Disturbance rejection-based LFC for multi-area parallel interconnected AC/DC system

AC/DC hybrid system plays an important role in large-capacity and long-distance power transmission. Moreover, load frequency control (LFC) of AC/DC hybrid system is very essential for the safe operation of power grid. Since LFC in essence stems from the power imbalance of the area caused by the variations of the generating and consuming party, this study presents a novel disturbance rejection-based (DRB) LFC scheme to eliminate this power imbalance, thus achieving frequency and AC tie-lie interchange power stability. This study assumes only part of the LFC system states information is measurable and utilises extended states observer to estimate the unmeasurable states including the disturbances. Moreover, then a composite feedback controller is designed utilising both the measurable and observed states information. The proposed DRB LFC schemes retain the structure of the LFC model and sufficiently utilise measurable states information for controller design, which has good engineering applicability compared with robust or intelligent LFC scheme. A multi-area system containing three subareas with parallel interconnected AC/DC link is studied and the simulation results show the effectiveness of the proposed methods.