15 research outputs found
Event-driven observer-based smart-sensors for output feedback control of linear systems
This paper deals with a recent design of event-driven observer-based smart sensors for output feedback control of linear systems. We re-design the triggering mechanism proposed in a previously reported system with the implementation of self-sampling data smart sensors; as a result, we improve its performance. Our approach is theoretically supported by using Lyapunov theory and numerically evidenced by controlling the inverted pendulum on the cart mechanism.Postprint (published version
Networked control systems in the presence of scheduling protocols and communication delays
This paper develops the time-delay approach to Networked Control Systems
(NCSs) in the presence of variable transmission delays, sampling intervals and
communication constraints. The system sensor nodes are supposed to be
distributed over a network. Due to communication constraints only one node
output is transmitted through the communication channel at once. The scheduling
of sensor information towards the controller is ruled by a weighted
Try-Once-Discard (TOD) or by Round-Robin (RR) protocols. Differently from the
existing results on NCSs in the presence of scheduling protocols (in the
frameworks of hybrid and discrete-time systems), we allow the communication
delays to be greater than the sampling intervals. A novel hybrid system model
for the closed-loop system is presented that contains {\it time-varying delays
in the continuous dynamics and in the reset conditions}. A new
Lyapunov-Krasovskii method, which is based on discontinuous in time Lyapunov
functionals is introduced for the stability analysis of the delayed hybrid
systems. Polytopic type uncertainties in the system model can be easily
included in the analysis. The efficiency of the time-delay approach is
illustrated on the examples of uncertain cart-pendulum and of batch reactor
Discrete and intersample analysis of systems with aperiodic sampling
International audienceThis article addresses the stability analysis of linear time invariant systems with aperiodic sampled-data control. Adopting a difference inclusion formalism, we show that necessary and sufficient stability conditions are given by the existence of discrete-time quasi-quadratic Lyapunov functions. A constructive method for computing such functions is provided from the approximation of the necessary and sufficient conditions. In practice, this leads to sufficient stability criteria under LMI form. The inter-sampling behavior is discussed there: based on differential inclusions, we provide continuous-time methods that use the advantages of the discrete-time approach. The results are illustrated by numerical examples that indicate the improvement with regard to the existing literature
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
A delay-dependent dual-rate PID controller over an ethernet network
n this paper, a methodology to design controllers able to cope with different load conditions on an Ethernet network is introduced. Load conditions induce time-varying delays between measurements and control. To face these variations an interpolated, delay-dependent gain scheduling law is used. The lack of synchronization is solved by adopting an event-based control approach. The dual-rate control action computation is carried out at a remote controller, whereas control actions and measurements are taken out locally at the controlled process site. Stability is proved in terms of probabilistic linear matrix inequalities. TrueTime simulations in an Ethernet case show the benefit of the proposal, which is later validated on an experimental test-bed Ethernet environment.Manuscript received June 07, 2010; revised September 05, 2010; accepted September 15, 2010. Date of publication October 18, 2010; date of current version February 04, 2011. The authors A. Cuenca, J. Salt, and R. Piza are grateful to Grant PAID06-08 by the Universidad Politecnica de Valencia, Grant dpi2009-14744-c03-03 from the Spanish Ministry of Education, and Grant gv/2010/018 by Generalitat Valenciana. In addition, A. Cuenca is grateful to Grant dpi2008-06737-c02-01 by the Spanish Ministry of Education, and A. Sala is grateful to the financial support of the Spanish Ministry of Education Research Grant dpi2008-06731-c02-01, and Generalitat Valenciana Grant prometeo/2008/088. Paper no. TII-10-06-0127.Cuenca Lacruz, ÁM.; Salt Llobregat, JJ.; Sala Piqueras, A.; Pizá Fernández, R. (2011). A delay-dependent dual-rate PID controller over an ethernet network. IEEE Transactions on Industrial Informatics. 7(1):18-29. doi:10.1109/TII.2010.2085007S18297
Tutorial on arbitrary and state-dependent sampling
International audienceThis tutorial, presents basic concepts and recent research directions about sampled-data systems. We focus mainly on the stability of systems with time-varying sampling intervals. Without being exhaustive, which would be neither possible nor useful, we try to give a structural survey of what we think to be the main results and issues in this domain
