948 research outputs found
Sufficient Conditions for Feasibility and Optimality of Real-Time Optimization Schemes - I. Theoretical Foundations
The idea of iterative process optimization based on collected output
measurements, or "real-time optimization" (RTO), has gained much prominence in
recent decades, with many RTO algorithms being proposed, researched, and
developed. While the essential goal of these schemes is to drive the process to
its true optimal conditions without violating any safety-critical, or "hard",
constraints, no generalized, unified approach for guaranteeing this behavior
exists. In this two-part paper, we propose an implementable set of conditions
that can enforce these properties for any RTO algorithm. The first part of the
work is dedicated to the theory behind the sufficient conditions for
feasibility and optimality (SCFO), together with their basic implementation
strategy. RTO algorithms enforcing the SCFO are shown to perform as desired in
several numerical examples - allowing for feasible-side convergence to the
plant optimum where algorithms not enforcing the conditions would fail.Comment: Working paper; supplementary material available at:
http://infoscience.epfl.ch/record/18807
Sufficient Conditions for Feasibility and Optimality of Real-Time Optimization Schemes - II. Implementation Issues
The idea of iterative process optimization based on collected output
measurements, or "real-time optimization" (RTO), has gained much prominence in
recent decades, with many RTO algorithms being proposed, researched, and
developed. While the essential goal of these schemes is to drive the process to
its true optimal conditions without violating any safety-critical, or "hard",
constraints, no generalized, unified approach for guaranteeing this behavior
exists. In this two-part paper, we propose an implementable set of conditions
that can enforce these properties for any RTO algorithm. This second part
examines the practical side of the sufficient conditions for feasibility and
optimality (SCFO) proposed in the first and focuses on how they may be enforced
in real application, where much of the knowledge required for the conceptual
SCFO is unavailable. Methods for improving convergence speed are also
considered.Comment: 56 pages, 15 figure
Correlation-Based Tuning of a Restricted-Complexity Controller for an Active Suspension System
A correlation-based controller tuning method is proposed for the ``Design and optimization of restricted-complexity controllers'' benchmark problem. The approach originally proposed for model following is extended to solve the disturbance rejection problem. The idea is to tune the controller parameters such that the closed-loop output be uncorrelated with the disturbance signal. Since perfect decorrelation between the closed-loop output and the disturbance signal is not attainable in the restricted-complexity controller design, the cross correlation between these two signals is minimized iteratively using the stochastic approximation method. Since control specifications can normally be expressed in terms of constraints on the sensitivity functions, a frequency-domain analysis of the criterion is performed. Straightforward implementation of the proposed approach on the active suspension system of the Automatic Control Laboratory of Grenoble (LAG) provides a 2nd-order controller that meets the control specifications very well
Iterative Correlation-Based Controller Tuning: Application to a Magnetic Suspension System
Iterative tuning of the parameters of a restricted-order controller using the data acquired in closed-loop operation seems to be a promising idea, especially for tuning PID controllers in industrial applications. In this paper, a new tuning approach based on decorrelation is proposed. The basic idea is to make the output error between the designed and achieved closed-loop systems uncorrelated with the reference signal. The controller parameters are calculated as the solution to correlation equations involving instrumental variables. Different choices of instrumental variables are proposed and compared via simulation. The stochastic properties of the correlation approach are compared with those of standard IFT using Monte-Carlo simulation. The proposed approach is also implemented on an experimental magnetic suspension system, and excellent performance using only a few real-time experiments is achieved
Implementation techniques for the SCFO experimental optimization framework
The material presented in this document is intended as a comprehensive,
implementation-oriented supplement to the experimental optimization framework
presented in a companion document. The issues of physical degradation, unknown
Lipschitz constants, measurement/estimation noise, gradient estimation,
sufficient excitation, and the handling of soft constraints and/or a numerical
cost function are all addressed, and a robust, implementable version of the
sufficient conditions for feasible-side global convergence is proposed.Comment: supplementary document; 66 page
On linear and quadratic Lipschitz bounds for twice continuously differentiable functions
Lower and upper bounds for a given function are important in many
mathematical and engineering contexts, where they often serve as a base for
both analysis and application. In this short paper, we derive piecewise linear
and quadratic bounds that are stated in terms of the Lipschitz constants of the
function and the Lipschitz constants of its partial derivatives, and serve to
bound the function's evolution over a compact set. While the results follow
from basic mathematical principles and are certainly not new, we present them
as they are, from our experience, very difficult to find explicitly either in
the literature or in most analysis textbooks.Comment: 3 pages; supplementary documen
Full-sky weak lensing:a nonlinear post-Friedmann treatment
We present a full-sky derivation of weak lensing observables in the
Post-Friedmann (PF) formalism. Weak lensing has the characteristic of mixing
small scales and large scales since it is affected by inhomogeneities
integrated along the photon trajectory. With the PF formalism, we develop a
modelling of lensing observables which encompasses both leading order
relativistic effects and effects that are due to the fully non-linear matter
distribution at small scales. We derive the reduced shear, convergence and
rotation up to order in the PF approximation, accounting for scalar,
vector and tensor perturbations, as well as galaxies' peculiar velocities. We
discuss the various contributions that break the Kaiser-Squires relation
between the shear and the convergence at different orders. We pay particular
attention to the impact of the frame-dragging vector potential on lensing
observables and we discuss potential ways to measure this effect in future
lensing surveys.Comment: 59 page
- âŠ