Direct voltage control in grids with intermittent sources using UPFC

This paper proposes the use of UPFC for direct voltage control in electric grids with highly intermittent generation sources such as wind generators. The variable characteristics of these sources strongly affect the voltage profile in the grids. The objective of this paper is to show through a conceptual analysis that it is possible to obtain precise and fast voltage control by using an UPFC. The UPFC rating is smaller than that of a STATCOM or SVC, which should be necessary for indirect voltage control. The UPFC does not have limitation due to the number of operation per day as in the case of transformers with on load tap changer. The UPFC based on single-phase VSC are analyzed and the series converter is connected directly to the grid without transformer. It controls the voltage independently in each phase, therefore balancing it, if necessary. Simulation results using PSCAD/EMTDC are presented to confirm all these advantages of the use of UPFC for direct voltage control.