber saturation power, modulation depth and relaxation time on pulse parameters of a soliton fibre laser

The influence of the saturable absorber saturation power, modulation depth and relaxation time on the energy and shape of fibre soliton laser pulses has been studied by numerical simulation. The results suggest that the use of a saturable absorber with a lower saturation power in a fibre laser ensures pulsed lasing onset at a lower gain. The fibre laser pulse energy decreases as the saturation power of the absorber or the relaxation time of its open state increases at a constant gain coefficient. In addition, increasing the absorber saturation modulation depth at a constant gain coefficient has been shown to reduce the pulse peak power and energy.

Learning, monetary policy rules, and macroeconomic stability

Several papers have documented a regime switch in US monetary policy from ‘passive’ and destabilizing in the pre-1979 period to ‘active’ and stabilizing afterwards. These studies typically work with DSGE models with rational expectations. This paper relaxes the assumption of rational expectations and allows for learning instead. Economic agents form expectations from simple models and update the parameters through constant-gain learning. In this setting, the paper aims to test whether monetary policy may have been a source of macroeconomic instability in the 1970s by inducing unstable learning dynamics. The model is estimated by Bayesian methods. The constant-gain coefficient is jointly estimated with the structural and policy parameters in the system. The results show that monetary policy was respecting the Taylor principle also in the pre-1979 period and, therefore, did not trigger macroeconomic instability.

Optimal LQI Synthesis for Speed Control of Synchronous Actuator under Load Inertia Variations

Direct drives applications are more and more common and rise up the control weakness to parameters variation. New method have been created but are most of time complex to tune and need powerful processor. In this paper, state feedback controllers optimized by Linear Quadratic principle are shown up. These methods achieve cost requirements due to constant gain coefficients. Methods tune criterion to let the closed loop stable and unsensitive to load variation. The first one uses an iterative algorithm on few tuned parameter. The last one blends poles placement and Linear Quadratic principle to achieve a fast synthesis method. Experimental results have been obtained taking into account internal current control and inverter limitation.

Assessing Mathematical Forms employed to Describe Evolutions of Perturbations Propagating inside Optical Fibers

Comparisons have been made with different mathematical forms used to represent perturbation fields in studying the modulation instability happened in optical fibers. Without an artificial constraint, self consistent solutions to the linearized nonlinear Schrodinger equation can be deduced, which has recovered a rich variety of evolution characteristics at the initial stage for the perturbations co-propagating with a strong CW radiation inside the optical fiber. Although previous theories have correctly predicted the perturbation gain coefficient, an effort of seeking a constant gain coefficient as suggested in literatures has directly focused the discussions to the asymptotic characteristics of perturbations and therefore failed to give a comprehensive description to the evolutions.

Learning, Monetary Policy Rules, and Macroeconomic Stability

This paper estimates a DSGE model with learning to re-examine the evidence on time variation in post-war U.S. monetary policy. Several papers document a regime switch, by showing that policy changed from `passive' and destabilizing in the pre-1979 period to `active' and stabilizing in the following decades. These papers typically work with DSGE models with rational expectations. This paper relaxes the assumption of rational expectations and it allows for learning instead. Economic agents form expectations from simple models and update the parameters through constant-gain learning. I estimate the model by Bayesian methods. The constant gain coefficient is jointly estimated with the structural and policy parameters of the system. I find that the feedback coefficient to inflation was well above 1 also in the 1960s and 1970s and therefore policy was not leading to macroeconomic instability. The results reconcile the evidence from DSGE models with what obtained by time-varying VAR studies, which typically find only modest changes in policy coefficients over the post-war sample.

Gain measurements on GaAs-based quantum cascade lasers using a two-section cavity technique

A two-section cavity device has been used to measure gain spectra and waveguide losses of a GaAs-based quantum cascade laser. The device operates at 8.9 /spl mu/m and optical confinement is obtained by means of Al-free cladding layers. We investigated the gain characteristics in a spectral window of /spl sim/60 meV and up to 200 K. For current densities ranging from 1 to 8 kA/cm/sup 2/, we report a constant gain coefficient of 13 cm/kA at 4 K and 6 cm/kA at 200 K. At low temperatures and for current densities above 8 kA/cm/sup 2/, we observe gain saturation which we attribute to a reduced electron injection in the active region caused by space charge effects. We report a value of 22 cm/sup -1/ for the waveguide losses in good agreement with previous measurements.

An averaging method for stochastic approximations with constant parameters: Small parameter values

Abstract : Stochastic approximations with constant gain coefficients and dependent noise and nonlinear or even 'discontinuous dynamics' have many applications in control, automata and communication theory. When the gain coefficient is small, an asymptotic theory is developed which gives much information on the character of the paths and errors. The method involves both 'averaging' and 'stability' ideas. The ideas are outlined. An example which illustrates the basic ideas and techniques is given. (Author)