Effect of parameter uncertainties on dynamic performance of an interconnected power system with AC/DC links

In the present work, a study on dynamic performance of two-area interconnected power system with parallel AC/DC links is performed. The optimal load frequency controller (LFC) designs based on optimal control theory and unity rank control concept are presented. A comparative study is carried out by considering variations in the parameters associated with power transmission system: (1) synchronizing coefficient of AC tie-line (Tiz) and (2) time constant associated with DC link (T dc ). The uncertainties considered in these parameters are in the range of 25% to 75% of their nominal values. The investigations carried out reveal that the system dynamic performance is highly sensitive to variation in synchronizing coefficient of AC tie-line but it is almost insensitive to variation in time constant of DC link. It is further inferred that the system dynamic performance may be improved considerably by implementing the proposed load frequency controllers. For the present study, DC link is considered to be operating in constant current control mode and incremental power flow through the DC link is modelled based on frequency deviation at rectifier end.