Robust Networked Control
Wojciech Grega · InTech eBooks · 2011
Most of integrated industrial control systems adopt a multilevel, vertical control hierarchy. Logically, such a system (Fig. 1) is structured in three levels: the direct (device) control level, the supervisory level and the management level (Grega, 2010, Tatjewski, 2007, Grega at al., 2009). The basic task of the direct (device) control level is to maintain the process states at the prescribed set values. The device controller level provides an interface to the hardware, either separate modules or microprocessors incorporated in the equipment to be controlled. Here, mainly PID digital control algorithms are implemented – in some cases these are more advances control methods such as multivariable control or adaptive functions. A number of embedded control nodes and Programmable Logical Controllers (PLC) are used as the frontends to take the control tasks. High speed networks and fieldbuses are implemented at the direct control level to exchange in real time the information between front-ends and the device controllers and, vertically, with the supervisory control level. This architecture has the advantage of locating the hard real-time activities as near as possible to the equipment.