Hybrid event-based control systems
Kontaktperson: Tobias Nößelt
Zeitraum: seit 01.04.2014
Beschreibung: In this project hybrid event-based control (HEBC) systems are investigated, where a continuous control loop is extended by an event-based controller (Figure1). The plant G has two input signals u1, u2. The control input u1 is adjusted continuously by the controller K0 in order to attenuate disturbances and force the plant to follow a command signal. The second control input u2 is switched based on discrete events, shifting the operation point of the plant.
Figure 1: Structure of HEBC systems
The motivation for hybrid event-based control systems comes from different applications in which continuous and event-based control principles are naturally combined. Examples involve automotive systems, energy supply systems and chemical or biological process plants. Typically the event-based switching of the control input u2 is necessary to prevent control input u1 from exceeding its limitations. Depending on the application, these limitations may hold for all times t·≥·0 or only in a steady state for t → ∞.
HEBC systems can be classified by the way in which the input signals u1 and u2 interact:
- In HEBC systems with the multiplicative interaction ures = u1, eff · u2, eff, the event-based controller changes the gain of the continuous control loop. Examples include the speed control of vehicles with automatic gear boxes and the terminal voltage control of electrical power plants.
- In HEBC systems with an additive superposition ures = u1, eff + u2, eff the two signals u1 and u2 affect the plant in an equal manner. Examples for this structure can be found in hybrid positioning systems or hybrid drive trains as well as chemical or biological process plants.
The combination of event-based switching and continuous adjustment of the control input signals leads to a closed-loop system with hybrid dynamics. The class of hybrid dynamical systems is characterized by an interconnection of continuous and discrete dynamics giving rise to several problems with regard to stability and existence of Zeno behaviour. Nevertheless, in many applications the hybrid character of the system is ignored and the controllers are tuned heuristically.