In a Static Synchronous Series Compensator (SSSC), a controllable AC voltage is
generated by a voltage-source converter. There are two control channels for controlling the magnitude
and phase of the voltage. When this device is used for damping inter-area oscillations in multi-machine
power systems, a damping stabilizer can be included in both channels. In this paper, a method for
the simultaneous coordinated design of a Power System Stabilizer (PSS) and a SSSC-based stabilizer
is presented using quadratic mathematical programming. In this method, the gain and phase of a leadlag
stabilizer can be simultaneously calculated. By this method the eect of the SSSC-based stabilizer in
both control channels on damping inter-area oscillations has been assessed. Obtained results including
eigenvalue analysis and non-linear simulations, on two multi-machine power systems under dierent
operating conditions, show that the usage of a SSSC stabilizer in a suitable control channel can signicantly
reduce the control cost of the stabilizer.