COI-based backstepping sliding-mode emergency frequency control for interconnected AC/DC power systems

A new COI-based backstepping sliding-mode method for emergency frequency control of interconnected AC/DC power systems is proposed in this paper. It aims to provide inter-area power support to the disturbed control area(s) through the intact interconnecting structure under emergency conditions, when the normal Automatic Generation Control (AGC) is suspended to avoid worsening frequency stability. With the assumption of area Center of Inertia (COI) frequency and the employment of Wide-Area Measurement System (WAMS), the control strategy is driving the area COI frequency to track the overall system COI frequency by virtue of coordination control of emergency generation and HVDC power such that the long-term frequency stability can be promisingly improved. The combined approach holds desired robustness to area load disturbances. Simulations have been conducted on a two-area interconnected AC/DC system in computer and the results demonstrate the feasibility and effectiveness of the proposed design method.