In this study, a new sampling strategy for networked control systems, called regular quantification with hysteresis (RQH), is proposed. This alternative presents some benefits with respect to symmetric-send-on-delta sampling, which is one of the most used strategies in the event-based proportional-integral-derivative (PID) control loops. The behaviour of the RQH is defined by two parameters, the signal quantification and hysteresis, whose effect on the overall system performance is studied and guidelines about its choice are given in terms of noise measurement and steady-state error. The limit cycle oscillations that could be induced by this sampling strategy are studied and new robustness measures to avoid them are proposed based on the describing function approach. The suitability of some tuning rules for continuous PI when applied to control systems with a RQH sampling is evaluated using the proposed measures. The results show that these tuning rules can be applied under certain conditions.

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.

A Grafcet is a standardized model for describing the behavior of systems which is popular among automation engineers. As the Grafcet standard excludes implementation details, the models are typically translated to automation software. Such software was traditionally programmed in one of the languages specified in IEC 61131-3. Nowadays, automation software is increasingly modelled in IEC 61499 which facilitates designing distributed control systems. In this paper, we define a standardized translation methodology, so that automation engineers can benefit from the advantages of IEC 61499 while continuing to use Grafcet. We discuss the differences between Grafcet and IEC 61499. We translated a Grafcet model into an IEC 61499 application to illustrate the process and derive guidelines for application designers. For the core concepts of Grafcet, we present the corresponding structure in IEC 61499.

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