In this paper, a secondary feedback signal is applied to introduce more flexibility in the controller design with regard to the achievable damping performance. A two-input singleoutput (TISO) controller for a TCSC device is designed in the IEEE 50-machine test system. The theoretical basis for using an additional feedback signal is presented and the results from the small signal analysis and dynamic simulations show that the TISO controller can achieve significantly better damping at each operating point than a single-input single-output (SISO) controller. Furthermore, the damping improvement from the TISO controller increases with the increase in system stress level. Thus the TISO controller can extend the system operating range with satisfactory damping.