Supplementary DC control in a two area AC/DC power system

The performance of supervisory control associated with a high voltage two area power system interconnected by HVAC and HVDC tie lines is examined. The system includes supplementary DC control interacting with the conventional AC area controls. Taking advantage of the fast controllability of DC links, supplementary control utilizing DC power modulation could simultaneously improve system dynamic stability, reduce area control error, and reduce inadvertent energy interchange. The supplementary DC power modulation is based on variation of the net power interchange due to step load disturbances in one of the control areas. A linear model was used for the power system to study small changes around a base reference state and only the power-frequency control aspects of the overall power system control problems were considered. Eigenstructure analysis of the state space model of the power system was used to evaluate system stability. Control optimization was achieved by minimization of a performance index which is a function of the area control error (ACE). Computer simulation was used to obtain power system dynamic responses to step load disturbances and to estimate the optimal controller parameters.