This paper presents an optimal LQR control for a static-series compensator (SSC) and propounds a design criterion for the choice of the LQR weights in order to mitigate grid-voltage dips. The authors present a SSC state-space model that considers the modelling of grid, transformer and R-L load. The proposed control works in the Stationary-Reference Frames (SRF) and implements AFC resonant controllers, allowing the direct control of unbalanced dips in a three wire grid-load connection.