Vicente Casanova

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.

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

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.

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

Multirate control for an ICCS environment. Part I: The random access delays

Abstract 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. This first part of the study proposes a multirate solution for the problem of the random access delays, involved on the resource sharing politics.

Multirate control for an iccs environment. Part II: The time skew problem

Abstract In an ICCS (Integrated Communication and Control System) as described in the part I of this paper, the controller-plant communication is made through a shared medium. 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 unstable the system. This second part proposes a solution, using the multirate controller, to adjust the system behaviour to the desired reference model in the presence of the time skew.

Networked Control Systems: control structures with bandwidth limitations

The aim of this paper is to propose a control to be used in Networked Control Systems. A periodic model of the plant, as it is seen by the controller, is proposed. It can be converted into a multivariable model and used to design a multivariable controller. A second structure becomes a periodic control that uses the plant to supply the lost information. Non linear behaviour, periodicity and any other irregularities can be included in the model. The control is tested on the control of X and Y axis from a model crane, using Profibus-DP to close the loop.

Multirate control with incomplete information over Profibus-DP network

When a process field bus-decentralized peripherals (Profibus-DP) network is used in an industrial environment, a deterministic behaviour is usually claimed. However, due to some concerns such as bandwidth limitations, lack of synchronisation among different clocks and existence of time-varying delays, a more complex problem must be faced. This problem implies the transmission of irregular and, even, random sequences of incomplete information. The main consequence of this issue is the appearance of different sampling periods at different network devices. In this paper, this aspect is checked by means of a detailed Profibus-DP timescale study. In addition, in order to deal with the different periods, a delay-dependent dual-rate proportional-integral-derivative control is introduced. Stability for the proposed control system is analysed in terms of linear matrix inequalities.

Algebraic Design of Multi-rate Control Systems for Environments with Limited Random Delays

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 can be found, for example, 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, or in networked control systems, where due to the existence of large distances and space limitations, several devices (controller, process and others) share a common communication bus. In both cases, these facts could imply the presence of limited random delays, leading to a non-regular non-periodic behavior and, as a result, the control performance can be degraded. In order to undertake this problem, a solution based on a modeling methodology for non-uniform sampled-data systems can be utilized. This technique permits the consideration of any cyclic sampling pattern. However, it can be adapted to deal with limited random delays, and later on, a multi-rate controller based on this model can be designed. In this way, if the considered non-conventional control system is implemented, a clear performance improvement can be observed