Julián Salt

Brief paper: Dual-rate adaptive control

An operator, called the dual-rate transfer function, describing a dual-rate discretized continuous-time system is presented. It can be easily related to single-rate transfer functions of the same system, and its parameters can be experimentally estimated. Based on these models, two adaptive control strategies are outlined, and some results are illustrated by a simple example.

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.

Model-based multirate controllers design

In many industrial control applications the control action updating can be faster than the output measurement, leading to multirate controllers. In this paper, some dual rate operations are used to model the controller as well as the controlled plant. The controller design is model-based and depends on the input to be tracked. The controller is split into two parts acting at different sampling rates and its design is approached based on the characteristics of each available sampling rate. The control target is to reach the similar performances to those the faster single rate controller would achieve. Model-based cancellation controllers are designed using this approach and promising results are obtained.

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.

Multirate control implementation for an integrated communication and control system

When controlling a large manufacturing plant, there are a great number of devices (sensors and actuators) to connect with the main controller. The long distance in this kind of control systems suggests a shared communication link. Certain additional control problems appear when the communication between controller and plant is not always available. A multirate solution for the problem of the random access delays, involved on the resource sharing policy, is proposed in this paper. In addition, as there is not an exclusive link, it is difficult to guarantee the synchronisation of sensor, controller and actuator. The time skew between the sample, control and application instants, in combination with the random access delay, causes a loss of information that can make the system unstable. Multirate control techniques can be used to adjust the system behaviour to the desired reference model in the presence of time skew.

Digital Regulators Redesign with Irregular Sampling

Abstract Although digital control provides the statement of design objectives not achievable with analog controllers, the well understanding and tuning of classical PlD controllers or pole placement state feedback often lead to the implementation of digital controllers through the previous design of analog ones. Periodic sampling to discretize either the process or the designed controller, as well as in the digital control implementation, is usually assumed. But many circunstances determine a variable, or even random, sampling period: the computation time, the availability of process variable measurements, the communication delays, and so on. In this paper an analog controller satisfying the control requirements is assumed. Then variations of the sampling period with respect to the nominal one are considered and their effect on the controlled process analyzed. In order to keep the design specifications, some modific ations of the classical PlD algo rithms and state feedback regulators are proposed. The posibility of adaptive controllers redesign is also considered. The problem a rised in process control applications when a composition measurement is used and the sampling interval is not totally fixed. The results are illustrated with s ome examples as well a s with the control of a raw materials mill in the cement industry.

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

Multirate LQG controller applied to self-location and path-tracking in mobile robots

Presents an approach to solving the linear quadratic Gaussian problem for controlling MIMO multirate sampled-data systems. The problem is split into three parts: first a generalized discrete multirate model is computed, second the solution of the linear quadratic regulator problem is computed and then a multirate Kalman filter is obtained. The model is composed by a time invariant single rate part, involving the basic process dynamics and a periodic one determined by the external sampling strategy. This allows an easy analysis of the effects of the multirate sampling on the plant. The approach has been applied to solve problems of self-location and path tracking in mobile robots. As is common in many auto-guided vehicles the sensory system is very complex, so some kind of sensor data fusion has been implemented.