Some aspects of hierarchical voltage-reactive power control

The paper presents some contributions regarding hierarchical voltage reactive power control. The studies for classification of the zones for the hierarchical voltage-reactive power control, led the authors to the conclusion that the use of mutual node voltage influence indices should be preferred to the use of nodal impedance matrix elements. For the Romanian power system, the zones determined for voltage control are not very much different than the existing zones for operation and control by hierarchical dispatching centers. The mathematical model of secondary control function for the Romanian power system was studied taking into consideration the case of constant reactive power circulation between zones and the case of modified reactive power circulation on the inter-zone links. For the optimisation function, specific to the tertiary level of voltage control, the authors propose a method that combines the robustness of the genetic algorithms and the fuzzy logic possibility to combine easy and intuitive different optimisation criteria into a single evaluation function. The model has been applied to the Romanian power system. The results have confirmed the efficiency of hierarchical voltage control for the Romanian power grid from the perspective of the UCTE interconnection.