The hierarchical voltage control to face the increase of uncertainty due to market structures

This paper deals with the exploitation of the advantages of a coordinated voltage control to face the growing uncertainties in the operation of modern power systems. In the past, the system operators had the complete control of the system (i.e., real power dispatch, voltage coordination and optimization, etc.); nowadays, some of those control variables are no more available to the TSO, at least for free: the different market sessions define the unit commitment and the real power dispatch. The main responsibility of TSOs is the power system security, versus both physical perturbations (e.g., contingencies) and “commercial perturbations” (i.e., the partially unpredictable output of the market). Thus, while the market increases the uncertainty, it put at disposal of the TSO a set of control actions less efficient than in the past. The voltage control is a function whose market is not always well settled, while it is very important for the power system security. In Italy, the previous vertically integrated utility, ENEL, studied and partially implemented a hierarchical voltage control (HVC) system. The goal of this paper is to show how the centralized HVC can still help the modern power system operators in obtaining a more robust voltage control against the overall power system uncertainty, increased by the presence of the electricity market. For this reason, the HVC should be implemented as a part of the ancillary services market, that mainly deals with voltage quality and security.