No abstract

No abstract

In this paper we present a new method for tuning PI controllers with Symmetric Send-On-Delta (SSOD) sampling strategy. First we analyze the conditions that produce oscillations in event based systems considering SSOD sampling strategy. The Describing Function is the tool used to address the problem. Once the conditions for oscillations are established, a new robustness to oscillation performance measure is introduced which entails with the concept of phase margin, one of the most traditional measures of relative stability in closed-loop control systems. Therefore, the application of the proposed robustness measure is easy and intuitive. Then the tuning method is developed to tune PI controllers to avoid the limit cycles. Because the method is based on the Describing Function, the effect of higher order harmonics has been studied to evaluate the validity of the proposal. Unlike some previous works concerning SSOD based PI, the results presented in this article are not restricted to specific model structures, instead they can be applied to a wide range of linear processes including dead-time, non-minimum phase and under-damped response. The tuning method is tested in simulations with a batch of models widely used in PI design methods testing. Furthermore, an actual laboratory scale application is presented to prove the feasibility of the proposal. Additionally, a Java application has been developed to aid in the design of SSOD based PI controllers according to the results presented in this paper.

A simple method to design PID controllers in the frequency domain based on a simplified constrained optimization is proposed. The method is based on the use of a single tuning parameter, defined as the quotient between the final crossover frequency and the zero of the controller. The tuning procedure is based on the maximization of the controller gain subject to an equality constraint in the phase margin and an inequality constraint in the gain margin. The main advantage of the proposed method is that, even though the maximization of the controller gain is straightforward, since there is only one parameter to be tuned, the solution is close to the optimal tuning obtained with direct numerical optimization methods. Moreover the method is applicable to any linear model structure, including dead time and non-minimum phase systems.

Versión / Versió:Postprint del autor This paper addresses the state estimation in linear time-varying systems with several sensors with different availability, randomly sampled in time, and whose measurements have a time-varying delay. The approach is based on a modification of the Kalman filter with the negative-time measurement update strategy, avoiding running back the full standard Kalman filter, the use of full augmented order models or the use of reorganization techniques, leading to a lower implementation cost algorithm. The update equations are run every time a new measurement is available, independently of the time when it was taken. The approach is useful for networked control systems, systems with long delays and scarce measurements, and for out-of-sequence measurements.

No abstract

The solar photodegradation of Sevnol, a commercial pesticide, based on carbaryl as active principle, was studied. Experiments have been carried out at laboratory and at pilot plant scale using titanium dioxide as catalyst. Complete dissappearance of carbaryl was achieved, while total mineralisation required longer irradiation. Active sludge respirometry showed significant detoxification of the solution. Finally, results obtained with commercial Sevnol were consistent with those of pure carbaryl, although the reaction was slower.

A procedure for tuning PID controllers with SSOD sampling for FOPTD systems is proposed. It is based on the definition of a new robustness measure to avoid limit cycle oscillations, called the Tsypkin margin (M T). This margin is based on the Tsypkin method and does not rely on the attenuation of high order harmonics, as the describing function approaches require. Therefore, the avoidance of limit cycle oscillations can be guaranteed for any system, as a difference with the describing function based procedures. The procedure allows to obtain the PID controller that minimizes the disturbance IAE while fulfilling constraints on robustness to oscillations and on control action bumps due to the SSOD sampling. A freely available Java tool has been developed in order to simplify the application of the tuning procedure. In case of a non FOPTD system, it first calculates an approximate FOPTD model. The paper shows that the derivative filter parameter, N is a critical tuning parameter in order to find a compromise between performance and control action bumps.