Angel Cuenca

A Delay-Dependent Dual-Rate PID Controller Over an Ethernet Network

In 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.

A retunable PID multi-rate controller for a networked control system

This paper introduces a control strategy based on retuning a multi-rate PID controller in accordance with the variable delays detected in a networked control system, in order to avoid a decreased control performance. The basic idea is minimising the first-order Taylor terms of a performance measure via gain scheduling, i.e., making the controller gains delay dependent. As network delay is time-variant, the stability of this control approach will be proved by means of linear matrix inequalities.

Implementation of algebraic controllers for non-conventional sampled-data systems

Nowadays, in industrial control applications, is rather usual to sample and update different variables at different rates, although it is common to consider all these activities equally and regularly spaced on time. These applications are implemented on real-time operating systems by decomposing them into several tasks in such a way that pre-emption and blocking may appear due to task priorities and resource sharing. This could imply the presence of delays, leading to a non-regular periodic behaviour and, as a result, the control performance can be degraded. In order to undertake this problem, a solution based on a modelling methodology for non-conventional sampled-data systems is proposed. This technique permits the consideration of any cyclic sampling pattern. Thus, these delays can be considered in the modelling step, and later on, a non-conventional controller based on this model can be designed. In this way, if the considered non-conventional control system is implemented assuming a real-time operating system (Tornado-VxWorks, in this case), a clear performance improvement can be observed.

Networked control systems over Profibus-DP: Simulation model

This paper deals with the problem of simulating the sequence of events in the communication through one of the most commonly used fieldbuses: Profibus-DP. Control systems using a fieldbus or any other kind of shared communication medium, are known as Networked Control Systems. A detailed description of the operation of Profibus, when transmitting a signal in a round trip between slave and master devices, is included. This operation is characterized with a collection of parameters whose values are determined by the practical implementation of the network. A simulation model, using Matlab/Simulink is built to emulate the behavior of the real system. This model has been validated, processing the transmitted signal and using histograms to compare the results obtained from real and simulated transmission.

A PID dual rate controller implementation over a networked control system

In networked control systems (NCS) environments is usual to find restrictions with data-acquisition frequency. If the control action updating can be faster than the output measurement, the use of a dual rate controller is a natural solution. Due to PIDs are useful controllers in industrial applications, in this paper a dual rate PID controller is designed splitting a conventional PID into two parts acting at different sampling rates. Its implementation over a specific NCS scenario (Profibus DP) is assumed. The study includes a description of a NCS, the introduction of a dual rate design methodology for PID controllers and also an analysis that validates the real implementation using this approach. Finally, theoretical and practical results are shown too

Hierarchical Triple-Maglev Dual-Rate Control Over a Profibus-DP Network

This paper addresses a networked control system application on an unstable triple-magnetic-levitation setup. A hierarchical dual-rate control using a Profibus-decentralized peripherals network has been used to stabilize a triangular platform composed of three maglevs. The difficulty in control is increased by time-varying network-induced delays. To solve this issue, a local decentralized H∞ control action is complemented by means of a lower rate output feedback controller on the remote side. Experimental results show good stabilization and reference position accuracy under disturbances.

Control of the rotary inverted pendulum through threshold-based communication

This paper deals with the real implementation of an event-based control structure for the classical rotary inverted pendulum. The communication between controller and plant is performed through Ethernet (TCP/IP) which leads to a Networked Control System. The bandwidth used by the control loop is reduced, compared with the one that needs a conventional control, by using a threshold-based communication. The values of the thresholds have been determined by means of simulation techniques. The results over the real plant show how this technique can reach a significant reduction of the bandwidth consumed with a negligible worsening of the performance.

A non-uniform multi-rate control strategy for a Markov chain-driven Networked Control System

In this work, a non-uniform multi-rate control strategy is applied to a kind of Networked Control System (NCS) where a wireless path tracking control for an Unmanned Ground Vehicle (UGV) is carried out. The main aims of the proposed strategy are to face time-varying network-induced delays and to avoid packet disorder. A Markov chain-driven NCS scenario will be considered, where different network load situations, and consequently, different probability density functions for the network delay are assumed. In order to assure mean-square stability for the considered NCS, a decay-rate based sufficient condition is enunciated in terms of probabilistic Linear Matrix Inequalities (LMIs). Simulation results show better control performance, and more accurate path tracking, for the scheduled (delay-dependent) controller than for the non-scheduled one (i.e. the nominal controller when delays appear). Finally, the control strategy is validated on an experimental test-bed.

Irregular Actuation and Sampling in a Networked Control System over Profibus-DP

Networked control systems are a special kind of control loops in which the main feedback is closed through a shared communication link. A number of undesirable influences appear when the link to communicate controller and plant is not always available. The aim of this paper is to analyze one of the drawbacks of these systems, irregular conversions that appear when different sampling periods are used in emitter, medium and receiver of the communication. A simulation model is developed to study this irregular conversions and to be employed on the design of control strategies

A Multirate Control Strategy to the Slow Sensors Problem: An Interactive Simulation Tool for Controller Assisted Design

In many control applications, the sensor technology used for the measurement of the variable to be controlled is not able to maintain a restricted sampling period. In this context, the assumption of regular and uniform sampling pattern is questionable. Moreover, if the control action updating can be faster than the output measurement frequency in order to fulfill the proposed closed loop behavior, the solution is usually a multirate controller. There are some known aspects to be careful of when a multirate system (MR) is going to be designed. The proper multiplicity between input-output sampling periods, the proper controller structure, the existence of ripples and others issues need to be considered. A useful way to save time and achieve good results is to have an assisted computer design tool. An interactive simulation tool to deal with MR seems to be the right solution. In this paper this kind of simulation application is presented. It allows an easy understanding of the performance degrading or improvement when changing the multirate sampling pattern parameters. The tool was developed using Sysquake, a Matlab-like language with fast execution and powerful graphic facilities. It can be delivered as an executable. In the paper a detailed explanation of MR treatment is also included and the design of four different MR controllers with flexible structure to be adapted to different schemes will also be presented. The Smiths predictor in these MR schemes is also explained, justified and used when time delays appear. Finally some interesting observations achieved using this interactive tool are included.