VO 328.011/UE 328.011 Digital Control
What is Digital Control?
Digital control is a branch of control theory that uses digital computers to act as system controllers. The use of digital computer controller devices has grown immensely during the past decades as the price and performance of digital computers have improved dramatically.
A digital control system uses digital signals and a digital computer to control a continuous process. The digital computer receives the control error in digital form and performs calculations in order to provide an output (control signal) in digital form. The computer may be programmed in any possible way to provide an output so that the performance of the controlled process is near or equal to the desired performance. Many computers are able to receive and manipulate several inputs, so that a digital control system can also be a multivariable system. A digital computer receives and manipulates signals in digital form, as contrasted to continuous signals. Sensor data are therefore converted from analog form to digital form by means of an analog-to-digital converter (ADC). After processing the inputs, the digital computer provides an output in digital form. This output is then converted to analog form by a digital-to-analog converter.
Digital control systems are used in many different application fields and are met literally everywhere: Machine tools, chemical processes, pharmaceutical industries, oil refineries, in-house temperature regulation or aircraft control. Digital control systems are used for purposes as diverse as ensuring save autopilot operation in passenger aircraft or controlling the engine spark timing in combustion engines in order to reduce automobile emissions and increase fuel economy. The major advantage of using digital control is the capability to easily reconfigure the control algorithm and to implement virtually unlimited complex control schemes.
This course is a comprehensive introduction to digital control system synthesis, reinforced with simulation examples and optional hands-on laboratory experience. The course covers elements of real-time computer architecture, input-output interfaces and data conversion. The synthesis and analysis of sampled-data control systems is described, introducing and making use of the z-transform. A thorough insight into the equivalence between discrete-time systems and their continuous counterparts is given.
Different methods for stability analysis of digital control systems are presented in the course. Further, the Nyquist– Shannon sampling theorem as a fundamental bridge between continuous-time and discrete-time signals is introduced. Controller design takes classical continuous controllers and their discrete equivalents as a starting point. On this basis, analytical design methods for digital control algorithms are introduced. They include popular approaches such as model following control and internal model control. Later on in the course digital control design methods in the state space are considered. It is shown how dynamic systems can be represented by discretetime state space models and how they can be analysed.
As a first control method state feedback control with pole placement introduced, followed by Luenberger observer design. The course is concluded by a first introduction into optimisation-based control of discrete-time systems and a treatment of nonlinear systems via feedback linearisation. The course material includes lecture notes, an excercise book as well as numerous examples in MATLAB/Simulink.