1,647 research outputs found
Two Globally Convergent Adaptive Speed Observers for Mechanical Systems
A globally exponentially stable speed observer for mechanical systems was
recently reported in the literature, under the assumptions of known (or no)
Coulomb friction and no disturbances. In this note we propose and adaptive
version of this observer, which is robust vis--a--vis constant disturbances.
Moreover, we propose a new globally convergent speed observer that, besides
rejecting the disturbances, estimates some unknown friction coefficients for a
class of mechanical systems that contains several practical examples
Modeling and Control of High-Voltage Direct-Current Transmission Systems: From Theory to Practice and Back
The problem of modeling and control of multi-terminal high-voltage
direct-current transmission systems is addressed in this paper, which contains
five main contributions. First, to propose a unified, physically motivated,
modeling framework - based on port-Hamiltonian representations - of the various
network topologies used in this application. Second, to prove that the system
can be globally asymptotically stabilized with a decentralized PI control, that
exploits its passivity properties. Close connections between the proposed PI
and the popular Akagi's PQ instantaneous power method are also established.
Third, to reveal the transient performance limitations of the proposed
controller that, interestingly, is shown to be intrinsic to PI passivity-based
control. Fourth, motivated by the latter, an outer-loop that overcomes the
aforementioned limitations is proposed. The performance limitation of the PI,
and its drastic improvement using outer-loop controls, are verified via
simulations on a three-terminals benchmark example. A final contribution is a
novel formulation of the power flow equations for the centralized references
calculation
An Energy-Balancing Perspective of Interconnection and Damping Assignment Control of Nonlinear Systems
Stabilization of nonlinear feedback passive systems is achieved assigning a storage function with a minimum at the desired equilibrium. For physical systems a natural candidate storage function is the difference between the stored and the supplied energies—leading to the so-called Energy-Balancing control, whose underlying stabilization mechanism is particularly appealing. Unfortunately, energy-balancing stabilization is stymied by the existence of pervasive dissipation, that appears in many engineering applications. To overcome the dissipation obstacle the method of Interconnection and Damping Assignment, that endows the closed-loop system with a special—port-controlled Hamiltonian—structure, has been proposed. If, as in most practical examples, the open-loop system already has this structure, and the damping is not pervasive, both methods are equivalent. In this brief note we show that the methods are also equivalent, with an alternative definition of the supplied energy, when the damping is pervasive. Instrumental for our developments is the observation that, swapping the damping terms in the classical dissipation inequality, we can establish passivity of port-controlled Hamiltonian systems with respect to some new external variables—but with the same storage function.
Energy Shaping Control of an Inverted Flexible Pendulum Fixed to a Cart
Control of compliant mechanical systems is increasingly being researched for
several applications including flexible link robots and ultra-precision
positioning systems. The control problem in these systems is challenging,
especially with gravity coupling and large deformations, because of inherent
underactuation and the combination of lumped and distributed parameters of a
nonlinear system. In this paper we consider an ultra-flexible inverted pendulum
on a cart and propose a new nonlinear energy shaping controller to keep the
pendulum at the upward position with the cart stopped at a desired location.
The design is based on a model, obtained via the constrained Lagrange
formulation, which previously has been validated experimentally. The controller
design consists of a partial feedback linearization step followed by a standard
PID controller acting on two passive outputs. Boundedness of all signals and
(local) asymptotic stability of the desired equilibrium is theoretically
established. Simulations and experimental evidence assess the performance of
the proposed controller.Comment: 11 pages, 7 figures, extended version of the NOLCOS 2016 pape
A robust adaptive robot controller
A globally convergent adaptive control scheme for robot motion control with the following features is proposed. First, the adaptation law possesses enhanced robustness with respect to noisy velocity measurements. Second, the controller does not require the inclusion of high gain loops that may excite the unmodeled dynamics and amplify the noise level. Third, we derive for the unknown parameter design a relationship between compensator gains and closed-loop convergence rates that is independent of the robot task. A simulation example of a two-DOF manipulator featuring some aspects of the control scheme is give
Improved Transients in Multiple Frequencies Estimation via Dynamic Regressor Extension and Mixing
A problem of performance enhancement for multiple frequencies estimation is
studied. First, we consider a basic gradient-based estimation approach with
global exponential convergence. Next, we apply dynamic regressor extension and
mixing technique to improve transient performance of the basic approach and
ensure non-strict monotonicity of estimation errors. Simulation results
illustrate benefits of the proposed solution.Comment: This paper is submitted for the ALCOSP 2016 conferenc
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