Systematic supervisory control solutions for under-load tap-changing transformers

Discrete-event systems (DES) can be found as essential integrated subsystems in many complex systems, e.g. electrical power systems. Under-load tap-changing (ULTC) transformers which obviously have discrete-event behavior are widely used in transmission systems to take care of instantaneous variations in the load conditions in substations. In this paper, the voltage control problem in ULTC is solved in different modes of operation, using DES-based solutions. These solutions include: DES supervisory control, timed DES supervisory control and a hierarchical structure for the control system. It is shown that the specifications are controllable and the closed-loop control system is non-blocking.