A Study on the Control of AC/DC Power Systems Based on System Dynamic COI

To improve the transient angle stability of an two- area interconnected ac/dc power system, robust controllers are suggested in this note both for excitation systems of generators and dc power modulation, based on the COI (center of inertia) dynamic information of the system. In the control strategy, the rotor angles and frequencies of all generators track the angle and frequency of the dynamic COI of the system which is available from WAMS to keep synchronous under large disturbances. The objective of dc power modulation is to damp out the oscillation of COIs of the two areas to help improve dynamic stability. The mathematical models are established first. The robust controllers are then designed using back-stepping method with model errors and disturbances considered. The digital simulation results based on 2-area-4-machine ac/dc power system prove that the control strategy can noticeably improve the transient stability of the power system.