1,222 research outputs found
Linear parameter-varying model to design control laws for an artificial pancreas
The contribution of this work is the generation of a control-oriented model for insulin-glucose dynamic regulation in type 1 diabetes mellitus (T1DM). The novelty of this model is that it includes the time-varying nature, and the inter-patient variability of the glucose-control problem. In addition, the model is well suited for well-known and standard controller synthesis procedures. The outcome is an average linear parameter-varying (LPV) model that captures the dynamics from the insulin delivery input to the glucose concentration output constructed based on the UVA/Padova metabolic simulator. Finally, a system-oriented reinterpretation of the classical ad-hoc 1800 rule is applied to adapt the model's gain. The effectiveness of this approach is quantified both in open- and closed-loop. The first one by computing the root mean square error (RMSE) between the glucose deviation predicted by the proposed model and the UVA/Padova one. The second measure is determined by using the ν-gap as a metric to determine distance, in terms of closed-loop performance, between both models. For comparison purposes, both open- (RMSE) and closed-loop (ν-gap metric) quality indicators are also computed for other control-oriented models previously presented. This model allows the design of LPV controllers in a straightforward way, considering its affine dependence on the time-varying parameter, which can be computed in real-time. Illustrative simulations are included. In addition, the presented modeling strategy was employed in the design of an artificial pancreas (AP) control law that successfully withstood rigorous testing using the UVA/Padova simulator, and that was subsequently deployed in a clinical trial campaign where five adults remained in closed-loop for 36 h. This was the first ever fully closed-loop clinical AP trial in Argentina, and the modeling strategy presented here is considered instrumental in resulting in a very successful clinical outcome.Fil: Colmegna, Patricio Hernán. Universidad Nacional de Quilmes. Departamento de Ciencia y TecnologÃa; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Sánchez Peña, Ricardo S.. Instituto Tecnológico de Buenos Aires; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Gondhalekar, R.. Harvard University; Estados Unido
A review of convex approaches for control, observation and safety of linear parameter varying and Takagi-Sugeno systems
This paper provides a review about the concept of convex systems based on Takagi-Sugeno, linear parameter varying (LPV) and quasi-LPV modeling. These paradigms are capable of hiding the nonlinearities by means of an equivalent description which uses a set of linear models interpolated by appropriately defined weighing functions. Convex systems have become very popular since they allow applying extended linear techniques based on linear matrix inequalities (LMIs) to complex nonlinear systems. This survey aims at providing the reader with a significant overview of the existing LMI-based techniques for convex systems in the fields of control, observation and safety. Firstly, a detailed review of stability, feedback, tracking and model predictive control (MPC) convex controllers is considered. Secondly, the problem of state estimation is addressed through the design of proportional, proportional-integral, unknown input and descriptor observers. Finally, safety of convex systems is discussed by describing popular techniques for fault diagnosis and fault tolerant control (FTC).Peer ReviewedPostprint (published version
Robust nonlinear control of vectored thrust aircraft
An interdisciplinary program in robust control for nonlinear systems with applications to a variety of engineering problems is outlined. Major emphasis will be placed on flight control, with both experimental and analytical studies. This program builds on recent new results in control theory for stability, stabilization, robust stability, robust performance, synthesis, and model reduction in a unified framework using Linear Fractional Transformations (LFT's), Linear Matrix Inequalities (LMI's), and the structured singular value micron. Most of these new advances have been accomplished by the Caltech controls group independently or in collaboration with researchers in other institutions. These recent results offer a new and remarkably unified framework for all aspects of robust control, but what is particularly important for this program is that they also have important implications for system identification and control of nonlinear systems. This combines well with Caltech's expertise in nonlinear control theory, both in geometric methods and methods for systems with constraints and saturations
Output-Feedback Synthesis for a Class of Aperiodic Impulsive Systems
We derive novel criteria for designing stabilizing dynamic output-feedback
controllers for a class of aperiodic impulsive systems subject to a range
dwell-time condition. Our synthesis conditions are formulated as
clock-dependent linear matrix inequalities (LMIs) which can be solved
numerically, e.g., by using matrix sum-of-squares relaxation methods. We show
that our results allow us to design dynamic output-feedback controllers for
aperiodic sample-data systems and illustrate the proposed approach by means of
a numerical example
Online Optimization of Switched LTI Systems Using Continuous-Time and Hybrid Accelerated Gradient Flows
This paper studies the design of feedback controllers that steer the output
of a switched linear time-invariant system to the solution of a possibly
time-varying optimization problem. The design of the feedback controllers is
based on an online gradient descent method, and an online hybrid controller
that can be seen as a regularized Nesterov's accelerated gradient method. Both
of the proposed approaches accommodate output measurements of the plant, and
are implemented in closed-loop with the switched dynamical system. By design,
the controllers continuously steer the system output to an optimal trajectory
implicitly defined by the time-varying optimization problem without requiring
knowledge of exogenous inputs and disturbances. For cost functions that are
smooth and satisfy the Polyak-Lojasiewicz inequality, we demonstrate that the
online gradient descent controller ensures uniform global exponential stability
when the time-scales of the plant and the controller are sufficiently separated
and the switching signal of the plant is slow on the average. Under a strong
convexity assumption, we also show that the online hybrid Nesterov's method
guarantees tracking of optimal trajectories, and outperforms online controllers
based on gradient descent. Interestingly, the proposed hybrid accelerated
controller resolves the potential lack of robustness suffered by standard
continuous-time accelerated gradient methods when coupled with a dynamical
system. When the function is not strongly convex, we establish global practical
asymptotic stability results for the accelerated method, and we unveil the
existence of a trade-off between acceleration and exact convergence in online
optimization problems with controllers using dynamic momentum. Our theoretical
results are illustrated via different numerical examples
Stabilization of systems with asynchronous sensors and controllers
We study the stabilization of networked control systems with asynchronous
sensors and controllers. Offsets between the sensor and controller clocks are
unknown and modeled as parametric uncertainty. First we consider multi-input
linear systems and provide a sufficient condition for the existence of linear
time-invariant controllers that are capable of stabilizing the closed-loop
system for every clock offset in a given range of admissible values. For
first-order systems, we next obtain the maximum length of the offset range for
which the system can be stabilized by a single controller. Finally, this bound
is compared with the offset bounds that would be allowed if we restricted our
attention to static output feedback controllers.Comment: 32 pages, 6 figures. This paper was partially presented at the 2015
American Control Conference, July 1-3, 2015, the US
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