Computerised Control


The objective of this unit is learning the concept of discrete time dynamic system, including the control design.

There are several derives concepts, namely:

  • what is a discrete system, how is characterized and what mathematical representations admits;
  • differences between continuous and discrete signals;
  • stability and performance;
  • discrete time domain and complex frequency domain;
  • feedback and closed loop stability;
  • application limits of digital control;
  • state-space representation;

the student should also know how to:

  • convert a continuos system in its discrete equivalent;
  • identify the poles and zeros of the transfer function and estimate the performance/stability from its pole-zero diagram;
  • plot and analyse Bode and Nyquist diagrams;
  • conclude about the stability of a closed loop system from its open loop Bode and Nyquist diagrams;
  • compute the eigenvalues of the state-space representation and conclude about the stability;
  • design a state variables feedback controller;

additionally, the student acquires the following non-technical competences:

  • make a report on experimental work; 
  • manage time and meet deadlines;
  • collaborative team work; abstract and formal reasoning;
  • abstract modelling of problems; sub-optimal solutions;

General characterization





Responsible teacher

Rui Alexandre Nunes Neves da Silva


Weekly - 4

Total - 52

Teaching language



Although not mandatory, because of the chaining subjects, it is desirable to have successfully performed before the discipline of Control Theory from the previous semester or equivalent in other school.

All the concepts learned in Control Theory are here transported to the discrete time using the transformation z, in place of the Laplace Transform used in continuous time.


Neves-Silva, Rui, Folhas da disciplina de Controlo por Computador. CLIP 

Franklin; Powell; Emami-Naeini, Feedback Control of Dynamic Systems, Addison-Wesley

Teaching method

-Theorectical classes and individual study for knowledge transmission.

-Practical and laboratory sessions to test acquired knowledge.

Evaluation method

There are two possible ways for successfully finishing this course:

1. An average above 9.5 points in 3 tests (~60 min) during the semester (with equal weights) and 3 labworks (also with equal weights) . The lab part contributes with 15% (3 in 20) of the final grade in the continuous evaluation process.

2. A mark above 9.5 points in the final exam. The final grade will be the grade of the exam.

Subject matter

Sampling, control law, discrete transfer function.
Response to impulse and step signals. BIBO stability.
Sampled transfer function of process with the invariant step, discretization of analog controllers.
Mapping between s to z domains. Root locus.
Frequency response, Nyquist and Bode diagrams, permanent error.
Stability criteria.
Control design in the state-space domain.


Programs where the course is taught: