Modeling and synthesis of DES supervisory control for coordinating ULTC and SVC

Discrete-event systems (DESs) can be found as an essential integrated subsystems in electrical power systems. The supervisory control theory is a general theory for synthesis of controllers for DESs. Under-load tap-changing transformers (ULTC) which obviously have discrete-event behavior are widely used in transmission systems to take care of instantaneous variations in the load conditions in substations. Also, the static VAR compensator (SVC) which has fast dynamic characteristic can be used to support system voltage following disturbance. The combination of an SVC and a ULTC can not work properly on the same bus without appropriate coordinated control rules as these two devices are designed to achieve voltage regulation target based on their own measurements. The paper discusses the issues involved in modeling and synthesizing of a supervisory control system in centralized and decentralized structures to coordinate the behavior of the ULTC and the SVC. The control specifications are modeled as some automata and it is shown that they are controllable. The designed closed loop control system is non-blocking.