System Simulation in Ansys Scade Suite Software — Lesson 4

The “OverallSystem” operator refers to the entire closed-loop system as shown in the Figure below.

The 'OverallSystem' operator, with the input '𝑅𝑒𝑓' and output '𝑂𝑢𝑡𝑝𝑢𝑡', has been modeled as shown in the Figure below using the 'Followed By' operator to set the initial value of 'nPID' and 'TransferFunction' operators and to initialize negative feedback as zero.

Figure 5 System Simulation

In Figure 6a, the response of the closed-loop system calculated with the coefficients provided in the Table of section Data types and constants for the 1st PIDBlock operator is depicted. Upon inspection, it is observed that the system is stable but settles very slowly. In Figure 6b below, the closed-loop response of the system associated with the coefficients provided in the Table of section Data types and constants for the 2nd PIDBlock is presented. As observed, the system is stable and, after a slight overshoot, settles to the desired reference value.

Figure 6a Response

Figure 6b Response

In the Figure below, the closed-loop response of the system associated with the coefficients provided in the Table of section Data types and constants for the 3rd PIDBlock is presented. When considering the settling time and overshot ratio, this response is the most ideal for this system. Observing all responses, it can be deduced that the closed-loop system remains stable even if any two of the PID blocks were to malfunction. As a result, the system's response with the PID coefficients selected by the voter algorithm is depicted in the right-side figure below. Here, the voter algorithm computed the PID gain coefficients by averaging the values calculated by the 2nd and 3rd PIDBlock operators. Consequently, it assumed that the input from the 1st PIDBlock operator would impact the stability of the system and thus did not include it in the closed-loop system. It can be observed that the system is stable and exhibits a slight overshot.

Figure 7a Response

Figure 7b Response