LQ-optimal Sample-data Control under Stochastic Delays: Gridding Approach for Stabilizability and Detectability
We solve a linear quadratic optimal control problem for sampled-data systems
with stochastic delays. The delays are stochastically determined by the last
few delays. The proposed optimal controller can be efficiently computed by
iteratively solving a Riccati difference equation, provided that a
discrete-time Markov jump system equivalent to the sampled-data system is
stochastic stabilizable and detectable. Sufficient conditions for these notions
are provided in the form of linear matrix inequalities, from which stabilizing
controllers and state observers can be constructed.Comment: 28 pages, 3 figure
Digital repetitive control under varying frequency conditions
Premi extraordinari doctorat curs 2011-2012, àmbit d’Enginyeria IndustrialThe tracking/rejection of periodic signals constitutes a wide field of research in the control theory and applications area and
Repetitive Control has proven to be an efficient way to face this topic; however, in some applications the period of the signal to
be tracked/rejected changes in time or is uncertain, which causes and important performance degradation in the standard
repetitive controller. This thesis presents some contributions to the open topic of repetitive control working under varying
frequency conditions. These contributions can be organized as follows:
One approach that overcomes the problem of working under time varying frequency conditions is the adaptation of the
controller sampling period, nevertheless, the system framework changes from Linear Time Invariant to Linear Time-Varying
and the closed-loop stability can be compromised. This work presents two different methodologies aimed at analysing the
system stability under these conditions. The first one uses a Linear Matrix Inequality (LMI) gridding approach which provides
necessary conditions to accomplish a sufficient condition for the closed-loop Bounded Input Bounded Output stability of the
system. The second one applies robust control techniques in order to analyse the stability and yields sufficient stability
conditions. Both methodologies yield a frequency variation interval for which the system stability can be assured. Although
several approaches exist for the stability analysis of general time-varying sampling period controllers few of them allow an
integrated controller design which assures closed-loop stability under such conditions. In this thesis two design
methodologies are presented, which assure stability of the repetitive control system working under varying sampling period
for a given frequency variation interval: a mu-synthesis technique and a pre-compensation strategy.
On a second branch, High Order Repetitive Control (HORC) is mainly used to improve the repetitive control performance
robustness under disturbance/reference signals with varying or uncertain frequency. Unlike standard repetitive control, the
HORC involves a weighted sum of several signal periods. With a proper selection of the associated weights, this high order
function offers a characteristic frequency response in which the high gain peaks located at harmonic frequencies are
extended to a wider region around the harmonics. Furthermore, the use of an odd-harmonic internal model will make the
system more appropriate for applications where signals have only odd-harmonic components, as in power electronics
systems. Thus an Odd-harmonic High Order Repetitive Controller suitable for applications involving odd-harmonic type
signals with varying/uncertain frequency is presented. The open loop stability of internal models used in HORC and the one
presented here is analysed. Additionally, as a consequence of this analysis, an Anti-Windup (AW) scheme for repetitive
control is proposed. This AW proposal is based on the idea of having a small steady state tracking error and fast recovery
once the system goes out of saturation.
The experimental validation of these proposals has been performed in two different applications: the Roto-magnet plant and
the active power filter application. The Roto-magnet plant is an experimental didactic plant used as a tool for analysing and
understanding the nature of the periodic disturbances, as well as to study the different control techniques used to tackle this
problem. This plant has been adopted as experimental test bench for rotational machines. On the other hand, shunt active
power filters have been widely used as a way to overcome power quality problems caused by nonlinear and reactive loads.
These power electronics devices are designed with the goal of obtaining a power factor close to 1 and achieving current
harmonics and reactive power compensation.Award-winningPostprint (published version