On-line retuning of PID controllers with fixed threshold samplers.

The appearance of limit cycle oscillations in control systems with fixed threshold based samplers degrades the performance of the control loop, accelerates the wear out of actuators, and introduces an unnecessary communication overhead in distributed control systems. In this paper, the role of the input signals to the control loop is taken into account when analyzing the existence of limit cycles induced by fixed threshold samplers. With this analysis, a methodology to re-tune PID controllers while running to avoid limit cycle oscillations generated by ramp-like excitation signals is presented.

A new method for tuning PI controllers with symmetric send-on-delta sampling strategy.

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.