A new optimal aim scheme for TCSC contingency control

After the contingent event of power system, if the permanent fault occurs, the structure of power system will be changed. Or, the structure of power system will remain unchanged for temporary fault. Since the structure of post fault power system can be prior known. For ease of design, the transient stability controller always aims to stabilize the angular speed. Thus, the post fault power angle may reach a new value for temporary fault. In addition, the post fault steady state value of transient stability controllers, such as FACT devices, may be close to its boundary value. If there is another contingent event occurs, the transient stability controller will no longer have enough capability to handle that event. This work develops a new optimal aim scheme to overcome the above problems. The proposed scheme is based on a self-correction two-machine equivalent model and very suitable for stability control of FACT devices. Shaping of the self-correction two-machine equivalent model uses only the real-time phasor signals available from the synchronous phasor measurement units (PMUs). Using the proposed scheme, the transient stability controller does not need the information of power system post fault structure. Meanwhile, the FACT devices can retain its maximum capability to handle the upcoming contingent event. Since the parameters and model uncertainties are also considered in the proposed scheme, this approach is adaptive and robust. The proposed optimal aim scheme is successfully applied to a three-areas six-machine test system that installed two thyristor controlled series capacitors (TCSCs) controllers. Simulation results indicate that the proposed scheme is effective and robust in stabilizing the transient swings between interconnected systems under various system conditions and the occurrence of severe faults.