Experimental study of two event-based PI controllers in a solar distributed collector field

In this work we focus on the study of limit cycles that appear in a control scheme which is based on the use of a PI controller with an event-based send-on-delta sampling (SOD), which can be used to sample either the process variable or the control variable. We use an algorithm to calculate the limit cycles properties and then we compare the results obtained in simulations with experiments performed on a real plant, a distributed solar collector field at the Solar Platform of Almería (PSA, Spain). The process is identified as a first order plus time delay (FOPTD). Practical issues, such as the implementation of an anti-windup mechanism and a bumpless transfer between the manual and automatic mode are also addressed.